الفهرس 
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Abstract
Improving the efficiency of water splitting process is one of the main obstacles that are facing the generation of renewable energy. charge carrier’s separation is always coupled with low visible light absorption and stability of the materials used. Various trials have been done in order to construct a full system of different materials that can absorb visible light efficiently, with an enhanced electron hole - pair separation process for efficient water splitting. In this thesis, we are introducing a new system of Titania nanostructures that are supported over graphene sheets, as a photo sensitizer and an efficient charge carrier collector and transporter.
Titanium oxide structures and their applications are briefly discussed. from the discussion, it is found that there are four main requirements need to be satisfied for efficient photo catalysts, these are, large chemical and physical stability; high carrier transport with low recombination rates; band edge straddling to drive the reaction; and capability to absorb large portion of the solar spectrum. These conditions need to be satisfied simultaneously for any photo electrode to be used in water splitting.
In the first part of the thesis, TiO2 hollow porous spheres, TiO2 nanoparticles and TiO2/Graphene nanocomposites photo anodes were investigated, based on the first part, it is revealed that the graphene act as an electron shuttle and the photocurrent was enhanced.
In the second part of the thesis, decorated TiO2HPS/Graphene and decorated TiO2 NP/graphene nanocomposites photo-anodes were investigated, also it is revealed that the decorated metal give promising performance for both the carrier generation and carrier transport
It was found 5% graphene passivate the trap states on the surface of TiO2 hollow porous spheres, while more than 5% acts to create more defect states, larger carrier concentration, larger dark Iv current, but for TiO2 nanoparticles/graphene nanocomposites it was found that the optimum amount of graphene was 1% resulted in higher charge carrier concentration and photocurrent.
Different characterization techniques were used throughout this thesis such as, SEM, XPS, TEM, XRD, Raman, FT IR, BET, PL, UV-Vis, and current amperometry to validate our results, and show the enhancement in the optical properties for the synthesized structures. The results showed interesting behavior and enhanced photo catalytic properties for the modified structures. Following these adjustment, we were capable to control the physical and chemical properties of various metal oxide semiconductors to be used as efficient photo-electrodes in different solar energy conversion applications.
Finally, we showed the possible new applications for Titania nanostructures that are supported on graphene Nano sheets.