General Flame Approach to Chainlike MFe2O4 Spinel (M = Cu, Ni, Co, Zn) Nanoaggregates for Reduction of Nitroaromatic Compounds

Unique chainlike MFe2O4 (M = Cu, Ni, Co, and Zn) nanoaggregates (NAs) have been prepared by facile flame spray pyrolysis of nitrates/ethanol precursor. Synthesized MFe2O4 are composed of primary nanocrystallites mainly ranging from 8 to 20 nm and show uniform aggregations with size of 200-400 nm. As heterogeneous catalysts, it is clearly noted that CuFe2O4 NAs have the highest catalytic activity for the reduction of nitroaromatic compounds compared to NiFe2O4, CoFe2O4, and ZnFe2O4. The highest rate constant of 36.17 min(-1).g(-1) is achieved at a low catalyst usage (10 mu L, 0.2 mg.mL(-1)). The remarkably enhanced catalytic performance of CuFe2O4 NAs is mainly attributed to the promoted electron transfer on Cu2+ active sites, which is facilitated by unique spinel structures and chainlike aggregate morphology. It is demonstrated that flame spray pyrolysis technique is an effective route to produce binary or complex oxides for potential industrial use.