Hierarchically crosslinked g-C₃N₄/aminated lignin/alginate aerogels for sustainable oil-in-water emulsion separation

Biomass-based materials face challenges in treating industrial oily wastewater, particularly stable oil-in-water emulsions, due to limitations like poor mechanical strength and fouling susceptibility. To address this, a robust g-C₃N₄/aminated lignin/sodium alginate (GNALS) aerogel was engineered via chemical/ionic dual crosslinking and freeze-drying. This design integrates exfoliated g-C₃N₄ nanosheets (providing roughness and photocatalysis) and amine-functionalized lignin (natural crust agent and antioxidant) into an alginate matrix, forming a multi-network structure with enhanced mechanical robustness (4250 times self-weight load capacity, 0.78 MPa wet tensile strength), superhydrophilicity (oil contact angles ≥159.3°), antioxidant activity (75.2 % DPPH scavenging), and photocatalytic functionality. The hierarchical micro/nano-roughness structure and superwettability surface enable efficient demulsification via droplet coalescence, and achieving 99.5 % separation efficiency for soybean oil-in-water emulsions with gravity-driven (485.48 L∙m^-2∙h^-1) and negative pressure-driven (1433.12 L∙m^-2∙h^-1) fluxes. The g-C₃N₄-driven photocatalytic self-cleaning degrades adsorbed pollutants, enables >98.5 % efficiency recovery after 10 cycles under xenon lamp irradiation. This work establishes a multi-component synergy strategy for biomass aerogels, advancing hierarchical engineering principles for sustainable wastewater remediation.