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Preparation and photocatalytic properties of silica modified by nano Ag-TiO_2 complex of business

Author: FanXuXin
Tutor: JingLiQiang
School: Heilongjiang University
Course: Physical and chemical
Keywords: oxidation silicon Ag-TiO2 silane coupling agent ethyl orthosilicate photocatalys
CLC: TB383
Type: Master's thesis
Year: 2012
Downloads: 67
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Abstract


Nowadays, environmental pollution and energy problem have drawn increasinglyserious people’s extensive concern. There has been intense study of TiO2as aphotocatalyst because of its nontoxicity, low cost, high chemical stability and excellentdegradation for organic pollutants. However, the large band gap and low quantum yieldsof TiO2prevent it from practical applications in the photocatalysis degradation fororganic pollutants. Many measurements adopted to solve the low quantum yields, noblemetals such as Ag, Au, Pt, and Pd deposited on a TiO2surface is one of the effectmethods to promot interfacial charge transfer processes in the composite systems. But,there still are some problems in the composite systems: first, Ag particle size is largeduring the preparation process which promots photoinduced carrier recombination onthe Ag surface; second, lacking effective compound between Ag and TiO2could inducethe low separative efficiency of photoinduced carrier. Based on the above problems, wedeveloped a silane coupling agent （SCA） modified solvothermal method to synthesizethe size-controlled AgNPs. SCA easily change into oxidation silicon by hydrolysisreactions and polymerization, which controls Ag nanoparticle size and improveseffective compound between Ag and TiO2by chemical bonding, in order to furtherimprove of the Ag-TiO2photocatalytic activity. Synthesis mechanism of the small-sizedAgNPs and mechanism of improved photocatalytic activity of oxidation siliconmodified Ag-TiO2composite systems are discussed.Si-modified small-sized silver nanoparticles have been successfully fabricated viaa SCA modified solvothermal method. The key of this method is to select bifunctional3-triethoxysilylpropylamine （KH550）. The produced-Si-O-Si-connections mayeffectively impede subsequent growth of nanocrystallites by hydrolysis reactions andpolymerization of SCAs. Functional groups, such as NH2-, may control AgNPsnucleation according to control Ag+concentration in the synthetic processes byeffectively coupling Ag+ions. Comparing to the nano-sized TiO2prepared by hydrolysis-hydrothermal process, the photocatalytic activity results of gas phase aldehyde andliquid phase RhB show that the compound Ag exhibit a good photocatalytic activity, but photocatalytic activity isn’t improved by present vast content Si.The compound suitable content SiO2coated Ag-TiO2was prepared by wetchemical method. Comparing to the TiO2prepared by hydrolysis-hydrothermal process,the photocatalytic activity results of gas phase aldehyde and liquid phase RhB show thatthe present right amout of SiO2exhibit better photocatalytic activity. Based on SPS,oxidation silicon modified Ag greatly improved the separative efficiency ofphotoinduced carrier in the composite systems. This provides an idea that furtherimproved photocatalytic activity of noble-semiconductor dioxide compound.

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