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Spectral sensitization of TiO 2 with electrodeposited PbSe: improvement of photocurrent stability and light conversion efficiency
Abstract
This work focuses on spectral sensitization of mesoporous TiO2 films and Nb-doped TiO2 films with polydisperse PbSe nanoparticles (TiO2/PbSe). For this, PbSe was electrochemically deposited from aqueous solution containing Pb²⁺ cations and SeO2. Chemical amount of electrodeposited PbSe was controlled by deposition time and impacted on the magnitude of sensitized photocurrents. The efficacy of different ions (Sn²⁻; I3⁻; H2PO4⁻; N2H5⁺; SO3²⁻; SCN⁻, SeSO3²⁻) as hole scavengers for TiO2/PbSe photoanodes was assessed by dynamics of photocurrent in polarization measurements. Electrolyte of Na2SO3 and Na2SeSO3 is reported as an effective one to attain stable photocurrent. Photoelectrochemical cells with TiO2/PbSe photoanodes show solar to electricity conversion efficiency of 0.09%, in spectral region up to 700 nm for undoped TiO2. Enhancement of the photoresponse was achieved by different level of Nb doping into mesoporous TiO2 film. Extension of spectral response up to 800 nm and photocurrent conversion efficiency of 0.24% is observed for TiO2/PbSe photoanodes with 2.5 at% Nb-doped TiO2. Doping with Nb results in positive shift on electrochemical scale of conduction band of TiO2. It favors the collection of photoelectrons from PbSe nanoparticles that have light absorption in wider spectral region.
... However, its bandgap is wider, and the absorption of excitation light is poor [128,129]. Therefore, the modification of TiO 2 was studied to promote its light conversion efficiency [130,131]. A new approach was proposed by Gao et al. [132]. ...
Efficient and accurate diagnostic methods are important for human health monitoring and prevention of major diseases, so the establishment of efficient and convenient testing methods for clinical diagnosis is urgent. Photoelectrochemical (PEC) biosensors have attracted much attention because of their high sensitivity, low detection background, and especially the advantages of combining photoexcitation and electrochemical detection. With the rapid development of integrated circuit technology many wireless transmissions of highly aggregated portable micro devices are manufactured, its small size, easy to carry, and the ability to visualize the results of the test is shown to be the potential for the application of such devices. This review aims to cover recent advances in PEC biosensing within the field of portable detection, including the principles of PEC biosensors, common photovoltaic materials, and scalable fabrication techniques for portable PEC biosensing. Future prospects in the field are also discussed.
... PbSe is a typical narrow bandgap semiconductor material with full application in infrared detectors. [1][2][3][4][5] For photodetectors, high quality PbSe film has been successfully fabricated by chemical bath deposition, [6] electrochemical deposition, [7] thermal evaporation, [8] and molecular beam epitaxy method [9] during the past two decades. When making devices from materials, it is often necessary to sensitize PbSe under an oxygen/halogen atmosphere to improve the stability of devices and reduce noise, which is a critical process that determines the performance of photodetectors. ...
High quality PbSe film was first fabricated by a thermal evaporation method, and then the effect of plasma sensitization on the PbSe film was systemically investigated. Typical detectivity and significant photosensitivity are achieved in the PbSe-based photodetector, reaching maximum values of 7.6 × 10 ⁹ cm⋅Hz 1/2 /W and 1.723 A/W, respectively. Compared with thermal annealing, plasma sensitization makes the sensitization easier and significantly improves the performance.
Antimicrobial nanomaterials provide numerous opportunities for the synthesis of next-generation sustainable water disinfectants. Using the keywords graphene and water disinfection and graphene antibacterial activity, a detailed search of the Scopus database yielded 198 and 1433 studies on using graphene for water disinfection applications and graphene antibacterial activity in the last ten years, respectively. Graphene family nanomaterials (GFNs) have emerged as effective antibacterial agents. The current innovations in graphene-, graphene oxide (GO)-, reduced graphene oxide (rGO)-, and graphene quantum dot (GQD)-based nanocomposites for water disinfection, including their functionalization with semiconductor photocatalysts and metal and metal oxide nanoparticles, have been thoroughly discussed in this review. Furthermore, their novel application in the fabrication of 3D porous hydrogels, thin films, and membranes has been emphasized. The physicochemical and structural properties affecting their antibacterial efficiency, such as sheet size, layer number, shape, edges, smoothness/roughness, arrangement mode, aggregation, dispersibility, and surface functionalization have been highlighted. The various mechanisms involved in GFN antibacterial action have been reviewed, including the mechanisms of membrane stress, ROS-dependent and -independent oxidative stress, cell wrapping/trapping, charge transfer, and interaction with cellular components. For safe applications, the potential biosafety and biocompatibility of GFNs in aquatic environments are emphasized. Finally, the current limitations and future perspectives are discussed. This review may provide ideas for developing efficient and practical solutions using graphene-, GO-, rGO-, and GQD-based nanocomposites in water disinfection by rationally employing their unique properties.
PbSe nanocrystalline films were prepared using magnetron sputtering with different sputtering powers and deposition times. The obtained samples were characterized by X-ray diffractometry (XRD), field-emission scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), confocal Raman spectroscopy, UV–Vis–NIR spectroscopy, and spectrofluorophotometry. The XRD and XPS results show that the crystallization quality improves and the Pb/Se atomic ratio tends toward 1:1 with increasing sputtering power and deposition time. The morphology of PbSe particles varies from near-spherical to rod-like or cotton-like and then to triangular with increasing deposition time, consistent with the changed main growth orientation. The optical band gap of PbSe films decreases with increasing film thickness and grain size. A visible photoluminescence peak is observed at 655 nm, and its intensity strongly depends on the crystallization quality and morphology of PbSe particles, which is well consistent with the XRD and SEM results. Therefore, PbSe films with good luminescence performance can be obtained by adjusting sputtering power and deposition time.
