الفهرس 
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Abstract
We tried in this thesis to participate in solving water pollution problem. Among various types of water pollutants organic synthetic dyes which produced from Textile and dyeing factories are considered to be one of the most dangerous contaminants as they have complicated compositions, and have non degradable nature under normal conditions. We focused in our study on Methyle blue dye as an organic dye pollutant. Methylene blue is safe under standard therapeutic doses (<2mg/kg), but if its concentration exceeds more than this value it will be toxic and carcinogenic. We used a heterogeneous photocatalysis technique for decomposition of Methyle blue dye as this technique has low cost and can decompose dyes to green products.
In the past few years TiO2 as a semiconductor has been the most concentrated in studies as a photocatalyst, but it showed some drawbacks as it has a wide band gab of about 3.2 eV, absorbs UV light only which occupies about 5% of intensity of solar energy, and inactive in visible irradiation. So Perovskite semiconductors showed a suitable advantages for heterogeneous photocatalysis purpose as they have thermal stability, low cost production, narrow band gaps, high absorbance for solar energy, high crystallinity and usually have structural defects in their structures which causes their high photocatalytic activity.
We concentrated in our work on perovskite LaFeO3 with orthorhombic structure as it is highly stable, not toxic and has small band gap about 2.0 eV. A lot of techniques have been utilized to prepare perovskite LaFeO3 nanoparticles with different morphologies, but we selected a template method to synthesize perovskite LaFeO3 nanofibers as this method is not expensive, environmentally friendly, and its components can be removed easily. Among different types of morphologies nanostructured fibers have a number of advantages like high surface area, small diameters and porous structure. Cotton fibers were used in preparation as a bio-template to get a fibrous morphology.
We prepared perovskite LaFeO3 hollow fibers by using lanthanum nitrate and iron nitrate as precursors and medical cotton as a template. Calcination at different temperature degrees(600 ◦C, 700 ◦C, 800 ◦C, and 900 ◦C for 3 h) was made to get rid of cotton.
Crystalline structure and phase of samples was recognized by XRD analysis. Morphological properties was known by SEM and TEM. Spectrofluorometer was used to obtain Photoluminescence (PL) spectroscopy for samples. BET surface areas were estimated from nitrogen adsorption-desorption isotherms technique. Zeta potential was measured for all samples.
Finally The photocatalytic activity of samples was estimated by measuring the photocatalytic degradation of MB alone and with four samples at room temperature under solar-simulated light Sol 1A at a wavelength of 300−800 nm at neutral pH 7.
XRD results showed that all samples have displayed the same diffraction peaks which get narrower by increasing calcination temperature referring to improvement in crystallization. also by increasing calcination temperature the crystal size increased. SEM showed that prepared perovskite LaFeO3 hollow fibers have the same morphology of the original cotton fibers template, with the removal of the cotton tissues. TEM displayed that fibers consist of many LaFeO3 grains with a grain size of 25-33 nm. BET surface areas of LaFeO3 hollow fibers decrease by increasing calcination temperature and the average pore size diameter increases. Zeta potential increased from (-7.22 to -1.70) when calcinating temperature increased. This indicated that by increasing calcinating temperature, the surface potential increased and its adsorption capacity towards cationic dye such as MB increased also. All LaFeO3 fibers samples display the main PL signal at wavelength 825nm and by increasing calcinating temperature, the PL spectrum intensity decreases. from XRD results by increasing calcinating temperature the crystallite size increase, so crystallinity of LaFeO3 hollow fibers increases, the separation rate of photo-induced
charge carriers increases, and so photocatalytic activity increases According to the band–band PL spectrum of semiconductor materials. So samples calcinated at 800 °C and 900°C have the same photocatalytic activity more than that calcinated at 600 °C and 700 °C.
from photocatalytic activity test Equilibrium value for MB adsorption with 600 °C, 700 °C, 800 °C, and 900 °C samples was 15%, 20%, 63%, and 62 % respectively so the adsorption capacity for samples increases by increasing calcination temperature, due to increasing the surface potential which confirms Zeta potential results. It can be also observed that by increasing calcinating temperature, the catalytic and photocatalytic activity of LaFeO3 hollow fibers gradually increases to reach to total MB removal of 45%, 51%, 79% and 78 % for 600 °C, 700 °C, 800 °C, and 900 °C samples respectively. so samples calcinating at 800 °C and 900 °C show the best photocatalytic activity, It could be due to that by increasing calcination temperature, the crystallinity of LaFeO3 hollow fibers increases which nourishes the photoinduced charge separation, also increasing the adsorbed O2 on the LaFeO3 surface promotes superoxide radicals. It can be also observed that increasing temperature after 800 °C did not show a significant difference.