| Titanium dioxide(TiO2) as a white pigment is primarily used in the manufacture of paint, and of surface coatings and as a filler in rubber, cosmetics and plastics, due to its brightness, high refractive index, nonotaoxic and resistance to discoloration. As one of the most important metal oxide, TiO2, which exhibits excellent photoactivities such as UV absorbance, photocatalysis, and acid catalysis properties, has received considerable attention. In this Article, the following four typical aspects had been studied:(1) The UV shielding performance of TiO2 pigments in aqueous medium was investigated using UV-Vis spectrophotometer and H2O2 photodecomposition, respectively. A series of pigments are can directly and effectively showed different UV shielding performances. This method is simple, fast and good reproducibility, and it would have significant implications for industry and actual usage.(2) Dimethyl toluene-2,4-dicarbamate(2,4-TDC) was selected as a model molecule to investigate the UV-shielding properties and photo-chemical behavior of TiO2 pigments. Based on the degradation kinetics constant of 2,4-TDC, the UV-shielding properties of different TiO2 pigments can be directly evaluated within 4 h. Moreover, it was found that the reactive species such as ·OH and holes still played a minor role on the photodegradation of 2,4-TDC in presence of TiO2 pigments. Commercial TiO2 pigments were used and characterized by UV–Vis spectroscopy, PL spectroscopy and FT-IR spectroscopy. Photodegradation experiments suggested that rutile TiO2 pigment retard the photodegradation of 2,4-TDC, while anatase TiO2 pigment accelerated the photodegradation of 2,4-TDC. With the help of the degradation intermediates during the photodegradation process and calculated data, such as point charges and bond length, the preliminary photodegradation mechanism of 2,4-TDC was also briefly elucidated, including the addition of hydroxyl radicals and direct the cleavage of the carbamate side chain. The photodegradation of 2,4-TDC was used to evaluate the photoreactivity of TiO2 pigments, which is proved as an efficient approach and has a potential application in industry.(3) Photocatalytic dedgradation kinetics of methyl orange(MO) as a model textile dye was investigated by commercial TiO2 pigments in the forms of anatase and rutile. The effects of various parameters, such as conceration of MO, catalyst amount, pH value, and some cations such as Fe2+, Cu2+, Mg2+, Mn2+, Zn2+, Na+, on the rate of degradation was studied. In addition, the roles of reactive species were also considered. The degradation of MO follows pseudo first-order kinetics by using Langmuir-Hinshelwood model. The presence of the Fe2+, Cu2+, Mg2+, Mn2+, Zn2+ ions leads to the reduction of the effectiveness of the photodegradation. However, the presence of Na+ increases the rate of the degradation. The results show that active species such as holes, hydroxylradicals(·OH), and superoxide radicals(O2?-) are involved in the photodegradation process of methyl orange.(4) Isomerization of styrene oxide as a model reaction was employed to investigate the surface acid properties of TiO2 pigment. The surface acid amount of TiO2 pigment was determined by pyridine adsorption using cyclohexane as a solvent. In addition, the effect of catalyst amount and solvent on isomerization of tyrene oxide was studied. At last, the possible mechanism for the formation of phenylacetaldehyde was proposed. The results show that rutile phase of TiO2 pigment was an efficient heterogeneous catalyst for the isomerization of styrene oxide into phenylacetaldehyde. At 80℃, the conversion of styrene oxide reaches 34.4% using cyclohexane as a solvent. The surface hydroxyl groups and Ti4+ site of TiO2 pigment as a mild Lewis acid catalyzes the isomerization reaction. |
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