|
Nano-TiO 2 as a photocatalyst in water treatment and gas purification and other environmental and photolysis of hydrogen field of new materials has broad application prospects, attracting widespread attention. But extensive research of nano-TiO 2 catalyst slurry phase system exists easily agglomerated, easy deactivation, difficult recovery and disadvantages of solar energy utilization low, thus limiting the practical applications of the technology. In this paper, a comprehensive overview of TiO 2 photocatalytic technology, modified approach, TiO 2 fiber synthesis and application status, based on the preparation and systematic study of nano-TiO 2 fibers (TiO 2 nanofibers, TF), to accommodate the TiO 2 photocatalytic technology in water treatment and environmental governance in the practical use of the urgent requirement. First, the sol - emulsion - gel synthesized TiO 2 nanopowders by XRD, TEM, FT-IR, Raman, XPS and other means to characterize them, compared to the sol - gel method Preparation of TiO 2 nano powder particle size decreases, the specific surface area increases, the agglomeration decreased bandgap energy increases, the UV absorption band edge blue shift. When the sol to pH 8.5, surface active agent and distilled water molar ratio of W = 1.08 is, TiO 2 particle size to a minimum of 7nm, the specific surface area of ??up to 273m2 / g, and the particle size distribution is uniform. As the heat treatment temperature and heat treatment time, the grain size increases, TiO 2 crystalline powder never finalized, after the end of anatase to rutile transformation. TiO 2 Eastman grain growth grain growth kinetics model of obedience. In the nano-TiO 2 powders as precursor, a simple hydrothermal method and heat treatment successfully prepared TF. The effects of reaction temperature, time and alkali concentration, washing conditions, the heat treatment temperature on the product structure and morphology. Found that with the reaction time, TF length and increasing the yield, 72h after complete conversion of the precursor fiber, length of micron; when the reaction temperature below 130 ℃, TiO 2 Powder incomplete conversion, 150 ℃ a more suitable reaction temperature is higher than 170 ℃, the morphology changes, a belt; KOH concentration is less than 8mol / L, only a small fiber-forming, more than 12mol / L, the product is flaky or short rod, can not grow into fibers; washing conditions do not substantially affect the morphology of TF, but TF structure and chemical composition have a greater impact, when pickling enough, ion exchange does not completely When, TF has more K2Ti6O13 ingredients; optimum calcination temperature was 400 ℃, the product uniform morphology, crystalline sound, with calcination temperature, TF sintering phenomenon gradually increased, reaching 550 ℃ when, TF visibly burn down. Samples in the heat treatment temperature is below 550 ℃ when anatase phase, when the heat treatment temperature exceeds 650 ℃, the anatase and rutile mixed crystal, when the heat treatment temperature reaches 850 ℃, the samples anatase completely transformed into gold Redstone phase. HRTEM, XPS, DRS and other analysis showed: TF is solid layered structure, consisting of Ti, O, C elements, relative to the TiO 2 raw material powder, UV absorption band redshift. Mechanism of its formation is anatase TiO 2 nanoparticles generated under the action of alkali K2Ti6O13 nuclei, follow these nuclei dissolved - crystal - growth mechanism, along the (010) crystal plane direction of growth, gradually long as nano K2Ti6O13 fibers. By ion exchange and heat treatment, converted into anatase TiO 2 nanofibers. From the photocatalytic reaction of the basic characteristics of studied photocatalytic reaction conditions of methylene blue (MB) Photocatalytic Degradation. TF on MB (3mmol / L) Photocatalytic Degradation of optimal reaction conditions are: ventilation rate of 56mL · s-1, the catalyst concentration is 2g / L, UV lamp power 40W, pH value of 6.0. Establishment of the initial concentration of organic compounds containing the UV lamp power, catalyst concentration, etc., the kinetic model, that under the same experimental conditions, TF E. coli (E.Coli) inactivation performance than P25. TF photocatalytic sterilization mechanism is: the TiO 2 under light irradiation to generate the active ingredient (· O2-, · OH, h) on the cell membrane damage, to produce holes, thereby resulting in cell membrane permeability of the active component changes, the active ingredient is passed through holes reach the cell membrane peroxidation occurs, resulting in cell death. Were used in situ method and the impregnation of the Ag-TF. By TEM, XRD, DRS, and XPS methods for different process conditions the product obtained crystal structure, morphology and chemical composition were characterized discussed Doping on the TF structure and properties. The results showed that: the fiber prepared by two methods significantly different surface morphology, prepared in situ Ag-TF smooth surface, prepared by impregnation with a fiber diameter of 2 ~ 5nm surface of the spherical particles exist and impregnation fiber XRD spectra appear Ag2O characteristic diffraction peaks in situ preparation of a fiber line no Ag2O diffraction peak of Ag embedded lattice, rather than deposited on the fiber surface of the particles. And in situ prepared Ag-TF lines compared to the fiber impregnation DRS spectral red shift. When the doping amount of Ce4 time TF, TF photocatalytic activity increases, the optimum doping was 0.5wt%. The appropriate heat treatment temperature and doping concentration, prepared Ce-TF of methylene blue photocatalytic activity than P25 well. The use of correlation analysis methods, the doping 0.5wt? 4, TF sample [Ce-TF (0.5)] were characterized, the results showed that: compared to undoped TF, Ce-TF (0.5) in the TiO 2 < / sub> nano particle size decreases, while Ce4 doped anatase to rutile phase transition has hindered, Ce-TF (0.5) of the fluorescence intensity decreased, quantum yield increases. The reason is as Ce4 doped electron - hole pairs capture position, reducing the electron and hole recombination rate. Through in-depth study of factors affecting TF synthesis and growth mechanism for large-scale preparation controllable morphology and size of a one-dimensional titanium-based nanostructures materials laid the foundation for research structure shows: TF on microorganisms and organic matter degradation with high photocatalytic activity and long continuous service life can be in the sewage treatment play an important role, has a very broad application prospects.
|