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Plasmonic Silver Incorporated Silver Halides for Efficient Photocatalysis
Abstract
The development of visible-light-responsive photocatalysts is a promising challenge in the disinfectant of environmental pollution. Silver-silver halides nano-photocatalysts have received intensive attention due to their excellent photocatacatalytic performance in recent years, where silver nanoparticles/nanoclusters demonstrate plasmonic enhanced light absorption efficiency and have been considered as an important component in various functional photocatalytic nanocomposite materials, serving for harvesting visible light. This review provides an overall survey on the state-of-the-art silver-silver halides-based photocatalysts, fundamental understanding of their plasmonically induced photo-reactions and their major environmental applications. We first discuss the basic concepts of localized surface plasmon resonance, and outline general mechanism of silver-silver halides-based photocatalysis. We then discuss the latest progress in the design and fabrication of silver halide based photocatalysis using various strategies. Next, we highlight some selected examples to demonstrate the new applications of silver/silver halides nano-photocatalysts. Eventually, we provide an outlook of the present challenges and some perspectives of new directions in this interesting and emerging research area.
... [11] Plasmonic nanoparticles (PNPs) mediated catalysts are currently actively researched towards the visible-light-driven reactions because PNPs strongly interact with light due to their unique optical properties arising from the collective oscillation of free electrons confined evanescently on the plasmonic metal surface, which is so-called surface plasmon effect (SPR). [12,13] Theoretically, SPR of plasmonic noble metal NPs can occur under sunlight or artificial light irradiation when the frequency of exciting photons equals the frequency of oscillating surface electrons [14]. A detailed account on SPR effect has been reported in our previous work. ...
... [15] A charge density oscillation on the plasmonic metal and the creation of electric field is the so-called surface plasmon resonance (SPR), which tremendously extends the photoabsorption capability. [14,46] Based on SPR effect, when a metal absorbs a photon, it generates hot electrons via electron transitions with conserved momentum. These reactive electrons may transfer to the E CB of the semiconductor. ...
The plasmonic metal-induced Bi2WO6/TiO2 ternary composite with unique electronic and structural properties was synthesized via a hydrothermal and chemical reduction route for sustainable energy and environmental remediation. The obtained Bi2WO6/TiO2-Ag (BWTA) exhibited a tremendous catalytic activity for Rhodamine B photodegradation (0.947×10⁻² min⁻²) than those of sole TiO2 and BW specimens. The radical trapping experiment discloses that superoxide O2⁻ and holes (h⁺) are the cardinal active species in the photocatalytic system. Further, recycling experiment was conducted to elucidate the stability of the photocatalyst. BWTA2.0 was able to produce 2.1330 mA/cm² of current density for oxygen evolution reaction and -1.5003 mA/cm² for hydrogen evolution reaction, which is much higher than those of other specimens. Besides, electrochemical detection of dopamine (DA) was performed through cyclic voltammetry; results showed that the ternary composite had better electrocatalytic activity for DA detection owing to the synergistic effects of noble metal incorporation into the semiconductor. Also, the antibacterial potential of the specimens was explored against Escherichia coli through the well-diffusion method. In terms of experimental results, a possible mechanism of ternary composite is thoroughly elucidated. Thus, this work validates that, plasmonic induced ternary composite has a great prospect for photocatalytic, electrochemical, sensing, and antibacterial applications.
... Silver salt-based photocatalysts often suffer from photocorrosion [42][43][44][45] . However, in the current system, the 0.12 equiv of initially added Ag 3 PO 4 successfully worked five consecutive photocatalytic cycles with only a slight decrease in efficiency (Fig. 3c), resulting in a turnover number of 13. ...
Photocatalytic redox reactions are important for synthesizing fine chemicals from olefins, but the limited lifetime of radical cation intermediates severely restricts semiconductor photocatalysis efficiency. Here, we report that Ag3PO4 can efficiently catalyze intramolecular and intermolecular [2 + 2] and Diels-Alder cycloadditions under visible-light irradiation. The approach is additive-free, catalyst-recyclable. Mechanistic studies indicate that visible-light irradiation on Ag3PO4 generates holes with high oxidation power, which oxidize aromatic alkene adsorbates into radical cations. In photoreduced Ag3PO4, the conduction band electron (eCB⁻) has low reduction power due to the delocalization among the Ag⁺-lattices, while the particle surfaces have a strong electrostatic interaction with the radical cations, which considerably stabilize the radical cations against recombination with eCB⁻. The radical cation on the particle’s surfaces has a lifetime of more than 2 ms, 75 times longer than homogeneous systems. Our findings highlight the effectiveness of inorganic semiconductors for challenging radical cation-mediated synthesis driven by sunlight.
... Silver salt-based photocatalysts often suffer from photo-corrosion. [40][41][42][43] However, in the current system, the 12 mol% of initially added Ag 3 PO 4 successfully worked ve consecutive photocatalytic cycles with only a slight decrease in e ciency (Figure 2c), resulting in a turnover number of 13. Photo-corrosion of Ag 3 PO 4 was observed as evidenced by its signi cant darkening after ve cycles. ...
Photocatalytic redox is an important method for synthesizing fine chemicals from olefins, but the limited lifetime of radical cation intermediates severely restricts semiconductor photocatalysis efficiency. Here we report that Ag 3 PO 4 nanoparticles (NPs) can efficiently catalyze intramolecular and intermolecular [2+2] and Diels-Alder cycloadditions under visible-light irradiation. The approach is additive-free, catalyst-recyclable, and can be scaled up using sunlight. Mechanistic studies indicate that visible-light irradiation on Ag 3 PO 4 NPs generates holes with high oxidation power, which effectively oxidize styrene adsorbates into radical cations. In photoreduced NPs, the conduction band electron ( e CB ⁻ ) has low reduction power due to the delocalization among the Ag ⁺ -lattices, while the NP surfaces have a strong electrostatic interaction with the radical cations, which considerably stabilize the radical cations against recombination with e CB ⁻ . Anethole radical cation on the NP’s surfaces has a lifetime of several hours, 10 ⁸ times longer than in the homogeneous systems. The reaction between an adsorbed styrene molecule and a radical cation, the rate-limiting step, is greatly accelerated. Our findings highlight the effectiveness of inorganic semiconductors for challenging radical cation-mediated synthesis driven by sunlight.
... Among techniques used to achieve the aforementioned goals, the photocatalytic degradation of dyes and disinfection are receiving increasing attention. For example, under ultraviolet (UV) light irradiation, a silver chloride (AgCl) photocatalyst can generate silver atomic clusters (Ag@), and through the surface plasmon resonance (SPR) effect of such clusters, a high concentration of electron-hole pairs can be generated under visible light irradiation to improve the photoluminescence catalytic efficiency [1][2][3][4]. According to Garg et al. [5], under continuous light irradiation, a AgCl photocatalyst continuously undergoes photoreduction to form Ag@, which results in a decrease in the concentration of the AgCl photocatalyst, hinders the generation of electron-hole pairs, and limits the photocatalytic efficiency. ...
In this study, we present a novel approach for the preparation of a highly ordered interconnected three-dimensional (3D) porous network structure of a silver atomic cluster (Ag@)/silver chloride photocatalyst using in situ precipitation 3D printing technique). The as-prepared photocatalyst structure exhibited high porosity and was tested for photocatalytic dye degradation and sterilization of Escherichia coli under visible and ultraviolet light irradiation. The results showed that the photocatalyst structure demonstrated strong degradation efficiency towards aqueous solutions of Orange II azo dye and methylene blue dye, and the kinetic properties followed a pseudo-first-order kinetics. The photocatalyst structure also exhibited efficient sterilization of E. coli, and the kinetics followed a pseudo-first-order and hyperbolic kinetics. Furthermore, after five cycles of dye degradation, the photocatalyst structure maintained high degradation rates of approximately 89.8% and 88.2% for Orange II azo and methylene blue dyes, respectively, indicating excellent durability and reliability of the prepared photocatalyst structure.
... For instance, Jiao et al. have constructed heterojunction between Ag/AgCl and Ag 2 MoO 4 . To improve the photocatalytic performance of Ag 2 MoO 4 , Ag/AgCl have been used for the formation of heterojunction due to the establishment of surface plasmon resonance in Ag nanoparticles (NPs) [89]. Ag/AgCl/Ag 2 MoO 4 have been synthesized by the mentioned author through precipitation method. ...
Photocatalysis has been regarded as one of the promising technologies in treating pollutants. Visible light-driven photocatalysis has attracted attention due to its potential in utilizing a greater portion of sunlight. Silver phosphate (Ag3PO4) is a visible light active photocatalyst that exhibited 90% quantum efficiency and showed excellent photocatalytic performance in decomposing pollutants. This review provides an overview of the selection of suitable synthesis methods used to obtain desirable Ag3PO4 and Ag3PO4-based for different types of photocatalytic applications utilizing visible light. The challenges and the prospects of improving the performance of Ag3PO4 and Ag3PO4-based visible light active photocatalysts have been discussed.
... In recent years, among the various plasmonic photocatalysts, Ag/ AgX (X = Cl, Br, I) nanostructures aroused widespread attention owing to their extraordinarily large photocatalytic performance and stability as well as excellent visible light response arising due to the SPR effect of Ag metal nanoparticles [150]. In addition, the Ag nanoparticles by decomposition of AgX can also behave as efficient electron sinks, thus contributing to the inhibition of electron-hole reconcilation and at the same time promoting interfacial charge transfer process. ...
As a fascinating visible-light active material, Bi12O17Cl2 has become a new research hotspot in the arena of semiconductor photocatalysis and drawn broad interdisciplinary attention as highly potent catalysts for solar energy conversion and environmental protection. The uniqueness of these layered bismuth-based oxides materials are their potential to harness energy in the visible range, their relative ease of synthesis, cost-effectiveness, great chemical stability, high photoactivity, strong adsorptivity, biologically inert nature, less toxicity, appropriate flat band potential, narrow band gap and environmentally benign. However, the quick reconcilation of the photoproduced charge carrier is a persistent bottleneck in this material. This issue generally manifests in the form of reduced lifetime of photoexcited e⁻-h⁺ decreasing the quantum efficiency of diverse light-driven applications. In current years, an enormous research interest is devoted in fabricating Bi12O17Cl2 based robust photocatalysts. This review summarizes the diverse strategies such as morphology control, growth mechanism, metal/non-metal doping, decoration with plasmonic metals, heterojunction/composite formation, the creation of oxygen vacancies etc adopted for improving photocatalytic performance of Bi12O17Cl2. Besides this, relevant achievements of pristine and Bi12O17Cl2-based photocatalysts on the removal of harmful emerging environmental pollutants such as dyes, pesticides, personal care-products, heavy metal ions, pharmaceutical waste, bacteria, gaseous pollutants etc have been discussed in detail.
Moreover, efforts are also made to provide a perspective for future research. It is hoped that this review will offer vision by providing some valuable guidance for designing Bi12O17Cl2 as a cocatalyst to fabricate more effective photocatalysts for practical application in environmental pollution management.
... Photo-catalytically, silver chloride layer AgCl plays a key role in the oxidation of water to O 2 (Lanz, Schürch and Calzaferri, 1999;Calzaferri et al., 2001). Due to Silver halide's excellent photocatalysts performance, it received huge attention from researchers (Changhua et al., 2016). (Masahiro et al., 2021) developed an in situ diffracted X-ray flash to observe high-resolution diffraction patterns from the single crystal grains with a time resolution of 50 ms. ...
Density functional theory (DFT) coupled with ) method are carried out to calculate the electronic structures of AgX (X; Br, Cl, and F). The effect of hybridizing between 4d orbital of Ag element and the p orbitals of the X in the valence band plays a very important role in the total density of states configuration. The electronic structure has been studied and all results were compared with the experimental and theoretical values. The importance of this work is that there is insufficient studies of silver halides corresponding the great importance of these compounds. Almost all the results were consistent with the previous studies mentioned here. We found the band gap of AgX to be 2.343 eV, 2.553 eV, and 1.677 eV for AgBr, AgCl, and AgF respectively which are in good agreement with the experimental results.
... Among these structures, metal micro-and nanopattern structures (MNPs) have provided highly accessible and widely applicable frameworks for most practical devices, including transparent electrodes, sensor platforms, and plasmonic templates [5][6][7][8][9][10] . For instance, silver (Ag) has been one of the most versatile MNP materials owing to its excellent mechanical malleability, robust electrical and thermal conductivity, and unique plasmonic and photonic characteristics [11][12][13][14][15][16] . ...
