Synthesis and characterization of cobalt nanoparticles containing anionic polymer hydrogel nanocomposite catalysts for fast reduction of nitrocompounds in water

Abstract

Design and development of hydrogel based metal nanocomposites is of vital signifcance in the feld of industrial waste management. In this study, the synthesis of poly (N-isopropylacrylamide-co-2-Acrylamido-2-methylpropane sulfonic acid) hydrogel and embedment of cobalt nanoparticles in the prepared hydrogel was demonstrated followed by the evaluation of catalytic potential of the as-prepared cobalt nanoparticles-hydrogel nanocomposite. The prepared hydrogel and corresponding nanocomposite were characterized by Fourier Transform Infrared (FTIR) spectroscopy to identify functional groups, Energy Dispersive X-ray (EDX) and Inductively Coupled Plasma—Optical Emission Spectrometry (ICP-OES) analysis to confrm the presence of cobalt, and Transmission Electron Microscopy (TEM) to assess the spatial morphology of cobalt nanoparticles. The prepared hydrogel showed absorption of water via non-Fickian mechanism, resulting in swelling as much as 69 times of its dry weight. The nanoparticles were found to be spherical in shape and having diameters around 25 nm. The potential catalytic properties of the cobalt nanoparticles-hydrogel nanocomposite were assessed while reducing 4-nitrophenol, 2-nitrophenol, 4-nitroaniline, and 2-nitroaniline to their corresponding amino compounds. The catalytic reactions were performed under varying temperatures and catalyst quantities, besides the catalyst was also subjected to rigorous repeated usage to evaluate its recycling potential. The thermodynamic parameters such as activation energy, activation entropy change, and activation enthalpy change were also calculated. The catalyst was found to be more efective in reducing 4-nitrophenol with a maximum rate constant of 4.67 min−1. A gradual decline in catalytic reduction rate was observed when the same catalyst was repeatedly used for fve consecutive cycles.