Electrochemical deposition of an atomic layer of Pb (underpotential deposition (upd)) was used to determine the electrochemically active surface area of PbSe and Bi2Te3 films obtained under various electrodeposition conditions. The investigations were carried out by cyclic voltammetry and scanning electron microscopy. It was shown that underpotential deposition of Pb atomic layers on PbSe makes it possible to trace the change in the PbSe area during film growth and also to compare the areas of Bi2Te3 films with different surface morphology.
The construction of semiconductor heterostructure photocatalysts is a promising strategy to extend the light absorption region and promote the electron-hole separation for improved solar-to-chemical energy conversion efficiency. The photocatalytic activity of the heterostructure is greatly determined by the efficiency of interfacial charge transfer. In this work, we demonstrate the facet engineered interface design of BiOCl-PbS photocatalytic structures. The PbS nanocrystals are selectively deposited on the (0 0 1) and (1 1 0) facets of BiOCl nanoplates to form BiOCl(0 0 1)-PbS and BiOCl(1 1 0)-PbS, respectively. It is found that the average H2 production rate of BiOCl(1 1 0)-PbS photocatalyst is 2.5 times higher than that of BiOCl(0 0 1)-PbS under broad-spectrum irradiation. This enhancement is mainly ascribed to the different interfacial charge transfer efficiencies. Owing to the different band energies between BiOCl(0 0 1) and (1 1 0) facets, a V-shaped band alignment is formed in the BiOCl(0 0 1)-PbS sample, which results in the accumulation of photogenerated electrons in BiOCl(0 0 1)-PbS interface and prevents the further charge transfer and separation between BiOCl and PbS, while a ladder-shaped band alignment of BiOCl(1 1 0)-PbS achieves the smooth charge transfer and high-efficient charge separation without electron accumulation in the BiOCl(1 1 0)-PbS interface. This work represents a step toward the interface design of high-performance hybrid photocatalyst through facet engineering.
Heralded as a major scientific breakthrough of 2013, organic/inorganic lead halide perovskite solar cells have ushered in a new era of renewed efforts at increasing the efficiency and lowering the cost of solar energy. As a potential game changer in the mix of technologies for alternate energy, it has emerged from a modest beginning in 2012 to efficiencies being claimed at 20.1% in a span of just two years. This remarkable progress, encouraging at one end, also points to the possibility that the potential may still be far from being fully realized. With greater insight into the photophysics involved and optimization of materials and methods, this technology stands to match or even exceed the efficiencies for single crystal silicon solar cells. With thin film solution processability, applicability to flexible substrates, and being free of liquid electrolyte, this technology combines the benefits of Dye Sensitized Solar Cells (DSSCs), Organic Photovoltaics (OPVs), and thin film solar cells. In this review we present a brief historic perspective to this development, take a cognizance of the current state of the art, and highlight challenges and the opportunities.
The presence of both organic and inorganic pollutants in water due to industrial, agricultural, and domestic activities has led to the global need for the development of new, improved, and advanced but effective technologies to effectively address the challenges of water quality. It is therefore necessary to develop a technology which would completely remove contaminants from contaminated waters. TiO
2
(titania) nanocatalysts have a proven potential to treat “difficult-to-remove” contaminants and thus are expected to play an important role in the remediation of environmental and pollution challenges. Titania nanoparticles are intended to be both supplementary and complementary to the present water-treatment technologies through the destruction or transformation of hazardous chemical wastes to innocuous end-products, that is, CO
2
and H
2
O. This paper therefore explores and summarizes recent efforts in the area of titania nanoparticle synthesis, modifications, and application of titania nanoparticles for water treatment purposes.
This review gives a detailed summary and evaluation of the use of TiO2 doping to improve the performance of dye sensitized solar cells. Doping has a major effect on the band structure and trap states of TiO2, which in turn affect important properties such as the conduction band energy, charge transport, recombination and collection. The defect states of TiO2 are highly dependent on the synthesis method and thus the effect of doping may vary for different synthesis techniques, making it difficult to compare the suitability of different dopants. High-throughput methods may be employed to achieve a rough prediction on the suitability of dopants for a specific synthesis method. It was however found that nearly every employed dopant can be used to increase device performance, indicating that the improvement is not so much caused by the dopant itself, as by the defects it eliminates from TiO2. Furthermore, with the field shifting from dye sensitized solar cells to perovskite solar cells, the role doping can play to further advance this emerging field is also discussed.
The continuous combustion of non-renewable fossil fuels and depletion of existing resources is intensifying the research and development of alternative future energy options that can directly abate and process ever-increasing carbon dioxide (CO2) emissions. Since CO2 is a thermodynamically stable compound, its reduction must not consume additional energy or increase net CO2 emissions. Renewable sources like solar energy provide readily available and continuous light supply required for driving this conversion process. Therefore, the use of solar energy to drive CO2 photocatalytic reactions simultaneously addresses the aforementioned challenges, while producing sustainable fuels or chemicals suitable for use in existing energy infrastructure. Recent progress in this area has focused on the development and testing of promising TiO2 based photocatalysts in different reactor configurations due to their unique physicochemical properties for CO2 photoreduction. TiO2 nanostructured materials with different morphological and textural properties modified by using organic and inorganic compounds as photosensitizers (dye sensitization), coupling semiconductors of different energy levels or doping with metals or non-metals have been tested. This review presents contemporary views on state of the art in photocatalytic CO2 reduction over titanium oxide (TiO2) nanostructured materials, with emphasis on material design and reactor configurations. In this review, we discuss existing and recent TiO2 based supports, encompassing comparative analysis of existing systems, novel designs being employed to improve selectivity and photoconversion rates as well as emerging opportunities for future development, crucial to the field of CO2 photocatalytic reduction. The influence of different operating and morphological variables on the selectivity and efficiency of CO2 photoreduction is reviewed. Finally, perspectives on the progress of TiO2 induced photocatalysis for CO2 photoreduction will be presented.
