Novel magnetically separable nanomaterials for heterogeneous catalytic ozonation of phenol pollutant: NiFe2O4 and their performances

Magnetic NiFe2O4 nanomaterials were proposed as novel ozonation catalysts for the first time. The samples which were synthesized by the hydrothermal method and the calcined method were dominated as NiFe2O4–H and NiFe2O4–C, respectively. Compared with ozonation alone, the presence of NiFe2O4–H significantly enhanced the degradation of phenol, while NiFe2O4–C was noneffective. The interaction between NiFe2O4–H and ozone was obviously stronger than that in ozonation/NiFe2O4–C. This interaction between catalyst and ozone was proved to be a surface process and played a vital role in the heterogeneous catalytic ozonation. Phosphate revealed significantly inhibitive influence on the decomposition of ozone and the degradation of phenol in ozonation/NiFe2O4. Lewis acid sites were proved as reactive centers for catalytic ozonation in aqueous solution. The results indicated that not only the more surface Lewis acid sites, causing the strong interaction between catalyst and ozone, but also the enhanced interfacial electron transfer lead to the higher catalytic activity of NiFe2O4–H than NiFe2O4–C. Furthermore, the NiFe2O4–H nanocatalyst could be easily and efficiently separated from the reaction mixture with an external magnet, which made it an attractive nanomaterial with prospective application in catalytic ozonation of organic pollutants in water treatment.

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► Nano-sized NiFe2O4 were proposed as ozonation catalysts for the first time.
► The great difference between NiFe2O4–H and NiFe2O4–C was discussed.
► The vital role of the interaction between ozone and NiFe2O4 were investigated.
► Lewis acid sites and interfacial electron transfer were responsible for catalysis.