Synthesis and characterization of silver nanoparticles supported on surface-modified poly(N-vinylimidazale) as catalysts for the reduction of 4-nitrophenol

Two types of bead-shaped stable heterogeneous nanoparticle catalysts, viz. polymer-supported poly(styrene) functionalized with poly(vinylimidazole) immobilized silver nanoparticles (PS-PVIm-AgNPs) were prepared from poly(styrene)-co-poly(N-vinylimidazole) polymer matrices derived from 2% (Type-I) and 10% (Type-II) cross-linking monomer divinylbenzene and AgNO3 as a metal precursor. The appearance of surface plasmon resonance peak at 422 nm in UV and Ag—N(str,ring) peaks noticed at 1664 cm―1 for Type-I and 1668 cm―1 for Type-II catalysts in FF-IR confirms the immobilization of AgNPs onto PS-PVIm. The SEM and EDAX results prove that the Type-I catalyst has heterogeneous morphology with more white patches and enhanced amount of surface nitrogen and AgNPs than Type-II. The size of the AgNPs on Type-I and Type-II catalysts was measured as 10 nm and 14.6 nm from XRD, respectively. The comparative catalytic study for the reduction of 4-nitrophenol reveals that the pseudo-first order rate constant (kobs) for Type-I catalyst was relatively superior (kobs =5.12 x 10-4) than Type-II (kobs = 1.20 × 10―4) due to the addition of high cross-linking load in Type-II. For the same reaction with Type-I catalyst, the variation of [substrate], [catalyst] and [NaBH4] was directly proportional to kobs. The stability and reusability of the catalyst were observed good and sustained even at six cycles.