Extremely small colloidal ZnS particles (diameter -1.7 nm) were made by either photo-degradation of 3 nm particles or rapid precipitation in phosphate containing solution at pH = 7-8. The absorption spectra of these particles are different from that of macrocrystalline ZnS, and the changes are regarded as an indication for the transition from semiconductor ZnS to polymolecular ZnS with decreasing particle size. - The dependence of the intensity of the fluorescence on particle size, temperature, photoanodic corrosion and the quenching of fluorescence were investigated for colloids on a silicon dioxide carrier, in phosphate solution, and without a stabilizer. Photo-anodic corrosion strongly improves the fluorescence properties. - One adsorbed Cd 2+ ion per colloidal particle is sufficient for efficient quenching of the fluorescence. However, a new fluorescence band appears which is explained by the formation of a layer of 1:1 co-colloid at the surface of the ZnS particles. - Methylviologen was also found to be a very efficient quencher. The decay of the fluorescence is wavelength dependent, i.e. the fraction of long-lived fluorescence is greater at longer wavelengths. - A mechanism is discussed, where the fluorescence centers are anion vacancies, and fluorescence is emitted when electrons trapped in states of different energies and exhibiting different life-times tunnel to the localized positive holes.

Photochemistry of colloidal metal sulfides. 7. Absorption and fluorescence of extremely small ZnS particles (The world of the neglected dimensions)

The polymerization of diisocyanates, such as hexamethylene diisocyanate, via reaction with water to form polyurea (PUA), has been utilized to immobilize nanoparticles, when formed in reverse micelles. Metal sulfide nanoparticles (CdS, ZnS, coprecipitated CdS−ZnS, and ZnS-coated CdS), as well as TiO2, AgI, and Ag nanoparticles, were immobilized successfully without undesirable particle coagulation, by the simple addition of diisocyanate to the micellar solution. The resulting PUA composites consist of powder of 0.01−0.1 mm in size and where the immobilized nanoparticles are more or less exposed to the external surface, such that they are utilizable as photocatalysts for the generation of H2 from 2-propanol aqueous solution. With tolylene 2,4-diisocyanate used as monomer, the resulting PUA composite is soluble in both DMF and DMSO, and a nanoparticle-containing transparent film can therefore be prepared by casting the resulting DMSO solution onto a quartz sheet.

Preparation of Semiconductor Nanoparticle−Polyurea Composites Using Reverse Micellar Systems via an in Situ Diisocyanate Polymerization

Colloidal Fe2O3 particles of various dimensions were prepared Their crystal structure and optical properties were studied These particles were used as photosensitizers for steady state water photolysis The yield of H2 generated is dependent on the particle size and the concentration of the colloids The pH dependence is different for different particle sizes The effects of methylviologen (MV2+) as an electron relay and CH3OH as a hole scavenger on the H2 yield were also studied

Size effect in the photochemical generation of hydrogen from water by colloidal Fe2O3 particles

Photocatalytic hydrogen production over CuGa2−xFexO4 spinel

https://www.uta.edu/cos/raj/pub/Rajms.pdf

Hydrogen Generation from Irradiated Semiconductor-Liquid Interfaces

Alumina-supported mixed semiconductor catalyst, ZnS·CdS/Al2O3, showed a significant rate of hydrogen generation from water under UV irradiation without an assistance of any noble metals. Singly supported catalyst, ZnS/Al2O3 or CdS/Al2O3, showed, however, less activity for photogeneration of hydrogen. The activity was not improved by physical mixture of ZnS/Al2O3 and CdS/Al2O3 although the amount of ZnS and CdS were the same as those in the ZnS·CdS/Al2O3 catalyst. This indicates that the intimate contacts between ZnS and CdS particles are necessary to photogeneration of hydrogen.

KitagushiKenichi

Papers

Photogeneration of hydrogen from water with mixed semiconductor catalyst