Green and sustainable pH-responsive adsorptive membrane using aminated-MXene mangrove filled polylactic acid ultrafiltration membrane for enhanced water permeability and microplastic removal

A green and sustainable pH-responsive adsorptive membrane using aminated-MXene mangrove filled (MXAM) polylactic acid ultrafiltration membrane was developed. The material synthesis involved employing the common in-situ HF acid-based etching method with Li⁺ intercalant, while membrane fabrication utilized the non-solvent induced phase inversion (NIPS) technique. The study tested pH-responsive adsorption and filtration using a 20 ppm synthetic polystyrene (PS) microplastic (MPs) suspension at pH 4, 7, and 10. Incorporating 1.5 wt% MXAM enhanced water permeability to 1855.6 LMHbar and achieved rejection rates of 79 %, 91.5 %, and 99.9 % for pH 4, 7, and 10, respectively. These improvements can be attributed to enhanced porosity, pore size, hydrophilicity, and surface charges. The kinetics of the adsorptive 1.5PLAMXAM membrane for PS MPs at 5 ppm and pH 7 showed psuedo-second-order kinetics (R² = 0.967) matching experimental adsorption (q_e,exp = 12.4 mg.g⁻¹), indicating chemical adsorption. The equilibrium data of 1.5PLAMXAM membrane fitting the Langmuir isotherm, showed an increase in q_e,exp from 5.69 to 12.79 mg.g⁻¹ at pH 4 and 10, respectively, attributed to a higher density of pH-responsive groups. The fitted Langmuir isotherm suggested a maximum monolayer coverage of q_m = 23.5 mg.g⁻¹.