الفهرس 
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Abstract
Water pollution has been a serious environmental concern in our society. The concern with water pollution has been motivating the formulation of specific regulations able to get rid of this phenome-non. Heterogeneous photocatalysis based on nanoparticles semi-conductors, is being considered a promising technology for the abatement of organic pollutants in waste water. The advantage of this technology is based on the generation of highly oxidizing radi-cals for degradation of organic pollutants to nontoxic intermediates or inorganic compounds such as water and carbon dioxide. Among several used semiconductors, TiO2 is the most widely used photo-catalyst in this technology because of its outstanding physical and chemical properties. However, the quantum efficiency of TiO2 is greatly diminished by fast electron-hole pairs recombination and light absorption only in the UV region. This thesis deals with three approaches aiming to improve the photocatalytic performance of titania nanoparticles through design of model systems.
In the first approach, a model consisting of TiO2/graphene nano-composites has been fabricated in different molar ratios to address the role of graphene on charge carrier dynamics and light absorp-tion. For this purpose, nanoparticles of TiO2 were synthesized by simple sol-gel method and graphene was synthesized by chemical reduction of GO according to Hummer method. TiO2 nanoparticles were loaded on graphene surface by two different methods. The physicochemical properties of the nanocomposites were investigat-ed using developed techniques as XRD, HRTEM, BET and DRS. The experimental results reveal the homogeneous distribution of titania nanoparticles on graphene sheets and reduce the titania crystalline dimensions to the nano scale. The photocatalytic activi-ty of the heterostructure photocatalysts was evaluated through degradation of methylene blue and p-aminophenol organic pollu-tant under UV and natural sunlight irradiation. The nanocompo-sites showed a significant enhanced photocatalytic activity in re-moval of methylene blue and p-aminophenol as pollutant models compared with bare TiO2 nanoparticles in the UV region. The en-hanced photocatalytic activity was attributed to improved charge carrier separation in the synthesized TiO2/graphene nanocompo-sites. The sunlight irradiation experiments showed slight enhanced photocatalytic activity for the nanocomposites in the visible region. Kinetic study for the photocatalytic degradation reaction was car-ried out in order to investigate the effect of several factors such as catalyst dose, initial concentration and initial pH of the solution on the degradation reaction and get the optimum conditions.
In the second approach, model systems consisting of TiO2 and bismuth titanate (Bi4Ti3O12) nanoparticles in different Bi/Ti molar ratios were designed using simple sol-gel manner to address the role of bismuth titanate in shifting the photocatalytic response of TiO2 nanoparticles to the visible region and taking advantage of all the spectrum of the natural sunlight. The influence of bismuth ti-tanate on the nanostructure of titania was investigated using XRD, N2-adsorption-desorption isotherm, HRTEM, DRS and PL tech-niques. The model systems were evaluated under both UV and sunlight irradiation with two different photocatalytic reactions (methylene blue and p-aminophenol degradation). A substantial enhanced photoactivity was observed for Bi4Ti3O12 /TiO2 compo-sites compared to bare TiO2. The enhanced activity was attributed to Interfacial charge transfer from TiO2 to Bi4Ti3O12, when they are in direct contact with each other which effectively separated the photoinduced charge carriers and narrow the band gap of the nanocomposites. The kinetics of the MB degradation reaction was studied and emphasis is given to understand the underlying photo-catalytic mechanisms.
In the third approach, a photocatalyst of (Bi4Ti3O12/TiO2/ gra-phene) was designed by loading the optimum composition ratio of the Bi4Ti3O12/TiO2 composite on graphene surface and tested under both UV and sunlight irradiation. The nanostructure, crystalline and textural properties were elaborated by HRTEM, XRD, surface analysis and XPS analysis. This novel photocatalyst exhibited a photocatalytic activity higher than both Bi4Ti3O12/TiO2 and /TiO2/graphene towards removal of organic pollutants.