Boosted visible-light Cr(VI) reduction via post-alkali-induced oxygen vacancies and flower-like nanostructures in TiO2/CuWO4 coatings
Solid State Communications, vol.417, 2026 (SCI-Expanded, Scopus)
- Publication Type: Article / Article
- Volume: 417
- Publication Date: 2026
- Doi Number: 10.1016/j.ssc.2026.116547
- Journal Name: Solid State Communications
- Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Chemical Abstracts Core, Chimica, Compendex, INSPEC, Academic Search Ultimate (EBSCO), Engineering Source (EBSCO)
- Keywords: Coating, Cr6+ photoreduction, Morphology development, Oxygen vacancy, Post-alkali treatment
- Ataturk University Affiliated: Yes
Abstract
In this study, a hydrothermal post-alkali treatment using NaOH as a reducing agent was applied to TiO2/CuWO4 composite coatings to enhance the photoreduction of hexavalent chromium (Cr(VI)) under visible light. This treatment simultaneously modified the surface morphology and introduced oxygen vacancies (OVs), as confirmed by XPS analysis, which revealed a decreased OL/OV ratio from 5.01 to 2.87, indicating a substantial increase in surface defect sites. Additionally, the treatment narrowed the band gap from 3.00 eV to 2.77 eV, extending light absorption into the visible region. Structural characterization revealed the formation of two new phases, Na2Ti3O7 and TiP2O7, while FESEM analysis showed the development of a needle-like flower-type nanostructure with needles averaging 96 nm in diameter, which increased surface area and promoted charge separation. The post-alkali-treated coating achieved 100% visible-light-driven Cr(VI) photoreduction within 5 h, whereas the untreated coating achieved only 43% after 6 h. Kinetic analysis revealed a reaction rate constant 2.92 times greater than that of the untreated coating. Radical scavenger experiments identified photogenerated holes (h+), superoxide anions (O2•-), and hydroxyl radicals (•OH) as the key active species. The enhanced performance is attributed to the synergistic effects of oxygen vacancies that suppress electron–hole recombination, the high-surface-area needle-like morphology that provides abundant active sites, the formation of new photocatalytic phases, and the narrowed band gap enabling improved visible-light harvesting. This work demonstrates that post-alkali treatment is a simple, cost-effective strategy for tailoring morphology and defect chemistry in photocatalytic coatings for water remediation applications.