Facile One-Step Route for the Development of in Situ Cocatalyst-Modified Ti³⁺ Self-Doped TiO₂ for Improved Visible-Light Photocatalytic Activity

Abstract

Development of visible-light-driven photocatalysts by employing a relatively simple, efficient, and cost-effective one-step process is essential for commercial applications. Herein, we report for the first time the synthesis of in situ Cu-ion modified Ti³⁺ self-doped rutile TiO₂ by such a facile one-step solution precursor plasma spray (SPPS) process using a water-soluble titanium precursor. In the SPPS process, Ti³⁺ self-doping on Ti⁴⁺ of rutile TiO₂ is found to take place because of electron transfer from the created oxygen vacancies to Ti⁴⁺-ions. In situ Cu modification of the above Ti³⁺ self-doped rutile TiO₂ by additionally introducing a Cu solution into plasma plume is also demonstrated. While the Ti³⁺ self-doping induces broad absorption in the visible-light region, the addition of Cu ion leads to even broader absorption in the visible region owing to resulting synergistic properties. The above materials were evaluated for various self-cleaning photocatalytic applications under visible-light illumination. Cu-ion modified Ti³⁺ self-doped rutile TiO₂ is noted to exhibit a remarkably enhanced visible-light activity in comparison with Ti³⁺ self-doped rutile TiO₂, with the latter itself outperforming commercial TiO₂ photocatalysts, thereby suggesting the suitability of the material for indoor applications. The broad visible-light absorption by Ti³⁺ self-doping, the holes with strong oxidation power generated in the valence band, and electrons in Ti³⁺ isolated states that are effectively separated into the high reductive sites of Cu ions upon visible-light irradiation, accounts for improved photocatalytic activity. Moreover, the synthesis process (SPPS) provides a valuable alternative to orthodox multistep processes for the preparation of such visible-light-driven photocatalysts.