Synthesis, characterization and fabrication of copper nanoparticles in N-isopropylacrylamide based co-polymer microgels for degradation of p-nitrophenol

Poly(N-isopropylacrylamide-co-acrylic acid) [P(NIPAM-co-AAc)] microgels were synthesized by precipitation polymerization. Copper nanoparticles were successfully fabricated inside the microgels by in-situ reduction of copper ions in an aqueous medium. The microgels were characterized by Fourier Transform Infrared Spectroscopy (FT-IR) and Dynamic Light Scattering (DLS). Hydrodynamic radius of P(NIPAM-co-AAc) microgel particles increased with an increase in pH in aqueous medium at 25 °C. Copper-poly(N-isopropylacrylamide-co-acrylic acid) [Cu-P(NIPAM-co-AAc)] hybrid microgels were used as a catalyst for the reduction of 4-nitrophenol (4-NP). Effect of temperature, concentration of sodium borohydride (NaBH₄) and catalyst dosage on the value of apparent rate constant (k_app) for catalytic reduction of 4-NP in the presence of Cu-P(NIPAM-co-AAc) hybrid microgels were investigated by UV-Vis spectrophotometry. It was found that the value of k_app for catalytic reduction of 4-NP in the presence of Cu-P(NIPAM-co-AAc) hybrid microgel catalyst increased with an increase in catalyst dosage, temperature and concentration of NaBH₄ in aqueous medium. The results were discussed in terms of diffusion of reactants towards catalyst surface and swelling-deswelling of hybrid microgels.