Preparation And Structure Activity Relationship Analysis Of Highliy Dispersed Nano-silver Loaded Poly (Styrene-co-acrylic Acid) Core-shell Composite Nanospheres Catalyst

In recent years,nanomatericals like composite microspheres consisting of dielectric polymer core and metallic shell have become a subject of intense interest.The interest stems from their unique catalytic and optical properties,which lead to widespread applications in catalysis,photonics,and so on.Therefore,the study of preparation,structural analysis and application of these microspheres has great theoretical meaning and broad application future.In this study,silver nanoparticles loaded in poly(styrene-co-acrylic acid)(nAg@PSA)nanospheres can be served as an effective catalyst for the reduction of 4-nitrophenol to 4-aminophenol in the presence of NaBH4.Then,the work has focused on the controllable preparation and structure activity relationship analysis of poly(styrene-co-acrylic acid)(PSA)nanospheres and nAg@PSA core-shell structure nanospheres.The detailed contents and results are shown as follows:(1)PSA nanospheres with uniform sizes were synthesized by soap-free emulsion polymerization with styrene(St)and acrylic acid(AA)as monomers and potassium thiosulfate as initiator in water.The key factors on the particle size and morphology of PSA nanospheres,including acrylic acid amount,initiator amount,monomer concentration and stirrer speed,were studied.The results show that the half-spheres uniformly distributed on the surface of PSA nanospheres protruded more with the feeding amount of AA or the ratios of AA and St increasing.PSA nanospheres with different sizes was prepared by adjusting acrylic acid amount,initiator amount,monomer concentration and stirrer speed.Besides,the amount of carboxyl groups was evaluated by a conductivity titration curve.The relationship of the carboxyl amount and the nanosphere volume/surface area combined with X-ray photoelectron spectroscopy and transmission electron microscopy images of the PSA nanospheres indicate that PSA is the styrene core/acrylic acid shell nanospheres,and the acrylic acid was mainly distributed on the surface of the polystyrene spheres with unnegligible thickness.(2)Ag nanoparticles(Ag-NPs)were well-dispersed on the surfaces of poly(styrene-co-acrylic acid)composite microspheres by in situ chemical reduction of AgNO3 using NaBH4 as a reducing agent in water.By means of TEM,HRTEM,XRD,UV-vis and EDX,it was proved that Ag nanoparticles were successfully deposited on the PSA nanospheres.The amount and distribution of colloidal silver per particle was related to the dissociation ratio of carboxyl groups in the PSA sphere.However,the dissociation of carboxyl groups on PSA is difficult to determine accurately via existing methods because the dissociation ratio will increase with increasing impurity ions during titration.We developed a technique to determine the dissociation ratio of PSA without impurity ions.This employs a novel distance-variable parallel electrode system.Thus,the relationship between nano silver distribution and dissociation of carboxyl groups on the surface of the PSA spheres was investigated for the first time.The number of dissociated carboxyl groups on the surface of nanospheres is a significant factor to control the content of Ag nanoparticles supported on composite nanospheres.The number of silver particles per PSA particle increased with the number of dissociated carboxyl groups.Measuring and controlling the dissociation facilitated the production of PSA spheres containing highly dispersed silver nanoparticles.(3)The reduction of 4-nitrophenol to 4-aminophenol is a model catalytic reaction and was employed to evaluate the catalytic activity of nAg@PSA nanocomposites.The influences of catalyst amount on reaction rate were studied.The results showed that the more the catalyst amount,the faster the reaction rate.The reaction rate was influenced by silver particle size,the amount of silver per square centimeter of PSA nanospheres surface and the amount of nanospheres per cubic centimeter of nAg@PSA suspension.These synthesized nAg@PSA nanospheres contained highly dispersed silver nanoparticles with high catalytic activity and good recyclability.