The Doping Modification Of Mesoporous TiO₂ And The Investigation Of Its Photocatalytic Activity

Mesoporous material with high specific area, large pore volume and narrow pore size distribution, have considerable potential for wide use in photocatalysis, ion exchange, molecular sieves, adsorption and separation applications. As a photocatalyst, it is not only nontoxic, inexpensive, photocatalytic, stable, but also has strong oxidation ability. However, TiO₂ is active only under UV light and this limits the commercial viability of these processes. Large efforts have been made to dope titania with several metals as well as non-metals so as to make it photocatalytically active in visible light. At the same time, it is a challenge to synthesize anatase mesoporous TiO₂ with high photocatalytic activity. The photocatalytic activity and efficiency of TiO₂ can be enhanced obviously and it also extend the absorbance wavelength to visible light, meanwhile, the degradation of black liquid from pulping and papermaking and usage of sunlight has a promising future by doping some transitional metal ions and non-mental ions to titania.In the present work, N doped and N/Yb co-doped TiO₂ were prepared by a sol-gel process. The properties of the prepared TiO₂ materials were characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM), energy-disperse X-ray spectrometer (EDX), N2 adsorption-desorption isotherms and UV-Vis diffuse reflectance spectroscopy (UV–Vis DRS). The XRD shows that all the samples are all anatase; TEM shows that the synthesized materials have lots of channels and possess a mesoporous structure; N2 adsorption-desorption isotherms show that the synthesized samples have mesoporous structures, and with the increment of doping, the pore size increases first and reduces then, and the BET reduces gradually. The EDX shows that N substitute O in TiO₂. From UV-Vis diffuse reflectance spectroscopy analysis, a considerable red shift in the absorbing band edge is observed and the red shift become more remarkable with the increased of N content, it enhances the usage of sunlight for modified TiO₂.The photocatalytic activities of N doped mesoporous TiO₂ prepared here are measured by photodecomposition of methyl orange (MO) in UV light as well as visible light, which shows excellent photocatalytic activity in both UV and visible light. Under UV light in three hours, the degradation rate of MO for 10% N/TiO₂ was more than 99.3%, and under visible light in six hours, the mesoporous 10% N/TiO₂ shows a good photocatalytic activity in the degradation of MO and its degradation rate was about 74.5%. Both of them are better than pure TiO₂.The photocatalytic activities of N/Yb co-doped mesoporous TiO₂ prepared here are measured by photodecomposition of black liquid from pulping and papermaking in ultra-violet light in aqueous solution. The results show that the photocatalytic activity of 3%N1.2%Yb co-doped TiO₂ is much better than the pure mesoporous TiO₂ in degradation of black liquid from pulping and papermaking, when the catalyst 3%N1.2%Yb co-doped usage is 1.0 g/L, the initial pH is 5; The photodegradation reaction was carried out in a cylindrical quartz reactor, which had water circulation facility at the outer wall of the reactor.; the chroma of the black liquid is completely removed in 4 h and after 12 h irradiation CODCr removal rate is about 62.6%.