| 内容提要: |
Metal-organic frameworks (MOFs) associated with functional materials has attracted considerable attentions due to excellent catalytic performance. Previous studies suggested that MOFs were semiconductors or photocatalysts with band gaps determined by the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gaps of the organic ligand molecules. The photocatalysis of MOFs is considered to be achieved by the electron transfer from the photoexcited organic ligands to metallic clusters within MOFs, which is termed as ligand to metal charge transfer (LMCT). However, few attentions have been paid to the photocatalysis of the heterostructured MOFs and photocatalytic performance is still not clear. In our work, mono-core-shell ZnO/ZIF-8 and multi-core-shell AuCo/ZIF-67 were synthesized by coating zeolitic imidazolate frameworks-8 (ZIF-8) and zeolitic imidazolate framework-67 (ZIF-67) on ZnO and AuCo, respectively. The core-shell heterostructure can be achieved by using a self-template method, where ZnO and AuCo were employed not only as the template but also as Zn(II) and Co(II) for the composition of ZIF-8 and ZIF-67, respectively. Because of the limitation of porous ZIF-8 framework, the activity of ZnO/ZIF-8 was shown to be the same as that of ZIF-8 during the degradation of methylene blue (MB), and the outer ZIF-8 shell dominated the photocatalysis via LMCT mechanism during the degradation. However, ZnO/ZIF-8 showed higher photocatalytic activity than ZnO in the presence of hydrogen peroxide due to the molecule size selective property. Furthermore, AuCo/ZIF-67 also showed a size-selective catalytic performance in the photocatalytic removal of Cr(VI) and MB attributed to the porous framework of ZIF-67. Although ZIF-67 shell contributed to the adsorption and photocatalytic degradation of MB by affinity of aromatic rings and ligand to metal charge transfer mechanism, the ZIF-67 shell still showed a significantly inhibitory effect on the removal of MB. This size-selective property could also be well described by the proposed interface transfer kinetics. Photocatalysis of core-shell heterostructured MOFs will facilitate new efforts in the treatment of pollutants. |