الفهرس 
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Abstract
Zinc aluminate belongs to a class of spinel compounds called the spinel oxides; it was found in nature as a mineral named gahnite with a chemical structure of ZnAl2O4. It was promoted by a variety of advantage properties; it has high thermal resistance, high mechanical strength, high chemical stability, low sintering temperature, low surface acidity, high corrosion resistance, ductility, better diffusibility, high mechanical resistance, wide band gab range and excellent optical properties. It was synthesized through several synthesis methods by a considerable attention, promoting it for utilizing in many important applications. It could be used as electroluminescence display, photo electronic devices, and stress imaging devices and sensors. Additionally, it was used widely as catalyst support in many organic sophisticated transformations, coating material and as a photocatalytic material in waste water treatments.
In this study, Zinc aluminate nanoparticles were synthesized through solid state, molten salt and co-precipitation methods using industrial wastes. Zinc and aluminum sludges were produced during the blast furnace operation and the aluminum sheet production in aluminum industry, respectively. Sludges were used in the form of solid powders and solubilized nitrate solutions for synthesizing zinc aluminate through different synthesis methods. Samples produced by molten salt and co-precipitation methods were doped with different amounts of cobalt under optimizing the reaction temperature. Industrial wastes were characterized by XRD, XRF and DTA investigations, whereas, the synthesized samples were characterized by XRD, FTIR, XPS, SEM, TEM, UV-visible and PL investigations. Single phases of zinc aluminate and cobalt doped zinc aluminate were produced in nanosize with the three methods, per se, different features were detected in the structural and optical investigations depending on the synthesis method adopted. The produced doped and undoped samples were utilized in the photocatalytic degradation of the brilliant cresyl blue dye (BCBD) under visible light irradiation. Degradation parameters were controlled and the degradation process was monitored by using UV-visible and total organic carbon (TOC) analysis.
This study is divided into four chapters:
Chapter one:
This chapter includes a general introduction to zinc aluminate, for discussing general features as like as, its properties, structure, thermal analysis, methods of preparation and applications, as stated by the previous studies.
Chapter two:
In this chapter: zinc aluminate nanoparticles were synthesized through solid state reaction and molten salt synthesis using solid industrial wastes. Solid wastes were mixed by 1:2 molar ratio of Zn: Al, compressed as pellets and heat treated at 1100°C. Whereas in case of molten salt synthesis; potassium chloride was added to wastes’ mixture by 4:1 of molten salt: zinc aluminate before compression. XRD analysis revealed that, single phase zinc aluminate was produced and the highest crystallinity was achieved by solid state sample, the average crystallite size was found to be 17.4 and 12.7 nm for solid state and molten salt samples, respectively. FTIR analysis revealed the appearance of zinc aluminate three characteristic bands at 496, 565 and 666 cm-1. In addition to the two bands appeared at 989 and 1429 cm-1 with high intensity for molten salt sample, they were attributed to Al-OH bond bending mode. The microstructure of molten salt sample is appeared more homogeneous, since particles participated from dissolved phase according to Ostwald ripening phenomenon. Molten salt sample was characterized by higher absorbance and lower bandgap energy (2.48 eV) than SSR sample (2.78 eV), this was attributed to the presence of larger amount of surface adsorbed water molecules represented by intense peaks of Al-OH bond bending in FTIR analysis. Adsorbed water molecules create oxygen vacancies which act as localized energy states in the bandgap. Consequently, the highest photocatalytic activity was accomplished by molten salt sample. Photocatalytic degradation of BCBD was operated under controlling the pH (5-10), dye concentration (40-80 mg/l) and sample dose (0.25-1 g/l). About 86 and 94.5 % degradation of dye (40 mg/l) achieved in 180 min at pH 10 using 1 g/l of solid state and molten salt samples, respectively. Photocatalytic stability of molten salt sample was checked for five cycles at the optimum conditions, sample proved a good photocatalytic stability under visible light irradiation.
Chapter three:
In this chapter: cobalt doped zinc aluminate was synthesized through molten salt synthesis using cobalt chloride powder. Cobalt was added to molten salt mixture by various amounts 3, 5 and 7 wt. % of cobalt: zinc aluminate, mixtures were heat treated at 1100°C. The XRD revealed that, single phase cobalt doped zinc aluminate was produced with all cobalt amounts and peaks didn’t show any shift to lower or higher angle after doping, unless the peaks intensity decreased then gradually increased. The crystallite size increased with doping, it was calculated to be 37, 52, 56.7 nm for samples containing 3, 5 and 7 % cobalt, respectively. In FTIR analysis, the three characteristic bands of zinc aluminate were replaced by two bands appeared at 551 and 680 cm-1, the former two peaks were interfered owing to zinc replacement by cobalt. The presence of zinc in the structure was confirmed by XPS analysis, in which zinc wasn’t completely replaced by cobalt and the synthesized samples are cobalt doped zinc aluminate by various cobalt amounts. The microstructure was improved by doping in which cubic structure could be clearly detected by SEM for sample containing 7 % cobalt, and for all doped samples by high resolution TEM investigation. Samples produced with improved optical properties, in which, high absorbance of cobalt doped samples was represented by three absorption peaks appeared at 545, 588 and 624 nm are corresponding to the absorption of yellow, orange and red colors and this implying the greenish blue color of samples. High deterioration in the bandgap energy with doping was observed, samples produced with 1.9, 1.8 and 1.6 eV for samples containing 3, 5 and 7 % cobalt, respectively. This reflects the low recombination rate of samples and the high catalytic activity of doped samples specially under visible light.
