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Effect of dopant concentration on visible light driven photocatalytic activity of Sn1-XAgxS2

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Abstract

Tin(iv) sulfide (SnS2), as a mid-band-gap semiconductor shows good potential as an excellent photocatalyst due to its low cost, wide light spectrum response and environment-friendly nature. However, to meet the demands of large-scale water treatment, a SnS2 photocatalyst with a red-shifted band gap, increased surface area and accelerated molecule and ion diffusion is required. Doping is a facile method to manipulate the optical and chemical properties of semiconductor materials simultaneously. In this work, SnS2 photocatalysts with varied Ag doping content are synthesized through a facile one-step hydrothermal method. The product is characterized by XRD, SEM, TEM and UV-Vis spectrometry. The photocatalytic activity of the as-prepared Sn1-xAgxS2 is studied by the degradation of methylene blue (MB) dye under solar light irradiation. It is found that increasing the Ag dopant concentration can effectively increase the solar light adsorption efficiency of the photocatalyst and accelerate heterogeneous photocatalysis. The optimal concentration of Ag dopant is found to be 5% with the highest rate constant being 1.8251 hour(-1). This study demonstrates that an optimal amount of Ag doping can effectively increase the photocatalytic performance of SnS2 and will promote the commercialization of such photocatalysts in the photocatalytic degradation of organic compounds.

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... 2.1. Sample preparation Solvothermal method was used to synthesize undoped and Ag-doped SnS 2 nano-flowers as reported elsewhere [33]. Tin (IV) chloride pentahydrate (0.1 M), thiourea (0.2 M) and silver nitrate were dissolved in ethylene glycol under constant stirring at room temperature. ...
... The core level characteristic peaks of S 2p appears at 159.63 ( ) p 3 2 2 and 160.64 ( ) p 1 2 2eV (figure (c)) and their separation energy is 1.01 eV, confirming the presence of S 2− . XPS results indicate that the Ag + ions successfully incorporated into SnS 2 matrix and a similar finding is also reported in the literature[32,33]. ...
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... Similarly, strenuous efforts have also been put into morphology control and to improve the optical and physicochemical properties of metal sulfides for enhanced performance in photocatalyst for pollutant degradation and PEC efficiency. It has been shown that doping in semiconductor can efficiently result in band gap narrowing, particle size reduction, and can act as electron/hole trap centers [19]. For example doping with Carbon and In in SnS 2 can enhance the visible light photocatalytic activity of CO 2 reduction and aqueous Cr (VI) [20,21]. ...
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... Similarly, many efforts have also been made in controlling morphology and enhancing the photoelectrical, chemical and physical properties for improving the device performance. Moreover, dopants in semiconductor could lead to reduction in particle size, narrowing of band gap and enhance the photoelectrical properties of SnS 2 [31]. Recently, V and Ti doped SnS 2 was reported to be an intermediate band material for application in wider solar absorption [32,33]. ...
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The nickel modified zinc oxide (ZnO) photocatalysts with nominal composition of Zn1-xNixO (x = 0.0–0.5) were synthesized by wet chemical approach. Optical studies were performed using Fourier transformed infrared (FTIR), electronic spectroscopy and X-ray diffraction (XRD) methods. Scanning electron microscopy (SEM) complimented with Energy Dispersive X-ray (EDX) was used to study the morphology and chemical composition of prepared photocatalysts. A significant hypsochromic shift has been observed with respect to un-doped ZnO nanocatalyst due to quantum confinement effect. Subsequently, the band gap has been tuned to the region of lower wavelength. X-ray results reveal that ZnO nanocatalyst are in hexagonal crystalline form. In addition, the effect of nickel impurity on photocatalytic activity of ZnO nanocatalysts in degradation of methylene blue (MB) was also investigated. Degradation results showed that the MB was degraded more effectively by Ni-doped ZnO photocatalysts due to large band gap under visible light irradiation.
