Synthesis and photocatalytic performance of hydrothermally TiO₂-coated-Sr₄Al₁₄O₂₅:Eu²⁺, Dy³⁺ phosphor beads

The TiO₂ nanoparticles were supported on as-fabricated Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺ long-lasting phosphor beads by hydrothermal coating for easy applications of photocatalyst such as an air purifier. Zeolite and sodium silicate were utilized as binders for the agglomeration of Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺ phosphor particles into 3 mm-beads. The hydrothermal coating of TiO₂ on the phosphor beads at pH 2–3 enhanced the growth of TiO₂ particles as nanocoral morphology, resulting in higher specific surface area (S_BET=3.04 m²/g) than that (S_BET=1.10 m²/g) of TiO₂ coated beads at low pH below 1.0. The photocatalytic performance of TiO₂-coated phosphor beads was analyzed through the photobleach of methylene blue dye solution and decomposition of toluene gas. Cu-impregnation and zeolite addition to phosphor beads improved the photocatalytic reactivity of TiO₂-coated phosphor beads. The photocatalyst of Cu-impregnated Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺/TiO₂ with zeolite addition showed higher photocatalytic efficiency than those of other samples: Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺/TiO₂ with zeolite and Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺/TiO₂ without zeolite by decomposing toluene gas completely within 75 min. A cyclic light-on and off procedure was used to analyze the photocatalytic reaction of TiO₂-coated phosphor beads under dark-state. The continous photocatalytic reaction occured in the darkness of light-off cycle is attributed to the persistent supply of light photons from Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺ phophor beads.