Efficient formation of ZIF-8 promoted by DBU for the preparation of ZnO and Ce/ZnO nanomaterials

In this work, the efficient preparation of zeolitic imidazolate framework-8 (ZIF-8) from Zn2+ and 2-methylimidazole (2-MI) promoted by 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) was presented. The mechanism obtained from NMR, MS, DFT calculations, and conductivity shows that [DBUH][2-MI] ionic liquid formed in-situ from proton transfer between DBU and 2-MI can ionize 2-MI to [2-MI]- and form electrostatic interaction between Zn2+ and [2-MI]-, resulting in the efficient self-assembly of Zn2+ and 2-MI to form ZIF-8. Moreover, the effect of the amount of DBU on ZIF-8 indicates that too much DBU will cause excessive deprotonation of 2-MI, leading to agglomerate of ZIF-8. Accordingly, the optimal ratio to form ZIF-8 is n(DBU): n(2-MI): n(Zn2+) = 2: 25: 1.25, which is also employed to prepare cerium-containing ZIF-8. Moreover, ZnO and Ce/ZnO nanomaterials are prepared by using ZIF-8 and cerium-containing ZIF-8 as precursors respectively, and their structure and morphology are characterized by XRD, FT-IR, SEM, and TEM. Interestingly, Ce content in Ce/ZnO obtained by EDS spectrum is basically consistent with the actual doping amount, indicating that DBU can effectively control the doping of Ce in ZIF-8. Finally, the photocatalytic degradation ability of ZnO and Ce/ZnO for Rhodamine B under visible light and sunlight is investigated in detail.