Synthesis Of Silver-based Core-shell Materials And Their Application In Pollutant Analysis And Chemical Catalysis

As the most common one of many forms of composite materials,core-shell structural materials are widely used due to their unique structure and superior properties.The excellent properties exhibited by Ag nanoparticles and the low-cost relative to other noble metals have become the highest precious metals with "cost-effectiveness." Ag nanoparticles are tending to agglomerate and easily oxidized resulting in decreased performance.Core-shell structure can effectively solve the problem of agglomeration and inactivation of Ag nanoparticles.This dissertation studies the application which two kinds of silver-based core-shell materials in pollutant analysis and chemical catalysis.They are Ag nanoparticles loaded on amino-modified silica microspheres(Ag@ASM)with Ag nanoparticles as the shell and Ag nanoparticles encapsulated within the organic metallic framework HKUST-1(Ag@HKUST-1)with Ag nanoparticles as the core.Two kinds of silver-based core-shell materials applicated in pollutant analysis and chemical catalysis.The specific research and results of the dissertation are as follows:1.We designed and prepared monodispersed and uniform Ag NPs anchored on silica microspheres(Ag@ASM core-shell structure)by the orientation of grafted amino groups,applied it as a SERS substrate for the detection of ultra-low concentrations of poisonous organic pollutants(Rhodamine 6G(R6G),crystal violet(CV),and melamine)with high sensitivity and reproducibility in aqueous solution.A ratio of 2:1 Ag@ASM exhibited optimum SERS performance,allowing the detection of 10-12 M of R6G with an enhancement factor of 6.36×107,as well as 10-8 M of CV and melamine.The density functional theory calculation also provided evidences that modified 3-triethoxysilylpropylamine molecules are interspaced,and the optimum Ag dosage further tuned the gap between Ag NPs as well as the size of Ag NPs.This approach can suggest new ideas for the design and synthesis of other improved SERS active substrates.2.MOF confined ultrafine Ag NPs(Ag@HKUST-1 core-shell structure)were synthesized by double-solvent approach using HKUST-1 as the template and support.HKUST-1 with narrow cage size distribution(0.5 to 0.9 nm)confined the growth of Ag NPs,while the uniform pores prohibited the entrance of olefins with the molecular size lager than 5.0 A,which endow the Ag@HKUST-1 with high catalytic activity and size selectivity for hydrogenation reaction.The hydrogenation of eight kinds of olefins with different molecular size(1-hexene,cyclohexene,1-octene,cyclooctene,styrene,1-decene,1,1-diphenylethylene,and 1-dodecene)catalyzed by Ag@HKUST-1 confirmed this hypothesis.The olefins with molecular smaller than 5.0 A were efficiently converted to the corresponding alkanes,whereas those greater than 5.0 A exhibited extremely low conversation.The catalyst also exhibited high recycle stability in the hydrogenation of styrene.