Polypyrrole complexation on biomass-derived powdered carbon for adsorptive elimination of emerging pharmaceutical contaminant Sulfamethoxazole: A comprehensive insight

Abstract

Carbon-based adsorbents are a preferred class of adsorbents for eliminating an array of pollutants owing to their rigid porous morphology. However, the limitation of nitrogen-containing functional groups limits their applicability in targeting organic pollutants like antibiotic species. Such groups offer positively charged surfaces for the efficient adsorption of anionic antibiotic species. The current study aims to enrich the surface of the prepared biomass-derived powdered carbon (PC) with nitrogen-rich polymer viz. Polypyrrole (PPy) via in-situ oxidative polymerisation to prepare an N-enriched adsorbent (PPy-PC) for the adsorptive elimination of emerging antibiotic contaminant Sulfamethoxazole (SMX) from aqueous setups. Efficient adsorptive interactions between PPy-PC and SMX were reported at pH 6.0, owing to strong electrostatic interactions between anionic SMX species (pKa = 5.7) and cationic polypyrrole states viz. Polaron (PPy+.) and bi-polaron (PPy++) state. Other interactions, viz. π-π electron donor-acceptor (EDA) interaction, hydrogen bonding, Lewis acid-base interaction, charge-assisted hydrogen bonding (CAHB) etc., also contributed to the adsorptive interactions. Isotherm model studies verified good fitting of both Freundlich and Langmuir isotherm models with the experimental data, verifying the possibility of multilayer and monolayer fashion of SMX's adsorption on PPy-PC. Elevating ionic strength of the SMX medium showed a slight decline in its adsorption capacity. Co-existing heavy metals had little effect on SMX's adsorption, whereas co-existing antibiotics significantly affected SMX's adsorption over the PPy-AC surface. Desorption and re-adsorption analysis verified the recyclability potential of the adsorbent for multiple cycles. Seed toxicity studies using Vigna mungo seeds verified the adsorbent's efficacy in remediating SMX solution. Continuous column studies verified lower column bed heights (cm), higher inlet feed concentrations (mg/L), and higher initial feed flow rates (mL/min) resorted to quick saturation of the packed bed column.