Estrutura e reatividade da Maghemita dopada com Cu2+ em um sistema Fenton heterogêneo: aspectos teóricos e experimentais

Abstract

In this work, a simple polymeric method was used to prepare undoped and Cu-doped iron oxides, catalysts for the H2O2 decomposition reaction. These catalysts were characterized by powder X-ray diffractometry (XRD), scanning electronic microscopy (SEM) coupled to an energy dispersive X-ray spectrometer (EDX), and H2-Temperature Programmed Reduction (H2-TPR). The SEM images showed that both samples are constituted by an agglomerated of inhomogeneous particles, which tend to decrease in size with Cu-doping. EDS mapping revealed that the Cu2+ ions were very well dispersed in the iron oxide matrix. The Rietveld refinement of the XRD patterns displayed that both samples are formed by hematite and maghemite, but that only maghemite had the octahedral Fe3+ ions isomorphically replaced by 2 wt.% Cu2+ ions. The TPR results revealed that Cu2+ doping caused a decrease in the reduction temperature of maghemite into magnetite when compared to undoped catalysts. The Cudoping was essential to produce an active catalyst to H2O2 decomposition. Catalytic tests using phenol as a radical scavenger showed that the H2O2 decomposition was strongly inhibited in the presence of Cu-doped catalysts, suggesting that the H2O2 may be decomposed by a radical mechanism. Phenol degradation kinetics confirmed that the doping of maghemite with Cu2+ causes significant improvement in catalytic activity. Theoretical calculations revealed that Cu-doping in the maghemite structure creates sites of low electronic density, which favor the interactions between the hydrogen peroxide oxygen atoms and the surface Cu2+ ions, thus improving the catalytic activity. This simple strategy can be extended to other materials to design active heterogeneous catalysts for use in environmental remediation processes.