Nickel nanoparticles decorated on electrospun polycaprolactone/chitosan nanofibers as flexible, highly active and reusable nanocatalyst in the reduction of nitrophenols under mild conditions

Abstract

Today, the reduction of nitro aromatics stands a major challenge because of the pollutant and detrimental nature of these compounds. In the present study, we show that nickel(0) nanoparticles (Ni-NP) decorated on electrospun polymeric (polycaprolactone(PCL)/chitosan) nanofibers (Ni-NP/ENF) effectively catalyze the reduction of various nitrophenols (2-nitrophenol, 2,4-dinitrophenol, 2,4,6-trinitrophenol) under mild conditions. Ni-NP/ENF nanocatalyst was reproducibly prepared by deposition-reduction technique. The detailed characterization of these Ni-NP/ENF based nanocatalyst have been performed by using various spectroscopic tools including ICP-OES, P-XRD, XPS, SEM, BFTEM, HRTEM and BFTEM-EDX techniques. The results revealed the formation of well-dispersed nickel(0) NP (dmean = 2.71–2.93 nm) on the surface of electrospun polymeric nanofibers. The catalytic activity of the resulting Ni-NP/ENF was evaluated in the catalytic reduction of nitrophenols in aqueous solution in the presence of sodium borohydride (NaBH4) as reducing agent, in which Ni-NP/ENF nanocatalyst has shown high activity (TOF = 46.2 mol 2-nitrophenol/mol Ni min; 48.2 mol 2,4-dinitrophenol/mol Ni min; 65.6 mol 2,4,6-trinitrophenol/mol Ni min). More importantly, due to the nanofibrous polymeric support, Ni-NP/ENF has shown a flexible characteristics along with reusability property. Testing the catalytic stability of Ni-NP/ENF revealed that this new catalytic material provides high reusability performance (at 3rd reuse 86% for 2-nitrophenol, 83% 2,4-dinitrophenol and 82% 2,4,6-trinitrophenol) for the reduction of nitrophenols even at room temperature and under air. The present study reported here also includes the compilation of wealthy kinetic data for Ni-NP/ENF catalyzed the reduction of nitrophenols in aqueous sodium borohydride solution depending on temperature and type of support material (Al2O3, C, SiO2) to understand the effect of the support material and determine the activation parameters.