Hybrid cryogels composed of P(NIPAM-co-AMPS) and metal nanoparticles for rapid reduction of p-nitrophenol

Temperature-responsive macro-porous cryogels of poly(N-iospropylacryamide-co-acrylamido-2-methylpropane sulfonic acid) [P(NIPAM-co-AMPS)] were prepared through redox-initiated cryo-polymerization at −12, −18 and −24 °C. Silver or gold nanoparticles (AgNPs or AuNPs) were formed inside P(NIPAM-co-AMPS) cryogels through the thermal reduction of absorbed AgNO3 or HAuCl4, resulting in hybrid cryogels immobilized with AgNPs or AuNPs. Fourier transform infrared spectroscopy, thermal gravimetric analysis and X-ray diffraction confirmed the chemical composition. Cryogel morphology and nanoparticle distribution were investigated through scanning and transmission electron microscopies. By checking swelling ratio in neutral water, the temperature response of cryogels was identified. The hybrid cryogels were used as the catalysts to reduce p-nitrophenol with NaBH4 at different temperatures and pHs. The hybrid cryogel with AuNPs had the higher catalytic activity than the counterpart hybrid cryogel with AgNPs. The catalytic activity of hybrid cryogels increased with temperature and pH. The temperature response of cryogels facilitated their isolation from the reaction mixture. Since AuNPs were fixed tightly onto the cryogel pore-wall and hardly lost, hybrid cryogels with AuNPs demonstrated no decrease in catalytic activity for 5 cycles of p-nitrophenol reduction.