Study Of Silver Nanoparticles Loading PH Stimulus Responsive Composite Nanogels

pH stimulus responsive nanogels with particles sizes ranging from 1 to 1000 nm are the intelligent nanogels which are able to respond to small environmental pH change. If metal nanoparticles are loaded into pH stimulus responsive nanogels, the formed composite nanogels have many unique properties, such as pH dependent optical property and catalytic activity of the loaded metal nanoparticles. Therefore, they have potential applications in microreactor, sensor, drug delivery, medical diagnosis, etc. In this thesis, the pH stimulus responsive nanogels with semi-interpenetrating polymer network (semi-IPN) structure were firstly synthesized by precipitation polymerization method. Then, the silver (Ag) nanoparticles loading composite nanogels were prepared using the pH stimulus responsive nanogels as microreactors. Finally, the pH responsiveness, optical property and catalytic activity of the composite nanogels were studied. The research work and the main results obtained are as follows:(1) The pH stimulus responsive nanogels with semi-IPN structure based on cross-linked poly(N-isopropylacrylamide) (PNIPAM) and linear poly(acrylic acid) (PAA) (PNIPAM/PAA semi-IPN nanogels) were fabricated by precipitation polymerization process without utilizing any organic solvent or emulsifier, so the process is of environment-friendly characteristic. Fourier transformation infrared spectroscopy (FTIR) and elemental analysis results indicate thatthe relative PAA contents within the nanogels increase with decrease of the pH values of reaction media. Their semi-IPN structure was confirmed by transmission electron microscopy (TEM) characterization. The results obtained by dynamic laser light scattering (DLLS) under different pH conditions show that the nanogels have very strong pH stimulus responsiveness, andtheir volume can be changed 120 times during their pH induced phase transition.(2) The Ag nanoparticles loading nanogels were prepared by in-situ reduction method using PNIPAM/PAA semi-IPN nanogels as microreactors. The Ag nanoparticles with face centered cubic crystal structure are homogeneously distributed within the composite nanogels. Their average diameters are within the range from 3 to7 nm, and their weight contents top 43%. With decrease of the pH values of the reaction media, the particle sizes of the Ag nanoparticles inside the composite nanogels are increased, while their weight contents are decreased. Under the same pH value of the reaction media, as the PAA contents inside PNIPAM/PAA semi-IPN nanogels raised, the particle sizes of the formed Ag nanoparticles hardly changed, whereas their weight contents increased significantly.(3) nano-Ag/(PNIPAM/PAA semi-IPN) composite nanogels have pronounced pH stimulus responsiveness, but it is weakened with the increase of the weight content of the loaded Ag nanoparticles. The Ag nanoparticles inside nano-Ag/(PNIPAM/PAA semi-IPN has the optical property of surface plasmon resonance, and the positions of the maximum absorption peaks in their ultraviolet and visible absorption spectrum curves are pH dependent, which indicates that the composite nanogels are expected to be used in the sensor for monitoring pH value. Nano-Ag/(PNIPAM/PAA semi-IPN composite nanogels have catalytic activity for the reduction reaction between NaBH4 and 4-nitrophenol, and they can be recycled by centrifugation separation method after adjusting the pH value of the reaction solution.