The effect of platinum and silver deposits in the photocatalytic oxidation of resorcinol

The effects of platinum (Pt) and silver (Ag) metallisation in the photocatalytic oxidation of resorcinol at pH 3 ± 0.5 have been investigated. The photocatalytic degradation of resorcinol was significantly improved by Pt/TiO₂, while the presence of Ag/TiO₂ enhanced the initial photocatalytic degradation rate of resorcinol slightly. Likewise, the photocatalytic mineralisation of resorcinol continued to be enhanced by Pt/TiO₂, but it was retarded when Ag/TiO₂ was used.

The function of Pt and Ag deposits on the surface of TiO₂ has been found to be markedly influenced by the interaction of resorcinol and its degradation products with the metal deposits. The presence of Pt or Ag on the surface of TiO₂ altered the distribution of degradation products of resorcinol as well as the production of photoactive species for the photocatalytic oxidation of resorcinol. The X-ray photoelectron spectroscopy (XPS), zeta potential and transmission electron microscopy (TEM) analyses have indicated that the contrasting effect of Pt and Ag deposits were governed by the oxidation states and the catalytic property of metal deposits. In addition to that, it has been found that the roles of metal deposits are specific and should not be generalised.     

Photodeposited CoOx as highly active phases to boost water oxidation on BiVO4/WO3 photoanode

Surface decoration of photoanodes with oxygen evolution cocatalysts is an efficient approach to improve the photoelectrochemical water splitting performance. Herein, ultrafine CoO_x was selectively immobilized on the surface of BiVO₄/WO₃ photoanode by using the photogenerated holes to in-situ oxidize Co₄O₄ cubane. The composited photoanode (CoO_x/BiVO₄/WO₃) displayed an enhanced photoelectrochemical (PEC) water oxidation performance, with a photocurrent density of 2.3 mA/cm² at 1.23 V_RHE under the simulated sunlight irradiation, which was 2 times higher than that of bare BiVO₄/WO₃. The characterization results for the morphological, optical and electrochemical properties of the photoelectrodes revealed that, the enhanced PEC performances could be attributed to the improved charge carrier separation/transport behaviors and the promoted water oxidation kinetics when the photoelectrodes were loaded with CoO_x.     

Properties and H2 production ability of Pt photodeposited on the anatase phase transition of nitrogen-doped titanium dioxide

The effect of calcination temperature on the properties and H₂ production ability of nitrogen-doped (N-doped) titanium dioxide (TiO₂) photodeposited with 0.2 wt% Pt (platinum) was studied. The increase in crystallinity of pre-calcinated N-doped TiO₂ initiated at temperatures higher than 131 °C transformed the morphology from anomalous nanostructure to texture composed of nanoparticles and enhanced the specific surface areas. At 200-400 °C, the anatase peaks gradually became sharper and the visible light absorption region decreased due to the growth of crystallites and the decrease of N-doping content, respectively. Maximum H₂ production was reached when N-doped TiO₂ was calcined at 200 °C followed by Pt photodeposition. The maximum condition is brought about by the formation of textures consisting of nanoparticles and a broad absorption region, thus creating superior active sites for photocatalytic H₂ production.     

Synthesis of magnetically recyclable porous CoFe2O4/Rh composites with large BET surface area for enhanced photocatalytic degradation of organic pollutant

The organic pollutants in water have been a great environment challenges to human beings, and photocatalytic degradation is an effective method to solve this problem. In this paper, the Rh-loaded cobalt ferrite CoFe₂O₄ (CFO) nanoparticles have been successfully synthesized by in situ photodeposition of Rh nanoparticles onto the porous CFO particles as the photocatalysts. After incorporating Rh nanoparticles, the CFO/Rh composite has a higher specific surface area and is more efficient in charge separation than the bare CFO. The photocatalytic efficiency of decomposing Malachite Green (MG) is improved from 70% over the bare CFO to 97% over the optimized CFO/Rh in 60 min. The CFO/Rh sample also demonstrates its durability for the degradation of MG in 5 photocatalytic reaction cycles. Additionally, hydroxyl radicals (?OH) and superoxide radicals (?O₂^?) are proved to be the crucial reactive species during the photocatalytic degradation of MG with CFO/Rh, evidenced by the active species capture experiments. This work provides a useful approach to enhance the photocatalytic activity of semiconductors for degrading organic dyes.     

Photocatalytic hydrogen production from water-methanol and -glycerol mixtures using Pd/TiO2(-WO3) catalysts and validation in a solar pilot plant

This paper is focused on the photocatalytic hydrogen production on Pd/TiO₂(-WO₃) catalysts from water-methanol and water-glycerol mixtures under UVA and solar irradiation. The photodeposition method for Pd was studied varying conditions such as Pd amount, catalyst concentration and methanol concentration. The catalysts were tested at lab scale under simulated solar light and UVA radiation and also at large scale (25 L) under solar energy using a pilot-scale solar Compound Parabolic Collector (CPC). The catalysts characterization was performed by means of ICP-OES, N₂ adsorption–desorption isotherms, XRD, HR-TEM, XPS and DR–UV–Vis spectroscopy. Hydrogen evolution was monitored by on-line gas chromatography.From results it was found the Pd photodeposition method plays a key role to increase the hydrogen evolution, affecting parameters like the Pd amount deposited, the Pd nanoparticles size and dispersion. The highest quantum efficiency (ϕ) obtained in this study was 11.8% and 41.2% under simulated solar and UVA irradiation, respectively, using Pd(0.24 wt%)/P25 in an aqueous solution of methanol (50 vol%). In the pilot-scale solar CPC, for Pd(0.24 wt%)//P25 catalysts in 5 vol% of methanol or glycerol as sacrificial agents, the quantum yield were 2.1 and 2.2%, respectively. When the concentration of the sacrificial agents decreased to 0.37 vol%, the quantum yields were 1.3 and 2.4% for methanol and glycerol, respectively. Compared to literature, the low noble metal content of these catalysts (0.25 wt%) seems to be a competitive factor considering their high price.     

