A copper ferrite synthesized by a sol-gel combustion method was calcined at different temperatures up to 800°C, determining changes in its structural characteristics and magnetic measurements and studying its catalytic performance in gallic acid removal by Fenton reaction. The main objective was to study the effect of the calcination temperature of copper ferrite on its crystalline phase formation and transformation, activity and metal ion leaching. The cubic-to-tetragonal transformation of the spinel occurred via its reaction with the CuO phase, displacing Fe3+ ions in B (octahedral) sites out of the spinel structure by the following reaction: 2Fe3+B+3CuO→Fe2O3+3Cu2+B. The catalysts showed superparamagnetic or substantial superparamagnetic behaviour. At higher calcination temperatures, catalyst activity was lower, and Cu ion leaching was markedly decreased. There was no Fe ion leaching with any catalyst. The as-prepared catalyst showed better catalytic performance than a commercial copper ferrite. Leached Cu ions acted as homogeneous catalysts, and their contribution to the overall removal mechanism was examined. Cu2O present in the as-prepared catalysts made only a small contribution to their activity. Finally, the reutilization of various catalysts was studied by performing different catalytic cycles.
Keywords: Catalyst reuse; Copper ferrite; Copper oxide activity; Cu ion leaching; Cubic-to-tetragonal transformation; Gallic acid removal; Heterogeneous Fenton reaction; Homogeneous Fenton reaction.
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