Sm-doped TiO2 Research Articles

Study of Multi-Variable Grey Model on Kinetics of Methyl Orange Photodegradation Reaction by Sm-Doped TiO<sub>2</sub>

Sm-doped TiO2 photocatalysts were prepared by doping samarium ions into TiO2 nanoparticles in a sol-gel process. The samples were characterized using transmission electron microscopy (TEM) and ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS). Their photocatalytic activities were evaluated by photodegradation of methyl orange (MO) in water under UV or stimulant solar light irradiation. The kinetics of MO photodegradation was further studied using multi-variable grey model. The experimental results indicated that the Sm3+ doping reduced the crystallite size, and appropriate doping induced red-shift of the absorption profile of TiO2. It was also found that the red-shift and absorptivity decreased in the range of 350-500 nm with the increase of Sm3+ doping and the optimal doping concentration was 0.05 mol%. Furthermore, the effects of Sm3+ doping concentration, the calcinating temperature of the samples, and the illuminating light on the photocatalytic activity of TiO2 were well simulated using multi-variable grey model.

Spectroscopic and crystal field study of Sm3+ in different phases of TiO2

A systematic study of the photoluminescence spectra of samarium-doped crystalline TiO2 was conducted within the temperature range 10–300 K in order to reveal the energy levels of the trivalent impurity ion in different phases of titania. The sol–gel route was used to prepare Sm-doped TiO2 powders. The nanocrystalline anatase phase was obtained by annealing up to 800 °C, whereas the rutile phase was developed by annealing above 1000 °C. Crystal field calculations of Sm3+ energy levels in the two phases of TiO2 (anatase and rutile) were performed for the first time. The obtained set of energy levels assuming positioning of the Sm3+ ions in regular TiO2 lattice sites was consistent with the experimental results. The effect of the different phases of titania on the impurity is discussed.

Photocatalytic Degradation of Methyl Orange in Water by Samarium-Doped TiO2

A series of Sm-doped TiO2 nanoparticles were prepared by the sol-gel method and characterized with X-ray diffraction (XRD), transmission electron microscope (TEM), and ultraviolet-visible diffuse reflectance spectra (DRS). Their photacatalytic activities were studied by photodegradation methyl orange in water under UV and simulant solar light irradiation, respectively. The results showed that Sm doping led to the crystal expansion and matrices distortion. Sm doping restrained a crystal size increase, which was beneficial for transportation and exchanges of organic and productions; furthermore, redounds to photogenerated carriers shifting to the surface of photocatalyst and preventing the recombination of the carriers, and then improving the photocatalytic activity. Appropriate concentration Sm doping induced the absorption profile red-shift of TiO2, which made Sm-doped TiO2 possess high catalyst activity under simulant solar light irradiation whose major emission was the focus on the visible light region. Sm doping was an effective means to improve the photocatalystic activity of TiO2 for degradation methyl orange in water whether under UV or solar light irradiation.

Emission of Rare Earth Ions Incorporated into Metal Oxide Thin Films and Fibres

ABSTRACTPhotoluminescence (PL) of undoped and Sm-doped TiO2, ZrO2and HfO2thin films and fibers was investigated at temperatures ranging from 6 to 300 K. The thin films were grown by the atomic layer deposition (ALD) technique and doped by using the ion implantation method. The fibers were prepared by using the sol-gel method whereas anin-situdoping was used to obtain the required concentration of Sm3+ions in the films. In undoped as well as doped materials, PL was efficiently excited via band-to-band transitions. The emission of undoped materials was attributed to the radiative recombination of self-trapped excitons (STE). In doped materials, intense emission of Sm3+was recorded. It is proposed, that there exists a concurrence between the radiative recombination of bound excitonic states and the energy transfer to Sm3+ions, particularly at lower temperatures.

Structure and Crystal Field of Sm-doped TiO2

The purpose of this work is to get some information on the correlation between the change in crystal structure of atomic long-range order and that in crystal field of short-range order during mechanochemical processes. The x-ray diffraction patterns and the fine structures of fluorescence spectra from doped Sm ions were observed on several TiO2 crystals which were prepared by various procedures. TiO2(Sm) of anatase type changed to that of rutile type by grinding. The fine structure of spectrum changed from anatase to rutile almost in parallel to the corresponding change in x-ray pattern. It shows that no essential difference exists between the long-range reordering and the short-range reordering during the mechanochemical phase change. The broadening of fine structures of spectra, however, was observed in neither well ground TiO2(Sm) nor amorphous TiO2 fired at temperatures lower than the crystallization temperature. Such amorphous phase of TiO2 is considered to have a definite crystal field due to the ionic surrounding having the short-range order. This seems quite different from usual inorganic glasses, which give fluorescence spectra with broad structures from doped Sm ions.