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
It was found that ZnO nanocrystals have photocatalytic activity in the formation of CdS during the reduction of sulfur in the presence of cadmium acetate. It was shown that mesoporous spheres measuring 150-170 nm and consisting of CdS/ZnO particles measuring 5-8 nm are formed during the irradiation of ZnO particles measuring 5.5 nm. During the photodeposition of CdS by the action of light on nanorods produced by ultrasonic treatment of microcrystalline zinc oxide nanotubes of CdS 0.5-0.8 µm in length and 15-110 nm in internal diameter are formed. A mechanism, in which they appear at the ends of the ZnO nanorods and grow on the surface of the CdS/ZnO heterojunction, is proposed for the formation of the CdS nanotubes.The most important conditions for the successful functioning of photocatalytic systems based on semiconductor (SCR) materials are effective spatial separation of the unlike photogenerated charges and saturation of the semiconductor surface by the substrates of the photocatalytic reaction. The first of these conditions can be realized, for example, with the use of composite photocatalysts consisting of two or more semiconductors, electron mediators, dark-stage catalysts, etc.[1].The second condition can be met by the appropriate spatial arrangement of the semiconductor-photocatalyst. Analysis of publications of recent years shows that progress in this direction has been associated with the use of ordered micro-and mesoporous materials and also of hollow semiconducting spheres and, probably, nanotubes [2]. In such spatially arranged photocatalysts a "depo" effect appears, i.e., accumulation of the substrate molecules, making it possible to maintain a sufficiently high concentration of them in the surface layer of the semiconductor and thereby weakening the effect of the diffusion-kinetic complications characteristic of many photocatalytic processes. At the same time the fairly rigorous conditions for the production of such structures and, in particular, the need to use high temperatures at many stages of the synthesis restrict their range largely to oxide systems [2,3]. This may explain the very small number of publications on the synthesis of mesoporous and hollow nanostructures based on sulfide semiconductors with photocatalytic activity. Thus, the production of mesoporous CdS involves the use of structure-directing directing templates such as liquid-crystalline matrices [4]. Familiar methods for the production of CdS nanotubes such as, for example, deposition from the gas phase [5] and synthesis in the pores of aluminum membranes [6] and in micellar media [7] are also quite complicated and in most cases do not make it possible to obtain materials that could be used directly as photocatalysts.In the present work it was discovered that zinc oxide has photocatalytic activity in the formation of CdS. It was found that as a result of deliberately changing the conditions it was possible to achieve the formation both of mesoporous nanodimensional spheres, consisting of CdS/ZnO nanoparticles, and of cadmium s...
A set of 20 composites was prepared by pyrolysis of Co2+ complexes with 1,10‐phenanthroline, melamine and 1,2‐diaminobenzene. These composites were tested as the catalysts for the hydrogenation of quinolines. As shown by powder X‐ray diffraction and TEM, the composited contained Co particles of several dozen nm sizes. The composition (elements content), Raman spectra X‐ray photoelectron spectra parameters of the composites were analyzed. It was found that there was no distinct factor that controlled the yield of 1,2,3,4‐tetrahydroquinolines in the investigated process. The yields of the respective products were in the range 90–100 %. The three most active composites were selected for scale‐up and hydrogenation of a series of substituted quinolines. Up to 97 % yield of 1,2,3,4‐tetrahydroquinoline was obtained on a 50 g scale. Five representative substituted quinolines were synthesized on a 10–20 grams scale using the Co‐containing composites as the catalysts.
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