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

Bimetallic (Fe-Cu) allophane nanoclays were synthesized using a two-step wet impregnation method with different Fe/Cu ratios. The catalytic activities of bimetallic (Fe-Cu) allophane were studied for phenol 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 modified with the bimetallic allophane nanoclays was used as working electrode. FTIR, SEM, X-ray diffraction, XPS, Mössbauer spectroscopy and N adsorption-desorption were used to characterize the catalysts, and indicated the formation of small copper oxide particles stabilized by iron oxide species. Phenol conversion by HEF process at initial pH 3.0 was near 100% for all bimetallic (Fe-Cu) allophane nanoclays in less than 2 h of reaction, following an exponential decay. The chemical oxygen demand (COD) removal was less than 47% for Cu-allophane and 65% for Fe-allophane, whereas for the bimetallic (Fe-Cu) allophane nanoclays the COD removal decreased with the amount of copper oxide in the catalyst, achieving an 80% COD removal with FeCu catalyst. These results showed the synergetic effect between the Fe and Cu ions present in the bimetallic (Fe-Cu) allophane nanoclays. Similarly, when the reactions were performed at initial pH 5.5 the phenol conversion was near 100% after 4 h for Fe-allophane and bimetallic (Fe-Cu) allophane with lower copper content. In the bimetallic (Fe-Cu) allophane clays the leaching of iron and copper into the solution was less than 1.25 mg/L and 0.638 mg/L, respectively, indicative of the high stability of the bimetallic (Fe-Cu) allophane catalysts.Peer Reviewe

On the dramatic increase with chain length of the oxidazability of linear saturated aliphatic alcohols on gold in alkaline media

© 2015 Elsevier Ltd. All rights reserved. The electrooxidation of linear saturated aliphatic alcohols from C1 to C8 on gold in alkaline media has been studied by cyclic voltammetry and with an electrochemical quartz crystal microbalance. The current density of alcohol oxidation very markedly increased and, correspondingly, the onset potential decreased, with increasing chain length, that is, with initially slightly increasing, and then constant, pKa. We attribute this oxidazability increase with chain length to the increasing hydrophobicity of the alcohol. Effectively, a molecular dynamics simulation of the hydration of alcohols and alcoholates shows that the hydrophobicity of the alcohols increases with increasing chain length. The higher activity of gold for the oxidation of organic, and also inorganic (CO), compounds in alkaline media is well known, and should be due to an activation of the gold surface by OH adsorption, and not to a change of the compounds themselves, the (majority) neutral alcohol being the oxidized species both in acid and alkaline media. At the potentials at which 1-heptanol oxidation starts, the mass in both base electrolyte and in 1-heptanol is at a minimum, or nearly so, which shows that water is driven away from the surface of gold prior to the oxidation of both gold and 1-heptanol.Peer Reviewe