Establishing a productive heterogeneous catalyst based on silver nanoparticles supported on a crosslinked vinyl polymer for the reduction of nitrophenol.

Abstract

The treatment of toxic nitrophenols in industrial wastewater is urgently needed from environmental, health, and economic points of view. The current study addresses the synthesis of the crosslinked vinyl polymer poly(acrylonitrile-co-2-acrylamido-2-methylpropane sulfonic acid) (poly(AN-co-AMPS)) through free radical copolymerization techniques using acrylonitrile (AN) and 2-acrylamido-2-methylpropane sulfonic acid (AMPS) monomers with different ratios and potassium persulfate (KPS) as an initiator in an aqueous medium. The prepared copolymer was utilized as a supporting matrix for silver nanoparticles (AgNPs) via the chemical reduction of silver nitrate within the copolymer framework. Different techniques were employed to characterize the prepared poly(AN-co-AMPS) and Ag/poly(AN-co-AMPS) composites, such as Fourier transform infrared (FTIR) spectroscopy, thermal gravimetric analysis (TGA), X-ray diffraction (XRD), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) analysis. The results exhibit that silver metal was excellently dispersed across the surface of poly(AN-co-AMPS) without any agglomeration, presenting as nanocrystals with an average particle size equal to 6.21 nm. Also, BET analysis confirmed that the Ag/poly(AN-co-AMPS) composite exhibits mesoporous characteristics with a surface area of 59.615 m2 g-1. Moreover, the Ag/poly(AN-co-AMPS) composite was effectively applied as a heterogeneous catalyst for the catalytic reduction of hazardous 4-nitrophenols (4-NP) with a rate constant equal to 0.28 min-1 and half-life time equal to 2.47 min to a less toxic compound in the presence of NaBH4 as a reductant. Furthermore, the reusability experiment confirmed the excellent stability of Ag/poly(AN-co-AMPS). The catalyst can be easily separated from the reaction mixture using a simple centrifuge and directly reused for up to four successive cycles without a remarkable decrease in its catalytic activity. The conversion percentage of 4-NP after the four cycles was found to be 93%.