from first principles PP-I-1

PP-V-7New Photocatalysts Based on Cadmium and Zinc Sulfides for HydrogenEvolution from Aqueous Na 2 S–Na 2 SO 3 Solutions under Visible LightLyubina T.P. 1 , Kozlova E.A. 1,21 Boreskov Institute of Catalysis SB RAS, Novosibirsk, Russia2 Novosibirsk State University, Novosibirsk, Russiat.lyubina@gmail.comThe rapid depletion of oil resources necessitates extensive mastering of alternative energy andraw material sources for the chemical industry. Serious attention is presently given to use ofhydrogen as a fuel. An advantage of hydrogen is its high heating value. Furthermore, theproduct of its combustion is water, an environmentally friendly substance. The photocatalyticdecomposition of water to hydrogen and oxygen using solar energy is one of the mostpromising methods of hydrogen production.Cadmium sulfide was the first photocatalyst to be employed in hydrogen production byirradiation of its aqueous suspensions with visible light using sulfide ions as electron donors.Cadmium sulfide is characterized by a band gap of 2.4 eV, and the positions of its valenceand conduction bands are suitable for the photocatalytic decomposition of water. However,the sulfide ion is readily oxidized to sulfate by the photogenerated holes, with Cd 2+ ionsescaping into the solution. Use of sulfides as electron donors diminishes the photocorrosion ofthe catalyst. A possible way of enhancing the photocatalytic activity of cadmium sulfide is todevelop composite materials based on CdS and broader band semiconductors, for example,ZnS. Zinc and cadmium sulfides have similar crystal structures, so they fairly readily formCd 1 – x Zn x S solid solutions.Efficient hydrogen evolution on the sulfide photocatalysts Cd 1 – x Zn x S is attainable withoutadding noble metals, which makes it possible to decrease the cost of the materials.In the present work, we propose a two-step method for preparation of cadmium–zinc mixedsulfides with a large specific surface area and developed porous structure.The activity of the synthesized materials was estimated in the photocatalytic hydrogenevolution from aqueous solutions of sodium sulfide and sodium sulfite (λ > 420 nm), that thehighest activity was shown by Cd 0.3 Zn 0.7 S, whose band gap is Eg = 2.71 eV. We studied theinfluence of the catalyst concentration, pH, and the initial substrate concentration on the rateof photocatalytic hydrogen evolution. At optimal process parameters, the quantum efficiencyof photocatalytic hydrogen evolution was up to 12.9%, which is a large value for a processoccurring under irradiation with visible light on a catalyst containing no noble metal.316