Fabrication of porous cubic architecture of ZnO using Zn-terephthalate MOFs with characteristic microstructures.

A method for synthesizing porous cubic-shaped ZnO particles a few tens of micrometers in size is described on the basis of a pyrolytic conversion of Zn-terephthalate metal-organic frameworks (MOFs). MOF crystals were initially grown in solutions containing Zn(NO3)2·6H2O and terephthalic acid as solutes and N,N-dimethylformamide (DMF) or N,N-diethylformamide (DEF) as a solvent under a solvothermal condition. It was the key to controlling the microstructure of MOF cuboids for their use as an intermediate compound for ZnO. Actually, many cracks were formed and hence the cubic microstructure was somewhat destroyed in the pyrolytic conversion from dense MOF crystals (grown in the DMF solution) to ZnO. In contrast, mesocrystal-like MOF cuboids (grown in the DEF solution) could maintain their shape during the pyrolysis because of the relaxation against a MOF-to-ZnO volume change. The resultant ZnO with a highly porous cubic structure showed intense visible photoluminescence upon irradiation with ultraviolet light.