Development of sustainable pH-responsive adsorptive modified mangrove-based polylactic acid ultrafiltration membrane for the removal of heavy metals from aqueous solution

A novel green pH-responsive adsorptive membrane was prepared by incorporating amino-activated carbon (AC) modified mangrove particles (MAC) into polylactic acid (PLA) ultrafiltration (UF) membranes via the non-solvent induced phase separation (NIPS) technique. The performance of MAC was investigated at various concentrations (ranging from 0 to 6 wt%). The successful synthesis of the material was confirmed through Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction, and scanning electron microscopy (SEM) coupled with energy-dispersive X-ray (EDS) spectroscopy. The membranes were characterized by SEM, surface zeta potential, pure water permeability, pore size, and porosity analysis, among others. Static adsorption and dynamic filtration were carried out to study the membranes' water permeability and rejection performance of pH responsiveness at pH 4, 7, and 10. The results demonstrated that the addition of MAC improved water permeability from 1336.4 ± 96.4 L.m⁻².h⁻¹.bar⁻¹ in the original PLA to 2306.6 ± 9.7 L.m⁻².h⁻¹.bar⁻¹ in the 3MAC-PLA membrane (3 wt% MAC). Moreover, the rejection of heavy metal ions increased from 18.15, 17.31, and 17.50% for Cu²⁺, Pb²⁺, Ni²⁺ ions at pH 4, to 99.95, 100, and 99.95% at pH 10 for the 3MAC-PLA membrane; respectively. According to the equilibrium data, the Freundlich isotherm provided the best fit for the experimental data, implying a non-uniform affinity for adsorption on heterogeneous surfaces via chemisorption. The maximum adsorption capacities achieved at pH 7 were 4.2 mg.g⁻¹ for Cu²⁺, 5.0 mg.g⁻¹ for Ni²⁺, and 6.8 mg.g⁻¹ for Pb²⁺; respectively. Overall, the addition of MAC enhanced the properties of the pristine PLA, opening new potential for these composite membranes in the wastewater treatment industry.