A facile and scalable lithography-free fabrication technique, named solution-processable electrode-material embedding in dynamically inscribed nanopatterns (SPEEDIN), is developed to produce highly durable electronics. SPEEDIN uniquely utilizes a single continuous flow-line manufacturing process comprised of dynamic nanoinscribing and metal nanoparticle solution coating with selective embedding. Nano- and/or micro-trenches are inscribed into arbitrary polymers, and then an Ag nanoparticle solution is dispersed, soft-baked, doctor-bladed, and hard-baked to embed Ag micro- and nanowire structures into the trenches. Compared to lithographically embossed metal structures, the embedded SPEEDIN architectures can achieve higher durability with comparable optical and electrical properties and are robust and power-efficient even under extreme stresses such as scratching and bending. As one tangible application of SPEEDIN, we demonstrate a flexible metal electrode that can operate at 5 V at temperatures up to 300 °C even under the influence of harsh external stimuli. SPEEDIN can be applied to the scalable fabrication of diverse flexible devices that are reliable for heavy-duty operation in harsh environments involving high temperatures, mechanical deformations, and chemical hazards.
... Recently, photocatalysis has been identified as an economically efficient and environmentally friendly advanced oxidation process (AOP), that is capable of mineralizing a wide range of organic compounds including recalcitrant phenolics (Adenuga et al., 2019). The most widely investigated photocatalysts are the TiO2-based nanoparticles (NPs) as they are inexpensive, non-toxic and structurally stable (An et al., 2016). However, the large band gap of TiO 2 (3.2 eV (Cui et al., 2015)), has limited its application. ...
In this study, highly efficient silver halide (Ag/AgX where X= Cl, Br, I), photocatalysts were successfully synthesized through hydrothermal method. The prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET). All three compounds were confirmed to be pure with the associated planes being identified. The photocatalytic activity of these photocatalysts were evaluated through the degradation of 2,4-dichlorophenol (2,4-2,4-DCP) under UV and visible light irradiation. Variant photocatalytic efficiency was exhibited dependent on the material used. The Ag/AgBr photocatalysts exhibited the best efficiency among all three catalysts, resulting in an 83.37 % and 89.39 % photodegradation under UV and visible light after 5 h, respectively, at a catalyst loading of 0.5 g/L.
In this study, polymeric graphitic carbon nitride (g-C3N4) semiconductors was synthesized via a thermal condensation method. Subsequently, Ag/AgBr nanoparticles with varying ratios were decorated onto the g-C3N4 surface using the water/oil emulsion method. The resulting nanocomposites were characterized using XRD for phase identification and structural analysis, HR-TEM and SEM&EDAX for morphological structure, particle size, and elemental composition analysis, and XPS for investigating the chemical state and electronic structure. The impact of Ag/AgBr content on the optical properties of g-C3N4 were also studied such as (optical bandgap (Eg), refractive index (n), extinction coefficient (k), optical conductivity (σopt) and dielectric function (ε*)), Electrochemical impedance spectroscopy (EIS), PL spectroscopy and Chrono-amperometric investigations were conducted to assess the charge transfer capabilities and long-term durability of the prepared nanocomposites. The results revealed a reduction in Ag/AgBr particle size with an increase in g-C3N4 content, accompanied by a decrease in the optical bandgap from 2.444 eV to 2.393 eV. Furthermore, the nanocomposites exhibited enhanced degradation efficiencies of RhB dye, with the highest tested content of Ag/AgBr achieving 100% degradation after 120 min of irradiation. However, the challenge of catalyst separation after the degradation process remained. To address this issue, we developed a novel approach by impregnating Ag/AgBr@g-C3N4 photocatalyst onto a floating porous sponge using a simple sugar-template technique, offering potential as a reusable photocatalyst material. Furthermore, the 3D PDMS − Ag/AgBr@g-C3N4 photocatalyst was evaluated and found to maintain nearly the same photocatalytic efficiency for up to 5 consecutive cycles.
In this study, the photocatalytic activity of nanomaterials Ag/AgX (X = Cl, Br, I) is reported. Highly efficient silver halide (Ag/AgX where X = Cl, Br, I) photocatalysts were synthesized through a hydrothermal method. The samples were characterized using a range of techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), and Brunauer–Emmett–Teller (BET) to check their structural, morphology, textural and optical properties. In addition, the photocatalytic activity of photocatalysts was evaluated through the degradation of 2,4-dichlorophenol (2,4-DCP) under UV and visible light irradiation. XRD analysis confirmed the presence of a single-phase structure (pure phase) in the synthesized photocatalysts. SEM micrographs showed agglomeration with a non-uniform distribution of particles, which is a characteristic of surfactant-free precipitation reactions in aqueous media. The Ag/AgBr photocatalyst exhibited the best degradation efficiency, resulting in 83.37% and 89.39% photodegradation after 5 h of UV and visible light irradiation, respectively. The effect of catalyst loading, initial solution pH, and 2,4-DCP concentration was investigated for the best-performing Ag/AgBr photocatalyst. The degradation kinetics were best described by the pseudo-first-order Langmuir–Hinshelwood model. The photocatalytic capacity of Ag/AgBr decreased by 50% after five reuse cycles. SEM images revealed heightened levels of photodegradation on the catalyst surface. The study proved the feasibility of using simple synthesis methods to produce visible light active photocatalysts capable of degrading refractory phenolic pollutants in aqueous systems.
In general, inorganic non‐metallic materials exhibit brittleness, and achieving plasticity in wide‐gap semiconductors or dielectrics poses an even greater challenge. Historically, silver halides have been suggested to be ductile; however, their deformability under different load modes has not been well demonstrated, and the underlying mechanisms are not fully understood. In this study, the authors demonstrate the excellent plasticity of AgCl and AgBr polycrystals at room temperature under tension, bending, compression, and roller pressing. In particular, the rolling reduction rate of AgCl/AgBr exceeds 97%, corresponding to the plastic extensibility from 3600% to 4200%. The metal‐like plasticity and multiple slip systems are attributed to the ionic features, specifically the Coulombic nature of the Ag‐Cl/Br interactions, and the appreciable polarization of the anions. Such less localized diffuse bonding can be readily switched upon atomic gliding, thus ensuring slip without cleavage. This study contributes to the advancement of the understanding and development of wide‐gap plastically deformable inorganic materials for applications in flexible, shape‐conformable high‐power electronics and dielectrics.
Structural, dielectric, and lattice dynamical properties of AgCl in the rock-salt structure are studied using density functional theory within generalized gradient approximation(GGA) in Perdew-Burke-Erzhenhof(PBE) parametrization and plane-wave pseudopotential method. The effect of van der Waals interaction (vdW) and Hubbard-U is investigated in detail for the lattice parameters, bulk modulus, dielectric, and phonon properties and compared to available experimental measurements. It is found that, inclusion of vdW interactions together with Hubbard U parameter to the standard GGA-PBE (PBE+vdW+U) improved the agreement with experimental lattice constant and bulk modulus of rock-salt AgCl. Moreover, PBE+vdW+U method is also correctly describes the acoustic and transverse optical (TO) phonon dispersion relation curves. The large underestimation (15%) of GGA-PBE in the longitudinal optical (LO) modes with respect to experiment is also decreased to 5% within the PBE+vdW+U method. This work demonstrates the applicability and accuracy of the van der Waals interaction and Hubbard-U term in predicting the structural, dielectric, and lattice dynamical properties of AgCl in the rock-salt structure.
Silver (Ag) containing nanomaterials were successfully prepared by varying synthesis
conditions to understand the influence of preparation conditions on the physicochemical and photocatalytic
properties of these materials. Different analytical techniques such as X-ray diffraction
(XRD), Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM), Diffuse
reflectance UV-vis spectra (DR UV-vis), X-ray photoelectron spectroscopy (XPS) measurements,
and N2-physisorption were used to investigate the physicochemical properties of synthesized Ag
containing nanomaterials. The samples (Ag-1 and Ag-2) prepared using AgNO3, NaHCO3, and
polyvinylpyrrolidone (PVP) template exhibited pure Ag metal nanorods and nanoparticles; the
morphology of Ag metal is influenced by the hydrothermal treatment. The Ag-3 sample prepared
without PVP template and calcined at 250 �C showed the presence of a pure Ag2O phase. However,
the same sample dried at 50 �C (Ag-4) showed the presence of a pure Ag2CO3 phase. Interestingly,
subjecting the sample to hydrothermal treatment (Ag-5) has not resulted in any change in crystal
structure, but particle size was increased. All the synthesized Ag containing nanomaterials were used
as photocatalysts for p-nitrophenol (p-NP) degradation under visible light irradiation. The Ag-4 sample
(pure Ag2CO3 with small crystallite size) exhibited high photocatalytic activity (86% efficiency
at pH 10, p-NP concentration of 16 mg L1, 120 min and catalyst mass of 100 mg) compared to the
other synthesized Ag containing nanomaterials. The high photocatalytic activity of the Ag-4 sample
is possibly due to the presence of a pure Ag2CO3 crystal structure with nanorod morphology with a
low band gap energy of 1.96 eV and relative high surface area.
Ag-based semiconductors have attracted significant attention as promising visible-light photocatalysts for environmental purification. In this study, electronic and photocatalytic properties of AgTi2(PO4)3 NASICON-type phosphate, have been addressed in detail, combining experimental results and theoretical calculations. The as-prepared sample was characterized for its morphological, structural and optical properties by various techniques. The generalized gradient approximation by Perdew-Burke-Ernzerhof (GGA-PPE) within density functional theory (DFT) was used to investigate the electronic structure. We have applied corrective Hubbard U terms to Ti 3d orbitals in order to better reproduce the experimental band gap of 2.6 eV. The photocatalytic activity has then been performed for rhodamine B dye degradation under visible light illumination. Efficient dye degradation up to 97.2 % was achieved in 120 min. In addition, the catalyst exhibited good stability over four consecutive cycles. Finally, combining experimental and theoretical findings, the origin of the photocatalytic activity was identified and a photodegradation mechanism was proposed.
In this study, it has been reported that the polymeric graphitic carbon nitride (g-C3N4) was modified by anchoring Ag/AgBr to improve its charge separation efficiency. When compared to g-C3N4 nanosheets...
A new type of perylene diimide attached AgCl photocatalyst (PDISA/AgCl) was prepared by one-step chemical precipitation method. Some characterizations, like XRD, SEM and XPS, etc, were measured to analyze its crystal structure, surface characteristics, elemental composition. From the characterization results, PDISA/AgCl exhibited broader light absorption range and higher separation efficiency of photoinduced charge. During the photodegradation process, PDISA/AgCl composites can effectively degrade rhodamine B (RhB), methyl orange (MO), methylene blue (MB) and tetracycline hydrochloride (TC), especially in the degradation of RhB, it shows excellent stability performance. Therefore, the PDISA/AgCl composite is an efficient and stable photocatalyst. Finally, the possible photocatalytic mechanism is proposed. The prepared new photocatalyst show good application prospects in photodegradation of water pollution and environmental treatment.
It is a useful strategy to use a solid electronic mediator with good conductivity to assist the separation of semiconductor photo-induced electron-hole pairs and the redox of semiconductor materials. In order to construct a photocatalyst for more efficient photocatalytic degradation of antibiotics, a simple hydrothermal and precipitation method was used to construct the Ag–AgBr/Bi2O2CO3/CNT Z-scheme heterojunction by using carbon nanotubes (CNTs) as electronic mediators. Compared with the pristine AgBr, Bi2O2CO3, Bi2O2CO3/CNT, the 30%Ag–AgBr/Bi2O2CO3/CNT photocatalyst has better photocatalytic activity under visible light irradiation, showing the best degradation ability to tetracycline (TC). Meanwhile, the photocatalytic properties of 30%Ag–AgBr/Bi2O2CO3/CNT in different pH and inorganic ions were studied. Finally, the degradation pathway and catalytic mechanism of 30%Ag–AgBr/Bi2O2CO3/CNT photocatalytic degradation of TC were also argued. The construction of the Z-scheme electron transport pathway, in which CNTs were used as electronic mediators, and the SPR effect of Ag and Bi metal, which enable the effective separation and transfer of photo-generated electron-hole pairs, are responsible for the significant improvement in photocatalytic performance. It opens up new possibilities for designing and developing high-efficiency photocatalysts with CNTs as the electronic mediator.
