الفهرس 
Synthesis of Nanostructured MaterialsOnly 14 pages are availabe for public view
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Abstract
In this work the structural and physical properties of some nano ferrites, namely NiFe2O4, CoFe2O4, CuFe2O4, Ni0.5Co0.5Fe2O4, Ni0.5Cu0.5Fe2O4 and Co0.5Cu0.5Fe2O4 have been studied. The study includes the preparation of ferrites in nano size range via different methods .The samples prepared were characterized by several techniques including XRD, FT-IR, SEM, and TEM. The effect of particles size and morphology of the produced materials on their physical properties (surface area, magnetic, optical and electrical) has been studied. Some applications of the produced ferrites were investigated.
The work is presented in five main chapters.
The first chapter includes the general introduction, which contains literature survey about the investigated samples and the aim of work.
The second chapter shows the experimental methods including the preparation of ferrites and the instruments used for characterization.
The third chapter describes the theoretical and calculation methods used for analyzing the results (DC-, AC- conductivity) , dielectrical constant (ε′) , dielectrical loss (ε′′) parameters , optical properties , evaluation of textural parameters via the adsorption of nitrogen , types of Hysteresis Loops and surface area .
The fourth chapter shows the characterization of the investigated samples where the results were reported and discussed.
The fifth chapter deals with the study of X-Ray Powder Diffraction Analysis, Fourier Transform Infrared Spectra (FT-IR), Scanning Electron Microscope (SEM) , DC - and AC - conductivity of ferrite samples over a temperature range between 303–380˚K .It includes also the results of the relative permittivity (ε′) and the dielectrical loss (ε′′) of the samples under investigation, UV- visible spectroscopy and energy band gap of all nanoparticles investigated, magnetization results ,surface area and acidic properties. It includes also some applications on the ferrites produced.
In this work, the main results are summarized as follow:
(1) Nano-sized nickel ferrite with cubic spinel crystal structure (confirmed from XRD and TEM) were obtained using several methods from solution containing nickel (II) and iron(II) ions.
(2) IR-spectra of prepared samples are discussed on the basis that the observed changes in IR peaks can be attributed to the peculiar cation distribution revealed by XRD in the studied samples.
(3) SEM analysis reveals that the morphology of the sample and their surface pore sizes depend mainly on their preparation route. The design and synthesis of the ferrites with nanosized dimensions has been made possible because of the ability of surfactants to self-assemble into well-defined structures. The structures formed by self-assembly of the surfactant are used as a kind of template for the synthesis..
(4) The grain size has been determined via electron microscopy and the crystallite size using X-ray diffraction. The X-ray measurements showed smaller sizes than that of TEM studies; this is due to the presence of non- crystalline material at the particle surface. Both techniques showed that the mean grain sizes of investigated samples lie between 8 and 152 nm.
(5) The electrical properties of the investigated samples are found to be dependent on the distribution of the iron and the divalent metal ions among the octahedral and tetrahedral sites of the spinel lattice.
(6) The conductivity as a function of temperature reveals the semiconducting nature of all samples. In general, the conductivity values of bulk samples have greater values than the corresponding nanostructure samples. The DC-conductivity obtained was found to increase according to the following order:
Ni Polymer > Ni Ppt > Ni Solid (NiFe2O4)
Co Ppt > Co Thermal > Co Solid (CoFe2O4)
Cu Sol (maleic 200 ͦ C) > Cu Ppt.(urea) (CuFe2O4)
The observed change in dc- electrical conductivity with the change in sample composition may be attributed to a large extent to the change occurring in the M2+/M3+ ratio in B sites. The activation energy was found to change with the sample composition due to the change occur in ionic distances in the spinel ferrite crystal structure.
(7) The ac- conductivity of all the investigated samples showed also semiconducting behavior in which the ac-conductivity increases with increasing temperature, especially at higher temperatures. This may be attributed to the increase in the drift mobility and hopping frequency of charge carriers with the increase in temperature.
(8) For all ferrites, the ac- conductivity is found to increase with increasing the grain size..
(9) For all samples, the activation energy is found to decrease with increasing frequency. The difference between the activation energies of σd.c and σa.c is explained on the basis of the effective DROP of the electric field within the bulk due to the presence of space charge accumulations at the electrodes which were noticed in dc –measurements.
(10) The dielectric constant and loss increases rapidly with increasing each of temperature and frequency, which may be due to the interfacial polarization.