Inorganic nano-scale heterostructures have many advantages over hybrid organic-inorganic dye-sensitized solar cells (DSSC or Grätzel cells), including their resistance to photo-bleaching, thermal stability, large specific surface areas, and general robustness. This study presents a first-of-its-kind low-cost all-inorganic lead selenide-anatase titania (PbSe/TiO2) nanotube heterostructure material for photovoltaic applications. Herein, PbSe nanostructures have been co-electrospun within a hollow TiO2 nanotube with high connectivity for highly efficient charge carrier flow and electron-hole pair separation. This material has been characterized by transmission electron microscopy (TEM), electron diffraction, energy dispersive X-ray spectroscopy (EDX) to show the morphology and material composition of the synthesized nanocomposite. Photovoltaic characterization has shown this newly synthesized proof-of-concept material can easily produce a photocurrent under solar illumination, and, with further refinement, could reveal a new direction in photovoltaic materials.
Evaporation-Induced Self-Assembly (EISA) method for the preparation of mesoporous titanium dioxide materials is reviewed. The versatility of EISA method for the rapid and facile synthesis of TiO2 thin films and powders is highlighted. Non-ionic surfactants such as Pluronic P123, F127 and cationic surfactants such as cetyltrimethylammonium bromide have been extensively employed for the preparation of mesoporous TiO2. In particular, EISA method allows for fabrication of highly uniform, robust, crack-free films with controllable thickness. Eleven characterization techniques for elucidating the structure of the EISA prepared mesoporous TiO2 are discussed in this paper. These many characterization methods provide a holistic picture of the structure of mesoporous TiO2. Mesoporous titanium dioxide materials have been employed in several applications that include Dye Sensitized Solar Cells (DSSCs), photocatalytic degradation of organics and splitting of water, and batteries.
Fast electron transfer from PbSe quantum dots (QDs) to the porous anatase TiO2 film was observed in transient absorption and luminescence, when the lowest unoccupied molecular orbital level of PbSe QDs is higher than that of TiO2. In PbSe QDs 2.7 nm in diameter linked to the TiO2 film the bleaching recovery and the luminescence decay shortened to 1 ps and 4.2 ns from 650 ps and 1.3 μs observed in the non-linked PbSe QDs, respectively. The electron transfer from both the quantum state and the localized state in PbSe QDs to TiO2 takes place fast and efficiently.
Cathodic electrodeposition of PbSe is carried out in aqueous alkaline selenosulfate (SeSO
32−) bath of lead complex ions at various conditions of electrolysis. Micro- and nanocrystalline PbSe thin films were grown onto glassy carbon (GC) substrates by potentiostatic and cyclic voltammetric (CV) methods respectively. Structure and surface morphology of thin films were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). X-ray diffraction indicates that the PbSe films have cubic structure without any impurities. The SEM micrograph showed the films cover GC substrate completely and consisted of irregular shaped grains.
The effect of spectral sensitization of photoelectrochemical processes on the surfaces of mesoporous TiO2 modified by electrochemically deposited PbSe nanoparticles has been observed.
The use of photoexcited electrons and holes in semiconductor nanocrystals as reduction and oxidation reagents is an intriguing way of harvesting photon energy to drive chemical reactions. This review focuses on recent research efforts to understand and control the photocatalytic processes mediated by colloidal II-VI nanocrystalline materials, such as cadmium and zinc chalcogenides. First, we highlight how nanocrystal properties govern the rates and efficiencies of charge-transfer processes relevant to photocatalysis. We then describe the use of nanocrystal catalyst heterostructures for fuel-forming reactions, most commonly H2 generation. Finally, we review the use of nanocrystal photocatalysis as a synthetic tool for metal-semiconductor nano-heterostructures.
The electronic structure of spherical PbS and PbSe quantum dots is calculated with a four-band envelope-function formalism. This calculation accounts for both exciton energies and wave functions with the correct symmetry of the materials. The selection rules and the strength of the dipole transitions of lead-salt quantum dots are derived accounting for the symmetry of the band-edge Bloch functions of the lead salts. The calculated energies of the optically allowed exciton states are found to be in good agreement with experimental data. The effects of many-body perturbations, such as Coulomb interactions and intervalley scattering, are also discussed.
Electron-transfer reactions from different electron donors to PbSe colloids with diameter size less than 5 nm were studied by pulse-radiolysis techniques. Colloidal particles accept electrons from redox couples whose redox potentials are more negative than –0.8 V(vs. NHE). The optical properties of injected electrons show formation of Pb+ in bulk semiconductor after 1 ms and then reduction to Pb° in a second slower step ca. 10 s after electron injection. This cathodic corrosion process is also the dominant process during illumination of the colloids in the presence of hole scavengers. The photoreductive corrosion can be partially suppressed in the presence of an electron acceptor. Reduction reactions that cannot occur in bulk materials can occur in sufficiently small particles. Other quantized metal selenides show similar behaviour. The largest yield of hydrogen was produced with extremely small ZnSe colloids.
A study based on photoluminescence and absorption measurements as a function of temperature and pressure for PbSe nanocrystals with sizes in the range 3-13 nm reveals the influence of size quantum confinement on the observed variation. In the case of the temperature variation, the effective bandgap changes from showing a positive rate of change to showing a negative one (for a quantum dot 3 nm in diameter), which can be accounted for by incorporating a linear variation of the carrier effective masses into a simple calculation of the exciton ground state in the quantum dot. In the case of the pressure variation, we observe a clear inverse correlation between the absolute value of the pressure coefficient and the nanocrystal size, a signature of quantum size confinement, with values changing from -76 to -41 meV GPa(-1) for quantum dots ranging from 13 to 3 nm in diameter, respectively, clearly smaller in absolute value than the rate for bulk PbSe (-84 meV GPa(-1)). We used again the hypothesis of a linear variation of the carrier effective masses with pressure in order to fit this experimental variation quantitatively.
