Coupling photoelectrochemical organic polymerization with hydrogen evolution for sustainable saline wastewater treatment

Saline wastewater with bio-refractory organics resists biological treatment. Although mineralization-oriented advanced oxidation processes (AOPs) have been developed for saline wastewater treatment, they face drawbacks of excessive oxidant consumption and intensive toxic byproduct formation. Herein, a photoelectrochemical (PEC) system employing a BiVO₄ photoanode modified with bismuth vacancies and a transition-metal hydroxide cocatalyst (namely NiFe(OH)_x@B_vVO) at a low peroxymonosulfate (PMS)-to-pollutant ratio of 2:1 is established to address these challenges. This novel polymerization-oriented PMS-assisted PEC chloride activation (PEC/Cl^-/PMS) system converts pollutants into polymerized products, achieving 95.8% total organic carbon (TOC) removal with 84.3% polymerized product recovery, coupled with 357 µmol hydrogen evolution within 40 minutes. Mechanistically, photogenerated holes co-activate chloride ions and PMS to promote Cl₂^•- formation. Albeit often regarded as a weak mineralization-oriented reactive species, Cl₂^•- effectively initiates phenoxy radical formation for subsequent polymerization through C–O–C and C–C coupling reactions. Benefiting from polymerized product & hydrogen recovery, mild bias & low PMS dosage, and minimized greenhouse-gas emissions, the PEC/Cl^-/PMS system respectively demonstrates a value-added, energy-efficient, and low-carbon treatment approach. Moreover, its potential applicability can be supported by robust performance across varying pH and wastewater compositions, reduced effluent biotoxicity, and stable 120 h continuous-flow treatment of real saline wastewater. The developed system integrates decontamination with multi-resource recovery, advancing sustainable wastewater management.