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In this paper, semitransparent TiO2 nanotube-films were prepared on fluorine doped tin oxide (FTO) glass by the electrophoretic deposition (EPD) process and their properties were characterized. Furthermore, dye-sensitized solar cells (DSSCs) based on the as-prepared TiO2 nanotube-films were assembled, and effects of the film thickness and EPD voltage on performance of the DSSCs were investigated. Power conversion efficiency with the maximum value of 7.10% was successfully achieved, indicating the semitransparent TiO2 nanotube-films are very promising for high transmittance substrates and high efficiency photovoltaic electrodes.
Article
Owing to its excellent electrocatalytic properties, cobalt disulfide (CoS2) is regarded as a promising counter electrode (CE) material for dye-sensitized solar cells (DSSCs). However, hindered by its relatively poor electrical conductivity and chemical instability, it remains a challenge to apply it into high-performance DSSCs. In this work, we have developed novel CoS2 embedded carbon nanocages as a CE in DSSCs, using ZIF-67 (zeolitic imidazolate framework 67, Co(mim)2, mim = 2-methylimidolate) as a template. The CoS2 samples sulfurized for different time lengths are prepared through a facile solution process. It is found that the sulfurization time can be optimized to maximize the DSSC efficiency and the DSSC based on the CoS2 embedded carbon nanocages sulfurized for 4 hours exhibits the highest photovoltaic conversion efficiency (PCE) of 8.20%, higher than those of DSSCs consisting of other CoS2 CEs and Pt-based DSSC (7.88%). The significantly improved DSSC PCE is contributed by the synergic effect of inner CoS2 nanoparticles and an amorphous carbon matrix, leading to a CE with high catalytic activity, good electrical conductivity and excellent durability. This study demonstrates that the CE based on inexpensive CoS2 embedded carbon nanocages is a prospective substitute to expensive platinum and provides a new approach for commercializing high-efficiency DSSCs.
Article
A series of La-promoted cobalt-copper catalysts with various Co:Cu ratios have been used to study the conversion of syngas to oxygenates and hydrocarbons. In particular, the effect of the Co:Cu composition on the selectivity to oxygenates versus hydrocarbons has been examined. Three bulk catalysts were synthesized by coprecipitation, reduced in H2/He flow, and then cobalt carbide was formed during CO hydrogenation. The composition of the catalysts was as follows: Cu:Co = 12:9, 7:13, and 0:21 (cobalt only). CO hydrogenation tests were performed at differential conversions and 30 bar, H2/CO = 2/1 and 250 °C. The C1 selectivity (methane + methanol + CO2) was ∼64% for the two catalysts containing Co and Cu, and slightly less for the Co-only catalyst (52%). These products are formed by three mechanisms: (1) CH4: hydrogenation of dissociatively adsorbed CO at metallic cobalt sites, (2) CH3OH: hydrogenation of associatively adsorbed CO at copper sites, and (3) CO2: water gas shift, also at the copper sites. C2+ alcohol selectivity for the two Cu-containing catalysts is greater than for the Co-only catalyst, while the Co-only catalyst has the highest selectivity to acetaldehyde. The formation of C2+ oxygenates is consistent with the CO insertion mechanism, in which associatively adsorbed CO is inserted into the CHx species and forms the first C-C bond, producing a CHxCO intermediate that can be hydrogenated into ethanol or acetaldehyde.
Article
A sandwich-like, graphene-based porous nitrogen-doped carbon (PNCs@Gr) has been prepared through facile pyrolysis of zeolitic imidazolate framework nanoparticles in situ grown on graphene oxide (GO) (ZIF-8@GO). Such sandwich-like nanostructure can be used as anode material in lithium ion batteries, exhibiting remarkable capacities, outstanding rate capability, and cycling performances that are some of the best results among carbonaceous electrode materials and exceed most metal oxide-based anode materials derived from metal orgainc frameworks (MOFs). Apart from a high initial capacity of 1378 mAh g(-1) at 100 mA g(-1), this PNCs@Gr electrode can be cycled at high specific currents of 500 and 1000 mA g(-1) with very stable reversible capacities of 1070 and 948 mAh g(-1) to 100 and 200 cycles, respectively. At a higher specific current of 5000 mA g(-1), the electrode still delivers a reversible capacity of over 530 mAh g(-1) after 400 cycles, showing a capacity retention of as high as 84.4%. Such an impressive electrochemical performance is ascribed to the ideal combination of hierarchically porous structure, a highly conductive graphene platform, and high-level nitrogen doping in the sandwich-like PNCs@Gr electrode obtained via in situ synthesis.
