Catalytic reduction of nitrophenols by a novel assembled nanocatalyst based on zerovalent copper-nanopolyaniline-nanozirconium silicate

Abstract

A novel nanocatalyst (Cu0-NPANI-ZrSiO4) was fabricated via solvent free microwave synthesis for surface immobilization of zerovalent copper nanoparticles (Cu0-NPs) on modified nanopolyaniline (NPANI) with nanozirconium silicate. The assembled nanocatalyst was characterized by different techniques to confirm the structure, thermal stability, surface morophology and nanoscale size. Cu0-NPANI-ZrSiO4 nanocatalyst was then subjected to extensive investigation and evaluation of its potential capability for reduction of a series of nitrophenol (NPhs) derivatives. The Langmuir-Hinshelwood mechanism was applied on the catalytic reduction of 2-nitrophenol (2NP), 3-nitrophenol (3NP) as well as 4-nitrophenol (4NP) and the reaction rate constants (k) were calculated through the pseudo-first-order kinetics due to the presence of excessive NaBH4. The results revealed a pseudo-first-rate type of reaction with high constant (k). The reduction of NPhs by NaBH4 as a reducing agent over Cu0-NPANI-ZrSiO4 was explored in different pH values (2–10) of NPhs and the results confirmed the strong dependency of the reduction process on the pH. In low pH, high reduction efficiency was established and confirmed from the pseudo-first-rate constant k (min−1) for 4NP, 3NP and 2NP as 0.811, 0.249 and 0.584, respectively at pH 2 and these values were then finally decreased to 0.112, 0.1 and 0.116 at pH 10, respectively. Rate constant (k) was in a good correlation with concentration of [H3O+] ion. An extrathermodynamic study for reaction rate (k) through isokinetic relationship was mathematically expressed. The calculated thermodynamic parameters led to an extrathermodynamic analysis as a type of compensation effect to give a good linearity plot with the slope to represent the isokinetic temperature, β that was identified as 298.82 at 298 K.