Hierarchically porous zeolitic imidazolate framework-8 with tunable mesostructure as Pickering interfacial catalyst

Abstract A new method was developed for the fabrication of hierarchically porous zeolitic imidazolate framework-8 (ZIF-8) as Pickering interfacial catalyst for boosting the efficiency of biphasic catalytic reaction. Hexadecyl trimethyl ammonium bromide (CTAB) and 1,3,5-trimethylbenzene (TMB) were utilized as soft template and pore-expanding agent to prepare the hierarchically porous ZIF-8 with tunable mesostructure. XRD and FTIR measurements were employed to show the structure of as-prepared ZIF-8 samples. Interestingly, the amphiphilic property of as-prepared ZIF-8 samples, which was important for the stability of as-formed Pickering emulsions, could be varied by only adjusting the ratio of CTAB/TMB. Optical micrographs of Pickering emulsion stabilized by the as-prepared ZIF-8 samples were also conducted to present the morphology of the formed emulsion droplet. Pickering emulsion system stabilized with the hierarchically porous ZIF-8 exhibited excellent performance in the yield and reaction rate for Knoevenagel condensation reaction. The recycle experiments were also investigated in the formed Pickering emulsion system for 5 times. The mechanism of hierarchically porous ZIF-8 as Pickering interfacial catalyst for Knoevenagel condensation reaction was proposed.