Article
The exploration of new inexpensive rechargeable batteries with high energy-density electrodes is a key to integrate the renewable sources such as solar and wind, and address the sustainability issues. Herein, a facile and scalable method is developed to prepare two-dimensional earth-abundant jarosite-KFe3(SO4)2(OH)6/rGO hybrid via a solution-phase oxidization process at elevated temperature. In this synthesis, single-layer graphene sheets serve as both structure-directing agents and growth platforms to directly grow monocrystalline KFe3(SO4)2(OH)6 nanoplates with unique hexagonal shapes, forming KFe3(SO4)2(OH)6/rGO hybrid that exhibits a high reversible capacity of 120 mAh/g after 100 cycles at a specific current of 2 C and thus retains 88% of the maximum capacity. The monocrystalline jarosite-KFe3(SO4)2(OH)6-nanoplates/rGO hybrid exhibit a discharge capacity of 109.5, 99.9, 89.0, 79.6, and 62.1 mAh/g at 1, 2, 5, 10, and 20 C, respectively, and retain a specific capacity of 136.1 mAh/g when the specific current returns from 20 C to 1 C, displaying an excellent rate capability. At the high rate of 10 C, the jarosite-KFe3(SO4)2(OH)6/rGO composites maintain 70.7 mAh/g after 300 cycles with a capacity retention of 78.2%, indicating remarkable cycling stability even at a high rate. In comparison with KFe3(SO4)2(OH)6 particles, the KFe3(SO4)2(OH)6/rGO nanocomposites exhibit remarkably prolonged cycling life and improved rate capability. Therefore, earth-abundant jarosite-KFe3(SO4)2(OH)6/rGO hybrid, demonstrates great potential for application as high-performance cathode material in new-generation lithium-ion rechargeable batteries.
Article
Tin disulfide (SnS2) has been considered as a prospective counter electrode (CE) material for dye-sensitized solar cells due to its good electrocatalytic property. However, its low electronic and ionic conductivities pose challenges for using it in high-performance dye-sensitized solar cells (DSSCs). Herein, doping is utilized in this study to improve the properties of SnS2 for application as the DSSC counter electrode. Ag-doped SnS2 samples with various doping amounts are prepared via a facile one-step solvothermal route. It is found that the DSSC based on 5% Ag-doped SnS2 CE demonstrates the best performance showing an impressive photovoltaic conversion efficiency (PCE) of 8.70 % which exceeds the efficiency of Pt-based DSSC (7.88%) by 10.41%, while the DSSC consisting of undoped SnS2 only exhibits a PCE of 6.47%. Such enhanced efficiency of DSSC is attributed to the effectively improved electrocatalytic activity and mixed conductivity resulted from Ag dopant. Therefore, the Ag-doped SnS2 CE proves a promising alternative to the expensive Pt CE in DSSCs and may pave a new way for large-scale production of new-generation DSSCs.
Article
Heterovalent doping represents an effective method to control the optical and electronic properties of semiconductor nanocrystals (NCs), such as the luminescence and electronic impurities (p-, n-type doping). Considering the phase structure diversity, coordination varieties of Cu atoms in Cu2S NCs, and complexity of Cu doping in II-VI NCs, monodisperse Cu2S NCs with pure hexagonal phase were synthesized firstly. Then through cation exchange reaction between Cd ions and well-defined Cu2S NCs, dominant Cu(I) doped CdS NCs were produced successfully. The substitutional Cu(I) dopants with controllable concentrations were confirmed by local atom-specific fine structure from X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS) spectroscopy, elemental analysis characterizations from X-ray photoelectron spectroscopy (XPS) and the electron spin resonance (ESR) measurement. The dominant and strong Cu(I) dopant fluorescence was verified by their absorption and photoluminescence (PL) spectra, and PL lifetime. Finally, the band positions and the p-type conductivities of the as-prepared Cu2S and Cu(I) doped CdS NCs were identified by ultraviolet photoelectron spectroscopy (UPS) measurements. The high monodispersity of NCs enables their strong film-scale self-assembly and will hasten their subsequent applications in devices.
