| The presence of a trace amount of toxic organic compounds, such as dyes and polymer additives, in water bodies and waste-water poses severe environmental pollution and health problems. In recent years, great efforts have been devoted to develop strategies to resolve these problems, which include chemical oxidation, solvent extraction, filtration, adsorption, and photocatalytic degradation. Among these methods, photocatalytic degradation by semicondutors has become more and more attractive due to its low cost, simplicity and high efficiency as well as low secondary pollution. In this paper, the mechanism of semiconductor photocatalysis, the main factor affecting photocatalytic properties of semiconductor photocatalyst are briefly summarized. On this basis, semiconductor nanostructures were chosen as a research system and microwave-assisted method as the main synthesis route, we have synthesized a kind of nanocomposite photocatalysts and investigated their photocatalytic activity. The paper mainly includes the following four parts:1. Coating colloidal carbon spheres with CdS nanoparticles:microwave-assisted synthesis and enhanced photocatalytic activityThis chapter describes the accurate coating of CdS nanoparticles on the surface of colloidal carbon spheres by a facile two-step, microwave-assisted method and the studies on the photocatalytic activity of the C/CdS core-shell spheres. For the coating of CdS nanoparticles, cadmium ions were incorporated into the hydrophilic shell of colloidal carbon spheres and reacted with an introduced sulfur source under a microwave field to obtain the C/CdS hybrid spheres. Using this process, the as-prepared hybrid structures preserved the good dispersity and uniformity of initial carbon spheres, and the thickness of the CdS nanoparticles shell could be varied or controlled by the irradiation time. Additionally, CdS nanospheres were successfully prepared in aqueous solution via amicrowave-assisted route, and the effect of irradiation time on the products was also investigated. The studies of the photocatalytic property demonstrate that these fabricated functional hybrid structures evinced a higher photocatalytic degradation activity when exposed to visible light irradiation than that of CdS nanospheres under the same conditions. To investigate the optimal photocatalytic synergistic effect, the above as-prepared of C/CdS hybrid microspheres were treated in a tube furnace by annealing at different temperatures (from300to800℃) in N2flow, which resulting in CdS nanoparticles assembled on the different carbon layers (from amorphous to graphite-like carbon). Further, the synergic effect between CdS nanoparticles and different carbon layers, which influence on the photocatalytic activity, were then investigated systematically. The combination of CdS and graphite-like carbon may be an ideal system to cause a rapid photoinduced charge separation and decreased possibility of recombination of electron-hole pairs by taking advantage of graphite-like carbon’s unique electron transport properties, which increased the number of holes participating in the photooxidation process and enhancing the photocatalytic activity.2. Magnetic-field induced formation of1D Fe3O4/CdS coaxial nanochains as highly efficient and reusable photocatalysts for water treatmentA novel strategy was developed for fabrication of one-dimensional (1D) Fe3O4/C/CdS coaxial nanochains via a magnetic field-induced assembly and microwave-assisted deposition method. First,1D pearl chain-like Fe3O4/C core-shell nanocables are successfully assembled via the hydrothermal reaction of Fe3O4nanospheres and glucose in water in the presence of an external magnetic field. The carbonaceous layer is about10nm in thickness, and it acts as the stabilizer for the nanochains. Afterwards, CdS nanoparticles are facilely deposited onto the1D nanochains via a rapid microwave-irradiation route to form1D Fe3O4/C/CdS coaxial nanochains. Further investigation has revealed that these magnetic nanocomposites possess significantly improved activity as a recyclable photocatalyst for the degradation of organic pollutants when exposed to visible light irradiation. This new synthesis strategy is not restricted to the specific material discussed in this work and should be versatile for a wide range of magnetically separable photocatalysts containing1D magnetic nanochains as the support and an outer layer of active semiconductor nanocrystals.3. Carbon/metal-sulfide composite template:a new facile route toward well-defined oxide hollow nanospheresA new and facile route has been demonstrated to improve the stability of metal oxide hollow spheres by reforming the carbon/metal-sulfide core/shell template. Unlike the traditional template methods, we first prepared a layer of metal-sulfide continuous phase on the surface of carbon spheres with a microwave irradiation technique, and then performed the calcinations to obtain desired metal-oxide hollow spheres. The significant advantage of this method is that the hollow spheres so obtained exhibit superior resistance to distortion, collapse, and shrinkage. Furthermore, we choosed ZnO hollow spheres as a photocatalyst and investigated its photocatalytic performance under UV-light illumination.4. A magnetically separable photocatalyst based on nest-like γ-Fe2O3/ZnO double-shelled hollow structures with enhanced photocatalytic activityMagnetic nest-like γ-Fe2O3/ZnO double-shelled hollow nanostructures have been successfully synthesized via a multi-step process. These interesting nest-like hollow nanostructures are composed of ZnO nanoflakes grown on the surface of y-Fe2O3hollow spheres. Importantly, these magnetic hollow nanostructures show very high visible-light photocatalytic activity for the degradation of different organic dyes including methylene blue (MB), Rhodamine-B (RhB), and methyl orange (MO). It is further demonstrated that these y-Fe2O3/ZnO hybrid photocatalysts are highly stable and can be used repeatedly. |
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