Synthesis of core-heteroshell structure for ZIF-67/VTM and its efficient activation of peroxymonosulfate in treatment of levofloxacin from an aqueous solution.

A core-heteroshell structural magnetic composite of ZIF-67/Vanadium-titanium magnetite (VTM) was successfully synthesized through a feasible solvothermal method and efficiently used in activation of peroxymonosulfate (PMS) for the treatment of levofloxacin (LVF) in an aqueous solution. The catalytic activity of the ZIF-67/VTM composite in LVF degradation was thoroughly evaluated, demonstrating the LVF removal rate could reach up to 93.3% within 60 min at ZIF-67/VTM composite dosage of 100 mg/L, PMS concertation of 75 mg/L, and the natural pH of 6.4. It is quite interesting that the carbon organic skeleton (in the ZIF-67 shell) have accelerated the internal electron transformation rate of the ZIF-67/VTM composite, thus efficiently promoting the O-O band (in PMS) breakage and the redox cycle of cobalt, further favoring the free radicals generation. The quenching experiments and EPR analysis results demonstrated that ·SO4- would play a crucial role in the LVF degradation process. Surprisingly, we have found that the introduction of Cl- (at some certain dosage) would not always decrease the LVF degradation ratio, for a new reactive oxygen species (singlet oxygen) was emerged in this system. What's more, the ZIF-67 (as the wrapping structure) could stabilize the VTM (the inner structure) in changing reaction conditions, prompting a good adaptability at a wider pH range (3-10) for inhibiting the leaching of various metal ions into the aqueous solution. This novel ZIF-67/VTM composite could provide new ideas and routes for the removal of emerging pollutants from an aqueous solution.