Powdered Opuntia ficus-indica as an effective adsorbent for the removal of phenol and 2-nitrophenol from wastewater: Experimental and theoretical studies

Abstract

Opuntia ficus indica was examined as a sustainable biosorbent for the removal of phenol and 2-nitrophenol from wastewater, it was used as an alternative to traditional biological treatments that are largely ineffective in removing phenolic compounds from wastewater. Factors like phenols adsorbent dose, concentration, contact time, temperature, and pH were tested. Results showed these factors influence phenol and 2-nitrophenol adsorption. Isotherm models, quantum chemistry, and thermodynamics were used to investigate equilibrium data. We studied the adsorption rate using kinetic models, intra-particle diffusion, pseudo-1st-order, and pseudo-2nd-order forms were applied to assess the adsorption process's kinetics. Langmuir model was the best isotherm model for both phenols (R 2 > 0.98), signifying that the phenol and 2-nitrophenol adsorption process was mainly monolayer adsorption on homogeneous surface. Maximum quantity of phenol and 2-nitrophenol that could be adsorbed was 25.58 and 25.60 mg/g at 298 and 303 K, respectively. The pseudo-2nd-order kinetic equation gave the most appropriate for the adsorption kinetics, based on the correlation coefficients for each kinetic equation. SEM examined Opuntia ficus-indica morphology. We calculated the three thermodynamic parameters, Gibb’s free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°). Negative ΔH° and ΔS° mean the adsorption process is exothermic and less unpredictable. Negative ∆G° confirms spontaneous process. FTIR analysis showed efficient and spontaneous phenols removal, suggesting Opuntia ficus-indica as a probable adsorbent for the treatment of wastewater containing phenols.