Optical And Catalytic Properties Of Silver-based Nanocomposites Confined In Nano-cavity

Nano-silver as a new functional material,has attracted increasing attention due to its unique physical,chemical and biological properties.Their fascinating physical and chemical properties,including high electrical and thermal conductivity,surface-enhanced Raman scattering effect,chemical stability,catalytic activity and nonlinear optical behavior,are considered to be extremely promising for practical applications in printing ink,microelectronics and medical imaging.Silver nanoparticles possess peculiar electrical,optical and catalytic properties that are obviously different from bulk metals,especially silver nanocomposites,hence,the fabrication of nanocomposites has attracted extensive attention.Single silver nanoparticle has many issues such as easy oxidation and aggregation,poor stability,and low catalytic activity.Therefore,the incorporation of Ag NPs into various substrates can effectively improve their stability.Porous materials,especially microporous aluminosilicate molecular sieves and mesoporous silica materials as the host in the assembly and preparation of host and guest materials,have recently attracted increasing attention.Among them,Linde-A(LTA)zeolites possess the appropriate molecularly sized cages and cation-exchange capacities that could facilitate the uptake and anchoring of silver ion precursors within their pores and cages,which can be used to confine the growth of metal clusters.The negative charge of the zeolite lattice and the coordinating properties of the lattice oxygen atoms provide an additional stabilization of metal clusters.Moreover,dendritic mesoporous silica nanospheres(DMSNs)are widely used in the fabrication of catalytic and luminescent materials because of their peculiar open 3D network pore structure.Their unique hierarchical porosity and special caged pores of several nanometers also make them employed as ideal confined matrices.The main contents of research are as follows:1.Deep understanding of the luminescence mechanism of supported silver clusters.Ag@LTA were synthesized by ion exchange and temperature-programmed reduction method(TPR)using LTA as the matrices.The Ag@LTA dispersed in different solvents(H₂O and DMSO)have different fluorescent emission,the photoluminescence spectra show that there are two emission peaks.Modulating the volume ratio of the two solvents causes a significant change in the relative intensity of these two emission peaks,which indicates that the luminescence of Ag@LTA may not come from silver clusters.Similarly,we also observed a reversible switching of the green/red emission through a hydration/dehydration process,suggesting that the luminescent properties of Ag@LTA are correlated to water.Meanwhile,the photoemission of as synthesized Ag@LTA was highly dependent on water molecules in the confined pore channel.Based on the experimental results,we first proposed the water cluster centered emission model to explain this phenomenon rather than the previously most proposed Ag clusters centered emission model.2.The functionalization of amino group on the surface of DMSNs was carried out by organosilane(APTMS)grafting method,besides,nano-silver catalysts were fabricated by the coordination interaction of the introduced amino groups with silver.The catalytic liquid phase reduction of 4-nitrophenol(4-NP)was chosen as probe reaction to investigate the influence of Ag loading amounts and valence states to catalytic performance,in which the sample with moderate loading amount(2.0%)showed the highest activity.Moreover,the catalytic activity was further modulated by introduced hydroxyl during the catalyst preparation or reaction process,and the proposed intermediate state model clearly answers the excellent catalytic activity on the 4-NP reduction which was further evidenced by the PL spectra.