Plasma electrolytic oxidation-derived WO3 and WO3@LDH hybrid coatings as immobilized photocatalysts for solar−driven water treatment

This study presents the development of immobilized photocatalytic coatings for the degradation of diclofenac (DCF), a persistent pharmaceutical pollutant, under solar light irradiation. Two-dimensional tungsten oxide (2D-WO3) nanoflakes were synthesized via hydrothermal treatment and incorporated into plasma electrolytic oxidation (PEO) coatings, together with Zn-single bondAl layered double hydroxide intercalated with 2-mercaptobenzothiazole (Znsingle bondAl LDH-MBT). This study demonstrates, for the first time, the synergistic effect of incorporating 2D-WO3 nanoflakes and Znsingle bondAl LDH into PEO coatings on Al, enhancing photocatalytic performance compared to previous WO3-containing systems. To the best of our knowledge, this is the first report on the use of WO3 nanoparticles combined with Znsingle bondAl LDH, an established PEO coating morphology modifier, within the PEO process for water remediation applications. Coatings were fabricated using silicate-, aluminate-, and tungstate-based electrolytes. Structural and morphological analyses confirmed the successful incorporation of WO3 particles and LDH-derived phases. Diffuse reflectance spectroscopy revealed a WO3 band gap of approximately 2.40 eV, suitable for solar light activation. Coatings with moderate WO3 loading (10 g/L) exhibited superior photocatalytic performance compared to those with higher loading (15 g/L), attributed to the formation of inactive metallic tungsten (W0) at increased WO3 concentrations. Photocatalytic degradation of DCF under solar light reached up to 92 % for WO3 powder and 92 %, 66 %, and 87 % for WO3-doped coatings in silicate-, aluminate-, and tungstate-based electrolytes, respectively. Incorporation of Znsingle bondAl LDH remained high activity and increased in the case of aluminum electrolyte from 66 to 87 %. The production of transformation products during the photocatalytic processes confirmed multi-step degradation. These results highlight the synergistic role of WO3 and LDH in PEO coatings, demonstrating their potential for scalable, solar-driven water treatment.