Sample containing 7 % cobalt was utilized in the photocatalytic degradation of BCBD and evidenced a high catalytic activity in comparison to the undoped sample. The pH, dye concentration and sample dose effects were investigated and complete degradation of dye (40 mg/l) was achieved in 120 min at pH 10 using 1 g/l of sample containing 7 % cobalt. Photocatalytic stability of cobalt doped sample was checked for five cycles at the optimum conditions, sample proved a high photocatalytic stability under visible light irradiation. Degradation percentage was checked by TOC analysis, resulting in 77.7 % degradation in 120 min at optimum degradation conditions, this implies the formation of uncolored by-products.
Chapter four:
In this chapter: zinc aluminate nanoparticles were synthesized through co-precipitation method using dissolved zinc and aluminum nitrates solutions. Nitrate’s solutions were mixed by 1: 2 molar ratio of Zn: Al and then precipitated under stirring using ammonium hydroxide solution, the precipitate heat treated at different reaction temperatures 500, 700, 900 and 1100°C. XRD analysis revealed that, single phase of zinc aluminate formation commenced at 500°C, while crystalline phase was synthesized at 700°C. The average crystallite size was found to be 4.8, 7.2, 13.5 and 24.2 nm at 500, 700, 900 and 1100°C, respectively. Two distinct broad bands appeared at 485 and 673 cm-1 in FTIR spectra for sample synthesized at 500°C, implying the incomplete formation. These bands were converted into the three characteristic bands of zinc aluminate at 700°C, implying the complete formation. The microstructure of samples synthesized at low reaction temperature consists of spheres like particles, which converted to cubic particles at 900°C with high crystallinity and crystallite size at 1100°C. The bandgap energy varied from 2.6 to 2.27 eV with varying the reaction temperature from 500 to 1100°C.
Cobalt doped zinc aluminate was synthesized by mixing cobalt chloride with the precipitated powder by various amounts 3, 5 and 7 wt. % of cobalt: zinc aluminate, mixtures were heat treated at 1100°C. XRD analysis revealed that, single phase cobalt doped zinc aluminate was produced with all cobalt amounts and a slight shift of peaks to lower angle was observed, whereas the peaks intensities slightly increased. The average crystallite size was found to be 71, 88.6 and 89.2 nm for samples doped with 3, 5 and 7 % cobalt, respectively. The FTIR spectra showed the appearance of the three characteristic peaks of zinc aluminate with slightly increasing in their intensities. XRD and FTIR analysis confirmed the incorporation of cobalt in zinc aluminate structure. The microstructure investigations revealed that, the cubic structure clearly noticed for all doped samples by SEM and this confirmed by TEM investigations. A high deterioration in the bandgap from 1.77 to 1.5 eV with increasing the cobalt amount from 3 to 7 %, respectively.
In order to optimize the structural and optical properties of sample containing 7 % cobalt, it was synthesized with controlling the reaction temperature from 500 to 1100°C. Cobalt doped zinc aluminate formation commenced at 500°C whereas, the reaction didn’t complete at temperature less than 900°C. The average crystallite size was found to vary from 6.4 nm to 89.2 nm with varying the reaction temperature from 500 to 1100°C, respectively. FTIR spectra evidenced that, bands shifted to lower wavenumber with appearance of two bands at 1696 and 3430 cm-1 for samples synthesized at 500-900°C and disappeared for sample synthesized at 1100°C. These bands were attributed to the bending and stretching vibrations of surface adsorbed water molecules. The microstructure consists of very small spherical particles at low temperature which converted to cubic particles at 900°C, in which agglomeration increased with increasing the reaction temperature. The bandgap energy was optimized at 1.4 eV for 7 % cobalt doped sample synthesized at 900°C. The high absorbance of sample synthesized at 900°C induced the dark greenish blue color of this sample, in which, sample with bright color was synthesized at 1100°C implying the bandgap energy increase.
Optimal doped and undoped samples were utilized in the photocatalytic degradation of BCBD at the optimum conditions of pH (10), dye concentration (40 mg/l) and sample dose (1 g/l). Complete degradation of the dye was achieved in 75 and 120 min using doped and undoped samples, respectively. The TOC analysis resulted in 77.7 % degradation in 75 min at optimum conditions using 7 % cobalt doped sample, this implies the formation of uncolored by-products.