Preparation,Characterization And Catalytic Properties Of Ag/Porous SiO₂/Polymer Composites

Polymers/inorganic composite nanoparticles,with excellent properties of both polymer and inorganic materials,feature excellent mechanical property,thermal stability,abrasion resistance and biodegradability,and therefore have been widely used in many fields.In recent years,temperature-sensitive modified silica materials have attracted much attention.Mesoporous silica nanoparticles combine the properties of mesoporous materials and nanomaterials,and therefore have been valued for their high specific surface area,large pore volume,and controllable particle size and shape.In this paper,the author prepares SiO₂@PNIPAM composites and core-shell mesoporous silica materials,applies loading and doping modification of silver nanoparticles respectively to the two kinds of materials and then makes an analysis on the catalytic properties of the modified composites.The main research content is as follows:?1?In this paper,the preparation of SiO₂@PNIPAM composite nanoparticles is studied in the first place.The surface-modified SiO₂-NH₂ nanoparticles can be produced by double hydrolysis of TEOS and APTES.Then the polymer PNIPAM is coated with SiO₂-NH₂ as the substrate.In this process,through the observation of solution pH value,reaction temperature and the amount of PNIPAM,SiO₂@PNIPAM composite nanoparticles,with regular shape and high degree of dispersion,are obtained.?2?With SiO₂@PNIPAM composite particles as the substrate and AgNO₃ as the precursor,Ag/SiO₂@PNIPAM composite nanoparticles are prepared through chemical reduction method.In the three experimental methods of this process,the optimum reaction condition is finally achieved by changing the time of adding reducing agent,the concentration of silver nitrate,the reducing time,and the type of reducing agent.In this way,the obtained Ag/SiO₂@PNIPAM composite nanoparticles have the best shape,and the loaded silver nanoparticles,with uniform particle size and dispersion and no agglomeration,have a most significant catalytic effect on the reduction reaction of P-nitrophenol.?3?In this paper,mesoporous SiO₂ nanoparticles with core-shell structure are made through sol-gel method in alcohol-water system with CTAB as the template and structure directing agent,TEOS as the precursor of silicon source,and ammonia as the catalyst.By changing the amount of TEOS and NH₃?H₂O and the aging time,the optimal experimental condition is reached.The obtained core-shell mesoporous SiO₂ nanoparticles have better dispersion and regular shape.There is a regular pore structure inside the core,and the pores of the shell tend to be amorphous,with specific surface area of 536.3m²/g,pore volume of 1.3cm³/g,and pore diameter of 2.2nm.?4?Using core-shell mesoporous SiO₂ nanoparticles as the substrate,Ag/SiO₂composite materials synthetised by hydro-thermal method under three different pH conditions,the catalyst showed better catalytic effect is obtained.The Ag/SiO₂ catalyst synthetised at pH=11.7 has the best catalytic effect on the reduction of PNP,the whole process can be completed in only 10min,However,Ag/SiO₂ composites,the original spherical structure of mesoporous SiO₂ completely collapsed and no pore structure existed.?5?Using core-shell mesoporous SiO₂ nanoparticles as the substrate,four different concentrations of AgNO₃ as the precursor,and trisodium citrate as the reducing agent,mesoporous Ag/SiO₂ composite nanoparticles are obtained in situ reduction,with silver nanoparticles attaching to the inside of mesoporous silicon channel and the surface of the substrate.The effect of catalyst on the reduction of PNP shows that when the concentration of AgNO₃ is 0.1mol/L,the catalytic performance of the obtained catalyst is the best and the reaction can be basically completed in only 18 min.It is not that the higher the AgNO₃concentration is,the better the catalytic effect is.