Preparation, Characterization And Photocatalytic Properties Of Mesoporous Codoped-Titania Nanocrystals Through Soft Chemical Method

There are many disadvantages of traditional titania photocatalysts, such as low utilization efficiency of sunlight, uncontrollable granule morphology, low thermal stability and low quantum efficiency. Focused on these problems, new mesoporous titania nanocrystals of N-doped, Si-doped and Y, N-codoped were successfully prepared by sono-assisted hydrothermal in this paper. The prominent features of synthesized samples are high efficiency and controllability. They were characterized by XRD, TEM, XPS, TOC, TG-DSC, FTIR and N2 adsorption-desorption. With the refractory azo dye solution of X-3B as target pollutants, photocatalytic activity of synthesized photocatalysts was evaluated under UV-light and visible-light. The results of cystal phase, granule morphology, particle size and surface states properties were correlated with their photocatalytic activities. The main factors that affected photocatalytic degradation activity were obtained. The contents of this paper were divided into three following parts.In the first part, N-doped mesoporous titania nanocrystals with controllable morphology and pore size were synthesized by sonochemical process with tetrabutyl titanate as Ti sorce and dodecyldiamine (DADD) as structure directing agent as well as nitrogen dopant. The charge of—NH2 on the ends of DADD could be changed by the fluctuation of pH. When the initial reaction pH was 9, the visible-light photocatalytic activity was the best, demonstrating that the removal rate reached 90% after irradiation for 30 min. Under the optimum hydrothermal temperature of 150℃, the synthesized titania possessed large BET surface area and regular pore structure with uniform distribution. The results of XPS analysis provided that nitrogen was highly dispersed into the anatase titania crystal lattice, which led to the narrower band gap. The results provided a new way of preparing N-doped titania photocatalyst with visible-light response.In the second part, to solve the problems of low thermal stability and activity, based on our group's preliminary work, Si-doped mesoporous titania with high crystallinity were synthesized by the hydrothermal process with tetraethyl orthosilicate as Si source. The products not only have excellent texture properties but also good thermal and crystal stability. The results showed that ambient amount of Si doped could suppress both the crystal transformation and grain growth. The crystal form, particle size and surface states properties were well controlled by adjusting Si content. In this experiment, the products with the amount of doped silica 5% and calcined under 450℃exhibited the highest photocatalytic activity for the degradation of X-3B. The removal rate reached 80% compared to pure titania after irradiation for 1 h under UV light and the mineralization reached 71.9% after 4 h. The sample with 5% mole ratio calcined under 800℃still maintained relatively high photocatalytic activity, which mainly attributed to perfect anatase crystal structure, large specific surface area, pore volume and strong absorption to UV light.In the third part, titania codoped with cation-anion has become the new reseach direction. Based on the preparation of N-doped titania by the hydrothermal process with DADD assisted, Y and N-codoped titania were successfully synthesized under soft chemical conditions of low temperature and short time (150℃,8h). The calcinations process at high temperature was avoided effectively. The study showed that the particle size could be effectively adjusted by changing the amount of yttrium doped. The specific surface area and pore volume of samples with codoped with Y, N obviously better than that of N-doped and pure titania. The products with the mole ratio 2.0% exhibited the best performance with large specific surface area of 313.5 m2/g and pore volume of 0.34 mL/g. The removal rate reached 90% after irradiation for 15 min under UV light and the degradation for calcined products could be completed after 45 min under visible light. The experimental results provided simple and effective theoretic evidence for exploring new codoped process and high-efficient use of sunlight with broad-spectrum.