Adsorption of antiretroviral drugs, efavirenz and nevirapine from aqueous solution by graphene wool : kinetic, equilibrium, thermodynamic and computational studies

Abstract

The increasing concentrations of pharmaceutical and personal care products in water bodies have attracted attention due to the risk of non-target exposures. The application of any graphene-based material for the remediation of antiretroviral drug contamination has not been reported, therefore graphene wool was synthesized by chemical vapour deposition as adsorbent for the removal of efavirenz (EFV) and nevirapine (NVP) from water. Results revealed that adsorption of EFV was best fitted to the intraparticle diffusion model, with multi-linearity (multiple adsorption steps). The pseudo-second-order model best describes GW-NVP interaction. Isotherm parameters revealed that Sips and Freundlich model best fit GW-EFV and GW-NVP interactions, with the least value of SSE < 0.04 and 1.27, respectively. GW demonstrated higher adsorption capacity and adsorption maxima for NVP with Kd and qm values of ∼ 2.54 L/g and ∼ 48.31 mg/g, compared to ∼ 1.48 L/g and ∼ 4.41 mg/g obtained for EFV adsorption. Isotherm parameters suggest that GW adsorbed NVP slightly better with stronger binding strength than EFV, with removal efficiencies of 84% (NVP) and 80% (EFV) under optimum conditions. A heterogeneous adsorption mechanism was suggested for GW-EFV sorption, in contrast to a less heterogeneous and multilayer adsorption mechanism for GW-NVP adsorption. NVP adsorption is a spontaneous exothermic process, while GW-EFV interaction is a spontaneous endothermic process. Experimental results were supported by computational studies, which revealed the influence of strong dispersion interactions and H-bonding at specific pH ranges.