The influence of the sacrificial agent nature on transformations of the Zn(OH)2/Cd0.3Zn0.7S photocatalyst during hydrogen production under visible light.

Photocatalysts based on zinc hydroxide and a solid solution of CdS and ZnS were prepared via the precipitation method and used for photocatalytic hydrogen production from aqueous solutions of inorganic (Na2S/Na2SO3) and organic (ethanol) sacrificial agents. The photocatalysts were tested in cyclic experiments for hydrogen evolution and studied using X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy, high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS) techniques. Different transformations of the ß-Zn(OH)2 co-catalyst were observed in the presence of inorganic and organic sacrificial agents; namely, ZnS was formed in Na2S/Na2SO3 solution, whereas the formation of ε-Zn(OH)2 was detected in solution with ethanol. The composite Zn(OH)2/Cd1-x Zn x S photocatalysts have great potential in various photocatalysis processes (e.g., hydrogen production, CO2 reduction, and the oxidation of organic contaminants) under visible light.

Synthesis of Cd1-xZnxS photocatalysts for gas-phase CO2 reduction under visible light.

Novel photocatalysts for CO2 reduction, which consist of a cadmium and zinc sulfide solid solution (Cd1-xZnxS), were successfully prepared by a simple two-step technique. The photocatalysts were characterized by X-ray diffraction, UV-VIS diffuse reflectance spectroscopy, and low-temperature N2 adsorption techniques and were tested in the gas-phase photocatalytic reduction of CO2 under visible light (λ = 450 nm). All the synthesized Cd1-xZnxS solid solutions were capable of enabling the chemical transformations of CO2 under the conditions considered. Carbon monoxide was the major product during the CO2 reduction over Cd1-xZnxS (x = 0-0.87). Methane and hydrogen were also detected in the gas phase in low amounts. The activity of the prepared samples and the distribution of the reduction products strongly depended on the actual cadmium to zinc ratio. The Cd0.94Zn0.06S photocatalyst showed the highest activity, 2.9 µmol CO per gram per hour, and selectivity, 95%, during CO2 reduction under visible light in the presence of water vapor. The achieved values are very high for the sulfide-based photocatalysts.