Degradation of organic pollutants by NiFe2O4/peroxymonosulfate: efficiency, influential factors and catalytic mechanism

摘要

Nickel ferrites (NiFe _(2) O _(4) ) were prepared through thermal decomposition of homogeneous nickel oxalate and ferrous oxalate, and the product displayed typical spinel structure, small nanoparticle size ( ca. 12?nm), high BET surface (53.5 m ~(2) g ~(?1) ), and good magnetic response (19.3 emu g ~(?1) ). The as-prepared NiFe _(2) O _(4) was applied in heterogeneous catalysis to generate powerful radicals from peroxymonosulfate (PMS) for the removal of recalcitrant pollutant. Herein, benzoic acid (BA) was employed as a stable model organic pollutant, and it was found that NiFe _(2) O _(4) /PMS system could realize 82.5% degradation in 60 min and maintain its catalytic efficiency during four recycling experiments. Such a catalytic performance of NiFe _(2) O _(4) was indeed superior to those from Fe _(2) O _(3) (23.5%), Fe _(3) O _(4) (48.0%), NiO (57.6%), and MnFe _(2) O _(4) (63.8%). Although NiFe _(2) O _(4) performed a slightly inferior BA degradation to CoFe _(2) O _(4) (86.2%), its nickel leaching (0.265 mg L ~(?1) ) was much less than cobalt leaching (0.384 mg L ~(?1) ) from CoFe _(2) O _(4) . In addition, some potential influential factors, including the dosages of PMS and NiFe _(2) O _(4) , the initial pH value, ion strength, and the concentrations of bicarbonate, natural organic matter, halide, were systemically investigated. More importantly, NiFe _(2) O _(4) /PMS were also effective for BA removal under some actual water background conditions, especially in surface water and the finished water from drinking water treatment plant: the degradation efficiencies of BA were still close up to 60%. Sulfate and hydroxyl radicals were confirmed to be the main reactive species in the NiFe _(2) O _(4) /PMS system. XPS spectra revealed that Ni sites on the surface of NiFe _(2) O _(4) were the primary active sites, and Raman spectra suggested that inner-sphere complexation between PMS and Ni sites derived peroxo species on the surface, which were further responsible for the efficient generation of radicals.