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Author name: محسن عطية خضير الطائي

Supervisor name: رعد سعدون صبري | يوسف كاظم عبد الامير

General topic: Physics

Specific topic: Physics

Degree: Doctorate

University: Mustansiriyah University - College Of Science

Language: English

University location: Baghdad

First pages:

Abstract: TiO2 nanostructures were synthesized by two different techniques : sol - gel and electrospinning methods. Each technique gives us specified nanostructure; nanoparticles can be resulted from the sol - gel method, whereas nanofibers are resulted from electrospinning method.In sol - gel method, the effects of gelatinization time (1, 3, 5) days and calcination temperature (500, 700, 900) oC were studied on TiO2 nanoparticles. The effect of applied voltage (15, 18, 21) kV, flow rate (1, 5, 10) ml/h, and PVP concentration (7, 10, 13) % are studied in the case of TiO2 nanofibers. Also Different ratios of Ag doped TiO2 nanofibers (3, 6, and 9) % were synthesized using electrospinning method. The resulting nanomaterials being characterized using XRD, AFM, FESEM,UV - Vis analysis, and PL measurements. X - ray diffraction measurements show that TiO2 nanoparticles were polycrystalline with anatase phase and transform to rutile phase at 900 oC. TiO2 nanofibers have only anatase phase. The crystallite size and lattice constants (a and c) for both anatase and rutile phases are calculated. No noticeable peaks of silver metal were observed in the XRD when Ag is doped in titania.The roughness average for TiO2 nanoparticles, which is estimated from AFM images increases when the gelatinization time and the calcination temperature increased, but at 900 °C it decreases. This may be attributed to the change from anatase to rutile phase. In the case of TiO2 nanofibers, the roughness average increases with the increases of applied voltage and decreases of the flow rate. While the maximum roughness occurring at 10 % PVP concentration. In general, the roughness average increases with the doping ratio. The diameter size distribution of both TiO2 nanofibers and nanoparticles show the favorite Gaussian distribution.The FESEM images show that the fiber has a uniform distribution and looks like mats. The grain size of TiO2 nanoparticles increase from (58 - 89) nm with the gelatinization time increase from (1 - 5) days respectively, also it increases from (58 - 111) nm with the calcination temperature increase from (500 - 900) °C respectively. In the case of TiO2 nanofibers, the average fiber diameter decreases with increase the applied voltage, and decrease both the flow rate and PVP concentration. Increasing Ag doping ratio will decrease the average fiber diameter, and convert the smooth surface of the nanofibers to granular surface. Silver doped TiO2 nanofibers are very clear in both AFM and FESEM images. The allowed direct band gap of TiO2 nanoparticles slightly decreases from 3.45 to 3.35 eV when the gelatinization time increases from (1 - 5) days respectively. When the calcination temperature increases from (500 - 900) oC, the band gap gradually decreases from(3.45 - 3.30) eV. The band gap of TiO2 nanofibers increase from (3.35 - 3.45) eV due to the increase of the applied voltage from (15 - 21) kV respectively, and decrease from (3.45 - 3.4) eV with increase the flow rate from (1 - 10) ml/h respectively. The decrease of Eg is also observed with the increase of PVP concentration. Finally the band gap decreases from (3.45 - 3.20) eV when the Ag doping ratio increases from undoped to 9 % respectively.PL spectra of TiO2 both nanoparticles and nanofibers are recordedat room temperature and excitation wavelength of 260 nm. Two groupsof peaks were observed, the first peaks lie in the UV region, which can be attributed to the emission of band gap transition related to the anatase structure of TiO2 nanofibers, whereas the second emission band lies in the visible region and originated from the charge recombination at the shallow - trap surface state.Photocatalytic properties in different concentrations (2, 10, and 20) mg/50 ml of both TiO2 nanoparticles and nanofibers were evaluated by photocatalytic degradation of methylene blue (MB) in water under UV light irradiation (λ= 365 nm). The outcomes indicate that Ag doped TiO2 nanofibers exhibited most efficient photocatalytic activity of up to 96 % after 160 min as shown by the degradation of the MB aqueous solution, followed in terms of efficiency the undoped nanofibers, and then nanoparticles respectively. These results make Ag doped TiO2 nanofiberis the most efficient material in water treatment field.