Article
Complex hierarchical structures have received tremendous attention due to their superior properties over their constitute components. In this study, hierarchical graphene-encapsulated hollow SnO2@SnS2 nanostructures are successfully prepared by in-situ sulfuration on the backbones of hollow SnO2 spheres via a simple hydrothermal method followed by a solvothermal surface modification. The as-prepared hierarchical SnO2@SnS2@rGO nanocomposite can be used as anode material in lithium ion batteries, exhibiting excellent cycleability with a capacity of 583 mAh/g after 100 electrochemical cycles at a specific current of 200 mA/g. This material shows a very low capacity fading of only 0.273% per cycle from the 2nd to the 100th cycle, lower than the capacity degradation of bare SnO2 hollow spheres (0.830%) and single SnS2 nanosheets (0.393%). Even after being cycled at a range of specific current varied from 2000 mA/g to 100 mA/g, hierarchical SnO2@SnS2@rGO nanocomposite maintains a reversible capacity of 664 mAh/g, which is much higher than single SnS2 nanosheets (374 mAh/g) and bare SnO2 hollow spheres (177 mAh/g). Such significantly improved electrochemical performance can be attributed to the unique hierarchical hollow structure, which not only effectively alleviates the stress resulted from the lithiation/delithiation process and maintains structural stability during cycling but also reduces aggregation and facilitates ion transportation. This work thus demonstrates the great potential of hierarchical SnO2@SnS2@rGO nanocomposites for application as high-performance anode material in next-generation lithium ion battery technology.
Article
The amorphous Co-doped MoS2 coated on high-crystallized pyrite-phase CoS2 hierarchical nanoarray exhibits ultrahigh activity towards acidic hydrogen evolution with a low onset potential (~44 mV) and a small overpotential of ~110.5 mV for driving the current density of ~10 mA cm-2, ascribed to the novel hierarchical structure and the Co doping caused synergistic effects.
Article
The fabrication of heterojunction between different crystalline phases has been considered to be an effective strategy for promoting charge separation during photocatalytic process. Herein, the mixed-crystalline-phase (MC), spindle-like TiO2 was prepared with a simple hydrothermal method, which was followed by a series of calcination processes. The final products are composed of two crystalline phases including anatase and brookite. The anatase/brookite ratio of the TiO2 is tuned by varying the calcination temperature. The MC TiO2 that consisted of 85.5% anatase and 14.5% brookite has the highest rate of photocatalytic hydrogen evolution (290.2 μmol h−1) compared to the purely anatase TiO2. This is attributed to the mixed-phase heterojunction structure that improves electron-hole separation, and therefore, enhances the photocatalytic hydrogen production.
Article
Graphene-like two-dimensional layered materials have attracted quite lots of interests because of sizable band gap and potential applications. In this work, monodisperse tin disulfide (SnS2) nanosheets were successfully prepared by a simple solvothermal procedure in the presence of polyvinyl pyrrolidone (PVP). Large PVP molecules absorbing on (001) facets of SnS2 would inhibit crystal growth along [001] orientation and protect the product from agglomeration. The obtained SnS2 nanosheets have diameters of ca. 0.81 μm and thickness of ca. 22 nm. Different experiment parameters were carried out to investigate the transformation of phase and morphology. The formation mechanism was proposed according to the time-dependent experiments. SnS2 nanosheets exhibit high photocatalytic H2 evolution activity of 1.06 mmol h-1 g-1 under simulated sunlight irradiation, much higher than that of SnS2 with different morphologies and P25-TiO2. Moreover, the as-obtained SnS2 nanosheets show excellent photoelectrochemical response performance in visible-light region.
