Preparation of TiO2-based photocatalysts and their photocatalytic degradation properties for methylene blue, rhodamine B and methyl orange

Different kinds of nanocrystalline TiO2-based photocatalysts, including pristine TiO2, oxidized multi-walled carbon nanotube/TiO2 (ox-MWCNT/TiO2) composite and Eu3+-doped ox-MWCNT/TiO2 (Eu3+/ox-MWCNT/TiO2) composite, were synthesized by using tetrabutyl titanate as precursor by a sol-gel method. The colloidal solutions were heat treated at 450 degrees C for 2 h to obtain the anatase TiO2 nanomaterials. The photocatalysts were characterized by X-ray diffraction, high-resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy. The photocatalytic activities of the TiO2-based catalysts for the degradation of methylene blue (MB), rhodamine B (RhB) and methyl orange (MO) in aqueous solutions were investigated. To compare the photocatalytic activity of the TiO2-based catalysts, the degradation rates for the abovementioned dyes under 365 nm ultraviolet (UV) light irradiation were calculated. And the 1% Eu3+/ox-MWCNT/TiO2 composite showed higher photodegradation rate constant (K' = 1.757 h(-1)) than those of pristine TiO2 (K' = 1.028 h(-1)), ox-MWCNT/ TiO2 (K' = 1.458 h(-1)) and 4% Eu3+/ox-MWCNT/TiO2 composite (K' = 1.295 h(-1)) toward MB. Meanwhile, the 1% Eu3+/ox-MWCNT/TiO2 composite possessed high photodegradation percentage of 95.77%, 97.21% and 90.72% toward RhB, MB and MO, respectively, which were higher than those of other three TiO2-based photocatalysts. It is proposed that the higher photocatalytic activity of ox-MWCNT/Eu3+/ TiO2 composite might be due to the decreased band gap, the plentiful introduced hydroxyl groups and its high specific surface area.