Here, sea urchin‐shaped nanoparticles were first fabricated by growing one dimensional polyaniline (1D PANI) nanowire array on carbon layer encapsulated Fe3O4 nanoparticles, and then Ag@AgCl photocatalyst were tightly anchored on the surface of PANI nanowire to form Fe3O4@C/1D PANI/Ag@AgCl bifunctional material as recyclable adsorption‐photocatalysts and surface enhanced Raman scattering (SERS) substrate to monitor photocatalytic degradation of dye molecules. Compared with Fe3O4@C/1D PANI, Ag@AgCl and Fe3O4@C/PANI/Ag@AgCl catalysts, the fast electron transfer characteristics of conductive 1D PANI nanowire array and the synergistic effect between the surface plasmon resonance of Ag and the photosensitive characteristic of AgCl, enabled the prepared Fe3O4@C/1D PANI/Ag@AgCl excellent adsorption‐photocatalytic efficiency for the degradation of RhB under visible‐light irradiation. PL spectra and a series of photoelectrochemical measurements were carried out to investigate the reasons for such enhanced photocatalytic activity and the possible improved photocatalytic degradation mechanism was proposed. Meanwhile, the detection of the presence of RhB and its degradation process were achieved with real‐time SERS technology employing the prepared Fe3O4@C/1D PANI/Ag@AgCl photocatalyst itself as the substrate. All the results made it great promise for simultaneously monitoring and removal of organic contaminants in water. Bifunctional material prepared by anchoring Ag@AgCl photocatalysts onto the 1D PANI nanowire array on the surface of sea urchin‐shaped Fe3O4@C/1D PANI were designed for enhanced adsorption‐visible light photocatalytic degradation and simultaneously in‐situ surface enhanced Raman scattering (SERS) monitoring of organic pollutants.
Silver halides with visible light-driven photocatalytic performances have attracted wide attention in the fields of water splitting, pollutant degradation and CO2 conversion. Generally, silver halides nanostructures with proper energy band and exposing facets determine the light absorption range and reactant adsorption, respectively, contributing to their photocatalytic performance. Moreover, the energy-band structures of silver halides are closely related to their morphology and compositions. Therefore, the controllable synthesis of well-defined silver halide nanostructures is of significant importance to investigate the structure-property relationship and the development of highly efficient silver halide-based photocatalysts.
In this article, we mainly focus on the progresses made in fabricating silver halide nanomaterials with various morphologies and compositions through highlighting the key factors, such as ion diffusion rate and morphology-directing agent, and summarizing general synthetic strategies in detail. In addition, the availability of well-defined silver halide nanostructures provides promising opportunities to explore their new properties and applications.
While the past decade has witnessed great successes in silver/silver halide-based (Ag/AgX, X = Cl,Br) plasmonic photocatalysts, a facile fabrication of ultrafine Ag/AgX nanoparticles (NPs), which is recognized to be an efficient avenue for boosted catalytic performances, still remains a formidable challenge. Ultrasmall sub-10-nm Ag/AgX, which are discretely distributed on graphene oxide (GO, sub10-Ag/AgX/GO), can be easily fabricated by an oxidation–halogenation treatment of Ag/GO precursors of sub-10-nm AgNPs (sub10-Ag/GO). Significantly, compared to Ag/AgCl/GO and Ag/AgBr/GO of hundred-nanometer-sized Ag/AgX, the sub10-Ag/AgCl/GO and sub10-Ag/AgBr/GO display substantially enhanced photocatalytic activity by a factor of ≈16.4 and 38.2 times, respectively, despite their inconspicuous visible-light absorptions. The ultrafine size of the sub10-Ag/AgX and their grafting on but not being enwrapped by GO, which cooperatively facilitate a superior spatial separation capability of photogenerated electrons and holes, a satisfactory accessibility/availability of the abundantly exposed active sites, and consequently promote a more efficient utilization of photogenerated charge carriers, play important roles in their superior catalytic activities. The investigation initiates a new way for ultrafine Ag-based nanocomposites, and by a simple treatment of chemically modifiable ultrasmall-sized precursors, it provides new clues for other desired ultrafine-sized advanced nanomaterials that are difficult to synthesize via conventional protocols.
Harvesting solar energy to drive the semiconductor photocatalysis offers a promising tactics to address ever-growing challenges of both energy shortage and environmental pollution. Design and synthesis of nano-heterostructure photocatalysts with controllable components and morphologies are the key factors for achieving highly-efficient photocatalytic processes. One-dimensional (1D) semiconductor nanofibers produced by electrospinning possess a large ratio of length-to-diameter, high ratio of surface-to-volume, small grain sizes as well as high porosity, which are ideally suited for photocatalytic reactions from the viewpoint of structure advantage. After the secondary treatment of these nanofibers through the solvothermal, gas reduction, in-situ doping or assembly methods, the multi-components nanofibers with hierarchical nano-heterostructures can be obtained to further enhance their light absorption and charge-carriers separation during the photocatalytic processes. In recent years, the electrospun-semiconductor-based nano-heterostructures have become a “hot topic” in the fields of photocatalytic energy conversion and environmental remediation. This review article summarizes the recent progresses in electrospinning synthesis of various kinds of high-performance semiconductor-based nano-heterostructure photocatalysts for H2 production, CO2 reduction, and decomposition of pollutants. The future perspectives of these materials are also discussed.
In situ synthesis of Ag/AgX nanoparticles (NPs) onto viscose fibers adds new functionalities and broadens their applications. In this study, Ag/AgX (X = Cl, I) NPs were in situ synthesized onto viscose fibers to impart brilliant colors, UV-protection, antimicrobial, self-cleaning, and photocatalytic properties. The AgX NPs were deposited on the fibers by ultrasonic irradiation, while Ag-NPs were formed by photoreduction of excess Ag + ions under UV irradiation. The Ag/AgX NPs-loaded onto viscose fibers endowed with pale yellow for Ag/AgI and pale purple/violet for Ag/AgCl. The colored viscose fibers showed excellent antimicrobial activity against Escherichia coli (gram-negative), Staphylococcus aureus (Gram positive), and Candida Albican. The Ag/AgX/viscose fiber also showed excellent photocatalytic and self-cleaning activity toward degradation of methylene blue.
Photocatalysis is considered to be an effective way to remove organic pollutants, but the key to photocatalysis is finding a high-efficiency and stable photocatalyst. 2D materials-based heterojunction has aroused widespread concerns in photocatalysis because of its merits in more active sites, adjustable band gaps and shorter charge transfer distance. Among various 2D heterojunction systems, 2D/2D heterojunction with a face-to-face contact interface is regarded as a highly promising photocatalyst. Due to the strong coupling interface in 2D/2D heterojunction, the separation and migration of photoexcited electron-hole pairs are facilitated, which enhances the photocatalytic performance. Thus, the design of 2D/2D heterojunction can become a potential model for expanding the application of photocatalysis in the removal of organic pollutants. Herein, in this review, we first summarize the fundamental principles, classification, and strategies for elevating photocatalytic performance. Then, the synthesis and application of the 2D/2D heterojunction system for the removal of organic pollutants are discussed. Finally, the challenges and perspectives in 2D/2D heterojunction photocatalysts and their application for removing organic pollutants are presented.
In view of their unique characteristics and properties, silver nanomaterials (Ag NMs) have been used not only in the field of nanomedicine but also for diverse advanced catalytic technologies. In this comprehensive review, light is shed on general synthetic approaches encompassing chemical reduction, sonochemical, microwave, and thermal treatment among the preparative methods for the syntheses of Ag-based NMs and their catalytic applications. Additionally, some of the latest innovative approaches such as continuous flow integrated with MW and other benign approaches have been emphasized that ultimately pave the way for sustainability. Moreover, the potential applications of emerging Ag NMs, including sub nanomaterials and single atoms, in the field of liquid-phase catalysis, photocatalysis, and electrocatalysis as well as a positive role of Ag NMs in catalytic reactions are meticulously summarized. The scientific interest in the synthesis and applications of Ag NMs lies in the integrated benefits of their catalytic activity, selectivity, stability, and recovery. Therefore, the rise and journey of Ag NM-based catalysts will inspire a new generation of chemists to tailor and design robust catalysts that can effectively tackle major environmental challenges and help to replace noble metals in advanced catalytic applications. This overview concludes by providing future perspectives on the research into Ag NMs in the arena of electrocatalysis and photocatalysis. This journal is
Recently, light-driven persulfate-based advanced oxidation processes (AOPs) employing heterogeneous catalysts to generate sulfate radicals (SO4•−) from persulfates [peroxydisulfate (PDS, S2O8²⁻) and peroxymonosulfate (PMS, HSO5⁻)] have been extensively investigated in the field of water remediation, to remove organic contaminants. This article aims to provide a comprehensive review of visible light-driven heterogeneous catalysis of persulfate activation, including the reaction mechanisms involved and the various types of heterogeneous catalysts utilized in organic contaminant removal, with particular focus on strategies for its enhancement. In the present review, we summarize three strategies for improving the visible light/persulfate/heterogeneous catalyst system, including photocatalyst design, photoelectricity coupling, and indirect activation mediated by homogeneous Fe(III) or Cu(II). This review highlights the advances in the photo-activation of persulfates for organic contaminant removal and also provides perspectives on the major challenges and opportunities involved.
Recently, polymeric carbon nitride (g-C 3 N 4) as a proficient photo-catalyst has been effectively employed in photocatalysis for energy conversion, storage, and pollutants degradation due to its low cost, robustness, and environmentally friendly nature. The critical review summarized the recent development, fundamentals, nanostructures design, advantages, and challenges of g-C 3 N 4 (CN), as potential future photoactive material. The review also discusses the latest information on the improvement of CN-based heterojunctions including Type-II, Z-scheme, metal/CN Schottky junctions, noble metal@CN, graphene@CN, carbon nanotubes (CNTs)@CN, metal-organic frameworks (MOFs)/CN, layered double hydroxides (LDH)/CN heterojunctions and CN-based heterostructures for H 2 production from H 2 O, CO 2 conversion and pollutants degradation in detail. The optical absorption, electronic behavior, charge separation and transfer, and bandgap alignment of CN-based heterojunctions are discussed elaborately. The correlations between CN-based heterostructures and photocatalytic activities are described excessively. Besides, the prospects of CN-based heterostructures for energy production, storage, and pollutants degradation are discussed.
Bi 2 O 2 CO 3 is a UV-light-driven photocatalyst. Bi 2 O 2 CO 3 nanoflakes modified with plasmonic Ag nanoparticles (Ag/Bi 2 O 2 CO 3 ) were obtained by a hydrothermal method. In the synthetic process, Ag 2 C 2 O 4 worked as the Ag source and C source for the simultaneous formation of Ag particles and CO[Formula: see text]. The optimum synthesis condition was found at [Formula: see text]C for 16[Formula: see text]h under alkaline condition. The binary heterostructure was then used for degrading 2, 4-Dichlorophenol (2, 4-DCP) and Rhodamine B in visible light, with an efficiency of nearly 80% for 2, 4-DCP and 100% for Rhodamine B after 4[Formula: see text]h and 2[Formula: see text]h reaction, respectively. The binary heterostructure exhibited improved photocatalytic activity compared to that of individual Ag and Bi 2 O 2 CO 3 due to Surface Plasmon Resonance (SPR) effect of Ag. Meanwhile, after five recycling experiments, Ag/Bi 2 O 2 CO 3 showed higher photocatalytic activity and lower performance degradation in comparison with the one prepared by photo-reduction of Ag[Formula: see text] on Bi 2 O 2 CO 3 nanoflakes. This indicated the advantage of one-pot synthetic method. This work is expected to provide an efficient photocatalyst for organic pollutants degradation.
Aqueous phase exfoliation of defect free graphene sheets is achieved employing nicotine based non-cytotoxic surface active ionic liquid (SAIL). The SAIL stabilizing the graphene acts as template, reducing agent and precursor of Br⁻ ions for in-situ preparation of of Ag/AgBr janus nanoparticles (JNPs) decorating graphene sheets under sunlight within 5 minutes of exposure, for the first time. Thus, prepared Ag/[email protected] nanocomposite (NC) shows 2.4 to 3.0 fold enhancement in photocatalytic activity towards degradation of an antibiotic, ciprofloxacin and Rhodamine-B dye, respectively in water under sunlight/visible light as compared to Ag/AgBr JNPs and other reported photocatalysts. Greater adsorption of contaminated molecules at Ag/[email protected] NC along with good elctron-hole separation lead to enhanced photocatalytic activity as compared to Ag/AgBr JNPs
Organic pollutants are widespread around our daily life that has brought serious environmental and health issues. Search for an effective technology to completely remove and ideally decompose organic pollutant is the main task for the scientists. There has been growing interest on the photocatalysis for degradation of organic pollutants in recent years, however, the fast recombination between the electrons and holes and the limited absorption in the visible-light range restrict its wide use. Nonlinear optical (NLO) materials with built in electric field are now proved to be a favorable approach for the new candidates and open a new chapter in the photocatalysis field. In this review, we described the fundamentals of NLO materials in the application of the photocatalysis field. The role of the built in electric field improved the charges separation was detailed explained, and next we introduced some classical NLO materials applied in the field of environmental containing the BaTiO3, SrTiO3, and the LiNbO3. In particular, we focused on the recent progress of mixed borate-based polar photocatalyst for the degradation of organic pollutants in our lab. We hope this review will offer a full understanding of borate-based NLO photocatalyst and facilitate the design of new photocatalytic materials for organic pollutant degradation.
