From commercial melamine foam to C-O-M coupled La-doped MgAl-borate LDH/nitrogen-doped carbon composite: a multipollutant adsorbent for wastewater remediation over a broad pH range

Developing cost-effective adsorbents capable of treating multipollutant wastewater under fluctuating pH conditions remains a major challenge for layered double hydroxide (LDH)-based materials. Herein, we report a La-doped MgAl-borate LDH/Nitrogen-doped carbon hybrid (LaMgAl-BLDH/NC) constructed through a C-O-M interfacial coupling, in which hydroxyl-rich N-doped carbon reacts with the metal‑oxygen layers of LaMgAl-BLDH to form robust covalent C-O-M linkages. This bonding-directed assembly produces a chemically durable and strongly integrated 3D porous network with enhanced charge heterogeneity and improved resistance to acidic or alkaline corrosion. Benefiting from this strengthened interfacial coupling and the synergistic effects of La incorporation, the LaMgAl-BLDH/NC composite exhibits high removal capacities toward structurally diverse pollutants, achieving maximum capacities of 995.20 mg/g for Congo red, 3020.19 mg/g for malachite green, and 151.34 mg/g for phosphate. Notably, compare with conventional LDHs that undergo structural degradation in acidic or alkaline environments, the C-O-M reinforced hybrid maintains excellent performance over a broad pH range of 4–10. The maximum adsorption capacities of the adsorbent for Congo red, malachite green and phosphate at pH 2, 4 and 12 correspond to 79.65%, 87.32% and 58.83% of those obtained at their respective optimal pH values. Mechanistic analysis reveals that electrostatic interaction, ion exchange, π-π stacking, pore filling jointly govern the removal process. Optimization via Box-Behnken response surface methodology further enhances removal efficiency by identifying favorable synthesis and operational conditions. This work establishes a generalizable, low-cost C-O-M bonding strategy for pH-tolerant LDH/carbon hybrids, enabling efficient remediation of multipollutant industrial wastewater.