Defect-engineered ZnO/BTO photoanodes for enhanced solar-driven photoelectrochemical desalination of high-salinity coal chemical wastewater

An efficient and stable photoanode is crucial for solar-driven photoelectrochemical desalination (SD-PED), especially for complex industrial brines. Here, a ZnO/Bi₄Ti₃O₁₂ (BTO) heterojunction photoanode with simultaneously introduced Bi and O vacancies (Biv/Ov) was fabricated through a sol-gel route followed by calcination. Using real high-salinity wastewater from the coal-chemical industry as the feed, this optimized photoanode delivered a photocurrent density of 4.65 mA cm⁻², and a salt removal rate of 148.52 µg (cm² min)⁻¹ under simulated solar illumination at zero external bias, representing a 65.94% improvement over pristine BTO. The SD-PED device effectively reduced the total salinity from 6912 ppm to 966 ppm, achieving >90% removal of Na⁺/Cl⁻ and >87.6% removal of co-existing ions, while maintaining stable operation over five cycles. The enhanced performance is attributed to the synergistic effect of the porous layered structure and the vacancy-rich heterointerface, which together enlarge the electrode/electrolyte active area and establish a built-in electric field that promotes charge separation and transport. This work provides a defect-engineering strategy for developing robust photoanodes for low-bias solar desalination of high-salinity industrial wastewater.