Mesoporous Metal Sulfide Nanocrystal Assembly And Their Composite Materials:Synthesis And Photocatalysis

Introduction of structural defects into the porous material can significantly improve the apparent optical properties.In this paper, the synthesis of a series of mesoporous metal sulfides and the corresponding composite materials with abundantdefects have been achieved, and the synthesized showed valuable optical properties, including photocatalytic degradation of organic dyes and photoluminescence.The following results and conclusions have been obtained in this dissertation:1. Mesoporous sphalerite ZnS nanomaterials with high surface area and well-structured mesoporosity were prepared through a sonochemistry-assisted method in an ethanol system, while the synchronously-formed NaNO3could inhibit the growth of the ZnS nanoparticles and further preserve the surface defects. Ultrasonic waves were essential to obtain a high specifi surface area and uniform pore size distribution due to the significant chemical and physical roles of sonochemistry. The synthesized ZnS with valuable optical properties showed outstanding pho-tocatalytic activity for the photodegradation of organic RhB molecules.2. Cadmium sulfide nanocrystals were synthesized under molten composite solid alkali environment in the absence of water or alcohol. The resultant low surface energy characteristics make the planes easily produce connection-oriented lattice defects, which could increase the adsorption and reactivity. Hydrochloric acid washing not only removed the non-active Cd(OH)2and excess alkali, but also attached protons to the surface of CdS. The present positively charged surface of CdS readily adsorbed molecules of Rhodamine B in weak acid solution through electrostatic interactions, increasing the effective contact with photogenerated hole and hydroxyl radicals over the CdS active sites, and thus promoting visible degradation rate.3. The nanocomposites composed of sulfides and titanium oxide were synthesized using a reaction solvent of molten solid. The sulfide nanocrystals of small size promoted the formation of self-assembled mesopority on titanium oxide nanosheets. Furthermore, the resultant same crystal planes tended to produce abundant lattice defects in the form of dismatched lattices. Hydrochloric acid washing made the nanocomposites possess fine particle dispersion and crystallinity. Photocatalytic decomposition of Rhodamine B could be achieved within20minutes under visible light, thanks to the synergetic effect of the established heterostructures between CdS and TiO2and the high specific surface area. The change of the internal structure of composite material and protonation of surface generated by hydrochloric acid washing enhanced adsorption efficiency of visible light and organic dyes. TiO2nanosheets could act as electron acceptor for the effective separation of photo-generated carriers and CdS nanocrystals could widen absorption range of the visible light as a capture agent. In addation, CdS/TiO2nanocomposites also showed the nature of the fluorescence emission of the ultraviolet and violet region, due to the recombination of CdS nanocrystals surface state level and the recombination of the captured carrier over internal defect sites. FeS/TiO2nanocomposite synthesized by the same method showed a better dispersion and higher crystallinity of the particles by further washing with hydrochloric acid that removed the non-active impurities and residual alkali. Protonation of surface generated enhanced absorption of dyes, and photocatalytic decomposition of35-60%Rhodamine was achieved within120minutes under visible light illumination.