The conventional inorganic synthetic procedures usually demand long reaction time, high temperature, and toxic solvents. Different from the traditional solvents, ionic liquids are potential green solvents with many advantages, such as negligible vapor pressure, low interface tension, supramolecular solvents, and microwave absorbing ability [1, 2]. Because of these excellent performances, ionic liquids can be the new “all in one” solvents, which are combination of solvent, template, and reactant . Compared with the traditional heating methods, microwave irradiation can obviously shorten the heating time. Moreover, microwave irradiation also has many other advantages, including volumetric heating, selectivity, fast kinetics, homogeneity, and energy saving [4–9]. Microwave-assisted ionic liquid reaction systems have been studied for the synthesis of inorganic materials, such as ZnO frameworks , high quality TiO2 nanocrystals , Bi2Se3 nanosheets , indium tin oxide nanocrystals , metal fluorides , cuboid-like crystallites , tellurium nanorods and nanowires , manganese oxide , CdF2 nanoflakes , and ZnO nanosheet aggregates .
Zn(OH)F has been demonstrated to be an important catalyst for the formation of pyridine from tetrahydrofurfuryl alcohol and ammonia, and it has also been used as the precursor for preparing ZnO [19, 20]. Huang et al.  have presented a simple hydrothermal route toward Zn(OH)F, which was then used as the precursor to prepare ZnO by calcination. As we know, ZnO has a wide range of applications in gas sensors, piezoelectric transducers, optical waveguides, acoustic–optical devices, catalysis, and solar cells, mainly due to its unique catalytic, electronical, and optoelectric properties [21–23]. Recently, porous ZnO with large specific surface area has generated considerable interest because of its potential applications in photocatalysis, environmental engineering to chemical, and gas sensors [24, 25]. Porous ZnO with various nanostructures have been reported, including hollow ZnO mesocrystals , porous ZnO nanoparticles , porous ZnO architectures , porous ZnO nanodisks , and porous ZnO nanowires .
Herein, for the first time, ionic liquid 1-Butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4) is used as the reactant and the template to synthesize novel flower-like Zn(OH)F via an easy and fast microwave-assisted route. Nanoporous ZnO is obtained by thermal decomposition of the Zn(OH)F.