MOF-derived Ni–Cu bimetallic interface synergy modified TiO2 for efficient photocatalytic conversion of CO2 to formate in ammonia nitrogen wastewater†

Abstract

To address the critical challenges in photocatalytic CO₂ reduction systems, including rapid recombination of photogenerated electron–hole pairs, indiscriminate product distribution, and oxidative degradation of liquid-phase intermediates, we designed a ZIF-8-derived Ni–Cu bimetallic modified TiO₂ (NiCu-GC-TiO₂) photocatalyst for synergistic formate synthesis from CO₂ and ammonia nitrogen wastewater The research results indicate that Ni–Cu forms a highly dispersed interface through N bridges, significantly enhancing charge separation efficiency. In the NH₃-N system at pH = 10, the formate yield reached 116.2 μmol L⁻¹ (99.4% selectivity), which was 9.4 times higher than that of TiO₂. Ammonia nitrogen serves as an oxidative substrate that accelerates hole consumption while inhibiting formate oxidation. Isotope experiments confirmed that formate protons originate entirely from ammonia nitrogen, and the protons released from ammonia nitrogen oxidation drive the directed conversion of CO₂ to formate. The system can directly utilize HCO₃⁻ as a carbon source, compatible with industrial carbon capture processes. Cycling tests and flow-phase experiments demonstrated excellent material stability and practical applicability. This research provides a novel strategy for synergistic mechanisms between photocatalytic CO₂ reduction and wastewater treatment, which contributes to both environmental sustainability and energy utilization.