We review computational contributions to the understanding of the physical principles underlying interface phenomena related to dye adsorption at the surface of titanium oxide, in the scope of dye sensitized solar cells applications. We focus our attention on the theoretical studies aiming at computationally representing dye-sensitized solar cells in realistic conditions, e.g. by including solvent and electrolyte in interaction with dye-sensitized TiO2 through protocols accounting for thermal nuclear motion. The impact of dye clustering and self-aggregation into monolayers on optical and transport properties is addressed. Computational studies of surface protonation, charge- and energy-transfer, or the influence of the presence of additive agent or co-sensitizers are also reviewed in relation with electronic, spectroscopic, kinetic and diffusion properties of self-assembled dye monolayers sensitizing TiO2.
Though there are many advantages for the TiO 2 compared to other semiconductor photocatalysts, its band gap of 3.2 eV restrains application to the UV-region of the electromagnetic spectrum (≤ 387.5 nm). As a result, development of visible-light active titanium dioxide is one of the key challenges in the field of semiconductor photocatalysis. In this review, advances in the strategies for the visible light activation, origin of visible-light activity, and electronic structure of various visible-light active TiO 2 photocatalysts are discussed in detail. It has also been shown that if appropriate models are used, the theoretical insights can successfully be employed to develop novel catalysts to enhance the photocatalytic performance in the visible region. Recent developments in theory and experiments in visible-light induced water splitting, degradation of environmental pollutants, water and air purification and antibacterial applications are also reviewed. Various strategies to identify appropriate dopants for improved visible-light absorption and electron–hole separation to enhance the photocatalytic activity are discussed in detail, and a number of recommendations are also presented.
An integrated approach involving the use of visible light absorbing CdS quantum dots (QDs) and near infrared light harvesting PbSe QDs, along with highly conducting carbon dots (C-dots), resulting in impressive power conversion efficiency (PCE) is presented. A photoanode assembly composed of TiO2/PbSe/CdS/C-dots was prepared for the first time. The charge transfer processes in photoanodes of different compositions are explained using absorption studies, emission quenching and lifetime analysis. Upon illumination, photo-excited electrons are injected from the conduction bands of C-dots, CdS and PbSe QDs into TiO2; C-dots serve as excellent electron conduits, and promote electron transport from the photoactive assembly to the current collector and they also function as photosensitizers. Quantum dot solar cells (QDSCs) were fabricated with PbSe, CdS and C-dots based photoanodes, a S2- ion conducting hole transport layer, and multiwalled carbon nanotubes (MWCNTs) as the counter electrode. The cell with the TiO2/PbSe/CdS/C-dots photoanode delivered a remarkably high PCE of 4.97% for the champion cell, which was 35.8 and 48.1% greater than the PCEs produced by the cells with TiO2/PbSe/CdS and TiO2/CdS photoanodes. The increased efficiency, especially in comparison to the cell based on sole CdS, highlights the ability of (a) PbSe QDs, with a band gap of 0.98 eV to harvest red photons and convert them into electricity, and (b) C-dots to channelize the photogenerated electrons to the current collector, by virtue of their high electrical conductivity. This was clearly confirmed by the altered profiles of external and internal quantum efficiencies in the NIR region, for their magnitudes increased from zero to finite in the wavelength range of 550 to 1000 nm, only in the presence of PbSe QDs. Intensity modulated photocurrent/photovoltage data analysis showed fast electron transport and slow recombination for the TiO2/PbSe/CdS/C-dots photoanode. These studies furnish the rationalization for integrating NIR absorbing PbSe QDs and conductive C-dots with other visible light harvesting dyes or QDs to achieve increased photoconversion efficiencies. This journal is
In this study, a novel visible-light-responsive PbSe-TiO2 nanocomposite photocatalysts were successfully synthesized through a facile sonochemical-assisted method, and characterized by XRD, SEM-EDX, TEM, and DRS to confirm its structure, morphology, composition, and optical property. In decolorization of rhodamine B, a significant enhancement in the reaction rate was observed with PbSe-TiO2 composite, compared to the pure TiO2. The generation of reactive oxygen species was detected through the oxidation reaction from 1,5-diphenyl carbazide (DPCI) to 1,5-diphenyl carbazone (DPCO). The high photocatalytic activity can be attributed to the synergetic effect of PbSe nanoparticles and TiO2 by extending the spectral response of TiO2 to visible region and also help to reduce the charge recombination. Finally, the possible mechanism for generation of reactive oxygen species under visible light irradiation was proposed as well.
Quantum dot–sensitized solar cells (QDSCs) present promising cost-effective alternatives to the conventional silicon solar cells due to their distinctive properties such as simplicity in fabrication, possibility to realize light absorption in wide solar spectrum regions, and theoretical conversion efficiency up to 44%. This review highlights recent developments of critical materials including quantum dots, photoanodes, counter electrodes (CEs), and electrolytes for QDSC applications. Among them, the electron recombination at the photoanode/electrolyte interface limits the evolution in high–efficiency QDSCs, therefore the optimized construction of the quantum dots, the various microtopographies of wide bandgap semiconductors (TiO2, ZnO) as well as arising CEs having good electrocatalytic activity are elaborated in this paper. We argue that these key factors can provide design guidelines for future successful applications and significantly promote development of QDSCs. The liquid, quasi–solid–state, and solid–state electrolytes for QDSCs are summarized, aiming at enhancing the long–term stability of QDSCs. This review presented below gives a succinct summary of the materials for QDSC applications, with a conclusion and future prospects section.
