Non-linear Regression, a Better Approach for the Optimisation of Hydroquinone, Resorcinol and Catechol Adsorption by Chemically Activated Carbon Based on Monkey Kola (Cola lepidota k. schum) Waste

Activated carbon was prepared from waste of monkey kola by pyrolysis and chemical activation using H3PO4. It was characterised by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and energy dispersive X–ray spectroscopy (EDX). Different physical properties namely bulk density, moisture content, volatile matter content, iodine number, pH of the solution, pHpzc and methylene blue adsorption were also determined. The activated carbon was used as an adsorbent for the removal of hydroquinone, catechol and resorcinol in solution. The process parameters of the sorption system such as pH of the solution, contact time and the amount of adsorbent were studied to understand their effects on pollutants removal. The optimised parameters are found to be pH: between 6 - 8, and the agitation time: 30 minutes. The experimental equilibrium data were analysed using five models (Langmuir, Freundlich, Redlich-Peterson, Sips, Langmuir-Freundlich). Non-linear regression analysis was employed, and three error analysis methods, correlation coefficient (R²), root-mean-square error (RMSE) and non-linear chi-square test (χ²) were considered to identify the best-fit isotherm and the best-fit kinetic model. Among all the adsorption isotherms considered, Langmuir was found to be a perfect representation of the experimental equilibrium data with high R² low RMSE and good χ². Batch kinetic experiments were carried out and experimental kinetics was fitted by non-linear regression. The sorption process was found to follow the pseudo first-order in case of the three pollutants. This study showed that the activated carbon can be used as a good adsorbent for the removal of phenol derivatives from water according to its maximum adsorption capacity which is about 66.57 µmol/g, 10.42µmol/g and 5.47 µmol/g respectively for hydroquinone, catechol and resorcinol.