Adsorptive and Photocatalytic Properties of Green Synthesized ZnO and ZnO/NiFe2O4 Nanocomposites for Tannery Wastewater Treatment

Abstract

This study investigated adsorptive and catalytic behaviour of ZnO and ZnO/NiFe2O4 nanocomposites for the removal and degradation of organic pollutants in tannery wastewater. ZnO and ZnO/NiFe2O4 nanomaterials were synthesized via a green method using Zn, Fe and Ni salts precursor and leaves extract of Anacardium occidentale (linn.). Subsequently, the synthesized samples were characterized by different analytical tools. The adsorptive and catalytic performance of the prepared nanomaterial were assessed using reduction in Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD) and Total Organic Carbon (TOC) in tannery wastewater as indicator parameters. High Resolution Scanning Electron Microscope (HRSEM), High Resolution Transmission Electron Microscope (HRTEM), and X-Ray Diffraction (XRD) analysis of ZnO and ZnO/NiFe2O4 confirmed the formation of hexagonal wurtzite nanoparticle and cubic spinel phase with an average crystallite sizes in the range of 13- 28 nm and 30.44 – 42.53 nm respectively. XRD analysis confirmed no change in the polymorph of ZnO upon the addition NiFe2O4. XPS spectrum showed the existence of the elements in the following oxidation state (+2) for Zn, (+1, +2) for Ni and (+2 and +3) for Fe. BET analysis revealed order of the specific surface area of ZnO/NiFe2O4 (44.61 m2/g) > NiFe2O4 (40.39 m2/g) > ZnO (8.91 m2/g). The adsorptive and photocatalytic results revealed that 3% ZnO/NiFe2O4 exhibits higher efficiency compared to ZnO and NiFe2O4 nanoparticles alone and in the order of 3% ZnO/NiFe2O4 > NiFe2O4 > ZnO. The study revealed that the prepared nanomaterial behaved better as photocatalyst than as nanoadsorbent.