Preparation and characterization of bimetallic Fe–Cu allophane nanoclays and their activity in the phenol oxidation by heterogeneous electro-Fenton reaction

Abstract

Bimetallic (FeeCu) allophane nanoclays were synthesized using a two-step wet impregnation methodwith different Fe/Cu ratios. The catalytic activities of bimetallic (FeeCu) allophane were studied forphenol oxidation by heterogeneous electro-Fenton reaction (HEF) at different initial pHs (3.0 and 5.5),and were compared with Fe-allophane and Cu-allophane catalysts. A glassy carbon electrode modifiedwith the bimetallic allophane nanoclays was used as working electrode. FTIR, SEM, X-ray diffraction, XPS,M€ossbauer spectroscopy and N2 adsorptionedesorption were used to characterize the catalysts, andindicated the formation of small copper oxide particles stabilized by iron oxide species. Phenol conversionby HEF process at initial pH 3.0 was near 100% for all bimetallic (FeeCu) allophane nanoclays inless than 2 h of reaction, following an exponential decay. The chemical oxygen demand (COD) removalwas less than 47% for Cu-allophane and 65% for Fe-allophane, whereas for the bimetallic (FeeCu) allophanenanoclays the COD removal decreased with the amount of copper oxide in the catalyst, achievingan 80% COD removal with Fe5.4Cu0.6 catalyst. These results showed the synergetic effect between the Fe3þand Cu2þ ions present in the bimetallic (FeeCu) allophane nanoclays. Similarly, when the reactions wereperformed at initial pH 5.5 the phenol conversion was near 100% after 4 h for Fe-allophane and bimetallic(FeeCu) allophane with lower copper content. In the bimetallic (FeeCu) allophane clays the leaching ofiron and copper into the solution was less than 1.25 mg/L and 0.638 mg/L, respectively, indicative of thehigh stability of the bimetallic (FeeCu) allophane catalysts.