(11) The values of σac, ε′ and ε″ were found to depend on the sample composition. At room temperature and frequency of 103 Hz, ε′ and ε″ increase according to the following order:
Ni Polymer > Ni Solid > Ni Ppt ( NiFe2O4)
Co Solid> Co Thermal> Co Ppt (CoFe2O4 )
Cu Ppt.(urea) > Cu Sol (maleic 200 ͦ C) (CuFe2O4 )
And σac increase according to the following order:
Ni Polymer > Ni Ppt > Ni Solid ( NiFe2O4)
Co Ppt > Co Thermal > Co Solid (CoFe2O4 )
Cu Sol (maleic 200 ͦ C) > Cu Ppt.(urea) (CuFe2O4 )
(12) The absorption spectrum of the NiFe2O4 shows that all produced nano-size samples display the photo absorption properties at visible light region. The spectrum shows absorption bands start in the range of 480-520 nm (1.58-2.05 eV in photon energy) which can arise due to the transition between valence band to conduction band.
(13)The absorption spectra of the CoFe2O4 show that the absorption bands start in the range of 640 - 663 nm. The value of the energy band gaps for all samples, found in the range of 1.54 -1.64 eV.
(14)The absorption spectra of the CuFe2O4 show strong absorption at ~ 280 nm. The values of the energy band gaps for all samples are higher than that found for bulk material, Due to the presence of impurities in the nano specimens.
(15) We have successfully prepared nano-crystalline ferrites with tunable magnetic properties. The magnetization values of the nanosized samples increase in most cases with the increase of the particle sizes. They are less than the reported value of the saturation magnetization experimentally observed for the corresponding bulk ferrites. The behavior of saturation magnetization with particle size was explained in view of surface effects .The saturation magnetization was found also to be dependent on the specific surface area of the particles.
(16) For doped ferrites, the magnetic properties were found to depend on the composition of the sample. This is attributed to the difference in the magnetic moment for each of Cu2+, Co2+ and Ni2+ ions.
(17) The surface and textural properties of the ferrite samples produced were found to depend also on the synthetic condition. Most samples showed surfaces with high surface areas and meso pores structure. The surface areas of all samples are higher than that of corresponding composition. And in most cases, the surface area increases with decreasing the particle size:
For NiFe2O4, SBET increases as the particle size decrease; except Ni Polymer sample that contains impurity phases as shown in XRD results ,giving an order:
Ni Solid > Ni Polymer > Ni Ppt
For CoFe2O4, SBET increases randomly as the particle size decreases referring to the influence of both particle morphology and the impurity phases on the surface properties. .
For CuFe2O4, SBET of samples increases as the particle size decreases. The samples prepared with sol gel method have high surface area. It can be also observed that the total pore volumes (Vp) increases as the particle size decreases.
(18) Acidic properties of NiFe2O4 shows the availability of Lewis acid as well as Brönsted acid sites, the concentration of them depend on the particle size obtained. Whereas, no correlation could be found between the acidic type and amount present on CoFe2O4 and CuFe2O4 surfaces and their particle sizes. It can be only said that these properties depend on the preparation rout.
(19) Application of NiFe2O4 as an adsorption for removing azo-dye acid red B (ARB) from aqueous solution has been studied. For all studied samples, the adsorption rate is very fast and increase with decreasing the particle size.The equilibrium adsorption is almost achieved within 40 min. Nisolid sample showed the best adsorption results. The effects of pH, temperature, and dosage of catalyst on the degradation rate of dyes were examined. The diffusion of dye molecules onto the active site adsorbent and the complexation between the dye molecules and adsorbent is increased with decreasing the particle size. Acidic condition at pH 5 is favorable for removing more than 97% ARB. Ten cyclic tests show that the magnetic catalyst is very stable, recoverable and highly active.
(20) Application of CoFe2O4 as a photocatalytic material for the degradation of methyl red dye in aqueous solution showed that it is effective to degrade the dye. The highest catalytic activity is observed for Cosolid sample indicating an increase in catalytic activity with increasing the surface area of ferrite. The photocatalytic ozonation, with cobalt ferrite nanoparticles (UV/O3 /ferrite), increases with increasing nanoparticle dosage up to .03 g/L, but a further increase in ferrite dosage does not improve the dye degradation due to light penetration problems. The technique used may be a viable one for treatment of large volume of aqueous colored dye solutions. Photocatalytic ozonation using cobalt ferrite nanocatalyst is able to decolorize and treat the colored dye without using high pressure of oxygen or heating.
(21)The catalytic activities of CuFe2O4 samples on thermal decomposition of AP were tested. All tested samples showed shifted the ammonium perchlorate (AP) thermal decomposition temperature downwardly to lower temperatures. The rate of decomposition increases with decreasing the particle size .This is due to the fact that with decreasing the particle size a large number of active sites would be available for the adsorption of reactants as a consequence; the rate of reaction would be increased. Two mechanisms based on proton and electron transfer processes have also been proposed for AP decomposition in the presence of nano-sized powder oxides.