Simultaneous degradation of ofloxacin and recovery of Cu(II) by photoelectrocatalysis with highly ordered TiO2 nanotubes.

A photoelectrocatalytic system for removal of ofloxacin and Cu(2+) complex was developed. In such a photoelectrocatalytic system, highly ordered titanium dioxide nanotubes served as a highly active photoanode for photoelectrocatalytic degradation of ofloxacin; and titanium plate was used as the cathode, on which Cu(2+) ions were electrodeposited. Compared with other treatment methods including photocatalysis, electrochemistry and direct photolysis, photoelectrocatalytic technique exhibited the highest removal efficiency for either ofloxacin or Cu(2+). To obtain the optimum photoelectrocatalytic operation conditions, some influencing factors such as current, pH and supporting electrolyte concentration were investigated systematically. The mutual influence analysis indicated that the photoelectrocatalytic removal efficiency of ofloxacin was first promoted by Cu(2+) but was then suppressed with prolonging the treatment time; whereas the removal of Cu(2+) was always promoted by ofloxacin over the whole photoelectrocatalytic treatment process. Furthermore, the photoelectrocatalytic removal of ofloxacin -Cu(2+) was studied by differential pulse voltammetry and high-performance liquid chromatography-mass spectrometry. The results indicated that although Cu(2+) influenced the removal rate of ofloxacin, it did not change the degradation mechanism of ofloxacin. The formation of an electroactive intermediate product during the photoelectrocatalytic process was clearly observed by voltammetric analysis. Based on intermediate products identified by high-performance liquid chromatography-mass spectrometry, a possible photoelectrocatalytic removal mechanism for ofloxacin -Cu(2+) was proposed.