Photo-driven self-regeneration in Ti-doped bismuth oxide: A sustainable catalytic platform for chloride removal from acidic industrial wastewater

The treatment of high-chloride acidic industrial wastewater, such as that from wet flue gas desulfurization (WFGD) and metallurgical effluents, presents a significant environmental engineering challenge due to the high corrosivity of chloride and its interference with downstream processes. Bismuth oxide (Bi₂O₃)-based precipitation shows promise; however, it is hindered by severe surface passivation caused by BiOCl, which leads to self-limiting reactivity. In this study, we engineered a titanium-doped bismuth oxide (Bi₁₂TiO₂₀) photocatalyst that addresses this limitation through a synergistic mechanism of "adsorption–precipitation–photoregeneration." Under optimal dark conditions (pH = 0.1, [Cl⁻]₀ = 5000 mg/L, for 2 h), Bi₁₂TiO₂₀ achieved a chloride removal efficiency of 96.4 %, significantly exceeding that of pure Bi₂O₃, which was 64.4 %. The introduction of simulated solar irradiation at pH = 1.0 further enhanced the removal efficiency from 54.0 % to 67.2 %, demonstrating effective photo-enhancement. Comprehensive characterization techniques, including X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS), and ultraviolet-visible-near-infrared (UV–Vis–NIR) spectroscopy, combined with kinetic modeling and electron localization function (ELF) calculations, revealed that Ti⁴⁺ serves as both a structural promoter—weakening Bi–O bonds to facilitate Bi³ ⁺ release—and a surface Lewis acid site that activates Cl⁻ adsorption. Importantly, photogenerated holes (h⁺) decompose the BiOCl passivation layer via the reaction BiOCl + 2 h⁺ → Bi³ ⁺ + ½O₂ + Cl₂↑, enabling in-situ regeneration of active interfaces and establishing a sustainable catalytic cycle. This work presents an efficient material for the initial bulk removal of chlorides, while also establishing a novel design paradigm for self-regenerative, energy-efficient water treatment technologies.