Activated carbon adsorbent derived from waste biomass, “Croton caudatus” for efficient removal of 2-chlorophenol from aqueous solution: Kinetics, isotherm, thermodynamics and DFT simulation

Abstract

The present study aims to prepare an activated carbon (AC) adsorbent developed from Croton caudatus biomass material for the adsorption of 2-chlorophenol (2CP) from wastewater. Activated carbon was prepared by KOH activation at 2:1 impregnation ratio and 700 °C temperature using a muffle furnace under self-generated atmosphere for 2 h. Several techniques and methodologies such as proximate analysis, ultimate (CHNS) analysis, BET, SEM, FT-IR, XRD and point of zero charge (pHpzc) have been used to determine physicochemical properties of the activated carbon. Batch adsorption studies were conducted for 2-chlorophenol adsorption and the optimum adsorbent dose, initial concentration, pH, reaction time and temperature were found to be 0.15 g/L, 80 mg/L, 4, 60 min and 298 K, respectively. The equilibrium isotherm study for 2-chlorophenol adsorption was fitted well to the Langmuir model with the adsorption capacity of 53.619 mg/g, while the adsorption kinetics was best described by pseudo-second order model. Thermodynamic parameters demonstrated a negative ΔH (exothermic) and negative ΔG (spontaneous) values. Studies on regeneration have shown that saturated carbon can be recycled up to five times with considerable removal efficiency. Besides, density functional theory (DFT) simulation revealed that the adsorption of 2-chlorophenol onto AC adsorbent is favorable. Among the oxygen-containing functional groups, the carboxyl group appeared to have a greater influence on the adsorption process than the hydroxyl and carbonyl groups with the highest negative Eadsorption of − 42.16 kJ/mol. Furthermore, the inclusion of three oxygen-containing functional groups improves the adsorption capacity of AC towards 2CP relative to a single functional group.