Exploring a Ni-N₄ Active Site-Based Conjugated Microporous Polymer Z-Scheme Heterojunction Through Covalent Bonding...

Designing photocatalysts with efficient charge transport and abundant active sites for photocatalytic CO₂ reduction in pure water is considered a potential approach. Herein, a nickel-phthalocyanine containing Ni-N₄ active sites-based conjugated microporous polymer (NiPc-CMP), offering highly dispersed metal active sites, satisfactory CO₂ adsorption capability, and excellent light harvesting properties, is engineered as a photocatalyst. By virtue of the covalently bonded bridge, an atomic-scale interface between the NiPc-CMP/Bi₂ WO₆ Z-scheme heterojunction with strong chemical interactions is obtained. The interface creates directional charge transport highways and retains a high redox potential, thereby enhancing the photoexcited charge carrier separation and photocatalytic efficiency. Consequently, the optimal NiPc-CMP/Bi₂ WO₆ (NCB-3) achieves efficient photocatalytic CO₂ reduction performance in pure water under visible-light irradiation without any sacrificial agent or photosensitizer, affording a CO generation rate of 325.9 µmol g^-1 with CO selectivity of 93% in 8 h, outperforming those of Bi₂ WO₆ and NiPc-CMP, individually. Experimental and theoretical calculations reveal the promotion of interfacial photoinduced electron separation and the role of Ni-N₄ active sites in photocatalytic reactions. This study presents a high-performance CMP-based Z-scheme heterojunction with an effective interfacial charge-transfer route and rich metal active sites for photocatalytic CO₂ conversion.