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Spectral sensitization of TiO 2 with electrodeposited PbSe: improvement of photocurrent stability and light conversion efficiency

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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.

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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).
Article
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.
Article
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).
Article
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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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
Article
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.
Article
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.
Article
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.