Beyond the permeability barriers: Unveiling the potential of dual-crosslinking hydrogel nanofiltration membranes for high-performance molecular/ion sieving

Membrane separation technology has shown great potential in resource recovery, energy utilization, and environmental protection, attracting extensive attention for the various practical applications. The alginate-based hydrogel membrane, derived from natural biomass, possesses sustainability and anti-fouling properties, effectively reducing the burden of waste membrane disposal. However, the limitations of alginate hydrogel include its high swelling ability, low permeability, and poor mechanical properties. In this study, we propose a straightforward method to fabricate orderliness hydrogels by employing lanthanide ion via dual cross-linking with CaAlg, resulting in the formation of lanthanum calcium alginate (La-CaAlg) hydrogel membrane. The La-CaAlg membrane exhibits superior mechanical performance and anti-swelling properties compared to LaAlg and CaAlg membranes. Additionally, through small-angle scattering and low-field nuclear magnetic resonance studies on the membrane's spatial orientation, and pore size distribution, we gained the comparable results into its internal structure for the design insight. Notably, the La-CaAlg membrane demonstrates outstanding performance in dye/salt separation, showcasing high selectivity and permeability. We propose the strategy that enhances the orderliness and durability of the alginate hydrogel membrane, providing the separation design insight to overcome the limitations associated with the permeability and rejection trade-off.