Synthesis And Catalytic Activity Exploration Of Metal ?Sub-? Nanocluster@SiO₂ Core-Shell Nanocomposites

Metal?sub-?nanoclusters have garnered a great deal of attention because of their unique properties in many fields,such as optics,electronics,and catalysis.However,application restrictions also arise due to their easy aggregation and deactivation.Explore facile synthesis methods which can meanwhile stabilize them has become a meaningful research.In this study,Pd sub-nanoclusters encapsulated in SiO₂ nanospheres with Pd@SiO₂ core-shell configuration was synthesized using a one-pot reverse microemulsion method in a water/CTAB/n-butanol/cyclohexane system.The Pd sub-nanoclusters disperse homogeneously in the whole SiO₂ shell and the mean size is 0.7 nm,which is the minimum size in the field of Pd based core-shell nanoparticles.The mechanism of formation of Pd sub-nanoclusters was explored through experiments and the main reason was due to the control of the nucleation and growth process of PdO·x H₂O precursor.Grafting of amino groups onto SiO₂ to form Pd@SiO₂-NH₂ configuration with some bigger Pd cores encapsulated in the center of SiO₂ nanospheres could improve the morphologies of their Pd@SiO₂ counterparts when the loading of Pd is high,meanwhile a considerable amount of small Pd sub-nanocluster cores still exist.The catalytic activity of Pd@SiO₂ and Pd@SiO₂-NH₂ catalysts in CO oxidation reaction was explored.The samples with the highest Pd sub-nanoclusters fraction had the best activity.Amino functionalization only improved the morphologies of Pd@SiO₂ catalysts and had little impact on the catalytic activity in CO oxidation reaction.The catalytic activity of Pd@SiO₂catalyst in hydrogenation of functionalized nitroarenes was explored.Pd@SiO₂ showed excellent activity in hydrogenation of nitro groups.Au based monometallic or bimetallic nanocluster@SiO₂ core-shell nanoparticles were synthesized using a one-pot reverse microemulsion method in a water/CTAB/n-butanol/cyclo-hexane system.The prepared Au@SiO₂,AuCu@SiO₂ and AuNi@SiO₂ samples have single core-shell configuration.The metal cores disperse homogeneously in the centre of SiO₂ shell,the mean size of the metal cores are 2.5,2.3 and 2.4 nm,respectively.Cu and Ni are mixed with Au sufficiently in AuCu@SiO₂ and AuNi@SiO₂ and show Au crystallinity integrally.The valence states of Cu and Ni in AuCu@SiO₂ and AuNi@SiO₂ are Cu and Ni²⁺,respectively.