| Nanogels,nanosized hydrogel particles formed with crosslinked polymer networks,integrate the advantages of nanogel and polyelectrolyte,such as high water content,high stability,good biocompatibility,enhanced permeability and retention etc.Polyelectrolyte nanogel is a special type of nanogels composed of charged polymer,which has a large amount of charges inside of the particles.Polyelectrolyte nanogels can effectively adsorb metal ions,and form nanocatalysts loaded with metal particles by in-situ reduction.Therefore,poly electrolyte nanogels have received extensive attention in the fields of disease diagnosis and treatment,biosensing,and catalysis.In this thesis,strong and weak polyelectrolyte nanogels were prepared based on electrostatic assembly directed polymerization,in which a polyion-neutral block copolymer was used as template to induce copolymerization of oppositely charged ionic monomers and cross-linker.The thesis systematically studied the effects of pH,salt concentration and cross-linker fractions on the synthesis and structure of different polyelectrolyte nanogels.Subsequently,strong and weak polyelectrolyte nanogels were applied as carriers to adsorb chloroauric acid ions through electrostatic interaction,and consequently,polyelectrolyte gels loaded with gold nanoparticles were prepared by the reduction of sodium borohydride.The effects of different nanogels on the loading and catalytic performance of gold particles were investigated.The specific research content is as follows:(1)Using the negatively charged polyethylene glycol-polyacrylic acid(PEO-b-PAA)diblock copolymer as template,the strong electrolyte methacryloxyethyltrimethyl ammonium chloride(METAC)and weak electrolyte 2-aminoethyl methacrylate hydrochloride(AEMH)as monomers,polyelectrolyte micelles were obtained by polymerization and assembly in the presence of cross-linker.The template was eluted at high salt concentration,leading to strong and weak polyelectrolyte nanogels.It was found that,adjusting the pH can control the charge interaction between the monomer and the template.Only strong interactions can obtain high monomer conversion and nanogels with controlled structure and size.For METAC and AEMH monomers,the optimal polymerization pH is 7.5 and 6.5,respectively.Increasing the amount of cross-linker fractions can increase the conversion of the two monomers and form a nanogel with a smaller size,but the size of the PMETAC gel decreases more significantly with increasing cross-linker fraction.Within a certain salt concentration,the conversion of strong and weak monomers decreases,while the particles size increases with increasing salt concentration.(2)Using PMETAC and PAEMH polyelectrolyte nanogels as carriers,nanocatalysts loaded with gold nanoparticles were prepared,based on the electrostatic adsorption of chloroauric acid ions and NaBH4 reduction.With p-nitrophenol as the substrate,the effects of strong and weak polyelectrolytic nanogels on the loading and catalytic performance of gold particles were comparatively studied.The results indicated that,the catalytic activity of gold nanoparticles loaded in strong polyelectrolyte gel was higher than the gold nanoparticles loaded in weak polyelectrolyte gel.This may be due to the pH response of the weak polyelectrolyte nanogels,that is,the shrinkage of the nanogels at alkaline reaction conditions leads to reduced catalytic activity.In view of this,the paper uses strong polyelectrolyte nanogel as the carrier to explore the effects of gel concentration,particle size and cross-linker fractions on the catalytic performance of gold particles.The results show that the size of the nanogel does not affect the catalytic activity of gold particles;however,a concentration increase of the nanogel leads to an increased catalytic activity of gold particles.The catalytic activity of gold particles increases first,then decreases with increasing cross-linker fraction of the nanogel,and the highest catalytic activity is achieved when the cross-linker fraction is 40%. |
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