Photoelectrocatalytic treatment of recalcitrant compounds and bleach stage pulp and paper mill effluent using Au-TiO2 nanotube electrode

A simple anodization technique has been adopted for the synthesis of Au doped TiO2 nanotubes (Au/TiO2NTs) electrode. The physicochemical properties of Au/TiO2NTs electrodes have been studied using FE-SEM, Raman spectroscopy, FTIR, XRD, and UV-vis DRS analysis techniques and, compared with un-doped TiO2NTs electrodes. The optimization of process parameters has been carried out for the photoelectrocatalytic (PEC) degradation of 4-CG (4-Chloroguaiacol) under batch-mode experiments. Au/TiO2 nanotube electrodes showed 84% degradation efficiency in 6 h under optimized conditions viz. 0.15 mM Au loading, 0.08 g L-1 electrolyte concentration, 0.03 A current and pH 3 under UV light irradiations. The degradation of 4-CG was validated with the quantification of generated (OH)-O-center dot and degradation intermediates/by-products during the batch-mode PEC treatment. The PEC process was observed to be more efficient for degrading and mineralizing 4-CG when compared to PC and EC processes, individually. PEC degradation of 4-CG has also been assessed in recirculation mode to study the feasibility of synthesized Au/TiO2NTs electrodes to treat large volume of contaminant polluted wastewater. For the feasibility of industrial scale applications, pulp and paper mill effluent was subjected to the PEC degradation under recirculation mode using Au/TiO2NTs electrodes and significant reduction in COD and TOC values were observed. Overall, the cost of electrical energy consumption was computed for all the batch and recirculation mode PEC treatment of 4-CG as well as real pulp and paper mill effluent.