Enhanced Photocatalytic Decomposition for Toluene Gas with the Heterojunction Photocatalyst of Zn-TiO₂/Sr₄Al₁₄O₂₅:Eu²⁺, Dy³⁺

In this study TiO₂ nanoparticles were coated on the Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺ long-lasting phosphor by a hydrothermal reaction processing. In addition, Zn was impregnated to improve the photocatalytic performance of the TiO₂/Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺ phosphor composite. For the hydrothermal coating of TiO₂ on the prepared phosphor beads, the titanium precursor solution was prepared by mixing a titanium isopropoxide (TTIP), ethanol, deionized water, and HNO₃ at an appropriate volumetric ratio. Zn was impregnated by mixing a Zn salt of Zn(NO₃)₂·6H₂O in the prepared Ti-sol and coated onto the phosphor supporter using a hydrothermal reaction. The material characteristics of Zn-TiO₂/Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺ composites were analyzed using a field-emission scanning electron microscopy(FE-SEM), X-ray photoelectron spectroscopy(XPS), energy dispersive X-ray spectroscopy(EDS), and photoluminescence spectroscopy. The photocatalytic response was measured as the decomposition of toluene gas under UV or visible light irradiation. The surface morphology of TiO₂ coating layers changed from granular-shaped clusters to be grown as a bundle of nano-plates with increase of reaction time. The effects of Zn concentration and hydrothermal reaction time on the photocatalytic decomposition for toluene gas were systematically investigated. The optimum photocatalytic performance occurred at the concentration of 0.1 M Zn addition. The highest photocatalytic efficiency for 0.1 M Zn-impregnated TiO₂/Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺ composite occurred at the reaction time of 1 h by decomposing 30 ppm of toluene by over 95% under UV light in 120 min.