In this paper we describe the use of differently sized PbSe quantum dots as photosensitizers for anatase TiO2 nanowires under visible light illumination. After the organometallic synthesis of PbSe quantum dots with three different average diameters (1.8, 2.5 and 4.7 nm), the nanocrystals were attached to the surface of nanowires with thioglycolic acid as a linker molecule. These quantum dot decorated nanowires were used as photocatalyst in the methyl orange degradation model reaction with promising results. The best performance achieved was 90% degradation of the initial concentration of methyl orange in six hours over 2.5 nm PbSe quantum dot sensitized nanowires using a 40 W quartz UV lamp equipped with a 400 nm cut-off filter.
Lead Selenide (PbSe) thin films have been deposited by Successive Ionic Layer Adsorption and Reaction (SILAR) method to investigate the effect of hydrazine hydrate on film properties. The peak behavior of the X-ray diffractogram corroborates crystalline nature of PbSe thin films. The intensity of the major peaks attributable to PbSe improved at higher concentrations up to 5 ml HH and gets reduced for 7 ml HH. The average crystallite size is in the range 18.18–33.37 nm. The film surface of lower HH sample is composed of spherical grains which are arranged in a compact manner. On increasing HH some clusters appears on the surface of the film over a homogeneous background. The AFM micrographs show that the surfaces of the lead selenide thin films consist of dense distribution of nanoscale particles with a range of grain sizes. The roughness obtained is in the range 13.7–76.3 nm. Highly crystalline sample, 5HH exhibits very good topography. The direct band gap values are in the range 1.425–1.803 eV. Thus by varying HH we have been able to tune the band gaps over a wide range. The highly crystalline sample 5HH with least strain and excellent topography exhibits maximum conductivity.
PbSe quantum dots (QDs) were formed on TiO2 by a two-step photodeposition technique. At the first step, UV-light irradiation of TiO2 in an ethanol solution of H2SeO3 yields Se QDs on the TiO2 surface in a highly dispersed state (Se/TiO2). At the second step, UV-light irradiation of Se/TiO2 in an ethanol solution of Pb(ClO4)2 transforms Se QDs into several tens of nanometer-sized cubic deposits identified as PbSe (PbSe/TiO2) by X-ray diffraction, electronic absorption measurements and X-ray photoelectron spectroscopy. Photochronopotentiometry measurements suggested that the PbSe QDs are formed on TiO2via the Pb(2+) ion-assisted reduction of Se particles.
Copyright © 2015. Published by Elsevier Inc.
Pyroelectric infrared detectors provide the advantage of both a wide spectral response and dynamic range, which also has enabled systems to be developed with reduced size, weight and power consumption. This paper demonstrates the deposition of lead zirconium titanate (PZT) and lead calcium titanate (PCT) thin films for uncooled pyroelectric detectors with the utilization of gold electrodes. The modified lead titanate thin films were deposited by pulsed laser deposition on gold electrodes. The PZT and PCT thins films deposited and annealed at temperatures of 650 °C and 550 °C respectively demonstrated the best pyroelectric performance in this work. The thin films displayed a pyroelectric effect that increased with temperature. Poling of the thin films was carried out for a fixed time periods and fixed dc bias voltages at elevated temperature in order to increase the pyroelectric coefficient by establishing a spontaneous polarization of the thin films. Poling caused the pyroelectric current to increase one order of magnitude.
Nb-doped anatase TiO2 nanoparticles were prepared by the sol-gel process followed by a hydrothermal treatment and successfully used as the photoanodes in organic dye-sensitized solar cells (DSSCs). Phase identification of the TiO2 samples was confirmed by X-ray diffraction and Raman shift spectroscopy. The electronic structure and Nb doping in the TiO2 lattice were confirmed by X-ray photoelectron spectroscopy and energy-disperse X-ray spectroscopy, respectively. Also, the conduction band edge (CB) shift due to the Nb-doping in the TiO2 lattice by UV-vis diffuse reflectance spectroscopy and the effect of Nb doping on the charge transporting and recombination behaviors of the DSSCs by electrochemical impedance spectroscopy (EIS) analysis were investigated. The Nb-doped TiO2 exhibited a positive shift of the conduction band edge (CB) compared to the undoped TiO2. Consequently, the increased driving force for electron injection, that is, the difference between the CB of TiO2 and the lowest unoccupied molecular orbital (LUMO) energy level of the dye, could correspondingly contribute to the enhancement of the electron injection efficiency, but the Voc has the opposite behavior. The Voc drop in the DSSCs based on the Nb-doped TiO2 could be prevented using a multi-functional HC-A as a coadsorbent instead of DCA. As expected, a PCE of 7.41% was obtained for the NKX2677/HC-A-sensitized DSSC based on the 2.5 mol% Nb-doped TiO2, which was an improvement of 11% relative to that of the DSSC based on the undoped TiO2.
The early stages of growth in chemical solution deposition of lead selenide thin films on GaAs(100) substrates were studied in detail. The deposition was found to depend strongly on substrate pre-treatment with sodium selenosulphate in an aqueous KOH solution. In cases where this stage of the process was neglected, film growth would not occur. The sequence of precursor addition and the pH of the solution were also found to be dominant factors affecting film growth. Film growth rate, grain size and the resulting roughness were all shown to increase with pH. Study of film growth kinetics revealed the selenide limited nature of the system. These factors are shown to be critical for reproducible deposition of high quality PbSe thin films.
