Photoelectrocatalytic Oxidation of Cu-cyanides and Cu-EDTA at TiO2 nanotube electrode

Oxidation of Cu-cyanides and Cu-EDTA complexes by a photoelectrocatalytic process was investigated at the TiO2 nanotube matrix electrode. The results indicated that Cu oxides were deposited onto the TiO2 nanotube anode in the individual oxidation of Cu-cyanide complexes with the conversion of CN− into OCN−. In the case of Cu-EDTA, Cu-EDTA was efficiently oxidized at the TiO2 nanotube anode and liberated Cu2+ was deposited onto the cathode with only little amount of Cu oxides deposited onto the TiO2 nanotube anode. The above reactions favored at acid conditions. Furthermore, simultaneous oxidation of Cu-cyanide and Cu-EDTA was performed at the TiO2 nanotube electrode with the various ratios of [EDTA]: [CN−]. The Cu mass distribution in the solution, at the anode, and the cathode were investigated in the reaction process. The results indicated that with the increase of [EDTA]: [CN−] ratio, the amount of Cu deposited onto the anode decreased with an increase of the amount of Cu deposited onto the cathode. Addition of EDTA into the reaction solution efficiently inhibited the formation of Cu-oxides onto the TiO2 anode and promoted the Cu deposition onto the cathode. The above results were furthermore confirmed by the SEM-EDX analysis of the anode and cathode under various processes.