Effect of activating agents on the photocatalytic activity of chromium oxide based porous carbon photocatalysts derived from chrome-tanned leather buffing dust waste for the degradation of 2-chlorophenol

Abstract

Porous chromium oxide containing semiconducting carbon was synthesised from the chrome-containing tannery waste. The role of the activating agents in imparting the semiconducting property and the changes in their surface chemistry were determined. The synthesised photocatalysts were characterised using X-ray diffraction (XRD), Fourier Transformer Infra-Red (FTIR), Field Emission Scanning Electron Microscopy (FESEM), Ultra Violet –Visible –Diffuse Reflectance Spectroscopy (UV-DRS), Brunauer-Emmett-Teller (BET) surface area analysis, Electron Paramagnetic Resonance (EPR) and Cyclic Voltammetry (CV) analysis. The sulphuric acid-activated materials (ACS) showed a low bandgap (2.36 eV) and exhibited better planes of eskolaite (α - Cr2O3 phase). The surface area of ACK (KOH activation) was high (834.3 m2/g) compared with other photocatalytic materials. The EPR spectrum reveals the symmetrical broad Lorentzian type peak (g = 1.98) in the ACS material corresponds to the paramagnetic Cr3+ ion interaction with the adsorbed paramagnetic oxygen. CV analysis showed the redox peak at around 0.46/-0.32 V, which confirms the presence of a p-type semiconductor (Cr2O3). The Nyquist curve of the ACS catalyst studied using electrochemical impedance spectroscopy analysis exhibited the smallest arc radius, indicating the lowest charge–migration resistance. The photocatalytic reaction of 2-chlorophenol using synthesised catalysts was studied at wavelengths of 254 nm and 365 nm. Carbonaceous material acts as cocatalysts to enhance semiconducting nature of the Cr2O3. Among the synthesised photocatalysts, the order of degradation efficiency is ACS > ACK > ACP (Phosphoric acid activation). High-Performance Liquid Chromatography (HPLC) analysis confirmed the 2-chlorophenol degradation via the formation of intermediates.