Kinetics and mechanism of thymine degradation by TiO_2 photocatalysis

The advanced oxidation processes were examined toward the degradation of thymine （CsH6N202）, a type of nucleic acid from the pyrimidine family. As observed, the photodegradation of thymine over TiO2 photocatalyst was rapid and significant in aqueous solution under UV irradiation. Different parameters were studied, including the adsorption of thymine onto TiO2 photocatalyst, the kinetics of degradation, and the effect of pH on the photocatalytic properties of thymine degradation. Additionally, the mineralization of the products obtained upon thymine photodegradation was studied. The disappearance and mineralization rates of thymine during the photocatalytic process were also compared and discussed. The mineralization of nitrogen was also investigated, and the identification of the intermediate products was established. Finally, electronic density calculations were used to propose possible chemical pathways for the photodegradation of thymine over TiO2 photocatalyst under UV irradiation.

The Synthesis, Characterization, Photocatalytic Evaluation and Deactivation Behavior of Sheet-like Nano Titania

The sheet-like nano TiO2 particles were prepared by using hydrothermal method, and were characterized by X-ray diffraction（XRD）, infrared spectroscopy（IR）, and transmission electron microscopy （TEM）. It is found that the nanoparticle sizes and crystallinity increase with the increase of hydrothermal temperature from 150 ℃ to 160 ℃, and then to 180 ℃. With the increase of particle sizes, the absorption capacities and photocatalytic abilities of as-prepared TiO2 particles for crystal violet become better and better. The nano TiO2 with big particles is more stable than that with small particles, although its initial photocatalytic activity is relatively lower compared with that of the small particle samples.

Black TiO_2(B)/anatase bicrystalline TiO_(2-x) nanofibers with enhanced photocatalytic performance

Black TiO2（B）/anatase bicrystalline TiO2-x nanofibers were synthesized from a porous titanate derivative by calcination in H2, and were characterized using field-emission scanning electron microscopy, Raman spectroscopy, N2 adsorption-desorption analysis, X-ray photoelectron spectroscopy, thermogravimetric analysis, ultraviolet-visible diffuse reflection spectroscopy and photoluminescence measurements. Characterization results showed that no Ti3＋ was present on the surface of black bicrystalline TiO2-x and oxygen vacancies were distributed in the bulk of both TiO2（B） and anatase phases. The O/Ti atom stoichiometric ratio of black bicrystalline TiO2-x was estimated to be 1.97 from the difference of mass loss between black bicrystalline TiO2-x and white bicrystalline TiO2 without oxygen vacancies. The photocatalytic activity of black bicrystalline TiO2-x was 4.2 times higher than that of white bicrystalline TiO2 and 10.5 times higher than that of anatase TiOz. The high photocatalytic activity of black bicrystalline TiO2-x was attributed to its effective separation of electrons and holes, which may be related to the effects of both bicrystalline structure and oxygen vacancies. Black bicrystalline TiO2-x also exhibited good photocatalytic activity after recycling ten times. The black bicrystalline TiO2-x nanofibers show potential for use in environmental and energy applications.

Preparation of erbium ion-doped TiO2 films and the study of their photocatalytic activity under simulated solar light

A series of erbium ion-doped TiO2（Er^3＋-TiO2） films were prepared by a sol-gel dip/spin coating method, and the effect of the dosage of erbium ion（0-2.0 mol%）, the films coating layers（1-5 layers）, and calcination temperature（400-700 ℃） on the film structure and photocatalytic activity were investigated in detail. The films were characterized by means of X-ray diffraction（XRD）, scanning electron microscopy（SEM）, thermal analysis（TG-DTG） and UV-Vis diffusive reflectance spectra（DRS）. The results showed that the films were composed of anatase, and no other TiO2 phases（rutile and brookite）. With the increase of the erbium ion dosage, the crystal size decreased. Erbium ion doping could enhance the thermal stability of TiO2 and inhibit the increase of the crystallite size. Meanwhile doping of erbium ions gave rise to three typical absorption peaks within the range of visible light（400-700 nm）, locating at 490, 523, and 654 nm, attributed to the transition of 4 f electrons. The higher calcination temperature led to higher crystallinity and bigger crystal grains. The photocatalytic performance of the films was evaluated by degradation of methyl orange solution under simulated solar light. The highest quality film we prepared was with 4 layers, 1.0 mol% dosage of erbium ion, and the calcination temperature of 500 ℃. With this film,the degradation percentage of 7.8 mg/L methyl orange solution was up to 53.3% under simulated solar light after 6 h photoreaction.