In this research, nanocomposites made of CuCr2O4-g-C3N4 accommodating distinct contents of CuCr2O4 (1–4 wt %) nanoparticles (NPs) were endorsed for hydrogen gas production after illumination by visible light in the presence of aqueous glycerol solution. The ultrasonication-mixture method was applied to assure the homogeneous distribution of CuCr2O4 NPs over synthesized mesoporous g-C3N4. Such nanocomposites possess suppressed recombination between the photoinduced charges. High-resolution transmission electron microscopy and X-ray photoelectron spectroscopy examinations affirmed the formation of CuCr2O4-g-C3N4 heterojunctions. The separation between the induced charges and the photocatalytic performance with the CuCr2O4 NP amount were investigated. The CuCr2O4-g-C3N4 heterojunction of 3 wt % CuCr2O4 content was documented as the optimal heterojunction. Upgraded hydrogen gas generation was attained over the optimal heterojunction with the extent of ten and thirty times as those registered for pure CuCr2O4 and g-C3N4 specimens, respectively, under illumination by visible light. The photocatalytic performance acquired by the diverse synthesized specimens was assessed not only by their effectiveness to absorb light in the visible region but also by their potential to separate the photoinduced charges.
Silver/silver halides (Ag/AgX, X=Cl, Br, I)-based photocatalysts with tunable energetic synergies have attracted intensive attention in solar-energy-conversion. Herein, we introduce an appealing ternary Au/Ag/AgCl nanochain with short curvilinear necklace-like nanoarchitectures via an ingenious one-step strategy by pulsed laser irradiation of metallic ions in solution. Compared with binary Ag/AgCl nanoparticles (NPs), the ternary nanochains with stronger intermetallic synergy exhibit improved absorbance capacity and enhanced localized surface plasmon resonance (LSPR) under broad visible-light irradiation. Then, the Au/Ag/AgCl nanochains can obviously accelerate photoinduced electron transfer and boost the separation of electron-hole on their surfaces, providing an excellent photocatalytic activity towards degradation of methylene blue (MB). Meanwhile, the enhanced synergistic coupling effect of the ternary nanocomposites also enables them to inhibit the photocorrosion under visible-light irradiation. Interestingly, compared to monodisperse NPs, the Au/Ag/AgCl nanochains with numerous interconnected NPs can be self-deposited on the bottom of solution after each photocatalytic reaction. Without the aid of extra and complicated nanocatalyst-separation procedures, then the clear-water will be easily obtained. Therefore, the unique photocatalyst possesses pronounced long-term stability, since ∼97.6% photodegradation rate can be maintained after 14 recycling tests within two weeks. Undoubtedly, these findings will bring new opportunities to prepare high-performance photocatalysts for diverse practical applications.
The efficient utilization of solar energy has received tremendous interest due to the increasing environmental and energy concerns. The present paper discusses, the efficient integration of a plasmonic photocatalyst (Ag/AgCl) with an Iron-based metal-organic framework (MIL-88A(Fe)), for boosting the visible light photoreactivity of MIL-88A(Fe). Two composites of Ag/AgCl@MIL-88A(Fe) namely, MAG-1 and MAG-2 (stoichiometric ratio of Fe to Ag are 5: 1 and 2: 1) were successfully synthesized via facile in situ hydrothermal methods followed by UV reduction. The synthesized composite materials are characterized by FTIR, PXRD, UVDRS, PL, FESEM/EDX, TEM and BET analysis. Ag/AgCl@MIL-88A(Fe) (MAG-2) hybrid system shows excellent photocatalytic activity for the degradation of p-Nitrophenol (PNP), Rhodamine B (RhB), and Methylene Blue (MB) under sunlight. We found that 91% degradation of PNP in 80 min, 99% degradation of RhB in 70 min and 94% degradation of MB in 70 min has taken place by using MAG-2 as catalyst under sunlight. The superior activity of Ag/AgCl@MIL-88A(Fe) (MAG-2) is attributed to the synergistic effects from surface plasmon resonance (SPR) of Ag NPs and the electron transfer from MIL-88A(Fe) to Ag nanoparticles for effective separation of electron-hole pairs. Furthermore, the mechanism of the degradation of PNP, RhB and MB is proposed by analyzing the electron transfer path in the Ag/AgCl@MIL-88A(Fe).
Are classical nucleation theory and the 1950 LaMer model of particle formation supported for a wide range of particle formations, or do competing models in the form of chemical reaction mechanisms have better experimental support? Read on to find out.
As a fascinating metal-free visible-light-responsive photocatalyst, graphitic carbon nitride (g-C3N4) has become a new research hotspot and drawn significant attention in the field of solar energy conversion and environmental remediation applications. Because of low charge separation efficiency, it is usually difficult for single-component g-C3N4 to achieve optimum photocatalytic performance for solar energy conversion. The hetero-structuring, in particular, Z-scheme charge transport mechanism that mimics the natural photosynthesis process is a constructive way to solve the aforementioned problem owing to its effectiveness for spatially separating photoinduced electron–hole pairs and optimizing the reduction and oxidation ability of the photocatalytic system. This chapter provides a comprehensive overview on the recent advances in the development of g–C3N4–based Z-scheme photocatalysts, with particular focus on mechanistic breakthroughs, and highlights current state-of-the-art systems, which are at the forefront of the various photocatalytic applications, including CO2 reduction, hydrogen generation, and pollutant degradation.
Photocatalytic degradation of Reactive Black 5 (RB5) solution using Ag3PO4 particles was studied under visible light irradiation as a function of the initial pH of the reaction medium. At pH 5 and 7, RB5 decolourization was limited to 43% and 27%, respectively, at the end of 2 h. Under identical experimental conditions, at pH 9 and 11, more than 90% of RB5 was decolourized. The typical blue colour of RB5 turned pinkish orange when RB5 was subjected to Ag3PO4 photocatalysis at pH 9 or greater, with a readily observable shift of the characteristic wavelength from 595 nm initially to approximately 500 nm at the end of 30 min irradiation. Liquid chromatography–mass spectrometry analysis revealed the accumulation of intermediates with imine (=NH) and hydroazo (–HN–NH–) groups, indicating partial oxidation of amines or partial reduction of azo links. Theoretical calculations of band potentials besides the experimental evidence indicated that oxidation of RB5 by hydroxyl radicals and photogenerated holes in the valence band occurred concomitantly with reduction by electrons in the conduction band. The effect of the presence of some common anions on RB5 degradation was studied. The presence of carbonate ions did not have an adverse effect on RB5 decolourization; however, sulfate ions significantly inhibited the decolourization. The extent of RB5 decolourization remained almost unchanged but the rate of reaction was slower in the presence of chloride ions.
This study describes a one‐pot synthetic strategy consisting of concerted stabilization and photo and chemical reductions of metal ions to yield precise anisotropic nanostructures. Photoirradiation of an aqueous precursor solution containing Au3+, Ag+, Br−, and polyvinylpyrrolidone (PVP) forms Janus nanoparticles (NPs) composed of Au having a tiny Ag shell and AgBr. The Au NPs are initially generated by photoreduction of Au3+ in the precursor solution, in which the formation of silver halides is strongly inhibited by the coordination bond between Ag+ and the carbonyl groups in PVP. The coordinated PVP chains are adsorbed on the surfaces of the Au NPs, with the concomitant release of free Ag+ ions. The part of the surface of the Au NP is covered with a few Ag atoms via chemical reduction of Ag+ by PVP. AgBr nanocrystals grow at a bare site on the surface of each Au NP, resulting in the formation of nearly monodisperse Janus Au−AgBr NPs in high yield. A characteristic light absorption profile emerges due to the interface formed between Au and AgBr, which is demonstrated by finite‐difference time‐domain simulation. The precise nanostructures may be leveraged to elucidate mechanisms of photoelectrochemical processes and to construct advanced plasmonic photocatalysts.
Among various advanced oxidation processes, heterogeneous semiconductor-mediated photocatalysis, in particular, has been perceived as one of the most reliable and
impressive method owing to its confirmed capability in the environmental
refinement of a widely spread range of contaminants. However, scientists have now identified that a single-component photocatalyst is extremely competent for impressive large-scale photocatalytic decontaminations due to the serious challenges of inadequate potential position of conduction and valence bands, the short-range light response, and low charge carrier separation capability, which results in low energy consumption efficiency for solar light and poor quantum efficiency for photocatalytic reactions. In the recent efforts to launch impressible photocatalytic systems, the fabrication of heterostructured composites with two or more components with various phases has been considered as a developed approach for increased solar energy usage and photocatalysis. These photocatalytic systems can be categorized into several kinds, such as type-I, type II, type-III heterojunctions, p-n & n-n heterojunctions, Schottky heterojunctions, and Z-scheme heterojunctions. It t is difficult for a type-II
heterojunction to exhibit both strong redox ability and efficient separation
of the charge carriers in interfaces. In contrast, by stimulating natural photosynthesis, newly developed Z-scheme configurations have gradually become a hot spot study field in
photocatalysis, owing to its unique electron/hole pairs movement path different
from conventional charge migration path and they can satisfy the aforementioned requirements for premier photocatalytic performance compared to the other systems.
Metal nanocrystals are of considerable scientific interest because of their uses in electronics, catalysis, and spectroscopy, but the mechanisms by which nanocrystals nucleate and grow to achieve selective shapes are poorly understood. Ab initio calculations and experiments have consistently shown that the lowest energy isomers for small silver nanoparticles exhibit two-dimensional (2D) configurations and that a transition into three-dimensional (3D) configurations occurs with the addition of only a few atoms. We parameterized an e-ReaxFF potential for Ag nanoclusters (N ≤ 20 atoms) that accurately reproduces the 2D-3D transition observed between the Ag5 and Ag7 clusters. This potential includes a four-body dihedral term that imposes an energetic penalty to 3D structures that is significant for small clusters but is overpowered by the bond energy from out-of-plane Ag-Ag bonds in larger 3D clusters. The potential was fit to data taken from density-functional theory and coupled-cluster calculations and compared to an embedded atom method potential to gauge its quality. We also demonstrate the potential of e-ReaxFF to model redox reactions in silver halides and plasmon motion using molecular dynamics simulations. This is the first case in which e-ReaxFF is used to describe metals. Furthermore, the inclusion of a bond-order dependent dihedral angle in this force field is a unique solution to modeling the 2D-3D transition seen in small metal nanoclusters.
Water reuse for drinking, irrigation, district cooling, process heating/cooling, landscaping, etc. remains pivotal to water security and sustainability. Advanced oxidation processes (AOPs) are at the heart of the industrial wastewater treatment especially the removal of contaminants of emerging concern. Recent studies conducted to advance the AOP technologies for the degradation of industrial wastewater pollutants generally encompass seven areas, namely artificial neural networks (ANNs), sustainability, plasma activation, catalyst structures, AOP-Bioremediation, and membrane-based AOPs. This review showcases the advancements in AOPs for the oxidation and removal of a wide range of contaminants of emerging concern from water. A detailed discussion and a critical examination of recently published works is presented in this article. Much of the reports have recorded technical progress in the form of, improved energy efficiency through the use of low-energy and renewable energy sources, successful prediction process performance and process control, improved light capturing capabilities through plasmonic effect, successful integration with biological treatment methods and membrane filtration. In spite of this progress, a number of challenges still persist such as the lack of appropriate ANN modeling structures, impractical spatial and temporal scales of investigation (i.e. scales that are too low for real operations), membrane fouling in membrane-based AOPs. These challenges have been pointed out and the strategies for addressing them have been highlighted in the article.
Objective
Bacterial adhesion and colonization on implanted devices are major etiological factors of peri-implantitis in dentistry. Enhancing the antibacterial properties of implant surfaces is a promising way to reduce the occurrence of inflammations. In this in vitro study, the antibacterial potential of two nanocomposite surfaces were investigated, as possible new materials for implantology.
Material and methods
The structural and photocatalytic properties of the TiO2 and Ag-TiO2 (with 0.001 wt% plasmonic Ag content) photocatalyst containing polymer based composite layers were also studied and compared to the unmodified standard sandblasted and acid etched Ti discs (control). The presence of visible light induced reactive oxygen species was also verified and quantified by luminol based chemiluminescence (CL) probe method. The discs with adhered Streptococcus mitis were illuminated for 5, 10 and 15 minutes. The antibacterial effect was determined by the metabolic activities of the adhered and proliferated bacterial cells and protein assay at each time point.
