Fabrication of kappa carrageenan-cellulose nanofiber/graphene oxide composite membrane for water purification

This research investigates the synthesis, optimization, and assessment of kappa-carrageenan (kC)-cellulose nanofiber (CNF)/glutaraldehyde (GA)coated with graphene oxide (GO) for seawater treatment. The kC hydrogel was crosslinked with GA to enhance mechanical strength and adsorption efficiency. The SEM, EDX, and FT-IR analyses revealed a well-defined porous structure, uniform coating, and significant functional groups. Based on swelling behavior, the average molecular weight between crosslinks (Mc) was calculated to evaluate network tightness. The addition of CNF increased the stiffness of the membranes and affected the internal network, resulting in reduced swelling, smaller Mc values, and decreased average pore radius. While this structural tightening reduced the water flux, it improved salt rejection. In the first stage, ion removal ranged from 85% to 92.7% but it decreased from 79.6% to 82.3% in the second stage, resulting in freshwater with a concentration of 692 mg/L. Reusability studies showed that the hydrogel maintained nearly consistent performance in multiple cycles, with a drop in rejection of 19% sodium chloride and 14% magnesium sulfate in 3 rd cycle, while water flux declined by 25.8% and 17.6% for sodium chloride and magnesium sulfate. Antifouling experiments conducted in multiple cycles at a 90% recovery rate found 89.7% water flux recovered after DI water cleaning in 1 st cycle and 82.5% in 3 rd cycle. The kC-CNF/GO-GA hydrogel provides a solution for the treatment of seawater that is not only cost-effective but also sustainable and environmentally friendly. • GA crosslinked kC-CNF membrane was coated with GO for fouling resistance • The optimized membrane with 2.5% CNF achieved best water flux and rejection rate • The membrane exhibited 97.5% and 98.2% rejection to NaCl and MgSO 4 • The membrane achieved 98% salt removal from seawater in two-stage filtration • The membrane recovered 82.5% of flux after 3 filtration cycles at 90% recovery