Activated carbon from single use surgical mask as an efficient adsorbent for 4-nitrophenol and 2,4-dicholorophenol from aqueous solution: adsorption kinetics, isotherms and thermodynamic study

The activated carbon was prepared from single use surgical masks (SUSM) by hydrothermal method, resulting in a synthesised material termed SMAC. The physico-chemical properties of SMAC were analysed. The XRD pattern showed the amorphous nature, the FT-IR spectrum displayed the characteristic peaks of polypropylene, zeta potential analysis revealed the negative surface charge, SEM analysis showed the fibre morphology and XPS results confirmed the presence of oxygen, carbon and sulphur compounds. The adsorption properties were analysed using 4-nitrophenol (4-NP) and 2,4-dicholorophenol (2,4-DCP) from aqueous solution. The linear and nonlinear pseudo-first order, pseudo-second order, Elovich, intraparticle diffusion, external diffusion models and adsorption isotherms with linear and nonlinear Langmuir, Freundlich, and Temkin models were examined using adsorption data. The nonlinear kinetics and isotherm models have a better fit compared with linear models. The results were better fitted with pseudo-second order (0.9987 & 0.9962) and Elovich model (0.9964 & 0.9962) and described the adsorption process was leading by chemisorption fairly than physisorption. The Langmuir maximum adsorption capacity of SMAC for 4-NP and 2,4-DCP was 89.46 and 141.88 mg/g, respectively. Further, the thermodynamic study explained that the adsorption process of 4-NP and 2,4-DCP onto SMAC is an endothermic reaction. Among two regenerating agents (HCl & NaOH), 0.1 M NaOH was favoured for desorption of 4-NP (46%) and 2,4-DCP (40%) from SMAC. The recyclability studies showed that 67% and 64% of 4-NP and 2,4-DCP were removed after third cycle, respectively. The results conclude that the SMAC was an efficient adsorbent for phenols and economically viable.