Results
The Ag-TiO2 containing surfaces with obvious photocatalytic activity eliminated the highest amount of the metabolically active bacteria, compared to the control discs in the dark, after 15 min illumination.
Conclusions
The plasmonic Ag-enhanced and illuminated surface exhibits significantly better antibacterial activity under harmless visible light irradiation, than the control Ti or TiO2 containing copolymer. The studied surface modifications could be promising for further, more complex investigations associated with dental research on infection prevention in connection with oral implantation.
Hollow-structured polyhedral nanostructures of AgI nanoboxes and cube-tetrapod Ag/AgI cages have been fabricated through the controlled reaction of I- ions with nanocubes and cube-tetrapods of AgCl based on the principle of the Kirkendall effect. The Ag-0 nanodomains in the source nanoparticles of AgCl:Ag are preserved in the final hollow Ag/AgI cages during the chemical conversion of AgCl to AgI. The obtained hollow cube-tetrapod Ag/AgI nanostructures exhibited enhanced light absorption in the visible region and photocatalytic performance towards hydrogen evolution from water reduction and decomposition of organic pollutants, owing to the contribution of the surface plasmon resonance (SPR) effect of silver nanoparticles (nanodomains). The present versatile route can be generalized to the preparation of other inorganic functional materials with hollow interiors for different applications.
The performance of a photocatalytic reaction is mainly determined by the quality of the photocatalyst. For real applications, significantly enhancing the stability and activity of the photocatalysts still remains a challenge for materials scientists and chemists. In this paper, we have achieved a highly efficient plasmonic AgCl-Ag nanophotocatalyst via photochemical conversion of AgCl nanocubes. Compared with reported photocatalysts, the as-achieved nanophotocatalyst exhibits superior activity, long-term stability, and wide applicability in the decomposition of organic dye pollutants. For example, only 30 s is needed to bleach methyl orange molecules assisted by AgCl-Ag nanoparticles. Furthermore, the catalyst can be reused up to 50 times without significant loss of activity. A possible mechanism was discussed and the specified photocatalytic reactions verified that both O-2(center dot-) and OH center dot radicals were the main active species in decomposing pollutants. The excellent performance of the present photocatalyst suggests promising applications in environmental remediation, clean energy creation, and solar cells.
In this paper, plasmonic photocatalyst Ag@AgCl nanotubes were prepared by a cost-efficient and template-based method and their photocatalytic properties were studied. In the synthesis, copper nanowires were firstly synthesized and Ag nanotubes were then obtained through the galvanic reaction between copper and Ag ions. The formation of Ag@AgCl nanotubes were finally achieved by in situ oxidation reaction upon the addition of FeCl3. The crystal structure of the product was characterized by X-ray powder diffraction (XRD). The morphology and composition of the composite were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) measurements. All the structure characterizations showed that tubulate product was produced by the synthetic processes. By using the obtained product as photocatalyst, the photodegradation of methyl orange (MO) was investigated under visible light. The experimental results showed that the as-prepared Ag@AgCl nanotubes exhibit excellent photocatalytic performance and high stability. Under visible light irradiation more than 92.58% MO dye has been decomposed in 10 min on the product with a 1:1 ratio of Fe/Ag. On the basis of the proposed mechanism, the improved photocatalytic activities of the Ag@AgCl hybrids can be ascribed to the enhanced surface area for dye molecule adsorption, enhanced visible light absorbance, and the efficient charge separation of the hybrid nanostructures.
Photon-coupling and electron dynamics are the key processes leading to the photocatalytic activity of plasmonic metal-semiconductor nanohybrids. To better utilize and explore these effects, a facile large-scale synthesis route to form Ag@AgCl cubic cages with well-defined hollow interiors is carried out using a water-soluble sacrificial salt-crystal-template process. Theoretical calculations and experimental probes of the electron transfer process are used in an effort to gain insight into the underlying plasmonic properties of the Ag@AgCl materials. Efficient utilization of solar energy to create electron-hole pairs is attributed to the significant light confinement and enhancement around the Ag/AgCl interfacial plasmon hot spots and multilight-reflection inside the cage structure. More importantly, an ultrafast electron transfer process (≤150 fs) from Ag nanoparticles to the AgCl surface is detected, which facilitates the charge separation efficiency in this system, contributing to high photocatalytic activity and stability of Ag@AgCl photocatalyst towards organic dye degradation.
The 2,3-bis(6′-methyl-2,2′-bipyridin-6-yl)pyrazine ligand L reacts with trifluoromethanesulfonate silver(I) to give a coordination polymer {[AgL](CF3SO3)}n in which metal ions are in a distorted tetragonal pyramidal coordination geometry. The complex has been characterized by spectroscopic techniques, elemental analysis, X-ray diffraction, and UV-Vis spectroscopy. The methylene blue (MB) degradation was studied using UV-Vis spectrophotometry. After 400 min of exposure to UV light MB was completely decomposed. Degradation of MB after exposure to sunlight was considerably slower: 34% after 400 min and 90% after 133 h. Photodegradation of the dye follows second-order kinetics. {[AgL](CF3SO3)}n is an active photocatalyst for MB degradation under UV-Vis and sunlight irradiation.
A metal doped coupled semiconductor oxide, Ag–ZnO–CdO was fabricated by a simple co-precipitation method and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), elemental mapping, high-resolution scanning electron microscopy (HR-SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET) surface area measurement, UV-Vis diffuse reflectance spectroscopy (DRS) and photoluminescence spectroscopy (PL). XRD and EDS reveal the presence of CdO and metallic Ag in the catalyst. FESEM shows a mixture of hexagonal nanosheets, nanoclusters and nanoparticles with a large number of cavities. HR-SEM and TEM images of the catalyst show that ZnO particles have pentagonal or hexagonal plate-like structure. Cadmium oxide and silver clusters are formed on the clear smooth surface of ZnO. Ag–ZnO–CdO has increased absorption in the UV and Visible region when compared to ZnO. This three component nanojunction system exhibited enhanced photocatalytic activity for the degradation of acid black 1 (AB 1) and acid violet 7 (AV 7) under sunlight far exceeding those of the single and two component systems. Ag–ZnO–CdO was found to be stable and reusable without appreciable loss of catalytic activity up to five runs. This metal doped coupled oxide shows increased hydrophobicity, when compared to CdO or ZnO. Our results provide new insights of the performance of a solar active photocatalyst with self-cleaning properties.
This work reports on a two-stage strategy towards the controlled Ag–AgBr deposition onto thorny anatase TiO2 tubes for excellent simulated solar-light photocatalytic activities. First, anatase TiO2 tubes with a thorny porous external surface were prepared using rod-like TiOSO4·2H2O as sacrificial template and a Ti source via a solvothermal process followed by annealing. The formation mechanism of the anatase TiO2 tubular precursor was investigated in detail. Then, the prepared anatase TiO2 tubes were used as a support for loading AgBrnanoparticles using the deposition–precipitation method, and the deposited AgBr was partially reduced to Agvia the calcination process to fabricate the Ag–AgBr/TiO2 tubular composites. X-Ray absorption near edge spectra (XANES), extend X-ray absorption fine structure (EXAFS) spectra and X-ray photoelectron spectroscopy (XPS) analyses indicated that both AgBr and Ag0 components coexist in the systems. Compared with conventional nanoparticles and nanotubes, there exist abundant microcavities in the roughly parallel nanothorns of the tubes, which can contribute to the stable deposition of the Ag–AgBr nanoparticles and the formation of effective nanojunctions. These composites exhibited superior photocatalytic activity in the degradation of phenol under simulated solar-light irradiation.
Studies of the optical properties and catalytic capabilities of noble metal nanoparticles (NPs), such as gold (Au) and silver (Ag), have formed the basis for the very recent fast expansion of the field of green photocatalysis: photocatalysis utilizing visible and ultraviolet light, a major part of the solar spectrum. The reason for this growth is the recognition that the localised surface plasmon resonance (LSPR) effect of Au NPs and Ag NPs can couple the light flux to the conduction electrons of metal NPs, and the excited electrons and enhanced electric fields in close proximity to the NPs can contribute to converting the solar energy to chemical energy by photon-driven photocatalytic reactions. Previously the LSPR effect of noble metal NPs was utilized almost exclusively to improve the performance of semiconductor photocatalysts (for example, TiO2 and Ag halides), but recently, a conceptual breakthrough was made: studies on light driven reactions catalysed by NPs of Au or Ag on photocatalytically inactive supports (insulating solids with a very wide band gap) have demonstrated that these materials are a class of efficient photocatalysts working by mechanisms distinct from those of semiconducting photocatalysts. There are several reasons for the significant photocatalytic activity of Au and Ag NPs. (1) The conduction electrons of the particles gain the irradiation energy, resulting in high energy electrons at the NP surface which is desirable for activating molecules on the particles for chemical reactions. (2) In such a photocatalysis system, both light harvesting and the catalysing reaction take place on the nanoparticle, and so charge transfer between the NPs and support is not a prerequisite. (3) The density of the conduction electrons at the NP surface is much higher than that at the surface of any semiconductor, and these electrons can drive the reactions on the catalysts. (4) The metal NPs have much better affinity than semiconductors to many reactants, especially organic molecules. Recent progress in photocatalysis using Au and Ag NPs on insulator supports is reviewed. We focus on the mechanism differences between insulator and semiconductor-supported Au and Ag NPs when applied in photocatalytic processes, and the influence of important factors, light intensity and wavelength, in particular estimations of light irradiation contribution, by calculating the apparent activation energies of photo reactions and thermal reactions.
The modification of photocatalysts by silver addition or deposition can be used to increase photocatalytic efficiencies by preventing photogenerated electron–hole recombination through electron trapping mechanisms, and by increasing visible light absorption of the composite materials through the surface plasmon resonance enhancement of silver nanoparticles. Nanosilver also possesses excellent antimicrobial activity, and can be used as a biocidal agent when incorporated into TiO2 photocatalysts. Alternatively, the host photocatalyst may also contribute to antimicrobial activity observed in the absence of irradiation, such as for AgX (X = Cl, Br, I) and ZnO. These silver-modified composites present a novel class of hybrid photocatalysts, which possess antibacterial and/or antiviral action in both dark and light conditions, and are discussed in detail in this review. In addition, other antimicrobial photocatalysts such as those based on copper are examined. Further work should be performed on these materials to distinguish the roles of acting mechanisms in the light-induced disinfection processes.
Ag-loaded ZnO mesocrystals with Fe3+ doped (PAZ) can be quantity-produced through an atmospheric self-induction synthesis method. This synthesis method avoids the use of a high-pressure instrument for the synthesis of mesocrystal catalysts. Compared with traditional Ag-ZnO catalysts, the threshold wavelength of 1FAZ mesocrystals was shifted to the full visible light region and the absorbance of catalyst in the visible region increased to more than 300%. The content of iron ion was found to be significant to the photocatalytic efficiency of FAZ mesocrystals. The experimental results demonstrated that the most optimal molar ratio of Fe3+ to Zn atoms was 1%, and the photocatalytic activity of 1FAZ mesocrystals was increased by 145% compared with Ag-ZnO obtained under visible light. A feasible water purification system with a continuous photodegradation reactor using PAZ mesocrystals was manufactured to utilize solar light as the energy to drive the running of the water purification system.
Ag/AgX/BiOX (X = Cl, Br) three-component visible-light-driven (VLD) photocatalysts were synthesized by a low-temperature chemical bath method and characterized by X-ray diffraction patterns, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and UV−vis diffuse reflectance spectra. The Ag/ AgX/BiOX composites showed enhanced VLD photocatalytic activity for the degradation of rhodamine B, which was much higher than Ag/AgX and BiOX. The photocatalytic mecha-nisms were analyzed by active species trapping and superoxide radical quantification experiments. It revealed that metallic Ag played a different role for Ag/AgX/BiOX VLD photocatalysts, surface plasmon resonance for Ag/AgCl/BiOCl, and the Z-scheme bridge for Ag/AgBr/BiOBr.
