| Titanium dioxide(TiO2) has become the first choice of catalysts to photocatalytic degradation of organic pollutants, because of its specific properties:photocatalytic activity, long-term stability, nontoxicity, and lowcost. However, there are many disadvantages of traditional titania photocatalyst, such as low quantum efficiency, low utilization efficiency of sunlight and difficult recyle Therefore, ultrosonic-hydrothermal method with DADD assisted and sol-gel method combined with dry spinning processes were used in this article, aims to improve the photocatalytic activity and the morphology of doping modified TiO2 materials. And a series of typical nonmetal doped mesoporous TiO2 photocatalysts were successfully synthesized, include N-doped dual-phase titanate/anatase with controllable morphology, F-doped TiO2 fibers, and N-F codoped TiO2 fiber with controlled crystal. They were characterized by XRD, TEM, SEM, XPS, UV-Vis DRS, TG-DTA, FTIR and N2 adsorption-desorption, the morphology, particle size, surface chemical composition, spectral response and specific surface area and pore structure features of products were analysized deeply. With the solution of azo dyes as target pollutants, photocatalytic activities of synthesized photocatalysts were evaluated under visible-light. The main factor that affected photocatalytic activities was obtained. The results provide a new basis for the preparation of highly active response to visible light photocatalytic materials and its application in water treatment. The contents of this paper were divided into three sections.In the first section, N-doped dual-phase titanate/anatase with controllable morphology and pore size were synthesized by ultrasonic treatment, hydrothermal method, and ultrasonic-hydrothermal method with tetrabutyl titanate as Ti sorce and dodecyldiamine (DADD) as structure directing agent as well as nitrogen dopant. Under optimum preparation condition, samples prepared in ultrasonic-hydrothermal system could process excellent texture properties and regular morphology, but also good thermal and crystalstability. The pH value of the aqueous solution system would change the electric charge of both ends and exist form of DADD, thus choose pH as the main influence factor. By varying the pH condition of preparation system, various morphologies of crystallines, such as spherical, flower-like shape composed by nanosheet or nanorod and nanowire could obtain selectively, achieved the preparation of crystal with controllable morphology simply and efficiently.Results showed that sample prepared under neutral condition possessed the largest surface area (135.8 m2/g) and unique double pore-size distribution. It was specific 3D flower like spherical particle composed of stable dual-phase titanate/anatase nanosheets. The photodegradation degree of MB reach up to 99.7% under 180 min visible light irradiation. Furthermore, XPS results demonstrated that DADD not only act as the structure-directing agent to regulate sample morphology, also as N source affecting the optical response of the products even photocatalytic activity.In the second section, for solving its difficulty to settle, separate and recycle of powder titanium dioxide as well as its low photocatalytic activity under visible light, uniform and dense F-doped self-supporting continuous TiO2 fibers with visible light response, were prepared based on a modified and simple sol-gel method which combined with dry spinning and steam-activated heat treatment, using TBOT as Ti source and TFA as chelating agent and F source. In this experiment, TFA as chelating agent could inhibit the strong hydrolysis of TBOT to form stable precursor sol. The rheological properties of TiO2 precursor sol was tested and showed it was homogeneous transparent newtonian fluid in orange, suggested the formation of the chain structure of organotitanium polymer with certain viscosity and excellent spinnability. The main composition of recursor sol ould be deduced by FT-IR and DSC-TG analysis, as well as the molecular structural formula of such polymer. Furthermore, TFA could also act as F source by doping F atoms into the lattice of TiO2 successfully. The crystal phase, crystal morphology, surface area and pore structure could be controlled by varying the contents of F and heat treatment temperatures. It was found that the proper addition of F could improve the thermal stability and crystal stability, and was beneficial to form Ti3+ and oxygen defects on surface which could exhibit the recombination of electron-hole pairs. When F/Ti molar ratio was 4, the product heated at 700℃ showed the best photocatalytic activity, and the degradation rate of X-3B in aqueous solution reached 98.5% after 120 min under visible light irradiation.In the third section, mixed crystal with certain proportion was expected to improve the photocatalytic activity of TiO2; this new exploration areas are arising the broad masses of the researchers’ attention. On the basis of previous work, N-F codoped composite-crystal TiO2 fibers were successfully synthesized through a modified and simple sol-gel method which combined with dry spinning and steam-activated heat treatment, using TFA as as chelating agent and F source, and DADD as crystal-control agent and N source. Such fibers not only overcome the defect of not expanding the response range of visible light of pure F doped TiO2 fiber, and realized the controllable preparation of crystal type of sample. The rate of anatase/rutile, surface area and pore structure could be controlled by varying the contents of DADD and heat treatment temperatures.When the volume ratio of DADD/TBOT was 0.15, the ratio of anatase/rutile of the product heated after 600℃ was 68:32, which was is extremely close to the commercial catalyst P25 (70:30), possed the optimal crystal phase composition, and showed the best photocatalytic activity. The degradation rate of X-3B in aqueous solution reached 100% after 90 min under visible light irradiation. The results showed that the best ratio of mixed crystal combined with N, F codoping could creat synergetic effects, expanding the visible light response by non-metal doping, reducing the recombination rate of photoproduction carrier simultaneously by took advantage of "mixed crystal effect", result in the improvement of the photocatalytic activity of TiO2 fiber. |
PDF Full Text Request