Preparation And Performance Of Layered Nano Composite Photocatalyst

With the rapid development of social economy and the dramatic expansion of thepopulation, peoples demand for energy increases rapidly, while the globalenvironmental issues are also increasingly prominent. The semiconductor photocatalysiscan break down water for hrdyogen, degradation of organic pollutants and reduction ofcarbon dioxide with abundant solar energy, which is significant for the global newenergy development and environmental governance. However, the traditionalheterogeneous photocatalytic materials as represented by titanium dioxide have verywide band gap, and can absorb only a small amount of ultraviolet sunlight. At the sametime, the photogenerated carrier is easy to recombine and quantum yields rates is low. Inorder to make the photocatalytic technology to practical, give full play to its inhydrogen energy development, environmental pollution and carbon dioxide and otheradvantages, the development of visible light photocatalytic material system model is aninevitable trend. Layered compounds with special structure of lamellar body layerspacing, usually within a few nanometers, at the molecular level, can be considered as aspecial nanomaterial. It is a kind of solid nanometer functional material, due to itsunique layered structure and interlayer chemical reactivity in the ion exchange,adsorption, conduction, separation and catalysis fields with the bright application future.This paper focuses on the study of layered double hydroxides (LDHs) and BiOBr twokinds of layered materials, its unique layered structure makes that the photocarrier caneffectively separate and transmission between layers. In addition, the interlayer ions hashigh activity and can happen embed, peeling, pillared and ion exchange reaction tochange the structure and optimize the photocatalytic performance. According to therelationship of the structure and the performance, through the study of structure design,controlled synthesis and functional assembly, to gain the highly effective visible lightcatalytic materials. The thesis research contents summarized as follows:1. Zn-Cr layered double hydroxides (LDHs) with different interlayer ionic(CO32-、Cl-) have been synthesized by co-precipitation method. A new visible-light drivenphotocatalyst Zn-Cr-AgCl nanoparticles were obtained by depositing AgClnanoparticles (NPs) onto the surface of Zn-Cr (LDHs), which keep the original structure.Zn-Cr-AgCl was investigated by the degradation of organic pollutants in water undervisible-light irradiation. Zn-Cr (LDHs) exhibits two maxima absorption bands in the visible region at410and570nm, respectively. It was found that the Zn-Cr (LDHs) hasexcellent photocatalysis performance. The as synthetized Zn-Cr-AgCl (LDHs) displayedsignificant photocatalytic activity for the degradation of catechol under visible-lightirradiation, nearly87%degradation percentage in120min compared with Zn-Cr(LDHs). The enhancement in photoactivity may be due to the heterostructural unitformed by the interaction of AgCl with LDHs, being benefit for the separation ofphotoelectrons and holes, thus improving the photocatalytic activity.2. NanoPt intercalated Zn-Ti layered double hydroxides (LDHs) have beensynthesized by ionic exchange and photochemical reduction method from Zn-Ti LDHsin H2PtCl6solution. The combination of Zn-Ti-LDHs and Pt introduces some propertiesof Pt into photocatalysis such as excellent conductivity and controllability. Remarkable17-fold enhancement in the degradation of rhodamine B (RhB) reaction was observedon as-prepared Pt/Zn-Ti LDHs compared with pure Zn-Ti LDHs under simulatedsunlight irradiation. The enhanced photocatalytic activity could be attributed to highspecific surface (111.46m2/g), extended photoresponding range, the negative shift inthe flat-band potentials and the high migration efficiency of photoinduced electrons,which may suppress the charge recombination effectively.3. Nano-structured Sn-doped BiOBr hollow microspheres with high visible lightphotocatalytic activity were successfully synthesized by a simple solvothermal method.The results showed that the doping greatly changed the microstructure, morphology andoptical properties of BiOBr, which may contribute to the enhancement of photocatalyticactivity. The photocatalytic activity of the prepared Sn-doped BiOBr photocatalyst wasinvestigated by the degradation of Rhodamine B (RhB) solution under visible lightirradiation. The effects of Sn amount on photoinduced charge property, mainlyinvolving charge separation, and photocatalytic activity of BiOBr hollow microsphereswere principally investigated. Compared with pure BiOBr, Sn-doped BiOBr had ahigher photocatalytic activity. The enhancement in photoactivity may be due to highersurface area, the strong absorption in visible region, the negative shift in the conductionband potentials and improvement the separation of photogenerated electron-hole pairs.