Of Ag @ Sio <sub> 2 </ Sub> Composite Particles Of Photochemical Reduction Method Prepare Research

Spherical silica is widely used in various fields because of its unique properties.In recent years, studies show that the metal silver,as one of the nano-materials,has unusual properties,such as antibacterial,catalysis,electrical conductivity,thermal conductivity,and surface-enhanced Raman scattering effect,which have good application prospects in medical biological materials,catalysis, micro-electronic circuits and optical electrical parts.If SiO₂ and Ag can be assembled into a system by specific methods,which not only maintains the stability of silver particles but also access to a single component of the physical and chemical properties,such as adjustable optics,optical non-linear enhancement effects and magnetic anomaly,it will have a breakthrough in the expected area of the original and new applications.Preparation of nano-materials is a key issue to control their reunion to get a good dispersion of nano-particles,so controlling the form of silver composite is one of the challenging topics.In this paper,TEOS was used as silicon source,the silica particles with spherical and modified structure were prepared by the modified sol-gel method with alkali catalyst.The results show the reaction conditions of preparation and modification of spherical silicon dioxide are more harsh.The shape and size are impacted largely by the reaction temperature,reaction time,raw materials and the amount of catalyst particle.Samples were characterized by laser particle size distribution instrument, transmission electron microscopy(TEM),Fourier transform-infrared spectroscopy(FT-IR),X-ray diffraction(XRD) etc.The optimum process parameters for the final preparation of spherical silica are as follows:reaction temperature 50℃,reaction time 8 h,the best dosage of TEOS,water, ammonia:0.02 mol,0.4 mol,0.08 mol.Under the best preparation parameters,the silica particles were modified.We got the following conclusions:(1) The modified SiO₂ particles were prepared with silane coupling agentγ-aminopropyl triethoxysilane silane(APS).The size distribution of modified SiO₂ particle is wide,its half-peak width is narrower than the one unmodified,and particals are in single-particle decentralized state,the tendency of particles gathering decreases obviously.(2) Addition of APS has not changed the composition and structure of SiO₂,only forming Si-O bond through part of hydroxyl and coupling agent on the SiO₂ surface,grafting functional APS group the surface,and generating modifying well,pro-oil hydrophobic enhanced and dispersed SiO₂ particles.(3) Controlling the modified temperature around 50℃in the modified time of 8 h,and APS modifier TEOS volume ratio of 0.04～0.22.It shows that with increasing of the amount of modifier, the average particle size of SiO₂ is reducing,and the loading rate is increasing gradually.Using the raw material AgNO₃ we prepared Ag@SiO₂ composite particles by a new method—the photochemical reduction method,which combines the two methods of photocatalytic reduction and sol-gel method,and then characterized the structure and optical properties of the samples.The results show that this method for preparing composite particle has the advantages such as unnecessary vacuum and high temperature condition,innocuous materials,simple synthetic process,low-cost,short reaction cycle,product of high purity,effective control of the particle aggregation and uniform distribution of Ag particles on the SiO₂ surface because of the uniformity of light distribution.The samples were characterized by Canon digital camera,transmission electron microscopy(TEM),X-ray diffraction(XRD) and UV-visible near-infrared spectrometer(UV-Vis). The results were obtained:(1) Concentration of AgNO₃ has great impact on the size of the silver particles in Ag@SiO₂ composite particles.With increasing of the concentration of silver,the size of silver particles in composite particles decreases firstly,and then increases,there is a quantity critical point of AgNO₃, located in the vicinity of 0.24 g in our experiment.(2) On the condition that the amount of AgNO₃ is 0.24 g,the size of composite particles we prepared is in 150～180 nm,and the size of silver particles is in 10～15 nm,while the silver particles have good face-centered cubic structure and distribute in the spherical dioxide silicon surface.(3) The plasma resonance absorption peak of silver particles is at 474 nm.With reducing of the size of silver particles in the composite system,the peak position shifts towards to the high-energy band(blue shift).