The influence of different synthetic solvents on photocatalytic activity of ZIF-8 for methanol production from CO2

In this article, we investigate the effect of synthetic solvents on the surface characteristics of the zeolitic imidazolate framework-8 (ZIF-8) and its photocatalytic activities. Different solvents (deionized (DI) water - ZIF-8(W), methanol - ZIF-8(M), and a combination of ammonia and ethanol - ZIF-8(A)) were employed to prepare three ZIF-8 samples at room temperature. The fourth sample was obtained after 24 h immersion of ZIF-8(A) in methanol to evacuate pores which we named ZIF-8(AM). These four samples were characterized using XRD, FTIR, FESEM, BET, DRS, and AFM. BET and AFM measurements revealed that all ZIFs have a specific surface area above 1300 m2/g while their surface roughness or heterogeneity differs. In contrast to ZIF-8(AM), with the highest level of surface heterogeneity, ZIF-8(M) displayed a very smooth and homogeneous surface. We tested all as-made ZIF-8s for methanol production via CO2 reduction under UV–vis light irradiation. The results indicate that ZIF-8(AM) produces a high amount of methanol (ca. 500 μmol.g−1cat) while ZIF-8(M) is almost inactive. These findings reveal that in addition to BET surface area, surface heterogeneity is a significant parameter on photocatalytic activity of ZIF-8.