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 . 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 , 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 . 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 . 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 . all reagents are of analytical grade and used without further purification . in a typical synthesis , 0.22 g ( 1 mmol ) of zn(ch3coo)22h2o powder was dissolved in 8 ml of distilled water under stirring at room temperature for 10 min , then 2 ml of [ bmim]bf4was added slowly while the stirring continued . afterward , the mixture was transferred to a 30 ml teflon - liner tube and kept inside a domestic microwave oven for 5 min ( 800 w , 40% of maximum power ) . the obtained white precipitate was washed with distilled water and pure ethanol and collected by centrifugation . the collected zn(oh)f sample was dried at 60 c in vacuum for 12 h. then , the zn(oh)f sample was calcined at 400 c for 2 h in air atmosphere , to yield final product zno . the obtained samples were characterized by x - ray diffraction ( xrd ) ( bruker d8 advance ) , field - emission scanning electron microscopy ( fesem ) ( leo 1530 ) , transmission electron microscopy ( tem ) ( jeol jem-2100 ) , and nitrogen adsorption  desorption analysis ( micromeritics asap2010 ) . the xrd pattern reveals that the main composition of the product is zn(oh)f ( jcpds 32 - 1469 ) and a few impurities can also be detected . as shown in fig . figure 1b shows the xrd pattern of the product after the heat treatment , and the pattern matches well with the standard pattern of zno ( jcpds 36 - 1451 ) . axrd pattern of as - prepared zn(oh)f , bxrd pattern of zno sem images of zn(oh)f are shown in fig . the sem images reveal that the sample is composed of regular hierarchical flower - like particles and the average size of the flower - like particles is about 7 m . all the flower - like particles have six petals and every petal is composed of lots of acicular nano - structures , which grow from the center to the edge . the average length of each petal is about 3 m . the magnified image of a typical petal is shown in fig . 2c . a  csem images of as - prepared zn(oh)f , d  fsem images of nanoporous zno figure 2d  f shows the sem images of zno sample . the images reveal that the zno sample retains the flower - like morphology after the heat treatment at 400 c . the size of the zno particles is similar to that of the precursor zn(oh)f . the magnified image ( fig . figure 3a gives the micrograph of a typical zn(oh)f petal and the selected area electron diffraction ( saed ) pattern of the circular area . the saed pattern indicates the acicular nano - structure possesses single crystal structure . besides , fig . 3a reveals that the petal of the flower - like particle does not have porous structure . after the heat treatment , the zno sample exhibits nanoporous structure , as shown in fig . the saed pattern reveals that the petal of the particle possesses quasi - single crystal structure . the high - resolution transmission electron microscopy ( hrtem ) images for the petal are presented in fig . 3c and d. figure 3d shows the lattice fringes , whose spacing is 0.2476 nm , which is corresponding to thedvalue of the ( 101 ) planes of zno . atem images of the precursor zn(oh)f and electron diffraction pattern of zn(oh)f ( inserta , corresponding to the circle area of panela),btem images of zno and electron diffraction pattern ( insertb ) , andc , dhrtem images of zno figure 4 shows the nitrogen adsorption  desorption isotherm and the pore size distribution plot of nanoporous zno . the isotherm is identified as type iv , which is corresponding to the characteristic of mesoporous materials . the bet surface area of the porous zno is about 38.2 m / g , which is obviously larger than that of commercial zno powder with a bet surface area of ca . 4b ) shows a broad peak in a region of 550 nm with an obvious maximum at about 17 nm . desorption isotherm for the porous zno , bbarrett  joyner  halenda ( bjh ) pore size distribution plot from adsorption branch based on the experimental results , it can be confirmed that the addition of ionic liquids and the microwave irradiation play important roles in the formation of zn(oh)f with novel structure . second , because ionic liquids are composed of inorganic anion and organic cation , they have high polarizability and conductivity . in addition , [ bmim]bf4 can decompose in the presence of transition metal salts with hydration water molecules when the temperature exceeds its boiling point , the reaction can be expressed as follows : ( 1 ) generally , when the ph value is between 6 and 9 , zn(oh)2 is obtained predominantly . but the znf complexes will form in the presence of f under neutral or weak alkaline conditions , and the nucleation of zn(oh)f occurs during further hydrolysis . a possible chemical mechanism can be expressed as follows:(2)(3 ) the experiment results show that ionic liquid [ bmim]bf4 plays a critical role in the formation of flower - like structure . in the reaction , supramolecular effects and solvent self - structuration of ionic liquid are important when it reacts with high concentration of zinc acetate . the extended hydrogen - bonding and  stack interaction of the neighboring imidazolium rings make ionic liquids molecular recognition and self - assembly . as solvent , the self - assembled ability of ionic liquid ( [ bmim]bf4 ) has an important influence on the structural orientation in the reaction . zno is obtained after the calcination of zn(oh)f at 400 c , the chemical reaction takes place as follows : zn(oh)f  zno + hf . during the thermal decomposition process , molecule - size pores generated when the hf molecules released from the flower - like particles . meanwhile , small zno units formed during this process . with the temperature increasing , the small zno units assembled into nanoparticles and the molecule - size pores became nanopores . because of the existence of nanopores , flower - like zno sample possesses a large bet surface area . novel flower - like zn(oh)f has been successfully synthesized via microwave - assisted ionic liquid route . in addition , nanoporous zno is obtained after the heat treatment of zn(oh)f , and the morphology is well retained . the ionic liquid [ bmim]bf4is used as the reactant and the template in the synthesis . it is expected that this method may be extended to the preparation of other inorganic materials . this work was supported by natural science foundation of jiangsu province ( bk2006195 ) , doctor innovation funds of jiangsu province ( bcxj06 - 13 ) , and national natural science foundation of china ( 50502020 , 50701024 ) .