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

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.