Preparation Of Mesoporous TiO₂ And TiO₂-SiO₂ For Photocatalytic Degradation Of Black Liquor

Mesoporous material with pore size between 2-50 nm, high specific surface area, large pore volume and narrow pore size distribution, have considerable potential for wide use in photocatalysis,ion exchange,molecular sieves,adorption and separation applications. Heterogeneous photocatalysis by semiconductors has unique advantages in water pollution control,especially in the treatment of waste water containing poisonous organic compounds which are hard to be destroyed. Titanium dioxide (TiO₂), which can decompose most organic pollutants into inorganic substances under UV irradiation, has become a hot research area because of its attractive application in the treatment of environmental pollutants. In this research, we prepared mesoporous TiO₂ and mesoporous TiO₂-SiO₂ complex materials with more high specific surface area, and the results show that the mesoporous TiO₂ has the better properties than the nano TiO₂ and the complex materials have more superior properties than the pure mesoporous TiO₂ or SiO₂, then they have better photocatalytic properties in the degradation of organic wastewater.Mesoporous TiO₂ and TiO₂-SiO₂ photocatalysts (with different molar ratio of Ti/Si) has been successfully synthesized by using nonionic triblock copolymer (P123) as template agent via sol-gel reactions of tetrabutyl titanate (TBOT) and tetraetethyl orthosilicate (TEOS), then the prepared material(safter calcined at 400℃for 4h) were characterized by Low-angle X-ray diffraction (SAXRD), X-ray diffraction (XRD), Transmission electron microscopy (TEM), Scanning electron microscope(SEM), Fourier transform infrared spectrophotometer (FT-IR), N2 adsorption-desorption isotherm, Ultraviolet-visible (UV-Vis), and so on. The SAXRD shows the samples possess a short - range ordered mesoporous structure but lack of a long - range ordered structure; the XRD shows the samples were all anatase and the silica or silicate in the prepared samples exists as amorphous state ; TEM shows that the synthesized materials have lots of channels and possess a short-range ordered mesoporous structure; FT-IR analysis shows the formation of the band for Ti-O-Si vibration between TiO₂ and SiO₂ matrix; BET analysis shows the synthesized materials possess the mesoporous structure(BET surface area=105.41m2g-1, total pore volume 0.2039 cm3g-1, average pore diameter 7.74 nm for TiO₂), also synthesized materials's the BET surface area increases and the pore diameter decreases with the increase of the silica content. From UV-Vis analysis, the absorption spectra of TiO₂-SiO₂ shifted toward visible light region and the absorbance dramatically increased with the increase of silica content.The presence of mesoporous structure and a little silica in TiO₂ crystalling were found to promote the photocatalytic activity of TiO₂ in degradation p-chlorophenol,p-nitrophenol and black liquor from pulping and papermaking. The results showed the mesoporous TiO₂ had the better photocatalytic properties than nano TiO₂ and the mesoporous TiO₂ with the little doption of silica had the better photocatalytic properties than mesoporous TiO₂. The influencing factors on the degradation of black liquor such as the kinds of catalyst, light application time, catalyst dosage, initial pH value, aerating mode etc. in the photocatalysis system were investigated. The presence of mesoporous structure and silica in TiO₂ crystal were found to improve the removement of efficiency of chemical oxygen demand (COD_Cr) greatly. Its COD_Cr was decreased from 450 mg/L to 46.14 mg/L and 23.07 mg/L, respectively. The removing rate of COD_Cr of black liquor from pulp was up to 89.7 % and 94.9 % and the removing rate of chroma was 92.6 % and 97.6 %. The best parameters during the photocatalysis processes were determined also, its best conditions were the catalyst (Ti/Si=100:1) dosage was at 1.5g/L, the initial pH = 6 with continuous aerating and reaction time 12h.