الفهرس 
Introduction and literature reviewOnly 14 pages are availabe for public view
Abstract
Energy is one of the key fundamentals for economic progress in this era. However, energy is becoming one of the most disturbing problems at a global scale. Approximately 90% of the world’s energy supply is based on fossil fuels. Understandably this is causing some fear and worry that our energy resources have been largely depleted. On the other hand, the pollution and climate changes caused by fossil fuels are becoming a major source of concern worldwide. Due to this situation and the need for a cleaner environment, interest in alternative and renewable fuels for energy production has increased rapidly around the world. Many recent studies suggest that the direct use of hydrogen as a fuel may provide a much cleaner and far less expensive fuel alternative. In addition, Hydrogen is a promising fuel to replace depleting fossil fuels. However presently, almost commercial hydrogen production is still based on raw fossil materials. Thus, nowadays challenge is to produce hydrogen from renewable resources.
Photocatalytic water splitting using semiconductor catalysts is an effective method for production of hydrogen fuel.
Titanium dioxide (TiO2) is one of the best materials for photocatalysis application. However, its photocatalytic properties are limited by hole-electron recombination, and it can only work under ultraviolet light due to its wide band gap. However, there are many strategies and efforts to reduce electron-hole recombination rates and increase photo-catalyst efficiency. So other complex mixed metal oxides have been increasingly explored as photocatalysts. Among various materials, layered perovskite-type oxides have attracted considerable attention due to their unique optical properties and excellent photocatalytic activity. Especially, metal titanates (MTiO3) display a suitable conduction/valence band position as desirable for photocatalytic water splitting. In particular, the NiTiO3¬ has substantiated highly photostability, corrosion resistance in aqueous solutions and its light absorption spectra show peaks in visible region.
Moreover, the combination of graphene with photocatalysts has been demonstrated to be an efficient way to promote the separation of photogenerated electron–hole pairs and then enhance their photocatalytic activity. Indeed, in photocatalyst-graphene composites, photogenerated electrons can be readily captured by graphene which acts as an electron acceptor, leading to an increasing availability of photogenerated electrons and holes participating in the photocatalytic reactions.
In this study, the simple created of perovskite (NiTiO3), Graphene and NiTiO3/Graphene nanocomposites in different concentration to achieve the highest efficient photocatalysts for hydrogen evolution under visible light illumination.
Objective of this work divided into two parts:
The First Part focuses on the following:
Synthesis of Metal Titanates (MTiO3) where M are transition metals (V, Cr, Mn, Fe, Co, Ni, Cu and Zn) were prepared by facile microwave ignition method.
Characterization of the prepared nanomaterial in titanates structure (MTiO3)
Evaluate the efficacy of prepared nanomaterials (MTiO3) to hydrogen production, to determine the highest efficient Nano catalyst which produces the maximum hydrogen flow rate.
The following are the main conclusion that may be drawn from the obtained results:
The XRD patterns revealed the formation of fine crystalline phase of perovskite VTiO3, CrTiO3, MnTiO3, FeTiO3, CoTiO3, NiTiO3, CuTiO3, and ZnTiO3.
The average crystallites sizes of powders have been calculated by Debye Scherrer’s equation, to confirm that all samples in nanocrystalline structure. And the result of XRD was confirmed by Fourier transform infrared spectroscopy and Raman spectroscopy
Transmission electron microscope (TEM) indicated that the nanocrystalline nature of the prepared Metal Titanates (MTiO3) were almost spherical or slightly stretched with limited aggregation.
The UV-vis diffuse Reflectance spectrum of the prepared samples was recorded for a wavelength range from 350 to 800 nm. The spectrum indicated that the samples show a maximum absorbance in the visible region. Band gap energy was observed in the range from 2.75 to 2.99 ev , this data clearly reveals that the band gap energy of perovskite Metal titanates (MTiO3) samples have smaller band gap than simple titanium oxide , thus leads to more efficient utilization of the solar energy.
The photocatalytic performance of the prepared samples (MTiO3) was achieved; to determine which the photocatalyst is the highest efficient. The results indicated that the activity of NiTiO3 photocatalyst achieves the highest rate of H2-production.
The activity of H2 production is related to the conduction band position. It can be seen that the conduction band position of NiTiO3 was more negative than all those prepared samples. thus, NiTiO3 shows the highest photocatalytic H2 production, indicating that NiTiO3 is a promising catalyst for water splitting into H2.
The Second Part is to develop what we began in the first part; we interested to get more improvement and the maximum enhancement of electrochemical performance of NiTiO3 (the result which obtained from 1St Part). And make composite between the obtained catalyst and graphene, to get more improving for the photocatalytic activity.
Therefore, the second part discusses the following:
The effect of combining of rGO with NiTiO3 in different ratio composites
Characterization of the prepared composites (NiTiO3/rGO).
Comparison between the photocatalytic activity of bare NiTiO3 (NTG0) and the prepared composites NTG1, NTG3, NTG5 and NTG7).
The photocatalytic activities of the samples were evaluated to hydrogen production, to determine the highest efficient catalyst which produce the maximum hydrogen flow rate.
The following are the main conclusion that may be drawn from the obtained results:
The prepared composites exhibited excellent properties. NTG5 was recorded the highly activity for hydrogen evolution than the bare NiTiO3 nanoparticles, under visible light, this can be attributed to the following reasons:
from BET surface area, (NTG5) have largest surface areas, the increase in the surface area lead to enhancement the adsorption-desorption of reactants and products during photocatalytic reaction.
from Diffuse Reflectance Spectroscopy (DRS), the low intensity of reflectance of NTG5 indicated the highly absorbance of light in visible range.
According Photoluminescence Spectra, The PL intensity obtained for NTG5 is lower than all prepared samples, indicated that NTG5 has a much lower recombination rate of photogenerated charge carrier.
The highest photocurrent (PC) response was obtained for the NTG5 sample, where NTG5 was approximately 3 times higher than bare NTG0 indicating significantly enhancement in the efficiency separation of the photogenerated electrons and holes
Electrochemical Impedance Spectroscopy revealed that The NTG5 sample is superior to all other prepared samples with the shortest semicircle confirming the rapid transport of charge carriers and an effective charge separation.
The possible reaction mechanism is that the electrons transfer from the conduction band of NiTiO3 to graphene sheet. This charge separation process effectively reduces the recombination of newly generated electrons and holes, and thus enhance the photocatalytic reactivity. The photocatalytic efficiency is slightly decreased by high content of grapheme (NTG7) due to an increasing coverage of graphene onto the surface of the NiTiO3, leading to hinder the passage of light through the sample. This work offers a new strategy for designing low cost photocatalysts with high efficiency for solar energy conversion to Hydrogen fuel.