Synthesis And Catalytic Properties Of Hierarchical Structured Transition Metal Nnanocomposite Materials

In the present thesis, hierarchically structured layered basic zinc carbonatenanocomposites have been synthesized through hydrothermal method withoutany temple or surfactant, and furhther modified by transition metal cation/oxide resulting in a series of functionalized hierarchical nanocomposites. Thestructure and physico-chemical properties of thus-obtained materials havebeen characterized by XRD, FT-IR, TG-DTA, ICP, SEM/TEM/HRTEM, BET,XPS and UV-vis DRS methods and their applications in the photocatalysis andindustry catalysis fields have been exploringly studied. The present thesisfocuses on the followed contents:（1） A three-dimensional hexagonal flowerlike hierarchically structuredbasic zinc carbonate （BZC） was synthesized by a hydrothermal route with ureaas precipitator and zinc nitrate as Zn source. The fundamental componentunits of BZC were layers with length of8μm, width of4μm and thickness of20nm. Followed heat treatment in300-500oC for BZC leads to a3Dhierarchically mesostructured （pore size ca.10-20nm） ZnO assembled bylayers orderly packed by20-30nm ZnO particles. Further modification via a deposition-precipitation method with HAuCl4as gold source resulting in agold decorated ZnO, which kept the hierarchical mesoporous structure with alittle smaller por size （8-10nm）. The Au particles of ca.7-8nm wereuniformly dispersed in the interstices of ZnO particles. The photocatalyticactivity of the obtained Au-ZnO was evaluated by using the degradation ofmethyl orange （MO） as a probe under UV light. The photocatalytic efficiencyof Au-ZnO is greatly improved, compared to ZnO, and is increased withincreasing Au content. The photodegradation rate constant k of10%-Au-ZnOreached1.2×10-2min-1as twice as that of mesoporous ZnO. These results canbe attributed to the heterostructural unit formed due to the interaction of Auparticles with ZnO phase, being benefit for the separation of photoelectronsand photoholes, thus improving the photocatalytic activity. The Au-ZnOcatalysts were recycled and used for three times without loss of activity.（2） Cu-doped hierarchically structured flowerlike basic zinc carbonate （8-12μm） has been obtained by replacing partial Zn with Cu ions and showsfundamental layer units with both length and width of1-2μm, smaller thanthose of BZC, while large thickness of20-60nm. With increasing Cu content,the layers possess much more smooth surface and compactly stacking mode.The SEM-mapping results show that the Cu cations uniformly dispersed onthe layers. The XPS data reveal the Cu-O-Zn linkage between Au and ZnO,indicating that Cu replaced partial Zn and formed the atomic level dispersionin the nanocomposite. The phenol conversion and biphenol selectivity of Cu-x-BZC in the phenol hydroxylation were gradually enhanced withincreasing Cu content. The conversion of Cu-20-BZC reached38.9%, muchhigher than the literature value （24.7%） of CuMgAl-hydrotalcite. The highcatalytic activity can be attributed to the atomic level dispersion of the activespecies Cu2+and the linkage of Zn-O-Cu in the composites, which lead to theformation of facile redox transition state Cu（I） by partial reduction of Cu（II）and accelerate the process of decomposition of H₂O₂into hydroxyl radicals,thus enhancing the activity of the phenol hydroxylation.（3） Hierarchically structured basic zinc carbonate supported TiO2compositesemiconductor hybrid materials （Z2T-100, Z2T-120） have been prepared by aone-step urea hydrothermal step using zinc nitrate and titanium tetrachlorideas Zn and Ti sources at aging temperature of100-120℃. The anatase TiO₂particles of10-20nm were uniformly dispersed in the interlayer intersticesand on the layers of micrometer BZC. The Z2T-100, Z₂T-120showed bettercatalytic activity （under2h ultraviolet light irradiation, the degradation MOrate increased from40%to60%） compared to the samples with mere TiO₂phases obtained at a little high temperature （130,150℃）. The reason might bethe isolation effect of hierarchically structured BZC support, leading to themore evenly distribution of the TiO₂particles, exposing more catalyticactivitive centers, thus showing better photocatalytic performance.Therefore, the environmetal benign route used in the fabrication ofhierarchically structured transition metal nanocomposites can be used to the design and assmbly of multifunctional nanomaterials which is very importantin the application of catalysis.