Photocatalytic production of hydrogen in systems based on Cd x Zn1–x S/Ni0 nanostructures

Abstract

A relation was established between the composition of Cd x Zn 1-x S nanoparticles and their ability to accumulate excess negative charge during irradiation. The rate of expenditure of the accumulated charge depends on the composition of the nanoparticles and is determined by their electric capacitance. A correlation was found between the photocatalytic activity of the Cd x Zn 1-x S nanoparticles in the release of hydrogen from solutions of Na 2 SO 3 , their composition, and their capacity for photoinduced accumulation of excess charge. It was shown that Ni 0 nanoparticles photodeposited on the surface of Cd x Zn 1-x S are effective cocatalysts for the release of hydrogen. It was found that Zn II additions in photocatalytic systems based on Cd x Zn 1-x S/Ni 0 nanostructures have a promoting action on the release of hydrogen from water-ethanol mixtures.A promising method for the synthesis of hydrogen, which may in the future have a role in hydrogen power generation, is the photocatalytic (photoelectrocatalytic) reduction of water [1] through solar energy. Significant advances in this direction today have been achieved through the use of semiconductor (SC) photocatalysts [1-3]. High quantum yields for the photorelease of hydrogen during the action of visible light are observed in systems containing nanostructured metal-sulfide semiconductors (CdS, Cd x Zn 1-x S, In 2 S 3 , Bi 2 S 3 , MoS 2 , etc.) and composites with broadband semiconductors based on them and also various electron donors, in the oxidation of which the water is reduced to hydrogen [2,3].Photocatalytic systems for the production of hydrogen on the basis of Cd x Zn 1-x S have two characteristic features that distinguish them from a number of other similar systems based on metal-sulfide semiconductors. It is the propensity of compounds of the Cd x Zn 1-x S series for photocatalytic reduction of water in the absence of metallic cocatalysts and the "bell-shaped" dependence of the photocatalytic activity of the semiconductor on its composition (the values of x) [4,5]. The reasons for these features of the Cd x Zn 1-x S compounds still remain a subject of discussion [6][7][8][9].It should be noted that the ability of these compounds to overcome the overpotential of hydrogen release without additional catalysts provides an indication that they change during irradiation into a more high-energy charged state similar to what occurs during the release of hydrogen at bulk [10] and nanodimensional metallic electrodes [11]. In the mean time there 12 0040-5760/09/4501-0012

Dynamics of the radiative recombination of charge carriers in CdS nanoparticles stabilized with polyethyleneimine

“…The CdS colloids were produced in the reaction of CdSO 4 and Na 2 S in a 0.25% solution of PEI at 18-20°C [1].…”

“…[2][3][4]. Among such characteristics it is necessary to mention the ultrasmall size of CdS-PEI nanoparticles (d = 1.8 nm), the narrow particle size distribution of the nanoparticles (~10%), and the fairly high quantum yield of photoluminescence (PL), amounting to 10%.…”

Semiconductor photocatalytic systems for the production of hydrogen by the action of visible light

“…In [28] it was shown by laser photolysis that the dependence of the ability of Cd x Zn 1-x S nanoparticles to accumulate under the conditions of pulse photoexcitation of the excess negative charge (photoinduced polarization of the semiconductor nanoparticles) on their composition is also described by a bell-shaped curve, and the position of the maximum corresponds to the position of the maximum on the dependence of the quantum yield for the release of hydrogen on x (Fig. 5).…”

“…Photocatalytic processes for the production of hydrogen involving metal sulfide microhetero transitions [8,10,12,16,19], photocatalysts based on mesoporous titanium dioxide [20,21,24,25,27], nanostructured semiconductors, etc. [14,15,18,19,22,23,26,28] were also investigated. In the course of these investigations a series of highly effective photocatalytic compositions sensitive to visible light were created for the production of molecular hydrogen from aqueous organic and aqueous inorganic media.…”

“…The dependence of the quantum yield for the photocatalytic release of hydrogen from an aqueous solution of Na 2 SO 3 on the composition of the Cd x Zn 1-x S nanoparticles stabilized with sodium polyphosphate (SPP) for [Cd x Zn 1-x S] = [SPP] = 5·10 -3 M, [Na 2 SO 3 ] = 1·10 -2 M, 20°C, and light intensity I = 2.3·10 15 quanta/s, l irr = 310-370 nm[28].…”