Nanocomposite kappa-carrageenan-GO/PEI membrane for wastewater valorization and metals recovery

To address the growing demand for clean water, this study developed a kappa-carrageenan (κC) hydrogel membrane enhanced with graphene oxide (GO) and polyethyleneimine (PEI) for sustainable water purification. GO improved membrane hydrophilicity, permeability, and ion rejection, while PEI enhanced structural stability and selective separation. Spectroscopic, microscopic, water contact angle, tensile strength, and pore size analyses confirmed the membrane's optimized physicochemical properties. The κC-GO.02 membrane with 0.02 % wt/v GO concentration showed optimized performance, with a 20 % increase in pure water flux, from 6.44 to 7.72 L/m²h, due to enhanced pore structure and membrane hydrophilicity. The membrane also demonstrated an outstanding selectivity, rejecting 93 % of NaCl and 97.13 % of MgSO₄. Prevalent separation mechanisms included electrostatic repulsion, size exclusion, and surface interactions, where the negatively charged GO surface and PEI functional groups contributed to ion rejection. In the storm wastewater tests, the membrane achieved nearly complete removal of Cd, Zn, Fe, Mn, Cr, Al, B, and Ni, with Pb and Co at 99.7 % rejection and Cu and Li at 94.11 % and 94.48 %, respectively. The material exhibited strong fouling resistance, as reflected by a flux recovery ratio (FRR) of 90.93 % after three filtration cycles, supporting its suitability for scalable and green water treatment processes. With its outstanding permselectivity, the synthesized hydrogel membrane has strong potential for the treatment and recovery of precious metals, such as Li, Co, and Ni, from wastewater treatment for environmental protection and sustainable development.