الفهرس 
Chapter 1: IntroductionOnly 14 pages are availabe for public view
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Abstract
Abstract
MoS2 is one of the transition-metal dichalcogenides (TMDs) that has gained a high reputation in recent years due to its distinct chemical, electronic, mechanical, magnetic, and optical properties. Its unique properties enabled its use in different applications, such as sensing applications, high-efficiency field effect transistors, energy and medical applications, and photocatalysis.
Pure MoS2, Mo1-xCoxS2, Mo1-xMnxS2, and Mo1-xFexS2 nanostructures as photocatalysts were synthesized by using the hydrothermal method and characterized via various characterization techniques such as powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray spectroscopy (EDX), and UV-visible spectroscopy (UV-vis) in order to investigate the structural, morphological, chemical compositional, and optical properties of the prepared nanoparticles.
The application of dyes in different industrial processes will cause environmental pollution (i.e., water pollution). Thus, the need for the removal of dyes using an advanced oxidation process is a vital issue to decrease the effect of dyes on both humans and the natural environment. An advanced oxidation process works based on the generation of hydroxyl radicals as an intermediate to take place during the photocatalytic process under UV or visible light irradiation. Methylene Blue (MB) and Rhodamine B (RhB) dyes are reported to be the major cause of water pollution, which results in the scarcity of clean water for human use. Thus, the aim of this study was to synthesize molybdenum disulfide (MoS2) nanostructure, evaluate its photocatalytic properties for water treatment, and study the possibility of incorporating transition metal ions such as Co, Mn, or Fe in the MoS2 lattice to investigate the effect of this incorporation on its physical properties and photocatalytic activity.
The obtained pure MoS2 nanoflowers (NFs) have excellent crystallinity with an average grain size of 6.84 nm. The optical bandgap was determined to be 1.82 eV. Their photocatalytic activity has been demonstrated by degrading both RhB and MB dyes under UV and visible light irradiation. The results reflected that in the case of using the UV source, the photocatalytic degradation speed of the MB dye is very close to that of the RhB dye, while the degradation of the RhB dye is still faster and more efficient, especially in the first 20 minutes of the irradiation period. However, in the case of using visible light, the MB dye degraded faster and more efficiently than the RhB dye. In addition, the photocatalytic mechanism has been explained, and MoS2 nanoflowers have shown excellent reusability. Under UV illumination, the efficiency was 84.31% in the case of RhB dye, while it was 75.97% in the case of MB dye through 180 minutes. However, when using visible light as a source of illumination, an opposite behavior was detected, and MoS2 was more efficient in degrading MB (84.25%) than RhB (73.99%) through 60 minutes of irradiation.
Co-doped MoS2 nanostructures Mo1-xCoxS2 (0 ≤ x ≤ 0.1) were successfully synthesized by using the hydrothermal route using ammonium molybdate tetrahydrate, thiourea, and cobalt nitrate hexahydrate as precursors. The crystal structure of the prepared samples was investigated by XRD, emphasizing that all the prepared samples had a hexagonal structure of MoS2, and revealed an increment in the average particle size from 5 to 8 nm with increasing cobalt ratio. The morphology was examined using SEM, and the recorded images of pure and cobalt-doped MoS2 show flower-like architecture clusters. FT-IR spectroscopy was carried out to detect functional groups and stretching and bending vibrations of chemical bonds existing in all the prepared samples, confirming the presence of Mo-O and Co-O-Co characteristic peaks. The chemical composition of the synthesized samples was determined by EDX analysis. The results confirmed the presence of Mo, S, and Co, which are consistent with the proposed formation of Mo1-xCoxS2 nanosystems. Optical properties were examined by UV-visible spectrophotometry, reflecting allowed direct transitions with an energy band gap that decreases from 1.9 eV to 1.53 eV with an increasing cobalt ratio. The photocatalytic degradation efficiency of methylene blue (MB) for pure and different ratios of cobalt-doped MoS2 was tested using visible light radiation (3 W LED lamp), and it was noticed that the MB degradation increased with increasing cobalt concentration. The photocatalytic degradation was enhanced to 58.2%, 61.7%, 66.5%, 69.4%, and 82.8% by increasing the concentration of cobalt to 2%, 4%, 6%, 8%, and 10% Co-doped MoS2, respectively, which means that the optimum photocatalyst concentration is 10% Co-doped MoS2 (Mo0.90Co0.1S2). Furthermore, the rate constant of degradation gradually increases with the content ratio of doping, reaching its maximum for 10% