Engineered MnO2-Multiwalled carbon Nanotube nanoheterostructures for efficient removal of nanoplastics and plastic-derived contaminant Bisphenol S from contaminated water

Abstract

This study explores the potential application of engineered MnO₂-Multiwalled Carbon Nanotube (MWCNT) nanoheterostructures (NHs) for the simultaneous removal of nanoplastics (NPs) and bisphenol S (BPS) from polluted water, two persistent pollutants from plastic degradation that pose substantial health and ecological risks. The presence of ε-MnO₂ in the nanoheterostructure, confirmed by XRD, HRTEM, and XPS studies, enhances its surface reactivity due to microtwinning defects and mixed oxidation states of Mn. Under optimized conditions, MnO₂-MWCNT NHs achieved complete removal of 10 mg/L NPs and 1 ppm BPS at a dosage of 1.5 g/L within 24 h at 25 °C. The NP removal was facilitated by heteroaggregation with MnO₂-MWCNT NHs, following a pseudo-first-order kinetic model with a rate constant of 1.87 mg/L·min, achieving approximately 90 % removal within the first hour. BPS adsorption was an endothermic process, well-described by the Freundlich, Sips, and Dubinin–Astakhov (D-A) isotherm models, indicating an adsorption capacity exceeding 2 mg/g at 25 °C, primarily controlled by liquid film diffusion. The MnO₂-MWCNT NHs were effective in removing BPS and NPs across varying water chemistry (pH and ionic strength) and natural water matrices, including river, estuary, and seawater. A 2 g/L dose of MnO₂-MWCNT NHs was sufficient for simultaneous NPs and BPS removal, while excellent reusability over multiple cycles demonstrated the potential for long-term water treatment applications of the material. Overall, MnO₂-MWCNT NHs offer a sustainable, efficient, and cost-effective solution for water remediation, with promising implications for global pollution control efforts.