Synthesis And Properties Of Gold Nanoparticles Composite Intelligent Hydrogels

The interpenetrating polymer networks （IPN） hydrogels of poly（2-acrylamido-2-methyl propyl sulfonic acid）（PAMPS）/Polyvinylpyrrolidone （PVP） was synthesizedby solution polymerization and interpenetrating polymer networks technology.PAMPS/PVP hydrogels as a template, AuCl₄-ions were absorbed into networks withsurfactant of cetyl trimethyl ammonium bromide （CTAB）, then the gold nanoparticleshydrogels （GNPs gel） was developed and networks were utilized for in situnanoparticles synthesis by reduction of glod ion absorbed with a reducing agent.Thepolyethylene glycol （PEG） modified gold nanoparticles hydrogels （PEG-GNPs gel）were also synthesized by using PEG2000as modification agents. The main contentand results of this paper are summarized as follows:1. The thermodynamic adsorpting HAuCl₄of two hydrogels were studied, theresults showed that the adsorpting process of PAMPS/PVP gel was in accordancewith Langmuir adsorption model, the rate of adsorption and the amount ofequilibrium adsorption significantly increased when the temperature increased. Theadsorpting process of PEGMH was Freundlich adsorption model, the process ofelectrostatic adherence was chemical integration between chelating groups andadsorbate. The driving force between the solution and gel （liquid-solid） enhanced byincreasing the concentration of HAuCl₄. The adsorption enthalpy values （ΔH） of twokind gel were104.6and60.8kJ/mol, were chemical adsorption process.2. The curve of the pseudo first order kinetic equation was in line with theadsorpting process kinetics of PAMPS/PVP gel, the amount of adsorption wasproportional to the time, the adsorbate spread to the surface of the gel by theelectrostatic force. Therefore, we could increase its adsorption capacity by extendingthe time of adsorption. The kinetics of PEGMH was pseudo two order kineticequation, the AuCl₄–ions were diffusing through the porous structure of gel withsolvent and it was chemical adsorption process, Therefore, we could change theadsorption capacity by adding the different dosage of PEG2000.3. GNPs were developed and networks were utilized for in situ nanoparticles synthesis by reduction of glod ions absorbed with NaBH4, the GNPs were between100and200nm in size. CTAB was usually required to allow dispersion of GNPs inthe chosen hydrogels and prevent the aggregation during the processing stage. As thePEG2000agent was added, the number of gold nanoparticles also increased.4. After Gold nanoparticles embedding into the network, it made the equilibriumswelling ratio of composite gel rapid decrease, the ESR decrease when the content ofnanoparticles increase The equilibrium deswelling state of PAMPS/PVP gel andGNPs gel were also investigated, the results showed that the GNPs gel got itsequilibrium deswelling state within70minutes in0.1mol/L NaCl solution and thetime of equilibrium deswelling decreased to20minutes under an electric field,polyion concentration within the gel was about0.001mol/L.5. The catalytic constant of reaction significantly increased to the maximumvalue of0.593mol/g·min under suitable condition. The same catalyst was utilizedrepeatedly up to five times for the reduction reactions, the conversion of4-NP got to81.68%with the fifth usage. Polyethylene glycol （PEG） modified gold nanoparticlesgel （PEG-GNPs gel） were synthesized from the solution radical polymerization,interpenetrating polymer technology and by using PEG2000as modification agents,the results showed that the gel performance the property of positive temperaturesensitivity and the volume phase transition temperature （VPTT） was about30℃,millipore structure was formed within PEG-GNPs gel, the diameter of apertures werebetween1and3um.6. The reduction of4-NP to4-AP by PEG-GNPs gel reaction were investigatedunder the same condition, the GNPs gel system was found to have an excellentcatalytic activity by adding PEG2000as modification agents. The catalytic constantof reaction increased by increasing the temperature and the catalytic constantsignificantly increased to the maximum of1.067mol/g·min when the consumption ofPEG2000was5%and the temperature was50°C.7. The reduction kinetics of nitro compound （2-NP,3-NP and4-NP） wereinvestigated under the same condition, the results showed the GNPs gel system wasfound to have an excellent catalytic activity and high conversion for4-NP reductionamong nitrophenol homologue, almost zero for3-NP implying no catalytic activity, even though they were homologue. GNPs gel system was found to have bad catalyticactivity for NB, but the embedded PEG2000endowed the composite gel withselective catalytic activity in the reduction of NB, the conversion rate of NB reached80%within55minutes.