Quantum dots (QDs) Ag@AgCl decorated on the surface of flower-like Bi2WO6 (hereafter designated Ag@AgCl/Bi2WO6) were prepared via a facile oil-in-water self-assembly method. The photocatalysts were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (DRS) and X-ray fluorescence spectrometer (XRF) etc. The characterization results indicated that QDs Ag@AgCl was observed to be evenly dispersed on the surface of Bi2WO6, and was approximately 10-20 nm in size. Ag@AgCl/Bi2WO6 composites exhibited excellent UV-vis absorption, due to quantum dimension effect of Ag@AgCl QDs, the surface plasmonic resonance (SPR) of Ag nanoparticles and the special flower-like structure of Bi2WO6. The photo-electrochemical measurement verified that the suitable band potential of Ag@AgCl and Bi2WO6 and the existence of metal Ag resulted in the high efficiency in charge separation of the composite. The photocatalytic activities of the Ag@AgCl/Bi2WO6 samples were examined under visible light irradiation for the degradation of Rhodamine B (RhB). The composite presented excellent photocatalytic activity due to the synergetic effect of Bi2WO6, AgCl, and Ag nanoparticles. The Ag@AgCl(20 wt.%)/Bi2WO6 sample exhibited the best photocatalytic activity, degrading 97.61% RhB after irradiation for 2 h, which was, respectively, 1.33 times and 1.32 times higher than that of Ag@AgCl and Bi2WO6 photocatalyst. Meanwhile, phenol was degraded to further prove the degradation ability of Ag@AgCl/Bi2WO6. Additionally, studies performed using radical scavengers indicated that O2−·, h+ and Cl0 acted as the main reactive species. Based on above, a photocatalytic mechanism for organics degradation over Ag@AgCl/Bi2WO6 was proposed.
A plasmonic Ag-AgBr/Bi2O2CO3 composite photocatalyst was prepared by a two-step synthesis method. The as-prepared Ag-AgBr/Bi2O2CO3 was characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray, X-ray photoelectron, ultraviolet-visible diffuse reflection, and photoluminescence spectroscopy. As probe pollutants, rhodamine B (RhB) and methylene blue (MB) were adopted to investigate the photocatalytic activity of the Ag-AgBr/Bi2O2CO3 composite photocatalyst under visible light irradiation. The as-prepared photocatalyst showed an enhanced photocatalytic activity for the degradation of RhB and MB under visible light, which was attributed to the heterostructured Ag-AgBr/Bi2O2CO3 and surface plasmon resonance (SPR) exhibited by Ag nanoparticles. Simultaneously, high stability of the sample was also investigated by five successive photodegradations of RhB under visible light. The relationship between photocatalytic activity and the structure of Ag-AgBr/Bi2O2CO3 is discussed, and possible reaction mechanisms are also proposed.
Monoclinic ?-AgVO<sub align="right"> 3 </sub> nanorods (thickness 30 nm) and monoclinic BiVO<sub align="right"> 4 </sub> nanobars (thickness 15 nm) with high aspect ratio are prepared by controlling the reaction kinetics of room temperature precipitation, without using any capping agents or surfactants. The nanocrystalline vanadates are characterised using XRD, SEM, EDAX, FESEM, TEM and AFM. Possible growth mechanisms of the nanocrystals are explained by the oriented attachment of flocs through an anisotropic growth. Ag nanoparticles are formed in-situ on AgVO<sub align="right"> 3 </sub> nanorods. Using diffuse reflectance spectral analysis the band gaps of ?-AgVO<sub align="right"> 3 </sub> nanorods and BiVO<sub align="right"> 4 </sub> nanobars are calculated and their photocatalytic behaviour is investigated by photodegradation of methylene blue. The ?-AgVO<sub align="right"> 3 </sub> nanorods have higher pore volume compared to BiVO<sub align="right"> 4 </sub> nanobars. The Ag nanoparticles attached on the surface of AgVO<sub align="right"> 3 </sub> nanorods serve as active sites for photocatalysis. Hence silver vanadate nanorods exhibit remarkably enhanced photocatalytic activity and are a good candidate for visible light driven photocatalyst.
AgCl nanoparticles with a diameter of 50–100 nm were synthesized in ethylene glycol with the assistance of poly(vinylpyrrolidone) at room temperature. A photoactivation process was then introduced by exposing the as-obtained AgClnanoparticle solution to common fluorescent lamp or direct sunlight irradiation to form a uniform layer of Ag nanoparticles (5–10 nm) on the surface of the AgCl nanoparticles. The AgCl/Ag nanocomposites showed higher visible light photocatalytic activity for decomposing organic pollutants [such as methyl orange (MO), methyl blue (MB), and rhodamine B (RhB)] under the irradiation of common fluorescent lamp or direct sunlight. Recycle photocatalysis experiments indicated that the AgCl/Ag nanocomposite exhibited higher stability. Moreover, the AgCl/Ag nanocomposites showed better antibacterial properties on Escherichia coli, Staphylococcus aureus, and Bacillus subtilis.
Heterostructured Ag@AgBr/AgCl nanocashews have been synthesized by an anion-exchange reaction between AgCl nanocubes and Br− ions followed by photoreduction. Compared to polyhedral Ag@AgBr nanoparticles, the obtained nanostructures exhibit enhanced photocatalytic activity towards decomposition of organic pollutants, i.e., rhodamine-B (RhB). For example, only 2 min is taken to completely decompose RhB molecules with the assistance of these novel heterostructured nanoparticles under visible light irradiation. Furthermore, the as-synthesized nanocatalyst can be reused 20 times without losing activity, showing its high stability. Interestingly, the novel heterostructured Ag@AgBr/AgCl nanophotocatalyst also shows efficient visible light conversion of CO2 to energetic fuels, e.g. methanol/ethanol. Therefore, the present route opens an avenue to achieve highly efficient visible-light-driven nanophotocatalysts for applications in environmental remediation and resourceful use of CO2.
Silver halide (AgX, X = Cl, Br, I)-based materials represent an emerging class of heterogeneous photocatalysts. Despite progress in the synthesis of carrier-separated AgX-based photocatalysts, a number of issues remain unaddressed, including complicated synthesis, unfavorably large size and therefore poor photocatalytic performance of the resultant structures. Here we show the one-step DNA-programmable synthesis of Ag/AgCl nanostructures that takes only approximately 1 min for photocatalytic application. The optimal DNA-encapsulated structures show DNA sequence-specific sizes down to less than 40 nm with a Ag/AgCl composition ratio of 2:1, affording a vastly increased surface area and higher photocatalytic activity than any Ag/AgX nanostructures reported previously by over two orders of magnitude. From a physical standpoint, importantly, the plasmonic nanostructured silver in Ag/AgCl accelerates the photocatalytic reaction in terms of fast electron injection to AgCl, leading to enhanced hole–electron separation and high-performance photocatalysis under visible light. To test the effect of DNA encapsulation on the Ag/AgCl nanostructures, both positively and negatively charged organic compounds serve as the model pollutants to assess their photocatalytic selectivity. Our results show that the photodecomposition of the positively charged compounds obeys a first-order rate law, whereas the negatively charged compound is decomposed with zero-order kinetics. This comparison offers a mechanistic insight into reaction kinetics on the DNA-encapsulated photocatalyst. We further find that the DNA-encapsulated Ag/AgCl photocatalysts are robust and can be recycled. To extend the applicability of the Ag/AgCl nanostructures, their use in the efficient photocatalytic inactivation of cancer cells is also demonstrated for the first time, opening up a new avenue to daylight-based theranostics.
Concave particles represent a new class of structures with their surfaces curving in or hollowed inward and thus presence of regions with negative curvatures. Owing to the potential high-index facets and negative curvatures, crystalline particles with concave surfaces are expected to show unexplored or substantially enhanced performance in comparison with the counterpart particles with convex surfaces. In this report, we highlight a facile approach for the first-time synthesis of concave Agl nanoparticles through a controlled etching of spherical Agl particles in a solution containing ethylenediamine, absolute alcohol, and polyvinylpyrrolidone. Physical parameters including morphology and size of the resulting concave Agl particles can be tuned by carefully controlling the reaction conditions such as the amount of precursors and the injection rate of precursor solutions. Most importantly, the concave Agl particles exhibit a much higher efficiency towards photocatalytic degradation of organic molecules than the corresponding spherical Agl particles. The as-synthesized concave Agl particles are expected to be useful not only for the fundamental investigation on shape- and composition-dependent properties but also for potential applications in photocatalysis, electrocatalysis, photonics, etc.
BACKGROUND: Plasmonic photocatalysts have attracted considerable attention because of their applications in the degradation of organic pollutants. In order to enhance the stability of AgX photocatalyst, Ag/AgCl, Ag/AgBr/WO 3 , and Ag@AgCl/RGO were developed. Results implied that silver halides could maintain stability if the metal Ag was well dispersed on the silver halide particles and could display high catalytic activity.
RESULTS: PVP acted as a structure‐directing agent, and a reducing reagent in the reaction. Results show that Ag–AgBr delivered a much higher photocatalytic activity than AgBr and Ag–AgCl. The high photocatalytic activity of the Ag–AgBr composites can be attributed to the presence of metal Ag and the smaller particle size of the samples. The photocatalytic reaction followed first‐order kinetics. The rate constant k for the degradation of MO by Ag–AgBr was 2 and 18 times higher than that of AgBr and Ag–AgCl, respectively.
CONCLUSIONS: The MO degradation efficiency of Ag–AgBr was 94% after 10 min. After 5 cycles of repeatability tests, the degradation efficiency of MO still remained at 90%. The high photocatalytic activity of the Ag–AgBr composites can be attributed to the presence of metal Ag and the smaller particle size of the samples. Copyright © 2012 Society of Chemical Industry
We explored how the visible-light energy absorbed by noble-metal nanoparticles (NPs) is converted to electrons and holes in the semiconductor in a visible-light plasmonic photocatalyst by studying the representative system Ag@AgCl on the basis of density functional calculations and classical electrodynamics calculations. These calculations suggest that the energy transfer from the Ag NPs to the semiconductor AgCl requires the presence of midgap defect states in the semiconductor and that the surface plasmon resonance (SPR) of the Ag NPs strongly enhances the optical transitions of the semiconductor involving the defect states. We verified this suggestion experimentally by preparing Ag@AgCl samples possessing different degrees of bulk and surface defects and subsequently by carrying out photodegradation experiments using these samples.
Usually, cocatalyst modification of photocatalysts is an efficient approach to enhance the photocatalytic performance by promoting effective separation of photogenerated electrons and holes. It is highly required to explore new and effective cocatalysts to further enhance the photocatalytic performance of photocatalytic materials. In the present work, Cu(II) cocatalyst was successfully loaded on the surface of various Ag-based compounds (such as AgCl, Ag3PO4, AgBr, AgI, Ag2CO3, and Ag2O) by a simple impregnation route, and their photocatalytic activity of Cu(II)/Ag-based photocatalysts was evaluated by the photocatalytic decolorization of methyl orange and photocatalytic decomposition of phenol solution under visible-light illumination. As one of the typical photosensitive Ag-based compounds, the photocatalytic activity of AgCl could be greatly improved by optimizing the amount of Cu(II) cocatalyst, and the highest photocatalytic performance of the resulted Cu(II)/AgCl was higher than that of the unmodified AgCl by a factor of 2.1. Significantly, the Cu(II) was demonstrated to be a general and effective cocatalyst to improve the visible-light photocatalytic performance of other various photosensitive Ag-based compounds (such as AgBr, AgI, Ag3PO4, Ag2CO3, and Ag2O) in addition to the AgCl photocatalyst. Based on the present results, it is proposed that the Cu(II) cocatalyst functions as electron scavengers to quickly capture photogenerated electrons from the excited photocatalysts and then works as reduction active sites to reduce O2 effectively, resulting in an effective separation of photogenerated electrons and holes. Compared with the expensive noble metal cocatalyst (such as Pt, Au, and Pd), the present promising Cu(II) cocatalyst can be considered to be one of the perfect cocatalysts for the smart preparation of various highly efficient photocatalysts in view of its abundance and low cost.
A hybrid quantum mechanics/classical mechanics (QM/MM) approach was developed to investigate photoinduced electron transfer (PIET) from a neutral Ag atom to an ionized tetrahedral Ag20+ cluster, both of which are solvated in water. In this approach, PIET was modeled as a coherent quantum process involving both vertical excitation and electron injection by our recently developed constrained real-time time-dependent density functional theory (C-RT-TDDFT) ( J. Phys. Chem. C 2011, 115, 18810), whereas the aqueous solvation structure for the (Ag–Ag20)+ complex was determined by the empirical flexible simple point charge (SPC/Fw) force field ( J. Chem. Phys. 2006, 124, 024503). An electrostatic embedding scheme was chosen to accurately represent the mutual polarization between the QM subsystem (the (Ag–Ag20)+ complex) and the MM subsystem (water molecules) in a self-adaptive manner that turns out to be critical to the relative stability of the electron transfer diabatic states in addition to their electronic coupling strengths in both ground and excited states. It was found that photoinduced electron transfer through an indirect coherent route, which is mediated by a short-lived virtual excited state, can be substantially faster than the sequential two-step process, which is typically limited by the light absorption efficiency. Moreover, the unusually wide plateau of near-unity quantum yields that we found near the plasmon-like resonance wavelength of the (Ag–Ag20)+ complex implies the possibility of designing exceptionally efficient plasmon-enhanced photocatalytic systems with an easily tunable range of activation wavelength by varying their plasmonic architectures.
