Activating inert cobalt sites via interfacial nitrogen vacancies in Co3O4@g-C3N4 heterojunctions for selective boron recovery from hypersaline brines

Batch adsorption experiments combined with density functional theory (DFT) calculations reveal that interfacial nitrogen vacancies act as electron sinks, inducing pronounced charge redistribution that renders adjacent Co sites more electron-deficient. This electronic modulation enhances their Lewis acidity, lowers the adsorption free energy (ΔG = -4.28 eV), and facilitates the spontaneous formation of robust Co-O-B coordination bonds.

Consequently, the optimized CoCN-5 delivers an equilibrium boron adsorption capacity of 128.5 mg g-1 at 25 °C within 120 min, significantly outperforming pristine Co₃O₄ (~8.2 mg g-1). Furthermore, the material demonstrates exceptional practical viability in actual hypersaline brines (LaGuoCuo: 81 mg g-1; ChaErHan: 79 mg g-1), achieving remarkably high separation factors against major competing ions (SF(B/Na) = ~217, SF(B/Mg) = ~159).

These findings establish interfacial defect engineering as a precise strategy for activating metal oxide sites, providing a molecular-level paradigm for selective boron recovery from complex aquatic systems.