Influence of ZIF-8 crystal growth interactions on C₃N₄ surface features and the consequences during CO₂...

Photocatalysis is an interesting method for producing industry-relevant chemicals from CO₂ using direct solar energy. Thus, this requires cheap photocatalysts and ways to tune reaction pathways towards the desired CO₂ photoreduction products. Metal-organic frameworks (MOFs), as a versatile material, can tune such pathways during photoreactions, while carbon nitride (C₃N₄) materials are cheap and synergetic photocatalysts. The one-pot growth of MOFs on C₃N₄ is a viable method for increasing the photocatalytic activity of composites and simplifying their preparation, but the interactions relevant to photocatalysis between C₃N₄ and MOFs under such conditions remain unclear. This work provides compelling evidence for this synthesis under conventional solvothermal conditions and a sub-ambient protocol to grow ZIF-8 onto graphitic and mesoporous C₃N₄ in relation to the photocatalytic activity. By relying on ¹³C-MAS-NMR, PXRD, UV-Vis spectroscopy, SEM and CO₂-TPD methods, the impact of the synthesis conditions on the structural features of the ZIF-8@C₃N₄ composite is investigated and methods to judge the state of the MOF-C₃N₄ interfacing are developed. Operando XAS serves to assess the differences observed under liquid- and gas-phase CO₂ photoreduction. The effects of structural features and synthesis conditions on electronic properties observed through spectroscopic characterization are discussed, with a focus on photocatalytic activity. Differences in productivity and product selectivity in CO₂ photoreduction reactions in the liquid and gas phases are presented as a function of synthetically induced structural differences in the photocatalyst and the capability to undergo changes during the photocatalytic process. By understanding these correlations, we provide new insights into the development of more efficient MOF-C₃N₄ composites.