الفهرس 
Chapter 1: Literature surveyOnly 14 pages are availabe for public view
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Abstract
Nanocrystalline materials are showing great prospects in industry and technology. This is mainly because they have some unique properties which are not shown by the bulk crystalline materials. Nanomaterials represent almost the ultimate in increasing surface area. Substances with high surface area have enhanced chemical, mechanical, optical and magnetic properties, and this can be exploited for a variety of structural and non-structural applications.
One-dimensional (1D) nanostructured materials as nanotubes, nanobelts, nanowires and nanorods are of great interest because of their distinctive geometries, novel physical and chemical properties specially TiO2 nanotubes (TiO2NTs). The filling or doping of TiO2 nanotubes is of great interest in order to avoid the recombination of the photogenerated charge carriers and to increase the range of catalytic activity from UV to visible region
Throughout this work it was found that:
1- Synthesis and characterization of TiO2 nanotubes filled with NiFe2O4 quantum dots
1. Titanium oxides NTs were prepared by a hydrothermal method followed by an ion exchange process at different times and temperatures. The titanium oxides NTs prepared at a longer time and higher temperature showed good crystallinity, high density and layered structures.
2. Anatase-phase TiO2NTs was formed by firing the titanium oxides NTs under a low flow rate of oxygen at 500oC for 2 hrs.
3. NiFe2O4 nanoparticles were prepared by the self-flash combustion method; the obtained nanoparticles are round with crystal sizes ranging from 9 to 12 nm.
4. Anatase-phase TiO2NTs was filled for the first time with NiFe2O4 Q.Ds under vacuum. The filling process depends on the concentration of Fe and Ni nitrates, standing time and finally vacuum time.
5. The absorption thresholds of the titanium oxides NTs, empty anatase-phase TiO2NTs and anatase-phase TiO2NTs filled with NiFe2O4 Q.Ds were estimated to be 386, 396 and 770 nm, respectively.
6. The anatase-phase TiO2NTs filled with NiFe2O4 Q.Ds has the lowest energy gap value, 1.61 eV, because the Q.Ds narrowed the NTs band gap.
2- Conductivity behavior & reduction of TiO2NTs filled with NiFe2O4 quantum dots
1- The conductivity behavior of empty anatase TiO2NTs, anatase TiO2NTs filled with NiFe2O4 Q.Ds and NiFe2O4 was studied in a hydrogen gas flow (1 L/min) at different temperatures (500-700oC). The electric conductivity of the three nanomaterials increased by increasing the reduction temperature which illustrates the semiconductor behavior of the three nanomatreials.
2- Empty anatase phase TiO2NTs achieved the highest values of conductivity at 550 and 600oC. But at higher temperature (650, 700oC) the conductivity decreases by increasing temperature which may be attributed to the destruction of tubular form of nanotubes.
3- The conductivity mechanism of anatase phase TiO2NTs towards H2 gas was found to be chemisorption of splitting hydrogen atoms mechanism.
4- Depending on conductivity and thermogravimetry techniques the activation energy values were calculated to determine the rate controlling mechanism. The all catalysts have the same mechanism ”combined gas diffusion and interfacial chemical reaction mechanism”. NiFe2O4 Q.Ds narrows the band gap of TiO2NTs and shifts their absorption edge to the visible region.
3- Novel visible light activity of TiO2 nanotubes filled with NiFe2O4
quantum dots
1- New photocatalysts including titanium oxides NTs, empty anatase phase TiO2NTs, anatase phase TiO2NTs filled with NiFe2O4 Q.Ds, anatase phase TiO2NTs filled with Ni-Fe nanoalloy and NiFe2O4 were examined for degradation of some organic pollutant for water treatment.
2- TiO2NTs filled with NiFe2O4 Q.Ds photocatalyst showed the highest photocatalytic activity for degradation of all examined dyes with high reproducibility and constant activity.
3- The filling process narrowing the band gaps of TiO2NTs and so shifts their response to visible light region. These phenomena reduced the potential required for generation of hVB+ eCB− pairs.
4- The absorption edges of titanium oxides NTs, NiFe2O4 nanoparticles, empty anatase phase TiO2NTs, anatase TiO2NTs filled with Ni-Fe and anatase TiO2NTs filled with NiFe2O4 Q.Ds, were 386, 395, 396, 470 and 770 nm respectively. These values are corresponding to the band gap energy of 3.21, 3.14, 3.13, 2.64 and 1.61 eV respectively
5- The degradation mechanism of Bp red dye was founded to be combined mechanism (photosensitized oxidation and Photocatalytic oxidation mechanisms) with more contribution for the later one.
6- The kinetic of Bp red dye degradation in aqueous solution under visible light irradiation follows an apparent first order reaction. The values of first order rate constant were summarized to be 0.0132, 0.0069, 0.011, 0.0351and 0.0154 min.-1 for titanium oxides NTs, empty anatase phase TiO2NTs, NiFe2O4, anatase phase TiO2NTs filled with NiFe2O4 Q.Ds and anatase phase TiO2NTs filled with Ni-Fe nanoalloy respectively.
7- Anatase phase TiO2NTs filled with NiFe2O4 Q.Ds showed high adsorption efficiency for the adsorption of Co, Cu, and Cd ions. It was found that there are more than one mechanism controlled the adsorption process.
4- Corrosion resistance, electrical and magnetic properties of TiO2 nanotubes filled with NiFe2O4 quantum dots and Ni-Fe nanoalloy
1- The corrosion protective performance of TiO2NTs was tested in 0.5M HCl solution at different temperatures (25, 50 and 75oC) for different times (20, 40, 60 and 150 min.) for protection of Ni-Fe nanoalloy
2- Weight loss (corrosion rate) of free Ni-Fe alloy is higher than that observed for coated Ni-Fe nanoalloy with TiO2NTs at all reaction conditions which indicating high protective performance of TiO2NTs
3- The values of inhibition efficiency were calculated to be 99.3 %, 99.2 % and 87.7 % at 25, 50 and 75 oC respectively. The higher inhibition efficiency values of TiO2NTs are attributed to ceramic protective barrier of TiO2NTs
4- The presence of TiO2 layer (nonmagnetic) on the surface of NiFe2O4 Q.Ds or Ni-Fe nanoalloy act as a magnetic dead layer on the surface, thus affecting the magnitude of magnetization
5- The electrical conductivity-temperature dependence of the empty anatase phase TiO2NTs, anatase phase TiO2NTs filled with NiFe2O4 Q.Ds, anatase phase TiO2NTs filled with Ni-Fe nanoalloy and NiFe2O4 compact disks were measured between room temperature and 850°C in air.
6- The empty anatase phase TiO2NTs, anatase phase TiO2NTs filled with Ni-Fe nanoalloy and NiFe2O4 have irreversible behavior because conduction in semiconductor materials is significantly affected by the oxygen vacancies and/or lattice defects within the sample
5- Gas sensing performance of TiO2 nanotubes filled with NiFe2O4 quantum dots and Ni-Fe for air purification
1- Anatase phase TiO2NTs, anatase phase TiO2NTs filled NiFe2O4 Q.Ds and anatase phase TiO2NTs filled with Ni-Fe nanoalloy were used for CO2 gas sensing at 350oC which is a typical for semiconductor type gas sensor.
2- The gas response increase linearly with increasing the CO2 concentration form 2sccm to 6 sccm. The new CO2 sensors were quite reversible.
3- There is a linear increasing of sensitivity at low CO2 concentration before saturation.