Recyclable polymer microgel stabilized rhodium nanoparticles for reductive degradation of para-nitrophenol

The purpose of present work is to fabricate rhodium nanoparticles in Poly(N-isopropylmethacrylamide-acrylic acid) [p(NMAA)] microgel system. Synthesized polymer [p(NMAA)] microgels and rhodium nanoparticles loaded [Rh-p(NMAA)] microgels were analyzed by FTIR (Fourier Transform Infra-red) spectroscopy, XRD (X-ray Diffraction) analysis and UV/Vis (Ultraviolet–Visible) spectroscopy. Catalytic reductive conversion of P-nitrophenol (P-Nph) into P-aminophenol (P-Aph) via Rh-p(NMAA) was used to evaluate the catalytic activity of the hybrid microgel [Rh-p(NMAA)]. Kinetic study of catalytic reductive conversion of P-Nph was explored by considering various reaction parameters. It was found that the value of first order observed rate constant (k obs) was varied from 0.019 to 0.206 min−1 with change in concentration of sodium borohydride (SBH) from 3 to 14 mM at given temperature. However, further increment in concentration of SBH from 14 to 17 mM, reduced the value of k obs from 0.206 to 0.156 min−1. The similar dependence of k obs on concentration of P-Nph was observed at specific concentration of SBH and Rh-p(NMAA) at constant temperature. Kinetic study reveals that conversion of P-Nph to P-Aph takes place on the surface of rhodium nanoparticles (RhNPs) by adopting different reactions intermediates and obeys the Langmuir-Hinshelwood mechanism. Reduction efficiency of recycled Rh-p(NMAA) catalytic system was also measured and no significant reduction in the percentage catalytic activity was obtained up to four cycles for P-Nph conversion into P-Aph.