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 m(2)/g) than that (S-BET=1.10 m(2)/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.