A barrier layer of undoped TiO2 was deposited on the Nb-doped TiO2 electrode to suppress the recombination at the Nb-doped TiO2/dye–electrolyte interface for highly efficient dye-sensitized solar cells (DSCs). The Nb content in TiO2 was varied in a range of 0.7–3.5 mol% to modify the TiO2 energy-band structure. Nb-doped TiO2/dye interfaces were characterized by a combination of ultraviolet photoemission spectroscopy and optical absorption spectroscopy measurements, allowing the determination of the conduction band minimum (CBM) of the TiO2 electrode and the lowest unoccupied molecular orbital of the N719 dye. The lowering of TiO2 CBM by Nb doping induced the increase in short-circuit current of DSCs. However, open-circuit voltage and fill factor are decreased, and this result was ascribed to the enhanced recombination at the Nb-doped TiO2/dye–electrolyte interface. The effect of doping on charge transport in DSCs was analyzed using electrochemical impedance spectroscopy. We have shown that by introducing of TiO2 barrier layer, the Nb doping content, which results in DSC highest efficiency, can be increased because of the suppression of the dopant-induced recombination. The energy conversion efficiency of the solar cells increased from 7.8% to 9.0% when undoped TiO2 electrode is replaced with electrode doped with 2.7 mol% of Nb because of the improvement of the electron injection and collection efficiencies. The correlation between the electronic structure of the TiO2 electrode, charge transfer characteristics, and photovoltaic parameters of DSCs is discussed. Copyright © 2012 John Wiley & Sons, Ltd.
Highly crystalline pure brookite and two-phase anatase/brookite TiO2 nanostructures were synthesized via a simple hydrothermal method with titanium sulfide as the precursors in sodium hydroxide solutions. The control of the phase composition has been demonstrated via solution concentration and reaction time, and the phase transformation mechanism has been elucidated. Photocatalytic activities of the as-synthesized two-phase anatase/brookite TiO2, pure anatase nanoparticles, and pure brookite nanoplates were appraised via photocatalytic hydrogen evolution in aqueous methanol solution. Results have shown that the photocatalytic activity is higher for the two-phase anatase/brookite TiO2 and brookite nanoplates as compared to pure anatase nanoparticles despite the lower surface areas of the two-phase anatase/brookite TiO2 and brookite nanoplates. From the Mott–Schottky analysis, brookite phase is shown to have a more cathodic conduction band edge potential than anatase phase, which leads to more energetically favorable hydrogen reduction. Moreover, femtosecond transient absorption spectroscopy measurements suggests that the photoexcited electrons transfer from brookite to anatase phase—leading to further enhancement of the photocatalytic activity. In comparison with the highly active two-phase commercial benchmark P25, our synthesized two-phase anatase/brookite TiO2 is 220% more active when measured by the H2 yield per unit area of the photocatalyst surface.
Carrier multiplication—the generation of multiple electron–hole pairs by a single photon—is currently of great interest for the development of highly efficient photovoltaics. We study the effects of infilling PbSe quantum-dot solids with metal oxides by atomic layer deposition on carrier multiplication. Using time-resolved microwave conductivity measurements, we find, for the first time, that carrier multiplication occurs in 1,2-ethanedithiol-linked PbSe quantum-dot solids infilled with Al2O3 or Al2O3/ZnO, while it is negligible or absent in noninfilled films. The carrier-multiplication efficiency of the infilled quantum-dot solids is close to that of solution-dispersed PbSe quantum dots, and not significantly limited by Auger recombination.
We report the transformation of several metal selenide nanocrystals (NCs), including PbSe, CdSe, ZnSe, and PbSe/CdSe core/shell NCs, in dimethyl sulfoxide (DMSO) in acidic solutions at room temperature. In this study, the DMSO solution of metal selenide NCs was mixed with nitric acid, which was used to adjust the pH of the solution. Upon mixing, the metal selenide NCs readily transformed into crystalline selenium (trigonal structure) nano- or microwires under ambient light, whereas little or no transformation occurred in the dark. Photocorrosion, where the photogenerated carriers within the NCs participate in the cleavage of the metal and selenium atoms, turns out to be responsible for the transformation. DMSO removes organic ligands on the NC surface and creates surface trap sites for photoinduced charge carriers. Then, nitric acid helps shift the reduction potentials, thereby promoting a "cathodic reduction". In this sense, the photocorrosion rate can be controlled by several parameters, such as the absorption cross section of the selenide NCs and the pH. The diameter and shape of the resulting selenium wires help gauge the transformation rate and thus unveil the transformation mechanism.
We report an Yb:Sr5(PO4)3F (Yb:S-FAP) laser emitting at 985 nm intracavity pumped by a 912 nm diode-pumped Nd:GdVO4 laser. A 808 nm diode laser is used to pump the Nd:GdVO4 crystal emitting at 912 nm, and the Yb:S-FAP laser emitting at 985 nm intracavity pumped at 912 nm. With incident pump power of 17.5 W, intracavity second harmonic generation has been demonstrated with a power of 131 mW at 492.5 nm by using a LBO nonlinear crystal.
The multifunctional and advanced semiconductor titania with superior physicochemical and opto-electronic properties is extensively investigated in wastewater purification mainly due to its non-toxicity, favorable band edge positions, water insolubility, multifaceted electronic properties, surface acid–base properties, super hydrophilicity and so on. However, large band gap and massive photogenerated charge carrier recombination hinders its wide application under natural solar light. Thus, altering the surface-bulk structure of titania is a major goal in the area of both materials and environmental chemistry for its better applications. The substitution of p block elements (B, C, N, F, S, P, and I) either at Ti4+ and O2− sites is a promising approach to overcome the aforementioned drawbacks. This review focuses on the photocatalytic activity of non metal doped titania for a wide variety of pollutants degradation under UV/visible light, with special emphasis on nitrogen doped TiO2. Further improvement in photoactivity of N–TiO2 is achieved via depositing with noble metals, co-doping with foreign ions, sensitization, surface modifications and heterostructuring with other semiconductors. The mechanism governing the photocatalytic reactions is discussed in the light of charge carrier generation–separation–transfer–recombination dynamics together with pollutant adsorption and their reactions with reactive oxygenated species in liquid or gaseous regime. We are positive that this review article will further stimulate our research interest on this intriguing hot topic.
