Exploring the adsorption of catechol and resorcinol onto Croton caudatus activated carbon: An integrated experimental and theoretical approach

Abstract

The present work aimed to examine the process for adsorption of Catechol (CT) and Resorcinol (RS) onto activated carbon that was obtained from Croton caudatus biomass (CAB). Using a batch method, the maximum removal efficiencies of 99.23 % for CT and 98.68 % for RS was achieved at adsorbent dosage-0.2 g L⁻¹, reaction time-60 min; concentration-100 mgL⁻¹ CT and 80 mgL⁻¹ RS; and pH 6.0 CT and pH 4.0 RS, respectively. A maximum equilibrium adsorption of 56.05 mgg⁻¹ and 61.85 mgg⁻¹ was achieved at pH 6.0 and pH 4.0 for CT and RS. The adsorption behavior of both adsorbates on activated carbon were best described by the Langmuir model (correlation coefficients (R²) = 0.996 for CT and 0.995 for RS) and the pseudo-second order kinetic model. The values of ΔG, ΔS, and ΔH suggest that the adsorption process is spontaneous and endothermic. Additionally, the adsorption process is easily reversible, enabling the reuse of the adsorbate even after fifth cycle. Further, density functional theory (DFT) simulations demonstrated that the CT and RS adsorption onto the AC adsorbent is favorable. Among the oxygen functional groups analysed, the carboxyl group showed the greatest effect on the adsorption process, exhibiting the most negative adsorption energy at −44.869 (CT) and −45.082 kJmol^-1 (RS), respectively. Therefore, the activated carbon derived from CAB has significant potential for effectively removing phenolic contaminants from wastewater.