Article
Combining quantum-mechanical simulations and synthesis tools allows the design of highly efficient CuCo/MoOx catalysts for the selective conversion of synthesis gas (CO+H2) into ethanol and higher alcohols, which are of eminent interest for the production of platform chemicals from non-petroleum feedstocks. Density functional theory calculations coupled to microkinetic models identify mixed Cu–Co alloy sites, at Co-enriched surfaces, as ideal for the selective production of long-chain alcohols. Accordingly, a versatile synthesis route is developed based on metal nanoparticle exsolution from a molybdate precursor compound whose crystalline structure isomorphically accommodates Cu2+ and Co2+ cations in a wide range of compositions. As revealed by energy-dispersive X-ray nanospectroscopy and temperature-resolved X-ray diffraction, superior mixing of Cu and Co species promotes formation of CuCo alloy nanocrystals after activation, leading to two orders of magnitude higher yield to high alcohols than a benchmark CuCoCr catalyst. Substantiating simulations, the yield to high alcohols is maximized in parallel to the CuCo alloy contribution, for Co-rich surface compositions, for which Cu phase segregation is prevented.
Article
Polyvinylpyrrolidone (PVP)/Ag2S composite fibres were successfully prepared by a facile method called the electrospinning technique. Scanning electron microscopy analysis revealed the fibre morphology of the composite. Transmission electron microscopy showed spherical nanoparticles of the Ag2S component with an average particle size of about 15 nm and a good dispersion. X-ray diffraction results showed that a pure beta-Ag2S phase was obtained in the PVP fibres. X-ray photoelectron spectra (XPS) proved that the Ag and S elements exist in PVP/Ag2S composite fibres and quantitative analysis of the XPS showed that the atomic ratio of silver and sulfur was about 2. Fourier transform infrared and ultraviolet-visible spectroscopy were used to characterize the structure of the PVP/Ag2S composite fibres.
Article
Novel Al-doped ZnO (AZO) photocatalysts with different Al concentrations (0.5–6.0 mol%) were prepared through a facile combustion method and followed by calcination at 500 °C for 3 h. The obtained nanopowders were characterized by powder X-ray diffraction (XRD), scanning electron microscope (SEM) combined with EDX, transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR), UV–vis spectroscopy and photoluminescence spectroscopy. The XRD patterns of AZO nanopowders were assigned to wurtzite structure of ZnO with the smallest crystallite size about 11 nm consistent with the results from TEM. The doping of Al in ZnO crystal structure successfully suppressed the growth of ZnO nanoparticles confirmed by XRD patterns. The absorption spectra analysis showed that the optical band gap energy (Eg) for the AZO nanopowders were in the range of 3.12–3.21 eV and decreased with increasing of Al dopant. The photocatalytic activities of the samples were evaluated by photocatalytic degradation of methyl orange under visible light (λ ≥ 420 nm) and sunlight irradiation. The results showed that the AZO photocatalyst doped with 4.0 mol% Al exhibited five times enhanced photocatalytic activity compared to pure ZnO. The enhanced photocatalytic activity could be attributed to extended visible light absorption, inhibition of the electron–hole pair's recombination and enhanced adsorptivity of MO dye molecule on the surface of AZO nanopowders.
