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

Abstract

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-1 H -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 PbO 2 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 CO 2 adsorption and contact angle tests reveal the preferential adsorption of CO 2 and H 2 O 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 CO 2 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.