Tailoring surface defects in Plasma Electrolytic Oxidation (PEO) treated 2-D black TiO2: Post-treatment role, and intensification by peroxymonosulfate activation in visible light-driven photocatalysis

Herein, we have developed a visible light-responsive black TiO2 photocatalytic coating with controlled formation of oxygen vacancies (OV) and Ti3+ species, crucial for enhancing photocatalytic reactions. The rational control of these semiconductor defects was achieved through plasma electrolytic oxidation (PEO), followed by NaOH post-treatment. The coating's effectiveness was evaluated by tetracycline (TC) degradation. The surface defects function as traps, reducing electron/hole recombination and forming mid-gap/localized-donor states, narrowing the band gap. Rigorous material characterization confirmed unaffected morphology and PEO coating phases, while increasing the density of OVs and Ti3+ species. As a result, TC photo-degradation was ∼3.5 times higher compared to plain PEO coatings. The material demonstrated exceptional stability and efficiency, while it was successfully intensified via peroxymonosulfate (PMS) activation, leading to high synergies (2.10). Scavenger tests revealed the existence of both radical/non-radical pathways, indicating the prevailing photocatalytic mechanism and the key differences achieved through this novel process.