Green Synthesis of ZnO Nanoparticles for kinetics and thermodynamics studies of the photocatalytic degradation of eriochrome black t and methylene blue dyes

Green Synthesis of ZnO Nanoparticles for kinetics and thermodynamics studies of the photocatalytic degradation of eriochrome black t and methylene blue

Abstract

This work presents a biosynthesis of zinc oxide nanoparticle (ZnO NPs) from the Vigna unguiculata L extract via co-precipitation method. The prepared photocatlyst was characterized using thermogravimetric differential thermal analysis (TG-DTA), Bruneur-Emmett-Teller (BET), X-ray diffraction (XRD), ultraviolet-visible (UV/Vis), Fourier transform infra-red (FT-IR) and energy dispersive x-ray fluorescence (EDXRF) analyses.TG-DTA results revealed that the calcination temperature was found to be 600 ℃. BET specific surface area was 190.04 m2g-1. The average crystallite size and band gap values were 50.10 nm and 3.25 eV, respectively. FT-IR analysis demonstrated that the vibrational absorption band of 637 cm-1 corresponds to the Zn-O bond. EDXRF result confirmed the presence of Zn and O atoms in the ZnO. The optimal degradation efficiencies of 98.05 & 97.51, 96.58 & 95.65, 96.45 & 94.98 and 96.75 & 93.25 % were achieved at 10.00 mg/L eriochrome black t (EBT)/ methylene blue (MB) initial concentrations, 1.50 g/L ZnO dosage, initial pH of 9.00 and 50.00 ℃ initial temperature in 120.00 min irradiation time respectively. The photocatalytic removal of EBT and MB over ZnO NPs was followed pseudo-first order kinetics with apparent rate constant of 5.33 x 10-2 and 4.91 x 10-2 s-1, respectively. Activation energy (Ea), enthalpy change (ΔH), entropy change (ΔS) and Gibbs free energy change (ΔG) were + 8.94 & + 14.65 k J mol-1, + 6.27 & + 12.02 k J mol-1, - 82.86 & - 61.56 J mol-1K-1 and + 31.37 & + 30.67 k J mol-1 for the photocatalytic removal of EBT and MB, respectively