Enhanced and rapid photocatalytic degradation of toxic dyes by cobalt oxide and modified cobalt oxide under solar light irradiation

Abstract

A solar light driven photo degradation approach for methylene blue (MB, model molecule of the thiazine dyes class) and malachite green (MG, model molecule of the triphenylmethane category) abatement by Co3O4 and Cr-Co3O4 spinel nanoparticles is reported. The effect of chromium load (5, 10 and 15%) in Co3O4 particles, synthesized by a simple co-precipitation process, was properly studied. The structural and morphological characteristics, chemical composition and optical properties of the materials were investigated by X-ray diffraction (XRD), Transmission Electron Microscopy(TEM), Field Emission Scanning Electron Microscopy – Energy Dispersive Spectroscopy (FE-SEM-EDS), FT-IR spectroscopy, UV–Vis diffuse reflectance spectroscopy (DRS),photoluminescence (PL) and BET surface area analysis. It was observed that properly tuning the initial pH, the initial dye concentration, the agitation time, and the photocatalyst dose, (10)Cr-Co3O4 exhibited an enhanced photocatalytic activity compared to that of pristine Co3O4, demonstrating the positive role of Cr doping In fact, the PL investigation showed that Cr doping in the Co3O4 lattice greatly increase the separation of electron-hole (e−/h+) pairs, whereas the UV DRS spectra and Tauc plot revealed a decrease in the band gap energy for Cr-Co3O4,. The investigations demonstrated that the MB dye degradation increases from 88% to 96% at pH = 11 after doping of Co3Oby 10% of Cr. Similarly, the Cr doping allowed to enhance the MG dye degradation from 85% to 92% at pH = 9. The photo degradation kinetics of both MB and MG dyes by Cr-Co3O4 and Co3O4 NPs were of pseudo-first-order mode. The active species involved in the photocatalytic process were properly identified using various scavengers by trapping holes and radicals. Finally, the photocatalysts showed good stability during recycling maintaining high performances after 5-time usage. .