Activation of chloride by oxygen vacancies-enriched TiO2 photoanode for efficient photoelectrochemical treatment of persistent organic pollutants and simultaneous H2 generation

Photoelectrochemical (PEC) activation of chloride ions (Cl-) to degrade persistent organic pollutants (POPs) is a promising strategy for the treatment of industrial saline organic wastewater. However, the wide application of this technology is greatly restricted due to the general photoanode activation of Cl- with poor capability, the propensity to produce toxic by-products chlorates, and the narrow pH range. Herein, oxygen vacancies-enriched titanium dioxide (Ov-TiO2) photoanode is explored to strongly activate Cl- to drive the deep mineralization of POPs wastewater in a wide pH range (2-12) with simultaneous production of H2. More importantly, nearly no toxic by-product of chlorates was produced during such PEC-Cl system. The degradation efficiency of 4-CP and H2 generation rate by Ov-TiO2 were 99.9% within 60 min and 198.2 μmol h-1 cm-2, respectively, which are far superior to that on the TiO2 (33.1% within 60 min, 27.5 μmol h-1 cm-2) working electrode. DFT calculation and capture experiments revealed that Ov-TiO2 with abundant oxygen vacancies is conducive to the activation of Cl- to produce more reactive chlorine species, evidenced by its high production of free chlorine (48.7 mg L-1 vs 7.5 mg L-1 of TiO2). The as-designed PEC-Cl system in this work is expected to realize the purification of industrial saline organic wastewater coupling with green energy H2 evolution.