Modified polystyrene waste in the adsorptive removal of crystal violet and Cu (II) ion from aqueous medium – Groundwater applicability, modelling and characterization studies

Abstract

The waste polystyrene in the sulfonated form was utilized as an adsorbent material for the exclusion of a crystal violet and copper (II) ion from synthetic solution and groundwater. The adsorptive removal of CV and Cu (II) ion as a function of time, pH, SPS dose, initial concentration and temperature was studied. The maximum uptake of CV and Cu (II) of 812 ± 6 mg/g (pH 3–10.5) and 257.3 mg/g (pH 6.03) was observed respectively at an equilibrium time of 60 min. An exothermic nature of sorption (− ΔH°) decreased the removal efficiency by 11 % and 16.5 ± 3.5 % for CV and Cu (II) respectively. The spontaneity of adsorption was reflected from the negative ΔG° values with decreasing randomness (− ΔS°) upon increasing the temperature. The adsorption kinetics (pseudo – first – order, pseudo – second – order, intra – particle diffusion and Elovich) and isotherms models (Langmuir, Freundlich and DKR) in compliance with the present (CV and Cu²⁺) adsorption systems were checked. The stability and efficiency for successive regeneration cycles (uptake of CV ≥ 78 % up to six cycles) inferred that SPS was superior for CV than that of Cu (II) ion. Conspicuously, the removal of 98 % of CV from groundwater was achieved, nonetheless, the Cu (II) ion removal was 56 % due to competing Ca²⁺ and Mg²⁺ ions in groundwater. The signature of copper oxides on the SPS was corroborated from the XRD patterns along with the expansion and contraction of SPS crystallites during the adsorption and regeneration processes respectively. The SEM and FTIR studies described the morphological and vibrational modifications of virgin and CV/Cu (II) laden SPS adsorbent. The twin application of SPS in CV and Cu (II) removal has been detailed with a plausible mechanism in this paper.