The hierarchical photocatalysts of Ag–AgCl@Bi20TiO32 composites have been successfully synthesized by anchoring Ag–AgCl nanocrystals on the surfaces of mesoporous single-crystalline metastable Bi20TiO32 nanosheets via a two-stage strategy for excellent visible-light-driven photocatalytic activities in the Z-scheme system. First, the single-crystalline metastable Bi20TiO32 nanosheets with tetragonal structures were prepared via a facile hydrothermal process in assistance with the post-heat-treatment route using benzyl alcohol. Especially, the mesoporous Bi20TiO32 nanosheets showed high photocatalytic activity for the degradation of rhodamine B dye under visible-light irradiation. Then, the as-prepared mesoporous Bi20TiO32 nanosheets were used as a support for loading Ag–AgCl nanocrystals using the deposition–precipitation method and irradiation–reduction process to fabricate the Ag–AgCl@Bi20TiO32 composites. Inspiringly, the hierarchical Ag–AgCl@Bi20TiO32 photocatalyst has the higher photocatalytic performance than Ag–AgCl nanocrystals and mesoporous Bi20TiO32 nanosheets over the degradation of rhodamine B and acid orange 7 dyes, which is attributed to the effective charge transfer from plasmon-excited Ag nanocrystal to Bi20TiO32 for the construction of a Z-scheme visible-light photocatalyst. This work could provide new insights into the fabrication of hierarchically plasmonic photocatalysts with high performance and facilitate their practical application in environmental issues.
Silver nanoclusters complexed with dihydrolipoic acid (DHLA) exhibit molecular-like excited-state properties with well-defined absorption and emission features. The 1.8 nm diameter Ag nanoparticles capped with Ag8 clusters exhibit fluorescence maximum at 660 nm with a quantum yield of 0.07%. Although the excited state is relatively short-lived (τ 130 ps), it exhibits significant photochemical reactivity. By introducing MV2+ as a probe, we have succeeded in elucidating the interfacial electron transfer dynamics of Ag nanoclusters. The formation of MV+• as the electron-transfer product with a rate constant of 2.74 × 1010 s–1 confirms the ability of these metal clusters to participate in the photocatalytic reduction process. Basic understanding of excited-state processes in fluorescent metal clusters paves the way toward the development of biological probes, sensors, and catalysts in energy conversion devices.
A synergistic strategy involving oxygen-vacancy generation and noble-metal deposition is developed to improve the photocatalytic performance of TiO2 under visible-light irradiation. Through a redox reaction between the reductive TiO2 with oxygen vacancies (TiO2-OV) and metal salt precursors, noble-metal nanoparticles (Ag, Pt, and Pd) are uniformly deposited on the defective TiO2-OV surface in the absence of any reducing agents or stabilizing ligands. The resulting M-TiO2-OV (M = Ag, Pt, and Pd) nanocomposites are used as visible-light-driven photocatalysts for selective oxidation of benzyl alcohol and reduction of heavy metal ions Cr(VI). The results show that the oxygen vacancy creation obviously enhances the visible-light absorption of semiconductor TiO2. Meanwhile, the noble-metal deposition can effectively improve charge-separation efficiency of TiO2-OV under visible-light irradiation, thereby enhancing the photoactivity. In particular, Pd-TiO2-OV, having the average Pd particle size of 2 nm, shows the highest visible-light photoactivity, which can be attributed to the more efficient charge-carrier separation of Pd-TiO2-OV than Ag-TiO2-OV and Pt-TiO2-OV. The possible reaction mechanism for photocatalytic selective oxidation of benzyl alcohol and reduction of Cr(VI) over M-TiO2-OV (M = Ag, Pt, and Pd) has also been studied. It is hoped that our work could offer a simple strategy on fabricating defect-based nanostructures and their applications in solar energy conversion.
This work reports on an additive-free method for the preparation of hybrid Ag@AgCl plasmonic nanoparticles (NPs) with a size less than 50 nm (average size 37 nm) using sugar cane juice as the only reagent for the first time. This is an ecofriendly, rapid (20 min), and economical protocol that avoids the use of additional external reducing agents, external capping agents, templates, solvents, and external halide ion sources. The effects of various parameters like the concentration of sugar juice, reaction temperature, and reaction time on the formation of Ag@AgCl with respect to morphology control and size distribution were also studied. The prepared NPs were well characterized using techniques such as FEG-SEM, XRD, TEM, XPS, UV–visible spectrometry, and EDS. Prepared Ag@AgCl nanomaterials exhibited good photocatalytic ability toward degradation of methyl orange and methylene blue azo dyes in aqueous solution in the visible region of light. The catalyst was tested up to four recycles and showed no significant loss of catalytic activity.
A graphene-supported Ag3PO4/Ag/AgBr water oxidation photocatalyst was prepared by a photoassisted deposition–precipitation reaction, followed by a hydrothermal treatment. The composite photocatalyst exhibits double the O2-production activity than that of bare Ag3PO4 under visible light irradiation. Moreover, it exhibits enhanced activity in comparison to unsupported Ag3PO4/Ag/AgBr, to graphene-supported bare Ag3PO4 powder as well as to Ag/AgBr powder. This increase in activity is attributed to a combination of depletion of the conduction band of the as-synthesized n-doped Ag3PO4 material and a downshift of the Ag3PO4 valence band due to the pinning of its conduction band at the silver Fermi level, a process that is assisted by charge transfer and distribution onto the graphene support.
Uniform cubic Ag@AgCl plasmonic photocatalyst was synthesized by a facile green route in the absence of organic solvent, in which a controllable double-jet precipitation technique was employed to fabricate homogeneous cubic AgCl grains and a photoreduction process was used to produce Ag nanoparticles (NPs) on the surface of AgCl. During the double-jet precipitation process, the presence of gelatin and Cl– ions at low concentration was necessary for the formation of cubic AgCl grains. Atomic force microscopy (AFM) was used to probe the morphological structure of Ag@AgCl grains for the first time, which showed that Ag NPs are anchored on the surface of AgCl grains like up-and-down mounds. Further characterization of the photocatalyst was also done by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV–visible diffuse reflectance spectroscopy (DRS). The as-prepared Ag@AgCl plasmonic photocatalyst exhibited excellent photocatalytic efficiency for the degradation of the azo dye acid orange 7 (AO7), phenol, and 2,4-dichlorophenol (2,4-DCP). The photocatalytic mechanism was studied by radical-trapping experiments and the electron spin resonance (ESR) technique with 5,5-dimethyl-1-pyrroline N-oxide (DMPO), and the results indicated that •O2– and Cl0 are responsible for the rapid degradation of organic pollutants under visible-light irradiation.
In this study, pure Ag4V2O7 was synthesized via hydrothermal method without surfactant at different temperatures (100°C, 120°C, and 140°C) and pH values (4 and 5) for the first time. Moreover, Ag4V2O7 nanoparticles with homogeneous size distribution about 200–300 nm can be obtained by adding polyvinylpyrrolidone to the synthesis system. Effects of hydrothermal synthesis conditions on photophysical properties and photocatalytic activity of Ag4V2O7 were investigated systematically. Ag4V2O7 sample prepared at 120°C and pH = 4 had the optimal photocatalytic activity among these samples, which almost completely degraded 10 ppm Rhodamine B within 3 h under visible light irradiation (420 nm 4V2O7 photocatalyst was proposed and discussed preliminarily.
H2 production by water splitting is mainly hindered by the lack of low cost and efficient photocatalysts. Here we show that sub-nanometric silver clusters can catalyze the aniso-tropic growth of Au nanostructures by preferential adsorp-tion at certain crystal planes of Au seeds, with the result that the final nanostructure can be tuned via the cluster/seed ratio. Such semiconducting Ag clusters are extremely stable, and retain their electronic structure even after adsorption at the tips of Au nanorods, enabling various photocatalytic experiments, such as oxygen evolution from basic solutions. In the absence of electron scavengers, UV-irradiation gen-erates photoelectrons, which are stored within the nano-rods increasing their Au Fermi level up to the redox pinning limit at 0V (RHE), where hydrogen evolution occurs with an estimated high efficiency of ≈ 10% . This illustrates the con-siderable potential of very small zero-valent, non-metallic clusters as novel atomic-level photocatalysts.
Owing to its unique two-dimensional structure and extraordinary physicochemical properties, graphene oxide (GO) is considered an ideal support for developing highly efficient photocatalysts. In this study, a novel Ag2O/GO nanocomposite, as a visible-light-induced photocatalyst, has been fabricated by a simple solution route. The electrostatic interactions between positively charged Ag+ and negatively charged GO sheets are responsible for the formation of the Ag2O/GO nanocomposite. The anchoring of the Ag2O nanoparticles on the GO nanosheets was confirmed by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The photocatalytic degradation of Methylene Blue (MB) under visible-light irradiation was studied to evaluate the photocatalytic activity of the Ag2O/GO nanocomposites. Due to the enhanced adsorption capacity, the smaller size of the Ag2O nanoparticles, and the improved separation of electron–hole pairs after the incorporation with GO sheets, the Ag2O/GO nanocomposites showed enhanced photocatalytic activity compared with bare Ag2O nanoparticles. In addition, the kinetics of the photocatalytic degradation reaction and a plausible photocatalytic mechanism are presented. The results pave the way to the design of highly efficient visible-light-responsive photocatalysts for the removal of organic pollutants for water purification.
In this work, we successfully prepared 1D AgBr@Ag nanostructures in high yield by a facile wet chemical method, and the plausible growth mechanism was discussed. The synthesis of as-prepared AgBr@Ag nanostructure is a dissolution and recrystallization process, and the PVP and DMSO have the synergistic and competitive effect on the preparation of 1D AgBr@Ag products. Moreover, the AgBr@Ag nanorods exhibit excellent photocatalytic activities under visible light illumination, which may be attributed to their large surface area as well as superior charge separation and transfer efficiency compared to AgBr@Ag particles.
The future development of chemistry entails environmentally friendly and energy sustainable alternatives for organic transformations. Visible light photocatalysis can address these challenges, as reflected by recent intensive scientific endeavours to this end. This review covers state-of-the-art accomplishments in visible-light-induced selective organic transformations by heterogeneous photocatalysis. The discussion comprises three sections based on the photocatalyst type: metal oxides such as TiO2, Nb2O5 and ZnO; plasmonic photocatalysts like nanostructured Au, Ag or Cu supported on metal oxides; and polymeric graphitic carbon nitride. Finally, recent strides in bridging the gap between photocatalysis and other areas of catalysis will be highlighted with the aim of overcoming the existing limitations of photocatalysis by developing more creative synthetic methodologies.
Our study proposes a novel strategy for the synthesis of Ag derivatives (AgX@Ag (X = Cl and Br) or Ag nano/microtubes) using the controlled chemical reduction or electron-beam irradiation of AgX nanowires (NWs), which are formed from the controlled dewetting of a AgX thin film on colloidal particles. The size of the AgX@Ag and Ag nano/microtubes can be controlled using the AgCl NWs as templates and varying the concentration of NaX. By controlling the concentration of NaBr, heterojunction-structured AgCl/AgBr NWs (H-AgCl/AgBr NWs) can be produced from the AgCl NWs due to a partial ion-exchange reaction (low concentration), and the AgBr NWs produced after a complete ion-exchange reaction between Cl- and Br- are further grown into micrometer-sized AgBr wires (high concentration). The resulting AgX NWs can be transformed into corresponding AgX@Ag or Ag nano/microtubes via a controlled chemical or physical method. The AgX derivatives (AgX@Ag nanotubes (NTs) and AgX NWs) are tested as visible-light-induced photocatalysts for decomposition of methyl orange. The AgX@Ag NTs exhibit the best photocatalytic activities due to the advantages of the core@shell structure, allowing multiple reflections of visible light within the interior cavity, providing a well-defined and clean Ag/AgX interface, and preventing direct adsorption of pollutants on AgX due to the shell structure. These advantages allow AgX@Ag NTs to maintain high catalytic performance even after multiple uses. The approach can also be used as a direct method for preparing Ag nano/microtubes with a tailored size and as a new method for incorporating a AgX NW core into a Ag nano/microtube shell. Our approach is useful for synthesizing various types of one-dimensional heterostructured NWs or metal NTs with controlled structures and properties.