PbSe was electrodeposited onto monocrystalline n-Si(1 0 0) wafers from 50 mM Pb(NO3)2 + 2 mM SeO2 + 0.1 M HNO3 solution. The mechanism of PbSe electrocrystallization on n-Si was studied. At initial stage, 3D Pb and 3D Se nuclei are simultaneously codeposited onto Si at potentials more negative than Si flat band potential and chemically interact resulting in PbSe formation. When n-Si/PbSe heterostructure is formed, the overvoltage of bulk lead deposition increases, as a result of redistribution of electrode potential. Further growth of PbSe is realized due to underpotential deposition (UPD) of Pb and overpotential deposition (OPD) of Se onto formed PbSe nuclei. With Pb UPD shift increase, amorphous Se inclusion is registrated in the deposit. When 2D Pb nucleation mechanism is changed to 3D mode, metal Pb cubic phase is codeposited with PbSe. Electrodeposition of PbSe onto n-Si is irreversible. PbSe anodic stripping does not take place in the dark due to the barrier on solid interface. Oxidation of PbSe on n-Si is observed only under illumination, when photoholes are generated in silicon substrate.
The electrochemical behaviour of PbSe, synthetized by a gas—solid reaction between PbSO4 and H2Se at 600°C, is investigated. Several preliminary experiments on lead and selenium are performed in order to observe the peak potentials of the oxidations (or reductions) occuring in the −1 to +1 V sce range in 0.1 M HCl or HClO4. Successively Pb2+, PbSO4, H2SeO3 (soluble), SeO2 and grey Se powder are tested. After mechanical grinding, PbSe is introduced in the paste. A preliminary oxidation or a preliminary reduction of the solid allows the observation of several reduction or oxidation peaks due to the destruction of a part of solid PbSe (particle size between 0.5–5 μm).
The use of PbSe quantum dots (QDs) as sensitizers for TiO2 samples has been primarily hampered by limitations on charge injection. Herein, a novel successive ionic layer adsorption and reaction (SILAR) method, allowing for an intimate TiO2/PbSe contact and a strong quantum confinement, is described. Photoelectrochemical experiments and transient absorption measurements reveal that charge separation indeed occurs when using either aqueous sulfite or spiro-OMeTAD as a hole conductor and that it can be further enhanced by attaching p-mercaptophenol (MPH) to the QD surface. These results suggest that MPH can promote an efficient funneling of the photogenerated holes from the PbSe to the hole scavenging medium, thereby increasing the yield of electron injection into TiO2. In a more general vein, this work paves the way for the fabrication of PbSe-sensitized solar cells, emphasizing the importance of controlling the QD/hole scavenger interface to further boost their conversion efficiency.
This paper describes the growth of lead selenide (PbSe) thin films on glass and on ITO-covered glass substrates at room temperature under normal pressure utilising the successive ionic layer adsorption and reaction (SILAR) technique. Aqueous precursor solutions, lead acetate complexed with triethanolamine and sodium selenosulfate, were used for lead and selenide, respectively. The films were found to be metallic and adherent. The properties of the films were characterised by means of X-ray diffraction (XRD), Rutherford back-scattering spectrometry (RBS), nuclear reaction analysis (NRA) and scanning electron microscopy (SEM).
A serial of surfactant-templated mesoporous TiO2 films with the thickness over several micrometers have been successfully synthesized by one-step dip-coating and subsequent evaporation induced self-assembly method. Three different pre-condensed TiO2 sols in the presence of surfactant (Pluronic F127) micelles with high viscosities were employed as the precursors for dip-coating. By treating the films in liquid paraffin as “shape protector” at certain high temperature for sufficient time, thick mesoporous films can be kept crack-free after calcinations. By employing the size-controlled titanium-oxo clusters in the sols as building blocks for self-assembly, the final obtained films represent tunable mesostructures. The mesoscopic characteristics of the films, such as Brunauer–Emmett–Teller surface areas, pore size distributions and pore wall crystallizations, have been comparatively studied. The results demonstrate that such tunable mesoscopic characteristics are greatly dependent on the structural and shape parameters of the initial formed inorganic clusters.
Cathodic electrodeposition of thin film from aqueous selenosulfite solution has been studied as a function of solution composition and electrode potential. The Cd:Se ratio has been determined using polarography and Rutherford backscattering spectrometry (RBS). Polarography gives a composition averaged over the whole film (ca. 3 cm²) while RBS gives local surface composition (1 mm²). The results of the two techniques agree within experimental error. The average Cd:Se ratio was found to be close to 1.0 for a variety of conditions. The effect of various deposition and annealing conditions on light to electrical power conversion efficiency are presented. Cyclic voltammetry has been used to explore the mechanism for the deposition process.
The thermodynamics equilibrium principle was used to construct the diagrams for the concentration of complex ions (pc) vs pH, the distribution ratio of lead hydroxyl complex ions (αn) vs pH, and the conditional solubility product of Pb(OH)2 vs pH in the Pb2+-H2O system. The relationship between the equilibrium concentration of each kind of lead hydroxyl complex ions in equilibrium with Pb(OH)2(s) and pH value was shown in the system. The minimum solubility of lead is at the pH value of 10.096–10.997. The distribution ratio of each kind of the lead hydroxyl complex ions is determined as a function of the pH value and the total lead concentration ([Pb]T). The diagram for the conditional solubility product, pKSP vs pH, shows that each kind of lead hydroxyl complex ions existing in the system is dependent upon an optimized pH value at the established concentration of [Pb]T, and that pKSP reaches the minimum at the pH value of 10.3–11.2. The results can provide a theoretical basis for removing lead ions from wastewater by the neutralization and hydrolyzation technology.
