ZnFe2O4 substituted with Cu atoms for ultra-efficient formation of sulfate radicals: Extremely low catalyst dosage for thiamethoxam degradation

Neonicotinoids as one of the newest major class of insecticides is a kind of persistent pollutants. Herein, copper-substituted zinc ferrites (Cu 0.75 Zn 0.25 Fe 2 O 4 ) prepared in subcritical aqueous solution has a nanosize of ∼2 nm with high crystallinity and strong magnetic property. At low catalyst dosage of 0.05 g L −1 , peroxymonosulfate (PMS) can be effectively converted into sulfate radicals in Cu 0.75 Zn 0.25 Fe 2 O 4 /PMS system. Thiamethoxam (THIA) degradation rate is in the order of Cu 0.75 Zn 0.25 Fe 2 O 4 > CuFe 2 O 4 > ZnFe 2 O 4 (124, 84, 21 × 10 −3 min −1 , respectively). At pH ∼7.0, THIA degradation efficiency can be over 99 % in 40 min. The radical species ( e.g. , HO • , SO 4 •− and 1 O 2 ) were demonstrated by EPR spectra using probe molecules. The majority effects in Cu 0.75 Zn 0.25 Fe 2 O 4 /PMS system with kinetics modelling were comprehensively investigated as well. This work provides that multi-metal coupling, i.e. , Cu(Ⅰ)/Cu(Ⅱ) & Fe(Ⅱ)/Fe(Ⅲ), in spinel structure by polyhedral design is an effective strategy for enhancing the catalytic activity. The Cu 0.75 Zn 0.25 Fe 2 O 4 /PMS system has promising for water treatment of neonicotinoid insecticide with ease of recycling catalysts by magnetic separation.