Black-TiO₂ based photoelectrochemical oxidation of flue-gas desulfurization wastewater for effective reuse in flow-electrode CDI

This study proposes two integrated electrochemical methods for the reuse of flue-gas desulfurization wastewater (FGDW): photoelectrochemical oxidation (PECO) using a self-doped black TiO₂ nanotube array (Black-TNA) catalyst and flow-electrode capacitive deionization (FCDI). The electrocatalytic activity and oxidative performance of the Black-TNA annealed at 600 °C were superior to those of the conventional Blue-TNA, as determined via Mott-Schottky and cyclic voltammetry plots. Furthermore, the removal of organic pollutants via PECO under sulfate-based conditions using the Black-TNA showed exceptional degradative results. Subsequently, FGDW was introduced to the FCDI system to evaluate its feasibility as a flow-electrode electrolytic solution in comparison with other synthetic electrolytes (NaCl, Na₂SO₄, and NaCl/Na₂SO₄ composite), and was confirmed for its feasibility. Thus, the integrated PECO-FCDI system was demonstrated to be an effective means of removing organic pollutants and salts without the use of additional chemicals.