Site-Specified MOF/COF Heteronanosheets for Enhancing Photocatalytic CO2 Reduction

Metal–organic and covalent–organic framework (MOF and COF) semiconductors are promising photocatalytic materials because of their large surface area, ordered pore structure, structural tunability, and chemical/thermal stability. However, due to their complicated nucleation and growth processes, constructing MOF- and COF-based heterostructures with controllable morphology, intimate interfacial coupling, and site-specified component distribution still remains a great challenge. In this work, site-specified MOF/COF heteronanosheets were obtained through a seed-mediated synthesis strategy, where the TTCOF (COF formed via a Schiff-base reaction between 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 1,3,5-triformylphloroglucinol) anchors preferentially on the edge of NZZ (MOF formed via the coordination of 2-methylimidazole and 5-amino-1H-tetrazole with Zn nodes) nanosheets by C–N covalent bonds derived from the Schiff-base reaction and subsequent imine-to-enamine tautomerization. Intriguingly, Pt and PbO2 photodeposition experiments indicate the isolation of photoreduction and photo-oxidation sites on the basal planes and edges of NZZ/TTCOF heteronanosheets, respectively, confirming the type-II spatial separation of charge carriers as clarified by the band structure analyses and density functional theory calculation. Moreover, the integration of ultraviolet-responsive NZZ and near-infrared-responsive TTCOF contributes to sufficient utilization of incident light irradiation. Additionally, the CO2 adsorption and contact angle tests reveal the preferential adsorption of CO2 and H2O on the NZZ photoreduction site and TTCOF photo-oxidation site of NZZ/TTCOF, respectively. Therefore, without the photosensitizer and cocatalyst, the NZZ/TTCOF heteronanosheets exhibited a markedly promoted gas–solid CO2 photoreduction activity compared to pristine NZZ and TTCOF, and it is also superior to those of many MOF- and COF-based photocatalysts. Our study could propel the rational design of advanced heteronanostructures for the efficient production of solar fuels.