| Nano TiO2 hydrosol is a photocatalytic product with anatase TiO2. It can simple to be used in degradation of organic pollutants in indoor air,and it was convenient transportation and preservation. However, it also has some shortcomings,including preparation process time-consuming long, inefficient, and product performance non-ideal and so on. These shortcomings have affected the application and promotion of nano TiO2 hydrosol. Considering the above problems, a new microwave-assisted preparation process of nano TiO2 hydrosol was established in this study. At the same time, in order to improve the photocatalytic ability and light response ability of nano TiO2 hydrosol, a nano Fe-Ce-TiO2 hydrosol, which can be applied to degradate indoor air pollution, was synthesized by microwave-assised preparation process.Nano TiO2 hydrosol was successfully obtained by microwave-assisted preparation process, which was under the continuous emission microwave irradiation instead of the traditional water bath heating. The optimal conditions found are as follows: the nano TiO2 hydrosol with transparent, uniform, and stable properties formed by peptized under microwave irradiation at 80℃for 40 min when n(H+)/n(Ti) = 1:1. Under these conditions, the nano TiO2 in hydrosol was anatase. The average particle size was 9.7nm and the distribution range was 6.2~15.6nm. The zeta potential was 50.6mV. It was found that the color removal of reactive red X-3B could attaind to 83.6% and TOC removal was 61.3% when the intensity of UV irradiation was 11μW/cm2 for 2h. Comparing the microwave-assisted preparation prcess and conventional water bath heating process, the nano TiO2 hydrosol prepared by microwave-assisted peptized has smaller average particles size, more narrow distribution of particles size, and higher zeta potential. These properties illustrate it was more stable.Based on the established microwave-assisted process, the research of codoping with Fe and Ce of nano TiO2 hydrosol was carried out.At the same time, the photocatalytic activity of nano TiO2 hydrosol prepared by two processed was evaluated respectively. The results showed that the nano-TiO2 hydrosol prepared by microwave-assisted process has higher photocatalytic activity. The results show that best codoping molar ratio was n (Fe): n (Ce): n (TiO2) = 0.05%: 0.1%: 1. The nano Fe-Ce-TiO2 hydrosol was characterized by XRD, DLS, TEM, XPS, DRS and SPS, and the codoping process and the modification mechanisms were discussed. Lattice parameters and lattice distortion calculationed from XRD indicated that the codoping process was like this: Fe3+ ion radius is smaller than Ti4+, it could enter into the TiO2 lattice smoothly, replacing Ti4+. This substitution process would lead to TiO2 lattice distortion that could provide opportunities to Ce3+ doped into the TiO2 lattice, so Fe and Ce codoping could be achieved. Summary, Fe3+ doped TiO2 not only impacted nano TiO2 lattice structure and performance, it also assisted Ce3+ doping. DRS, SPS and photocatalytic experiments showed that the nano Fe-Ce-TiO2 hydrosol not only has high UV catalytic activity, but also has ability to respond to visible light. The mechanism of codoped was as follow: the 3d orbit of Fe can overlap partly with the 4f and 5d orbit of Ce, and this orbital overlap would lead to a new hybrid energy band formed in TiO2 band by hybridization. So Fe-Ce-TiO2 has a strong UV absorption capacity, and can respond to visible light of about 450nm.Nano-Fe-Ce-TiO2 hydrosol can apply to the photocatalytic degradation of formaldehyde through a simple spray and drying process. At room temperature 20℃and humidity of 40%, efficiency of photocatalytic degradation of formaldehyde of 0.771mg/m3 could reach 81.8% under UV irradation for 4h.And nano-Fe-Ce-TiO2 hydrosol coating durability test showed that it could photocatalytic degradate formaldehyde repeatedly after necessary ventilation treatment to supplement the oxygen consumed of the reaction system. Simulating on indoor formaldehyde pollution characteristics, the experiments of the photocatalytic degradation of the release formaldehyde were carried out. Results showed that the formaldehyde concentration could be reduced to 0.08mg/m3 under natural light irradiation of 4.6h, 4h and 2.5h, while the initial formaldehyde concentration were 0.621mg/m3, 0.324mg/m3 and 0.175mg/m3, respectively. It indicated that nano Fe-Ce-TiO2 hydrosol is a kind of photocatalytic product which can be applied to photocatalytic degradation of indoor formaldehyde.The results of photocatalytic degradation kinetics of formaldehyde showed that the photocatalytic degradation process of formaldehyde consistent with Langmuir-Hinsherwood dynamic model when the initial concentration of formaldehyde in the range of 0.771 ~ 2.540mg/m3, and the reaction order was first-order. Reaction rate constant of photocatalytic degradation was related to the initial concentration of formaldehyde, and the relation equation calculated was lnk = -5.0426-0.9768lnC0.The antibacterial properties of nano Fe-Ce-TiO2 hydrosol were researched, and the results of antibacterial experiments showed that the antibacterial properties of nano Fe-Ce-TiO2 hydrosol were good. For 6h under natural light conditions, the sterilization efficiency of nano-Fe-Ce-TiO2 hydrosol to cultured strains and natural bacteria was up to 96% or more. The sterilization process of E. coli was observed by TEM, the results showed that bacterial cell wall was the direct action site. Therefore, the composition of cell wall was a direct factor affecting the efficiency of sterilization. Because the cell wall of Gram-negative bacteria (G-) has the outer lipid layer, while the cell wall of Gram-positive bacteria (G+) only has peptidoglycan network structure, the nano-Fe-Ce-TiO2 hydrosol can degradate more fastly to G+ compared G- .
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