Young In Choi

Recyclable magnetic CoFe2O4/BiOX (X = Cl, Br and I) microflowers for photocatalytic treatment of water contaminated with methyl orange, rhodamine B, methylene blue, and a mixed dye

The recycling of photocatalysts and improving their activities by hybridizing two materials are important. Herein, nanosize ferromagnetic (Ms = 62.3 emu g−1) CoFe2O4 nanoparticles (NPs) were embedded into nanosize-assembled BiOX (X = Cl, Br and I) microflowers and examined by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, UV-visible absorption spectroscopy, Fourier-transform infrared spectroscopy, and photoluminescence spectroscopy. The adsorption and photocatalytic performance of CoFe2O4/BiOX for methyl orange (MO), rhodamine B (RhB), methylene blue (MB), and a mixed dye (MO + RhB + MB) were examined under UV and visible light irradiation. The adsorption capacity of CoFe2O4/BiOI for RhB was 160 mg gcat−1, which is significantly larger than the <5 mg gcat−1 obtained for CoFe2O4/BiOCl and CoFe2O4/BiOBr. The photocatalytic activity was observed in the order of CoFe2O4/BiOBr < CoFe2O4/BiOCl < CoFe2O4/BiOI for RhB. Their adsorption and photocatalytic performances were also investigated with pure MO, pure MB and a mixed dye. MO in the mixed dye was the most easily removed by the catalysts under light exposure. Based on the scavenger tests, h+ and ˙O2− play major and minor roles in the photodegradation of the dyes, respectively. Although the ˙OH radical was formed for CoFe2O4/BiOBr and CoFe2O4/BiOCl, it has a much smaller role than the other active species.

Photoluminescence profiles and fast/slow annealing effects of Eu(III)/Tb(III)-codoped silica phosphor materials.

A silica (SiO2) nanoparticle matrix was codoped with luminescent Eu(III) and Tb(III) ions using a modified Stöber method. The effects of fast and slow thermal annealing on photoluminescence profile imaging were examined. Slow annealing treatment suppressed more quenching sites than fast thermal annealing to further increase the photoluminescence signals. The photoluminescence signals observed between 450 and 720 nm were assigned to the (5)D(0)  → (7)F(J) (J = 0,1,2,3,4) of Eu(III) and the (5)D(4)  → (7)F(J) (J = 6,5,4,3) transitions of Tb(III). Photoluminescence was largely sensitized by indirect excitation and was much stronger than that generated by direct excitation. The Eu(III) and Tb(III) ions were doped at lower symmetry sites in the silica matrix.