Nanostructured AgI/TiO2 photocatalyst was synthesized through deposition-precipitation using AgNO3, KI and Ti(OBU)4. Then the photocatalyst was further treated by PdCl2 solution, which resulted in a color change from yellow to green and PdCl2 reacted with AgI as indicated by X-ray diffraction analyses. The diffusive reflectance UV-vis spectroscopy of this modified photocatalyst shows a remarkable enhancement of the absorption intensity in the range of visible light. As nanostructured AgI/TiO2 shows a considerable visible light photocatalytic activity for the photodegradation of methylene blue, PdCl2-modified AgI/TiO2 exhibits a much larger visible light photocatalytic activity for the photodegradation of methylene blue.
Novel Z-scheme AgI/Ag/AgBr composite was synthesized through a facile in-situ ion exchange method along with light reduction. The as-prepared AgI/Ag/AgBr was characterized by XRD, SEM, DRS, XPS, EDS, BET and PL technology to study its phase structures, morphologies, optical properties, element components and surface areas. AgI/Ag/AgBr displayed excellent photocatalytic activity for the degradation of methyl orange under visible light (λ > 420 nm), which can be ascribed to the efficient separation of photogenerated electrons and holes through Z-scheme system composed of AgI, Ag and AgBr. The photocatalytic mechanism investigation demonstrates that •O2− was the main reactive species for methyl orange (MO) degradation.
The Ag2S loaded ZnO (Ag2S–ZnO) was successfully synthesized by precipitation of zinc oxalate and Ag2S and calcination of the mixed precipitate at 400 °C for 12 h. The catalyst was characterized by X-ray diffraction (XRD), high resolution scanning electron microscope (HR-SEM) images, energy dispersive spectra (EDS), diffuse reflectance spectra (DRS), photoluminescence spectra (PL), cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS) and BET surface area measurements. XPS reveals that all the Ag in the catalyst are present in the form of Ag+ before irradiation. The photocatalytic activity of Ag2S–ZnO was investigated for the degradation of Acid Black 1 (AB 1) in aqueous solution using solar light. Ag2S–ZnO is found to be more efficient than commercial ZnO, prepared ZnO, TiO2–P25 and TiO2(Merck) at pH 9 for the mineralization of AB 1. The effects of operational parameters such as the amount of photocatalyst, dye concentration, initial pH on photo mineralization of AB 1 have been analyzed. The mineralization of AB 1 has been confirmed by COD measurements. The catalyst is found to be reusable.
Semiconductor photocatalysis is considered to be one of the most promising technologies to solve the worldwide environmental and energy issues. In recent years, silver halide (AgX)-based photocatalytic materials have received increasing research attention owing to its excellent visible light-driven photocatalytic performances in the applications of organic pollutant degradation, H2/O2 generation, and disinfection. AgX-based materials used in photocatalytic fields can be classified into three categories: AgX (Ag/AgX), AgX composites, and supported AgX materials. For the AgX (Ag/AgX) photocatalysts, it has been widely accepted that the final photocatalytic performances of photocatalysts are severely dependent on their morphological structures as well as exposed crystal facets. As a result, considerable efforts have been devoted to fabricating different morphological AgX photocatalysts as well as exploring the relationship between the morphological structures and photocatalytic performances. In this review, we mainly introduce the recent developments made in fabricating morphology and facet-controllable AgX (Ag/AgX) photocatalytic materials. Moreover, this review also deals with the photocatalytic mechanism and applications of AgX (Ag/AgX) and supported AgX materials.
Au–Ag–AgI nanoparticles (NPs) were uniformly dispersed onto mesoporous alumina by deposition–precipitation and photoreduction at low temperature. Compared with Ag–AgI/Al2O3, the catalyst showed higher photocatalytic activity under visible irradiation. In particular, the release of metal ions from the catalyst was significantly inhibited during photodegradation of pollutants. Electron spin resonance and cyclic voltammograms studies under a variety of experimental conditions verified that the coupling of Au and Ag NPs increased the efficiency of light energy conversion and accelerated interfacial electron transfer processes. The main active species involved in the photoreaction of Au–Ag–AgI/Al2O3 were O2•− and excited h+ on the metal NPs. The presence of several ubiquitous anions, including HCO3−, SO42−, and NO3− could act as electron donors trapping excited h+ on the metal NPs to facilitate electron circulation. The results obtained herein indicated that coupled, noble, bimetal NPs exhibited high photosensitivity and photostability due to enhanced surface plasmon resonance and interfacial electron transfer.
Graphical Abstract
Addition of Au made Au–Ag–AgI nanoparticles (NPs) disperse more uniformly onto mesoporous Al2O3 and showed higher photocatalytic activity under visible irradiation.
Owing to far-ranging industrial applications and theoretical researches, tailored synthesis of well-defined nanocrystals has attracted substantial research interest. Herein, β-AgI nanoplates have been synthesized through a facile polyvinylpyrrolidone (PVP)-assisted-aqueous-solution (PAAS) method under mild conditions. The parametric studies on the effect of ratio of reactants, solvents and surfactants were performed, revealing that a molar ratio of I(-) to Ag(+) of 1.2 in deionized water and the presence of appropriate PVP as stabilizing agent can stimulate the preferred orientation growth of AgI nanoplates. The as-synthesized AgI nanoplates exhibit excellent photocatalytic activity and enhanced durability towards the degradation of organics, i.e., rhodamine B (RhB), under visible light illumination in comparison with corresponding bulk nanoparticles. A possible photocatalytic reaction mechanism was discussed, revealing O2˙(-) and h(+) are main reactive species and free ˙OH radicals in solution also contribute to the degradation reaction. The superior photocatalytic performance renders the as-achieved AgI nanoplates promising candidates for applications in the fields of environmental purification or water disinfection. The present work opens an avenue to the synthesis of other shaped silver halide nanophotocatalysts.
Ag@AgCl core–shell nanocomposite was synthesized by using [Bmim]FeCl4 IL etching Ag nanowires into Ag@AgCl in solution at room temperature. The obtained samples exhibited highly visible-light photocatalytic ability for the degradation of methyl orange and 4-chlorophenol in water solution. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) confirmed the presence of Ag and AgCl crystals. Scanning electron microscopy (SEM) images and X-ray energy-dispersive spectroscopy (EDS) of the samples revealed that AgCl nanoparticles (NPs) formed on the surface of Ag nanowires. UV–vis spectroscopy showed that Ag@AgCl core–shell structure enhanced its absorption in the visible-light region. The results showed that the absorption ability of Ag@AgCl was related to the change of Ag@AgCl. The absorption ability of the samples increased with the increasing etching time, and the enhancing photocatalytic ability was due to the increasing plasmonic absorbance of the photocatalysts. The effect of the etching time on the photocatalyst activity was studied, and the reaction mechanism was proposed.
A new composite photocatalyst Ag/AgCl core–shell sphere was synthesized at room temperature by using a simple and generic approach. SEM images revealed that the as-prepared catalyst showed a uniform morphology with an average size of about 2 μm. The photocatalytic activity was significantly dependent on the molar ratio of Ag0:Ag+ on the surface of the catalyst, the optimum ratio being 0.035. Recycling experiments confirmed the excellent stability of the catalysts, without any silver leaching from the surface of the catalyst, suggesting that the photocatalyst Ag/AgCl core–shell sphere was a form of active and stable visible-light driven plasmonic material.
In this work, we describe an effective route to synthesize Ag-AgCl/WO3 hollow sphere with flower-like structure, which displayed excellent visible light response photocatalytic activity and recycling ability for the degradation of 4-chlorophenol. Its high photocatalytic activity can be attributed to the surface plasmon resonance effect of Ag nanoparticles, which were highly dispersed on the surface of Ag-AgCl/WO3. N2 adsorption and desorption isotherm spectra, X-ray diffraction, X-ray photoelectron spectroscopy, and electron microscopy were used to determine the correlation between the micro-structure and the catalytic properties of the as-prepared photocatalysts.
AgBr/ZnO nanocomposite was synthesized via chemical precipitation from pure ZnO nanowires, AgNO3, and NaBr. Inductively coupled plasma optical emission spectroscopy, X-ray diffraction, and high resolution transmission electron microscopy results confirmed the forming of AgBr/ZnO nanocomposite. High resolution transmission electron microscopy results of the as-synthesized AgBr/ZnO nanocomposite revealed that AgBr nanoparticles were attached to the surface of ZnO nanowires. UV–vis diffuse reflectance spectra of both pure ZnO and AgBr/ZnO nanocomposite displayed a band gap edge at about 350–380 nm. However, compared with pure ZnO, an additional broad tail from approximately 400 nm to 700 nm appeared in the UV–vis diffuse reflectance spectrum of AgBr/ZnO nanocomposite. The photocatalytic studies indicated that the as-synthesized AgBr/ZnO nanocomposite was a kind of promising photocatalyst in remediation of water polluted by some chemically stable azo dyes under visible light.
Nanoparticles of zinc oxide (ZnO) sensitized with silver iodide (AgI) were synthesized by a chemical precipitation method and were found to be a visible light driven photocatalyst. The characterization of prepared photocatalyst was studied using UV–visible diffuse reflectance spectroscopy (UV–vis-DRS), X-ray powder diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS). Average crystallite size determined by XRD was 21.56 nm for ZnO and 23.44 nm for AgI sensitized ZnO (AgI-ZnO). The photocatalytic efficiency of AgI-ZnO was evaluated by the decolorization of rosaniline hydrochloride dye (RA) under visible light irradiation. The influence of various operational parameters such as the effect of pH, catalyst dosage and initial dye concentration on the photodecolorization was investigated in detail. The removal percentage of chemical oxygen demand (COD) and total organic carbon (TOC) was determined to evaluate the mineralization of RA during photodecolorization. Maximum decolorization, COD removal and total organic carbon (TOC) reduction were 88%, 75% and 68% respectively, under the optimum conditions.
Simulated solar light responsive Ag/AgCl/WO3 composite photocatalyst was synthesized by microwave assisted hydrothermal process. The synthesized powders were characterized by X-Ray Diffraction (XRD) spectroscopy, X-Ray Photoelectron Spectroscopy (XPS), Transmission Electron Microscopy (TEM), Diffuse Reflectance Spectroscopy (UV–Vis DRS), and BET surface area analyzer to investigate the crystal structure, morphology, chemical composition, optical properties and surface area of the composite photocatalyst. This photocatalyst exhibited higher photocatalytic activity for the degradation of rhodamine B under simulated solar light irradiation. Dye degradation efficiency of composite photocatalyst was found to be increased significantly as compared to that of the commercial WO3 nanopowder. Increase in photocatalytic activity of the photocatalyst was explained on the basis of surface plasmon resonance (SPR) effect caused by the silver nanoparticles present in the composite photocatalyst.
Titania thin film system containing noble metallic nanoparticles such as Au, Ag, and Cu have been prepared by utilizing radio frequency reactive magnetron cosputtering method. The structural and morphological properties of the thin films were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM). Surface chemical composition of the films was determined by X-ray photoelectron spectroscopy (XPS). Optical properties of the TiO 2 annealed films containing Au, Ag, and Cu metallic nanoparticles were investigated by UV-visible spectrophotometry showing surface plasmon resonance of the metals. The photocatalytic activity of all synthesized samples annealed at 600 °C in an Ar + H 2 (80 + 20%) environment was evaluated by measuring the rate of photodegradation reaction of methylene blue (MB) under similar conditions in the presence of UV and visible light irradiation. The Au:TiO 2 and Cu:TiO 2 thin film systems significantly enhanced photodecomposition of MB resulting in 80 and 90% of its initial concentration after 200 min photoirradiation, respectively. The increase in the surface roughness measured by AFM observation and the presence of the Ti 3+ oxygen vacancy in the photoirradiated thin films were found responsible for the enhancement of the MB photodegradation reaction. The photoenhancement of the studied was determined in the following order: Cu:TiO 2 > Au:TiO 2 > Ag:TiO 2 > TiO 2 .
Ripening of AgClnanoparticles with a bimodal size distribution has been carefully studied in ethylene glycol containing poly(vinyl pyrrolidone) (PVP) as capping molecules and at elevated temperatures (e.g., 160 °C). The resulting AgCl particles exhibit high uniformity in size and cube-tetrapod morphology that are significantly different from the original AgClnanoparticles. In addition, enhanced reducing ability of ethylene glycol at high temperature partially reduces AgCl to form Ag nanocrystalline domains in the AgCl particles, leading the AgCl particles to be efficiently absorbing visible light and to serve as a class of visible-light-driven photocatalysts due to the strong surface plasmon resonance (SPR) associated with the Ag nanocrystallites.
AgBr microcrystals with different morphologies were synthesized by an ionic liquids (ILs)-assisted hydrothermal method. A plausible growth mechanism, and influence of ionic liquids on the morphology of AgBr, were proposed and studied systematically. The samples were characterized by scanning electronic microscopy and X-ray diffraction. The relationship of morphology and photocatalytic activity of samples was studied.