Article
In this work, Fe-doped ZnO thin films were prepared by sol–gel method on Si and glass substrates and influence of Fe-doping concentration on the structural and optical properties of the films was studied. The X-ray diffraction (XRD) analyses show that all the ZnO thin films prepared in this work have a hexagonal wurtzite structure and are preferentially oriented along the c-axis perpendicular to the substrate surface. After 1 at% Fe is doped, the crystalline quality and the preferential orientation of ZnO thin film are improved. However, when Fe-doping concentration is above 1 at%, the crystalline quality and the preferential orientation of ZnO thin film is weakened in turn. The surface morphology analyses of the samples show that the ZnO grain sizes tend to decrease with the increase of Fe-doping concentration. Fe-incorporation hardly influences the transmittance in the visible range, but the optical band-gaps of ZnO thin films gradually increase with the improved Fe-doping concentration. The photoluminescence spectra display that all the samples have an ultraviolet emission peak centered at 381 nm and the 1 at% Fe-doped ZnO thin film has the strongest ultraviolet emission peak. The above results suggest that 1 at% Fe-incorporation can improve the crystalline quality and enhance the ultraviolet emission of ZnO thin film.
Article
Less-textured, homogeneous, dense and crack-free (ZrO2)0.92(RE2O3)0.08 (RE = Sc, Y, Nd, Gd, Dy, Er, Yb) nanocrystalline thin films on Si(100) substrate were fabricated by a modified Pechini-type sol-gel method. For the as-deposited films, the average grain size determined by Scherrer equation, integral breadth analysis, and SEM are reliable in each case.
Article
SnS₂/SnO₂ nanocomposites with tunable SnO₂ contents were prepared via in situ hydrothermal oxidation of SnS₂ nanoparticles in 0.375-4.5 mass% H₂O₂ aqueous solutions at 180 °C for 0-12 h. The structure, composition and optical properties of the as-prepared SnS₂/SnO₂ nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, Brunauer-Emmett-Teller (BET) surface area analysis, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and UV-vis diffuse reflectance spectra. Furthermore, their photocatalytic properties were tested for the degradation of methyl orange in water under visible light (λ > 420 nm) irradiation. It was found that the as-prepared SnS₂/SnO₂ nanocomposites with suitable SnO₂ content not only demonstrated superior photocatalytic activity to both SnS₂ nanoparticles and physically mixed SnS₂/SnO₂ composite nanoparticles, but also had remarkable photocatalytic stability. The tight attachment of SnO₂ nanoparticles to SnS₂ nanoparticles, which can facilitate interfacial electron transfer and reduce the self-agglomeration of two components, was considered to play an important role in achieving the high photocatalytic performances exhibited by the as-prepared SnS₂/SnO₂ nanocomposites.
Article
A single dose (100 mg/kg) of purified Direct Black 38, a benzidine-based azo dye, or Pigment Yellow 12, a 3,3'-dichlorobenzidine-based azo compound, was administered to hamsters to determine whether these chemicals are cleaved to potentially carcinogenic aromatic amines. These metabolism studies were conducted in accordance with an interagency agreement between the National Institute for Occupational Safety and Health and the Food and Drug Administration to assess the hazards that may occur if workers in the dye and pigment industries are occupationally exposed to these chemicals. Sensitive and specific assays of the urine by parallel electron-capture gas chromatography and high pressure liquid chromatography revealed the presence of high levels of benzidine, monoacetylbenzidine, diacetylbenzidine, 4-aminobiphenyl, and alkaline hydrolyzable conjugates of benzidine and 4-aminobiphenyl during the first 8 hr of excretion after administration of Direct Black 38. The levels of all metabolites and conjugates except monoacetylbenzidine and alkaline hydrolyzable conjugates of benzidine began to diminish markedly 16 hr after administration of the dye and dissipated to background levels during the 7 day test period. However, appreciable residues of monoacetylbenzidine and alkaline hydrolyzable conjugates of benzidine were still present in the urine at the time that the experiment was terminated. Selected urine samples from treated animals were tested for mutagenic potential via the modified Ames Salmonella/microsome assay. Contrasting results were obtained from a limited study with Pigment Yellow 12. None of the anticipated metabolites were found in the urine at intervals up to 8 days after the pigment was administered. The results are in agreement with other similar laboratory studies. Although no evidence was found for in vivo cleavage of Pigment Yellow 12, the results of the authors' studies with Direct Black 38, coupled with data obtained by other investigators, indicate that workers exposed to this dye could be at risk of contracting bladder cancer.
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