Lead sulfide thin films were grown at room temperature by the successive ionic layer adsorption and reaction (SILAR) technique on soda lime glass, ITO and Al2O3 covered glass, SiO2, (100)Si and (111)Si substrates. SILAR utilises sequential treatment of the substrate with aqueous precursor solutions. Dilute solutions of lead acetate and thioacetamide were used as precursors for Pb2+ and S2–, respectively. The lead precursor solution also contained triethanolamine (tea) as a complexing agent, with a Pb: tea mole ratio of 1 : 2. On glass the growth rate was 0.12 nm per cycle with 0.2 mol dm–3 lead and 0.4 mol dm–3 thioacetamide solution. The appearance of the films was metallic. X-Ray diffraction studies revealed a strong [200] orientation of the films. According to the Rutherford back-scattering (RBS) and nuclear reaction analysis (NRA) results the films were stoichiometric PbS and contained small amounts of some lighter impurities, possibly O and H. Scanning electron microscope (SEM) images revealed that the films were rather rough and consisted of grains with a diameter approximately corresponding to the thickness of the film.
The process of the underpotential deposition (UPD) of Pb adatoms (Pbad) onto Se was used to produce nanocomposite films consisting of amorphous Se and nanosized PbSe clusters distributed throughout the film bulk. It was found that doping lead into Se films modifies their optical and photoelectrochemical properties and increases the efficiency of the charge transfer both in the film bulk and through the semiconductor | electrolyte interface. Introducing lead into the bulk of Se films significantly promotes the process of Pbad UPD onto Se surface. The underpotentially deposited Pbad interact chemically with Se surface atoms, resulting in the formation of a PbSe monolayer. The PbSe formed can be identified by the anodic peak corresponding to its electrochemical oxidation.
The oxidation of thiocyanic acid by selenous acid has been shown to take place in an analogous way to that found for selenous acid oxidation of most thiols and thiolates to give the corresponding selenotrisulfide and disulfide productsThe products of this reaction have been studied by IR, Raman, and Se-77, C-13, and N-15 NMR spectroscopy. The vibrational spectra of the solid Se(SCN)2 have been assigned based on S-bonded thiocyanate ligands and, through NMR and vibrational spectroscopy, both this linkage isomer and the isomer with N- and S-bonded thiocyanate have been identified and characterized in solutions of Se(SCN)2. A complex combination of scalar relaxation processes, involving chemical exchange and quadrupolar effects, accounts for the line broadening observed in the carbon-13 NMR spectra. Key words: selenite, thiocyanate, selenium dithiocyanate, Se-77, N-15, and C-13 NMR; Raman spectroscopy; linkage isomerism
A simple approach to heterostructured thin film catalysts consisting of PbSe nanocrystals and layer-by-layer deposited TiOx is presented. Strong quantum confinement raises the conduction band of PbSe nanocrystals above that of TiOx, leading to a type II band offset. Photogenerated electrons in PbSe nanocrystals are transferred to catalytic TiOx which in turn initiate catalysis. Photocatalytic activity of the heterostructured films is found to be dependent on the size of the PbSe nanocrystals with the onset of catalysis coinciding at a photon energy of similar to 2.5 times the band gap of the nanocrystals. Photocatalysis in the visible spectral region out to 650 nm is demonstrated.
Applied Catalysis B: Environmental j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / a p c a t b a b s t r a c t Fujishima and Honda (1972) demonstrated the potential of titanium dioxide (TiO 2) semiconductor mate-rials to split water into hydrogen and oxygen in a photo-electrochemical cell. Their work triggered the development of semiconductor photocatalysis for a wide range of environmental and energy applica-tions. One of the most significant scientific and commercial advances to date has been the development of visible light active (VLA) TiO 2 photocatalytic materials. In this review, a background on TiO 2 struc-ture, properties and electronic properties in photocatalysis is presented. The development of different strategies to modify TiO 2 for the utilization of visible light, including non metal and/or metal doping, dye sensitization and coupling semiconductors are discussed. Emphasis is given to the origin of visible light absorption and the reactive oxygen species generated, deduced by physicochemical and photo-electrochemical methods. Various applications of VLA TiO 2 , in terms of environmental remediation and in particular water treatment, disinfection and air purification, are illustrated. Comprehensive studies on the photocatalytic degradation of contaminants of emerging concern, including endocrine disrupting compounds, pharmaceuticals, pesticides, cyanotoxins and volatile organic compounds, with VLA TiO 2 are discussed and compared to conventional UV-activated TiO 2 nanomaterials. Recent advances in bac-terial disinfection using VLA TiO 2 are also reviewed. Issues concerning test protocols for real visible light activity and photocatalytic efficiencies with different light sources have been highlighted.
Monodisperse lead selenide nanoparticles have been successfully prepared via a sonochemical route from an aqueous solution of lead acetate and sodium selenosulfate in the presence of complexing agents under ambient air. It was found that when trisodium citrate was used as the complexing agent, the product was spherical nanoparticles with an average size of ca. 8 nm. If potassium nitrilotriacetate was used, the product consisted of rectangles with an average size of ca. 25 nm. The products were characterized by powder X-ray diffraction, transmission electron microscopy, selected area electron diffraction, and X-ray photoelectron spectroscopy. A probable mechanism for the sonochemical formation of PbSe was proposed. Several factors that affected the nature and morphology of the products were also discussed such as the pH value, the complexing agents, and the intensity of the ultrasound irradiation.