Green Synthesis Of Hierarchically Structured Semiconductor Materials With Efficient Degradation Of Organic Pollutants

In this dissertation, we have explored the controllable synthesis of hierarchically-structured semiconductor micro/nano materials via a facile and green chemical technique, in order to developing their promising application in aspects of environmental pollution treatment. The plausible crystal formation mechanisms of those novel hierarchical micro/nanostructures have been analyzed. Meanwhile, the corresponding structure-dependent degradation of organic pollutions on as-obtained hierarchically structured micro/nano materials has been also investigated. The details are summarized briefly as follows:1. The hierarchically structured hollow microspheres composed of copper sulfide (CuS) nanoplatelets have been successfully fabricated via a one-pot and green sonochemical process for the first time, using copper acetate and thiourea aqueous solution as precursors without surfactant or template. Large-scaled hollow architectures with outer diameters in the range of1-1.2μm are assembled by pure hexagonal single crystalline CuS nanoplatelets, being of about20nm in thickness with stacking faults in the crystal lattice. Moreover, the possible growth mechanism for CuS hollow spheres is proposed on the basis of the temporal evolution controlled experiments. More importantly, this hierarchically structured CuS semiconductor material show highly efficient Fenton-like degradation activity of highly concentrated dye containing solution with the help of hydrogen peroxide, suggesting a promising application in wastewater purification.2. Three kinds of CdS nanostructures, that is, hexagonal nanospheres, hierarchical caterpillarfungus-like hexagonal nanorods and hierarchical cubic microspheres, were controllably synthesized by a facile and one-pot microwave-assisted aqueous chemical method using ethanediamine as a phase and morphology controlling reagent. The characterization results show that hexagonal nanospheres is monodispersed with average diameters of about100nm; hexagonal caterpillarfungus-like nanorods has lengths in the range of600-800nm and diameters of40-60nm, assembled by nanoparticles about20nm in diameter; and hierarchical cubic microspheres is pure cubic microspheres with diameters in the range of0.8-1.3mm, aggregated by tiny nanograins with size of5.8nm. The visible light photodegradation of methylene blue and rhodamine B in the presence of CdS photocatalysts illustrate that all of them display high photocatalytic activities. Significantly, the hierarchical cubic microspheres exhibit the highest photocatalytic efficient in degradation of organic dyes, which is closely related to the phase and morphology structure of cubic CdS material.3. Novel hollow BiOBr eggshells with inorganic fullerene-like structure have been successfully fabricated on a large scale via a facile ultrasound-assisted anion exchange reaction and subsequent heating treatment process. The products demonstrate that the hollow eggshells possess a pure tetragonal phase BiOBr, with the average thickness of about12nm, opening diameters of500-800nm and depths of400-600nm. The walls of eggshells, owning inorganic fullerene-like layered structure, are constructed by nanograins with size of about10nm. The average pore diameter of intercrystal mesopore is2.8nm. A possible formation mechanism for BiOBr hollow eggshells is proposed. According to the photodegradation of Rhodamine B under visible light irradiation, the hollow BiOBr eggshells exhibit excellent photocatalytic performance compared to P25catalyst.4. Novel hierarchical self-supported Bi19S27Br3superstructures have been synthesized on a large scale by a facile and green microwave-assisted aqueous chemical process for the first time. The products have been characterized and the results reveal that the self-supported fabric-like Bi19S27Br3superstructures possess a hexagonal phase with diameters of4-5μm, constructed by cross-bedded nanofibers with average diameters of about80nm. Further, the nanofibers are aggregated by ultrafine nanosilks containing stacking faults. According to the photodegradation of RhodamineB under visible lighting, the self-supported Bi19S27Br3superstructures display high efficient catalytic performance. This work may reignite the intensive study of the higher-order sulfohalogenides for their application in solar and near-infrared light driven photodegradation of organic pollution.