Impact of the reaction conditions on the photocatalytic reduction of water on mesoporous polymeric carbon nitride under sunlight irradiation

Sacrificial hydrogen evolution was studied with sol–gel prepared carbon nitride photocatalysts loaded in-situ with platinum in a photocatalytic setup with defined geometry and a solar simulator as light source. Reaction conditions (e.g. photocatalyst concentration, triethanolamine concentration, amount of Pt precursor, water quality, etc.), and catalyst properties (e.g. BET surface area) were varied to optimize the catalysts for hydrogen evolution. We found that most of the parameters strongly influence the in-situ co-catalyst loading. The optimum platinum loading is between 0.03 and 0.09 wt%, which is less than 5% of the initial amount of platinum. A long term stability test was conducted showing a stable hydrogen evolution rate for more than 10 days indicating a stable catalyst under applied reaction conditions. We found that a change in the BET surface area affects the photocatalytic activity rather than the experimental conditions.     

Preferential CO oxidation over Au/ZnO and Au/ZnO–Fe2O3 catalysts prepared by photodeposition

Preferential CO oxidation in a H₂-rich stream was studied over Au/ZnO and Au/ZnO–Fe₂O₃ catalysts prepared by photodeposition under UV–vis light. The high catalytic activities of both Au/ZnO and Au/ZnO–Fe₂O₃ catalysts are presented over a temperature range of 30–130 °C. TEM results revealed that the average particle size of Au over the Au/ZnO and Au/ZnO–Fe₂O₃ catalysts, is in the range of 3–5 nm. Moreover, DR/UV–vis spectra showed that the prepared catalysts contained Au^δ+ and Au⁰ (active sites for the PROX reaction) on the catalyst support. Based on the experiment observations, it can be concluded that the catalysts prepared by a photodeposition exhibited excellent catalytic activity, even when both CO₂ and H₂O were added to the simulated stream.     

Photochemical synthesis of AZrO3−X thin films (A=Ba,Ca and Sr) and their characterization

(Ba, Ca, Sr)ZrO_3−X thin films were prepared by a photochemical method using thin films of β-diketonate complexes as precursors. The photolysis of these films induces the fragmentation of the 2,2,6,6-tetramethyl-3,5-heptanedionate ligand and the partial reduction of metal ion together with volatile organic compounds as sub-products. When the metallic complexes are irradiated in air, the final product of the reaction are ternary metal oxides. The photoreactivity of these films was monitored by FT-IR spectroscopy by a period of 72 h, followed by post-annealing at 950 °C. X-ray photoelectron spectroscopy and X-ray diffraction techniques were used to analyze the chemical composition and the crystalline structure of the films obtained. The results indicate that Ba, Ca, Sr, Zr and O are present in the form of perovskita, preferably adopting an amorphous structure. The surface morphology examined by atomic force microscopy revealed a rough and irregular surface. The UV–vis measurements suggest a slight increase in the optical band gap values, which promote a reduction of the intermediary energy levels or defects.     

Toward the design of asymmetric photocatalytic membranes for hydrogen production: Preparation of TiO2-based membranes and their properties

Hydrogen production from water using solar light energy is a significant contribution to green renewable energy economy. Separation of water splitting products is essential for this and approached by creating membrane photocatalytic system (MPS) without macroscopic metallic electrodes. The MPS has a layered structure Pt/chemically loaded TiO₂/filtration loaded TiO₂/porous polymer membrane/support. Influence of MPS preparation conditions on its TiO₂ content, permeability, diffuse reflectance spectra, mechanical stability, Pt loading and membrane morphology was investigated. Chemical bath deposition of TiO₂ followed by aging was found to be essential for mechanical stability and high activity in hydrogen production. Loading TiO₂ by filtration alone is ineffective for achieving low permeability. The detected products of ethanol dehydrogenation in gas phase were H₂, CO₂, CH₄ and C₂H₆ and in liquid phase CH₃COOH and CH₃CHO. Optimum mass of TiO₂ and photodeposited Pt were found for high rate of H₂ generation. The highest quantum efficiency of H₂ production was 13%.     

Construction of Z-scheme type CdS–Au–TiO2 hollow nanorod arrays with enhanced photocatalytic activity

The Z-scheme type CdS–Au–TiO₂ hollow nanorod arrays have been constructed on glass substrates by following these simple steps: firstly, highly ordered TiO₂ hollow nanorod arrays (THNAs) were synthesized by liquid phase deposition (LPD) using ZnO nanorod arrays as templates; then both Au core and CdS shell nanoparticles were achieved on the THNAs by in situ photodeposition. The prepared three-component films were characterized by field-emission scanning electron microscopy (FSEM), high-resolution transmission electron microscope (HRTEM), Raman scattering and ultraviolet–visible absorption spectrum. The results showed that Au–CdS core–shell nanoparticles were well dispersed on wall of anatase THNAs from top to bottom. The three-component nanojunction system was evaluated for their photocatalytic activity through the degradation of methylene blue (MB) in aqueous solution. It was found that the CdS–Au–TiO₂ three-component hollow nanorod arrays exhibited significantly enhanced photocatalytic activity compared with single (THNAs) and two components (Au-THNAs or CdS-THNAs) systems. Reasons for this enhanced photocatalytic activity were revealed by photoluminescence (PL) results of our samples.