Peculiar synergetic effect of γ-Fe2O3 nanoparticles and graphene oxide on MIL-53 (Fe) for boosting photocatalysis

Special enhanced synergistic effect of ultra-small gamma-Fe2O3 and graphene oxide (GO) on MIL-53 (Fe) was achieved for boosting photocatalysis. Compared to traditional methods of surface coverage, the incorporation of gamma-Fe2O3 (average size 2-3 nm) inside MOFs particles not only increased the light absorption of catalyst, but also formed numerous micro-heterojunctions with MOFs units and thus effectively facilitated the separation of photogenerated carriers. By supplying attachment sites for MOFs crystal, the functionalized GO reduced the size of MOFs particles to 100-200 nm, meanwhile improved their dispersibility. The active sites and quantum yield of photocatalytic reaction were also intensified benefiting from the large surface area and high electronic conductivity of GO. Therefore, the novel gamma-Fe2O3-MIL-53(Fe)-GO composite exhibited the highest photocatalytic activity towards norfloxacin, with a removal rate of 92.8% in 90 min. The kinetic constant was 4.49-fold higher than that using pure MIL-53 (Fe), and 1.43-time greater than that in the system of MIL-53 (Fe) and hydrogen peroxide, which usually acted as efficient electron acceptors to increase the quantum yield and final photocatalytic performance of MOFs. Based on the identified intermediates, three NOR degradation pathways including the cleavage of piperazine ring, defluorination and decarboxylation, as well as the conversion of quinolones group were proposed. Photocatalytic mechanism investigation revealed the holes and hydroxyl radicals came from the reaction of electrons with oxygen played the important role in gamma-Fe2O3-MIL-53(Fe)-GO photocatalysis. Moreover, the utilization of magnetic nanoparticles improved the recovery and recyclability of ternary catalyst.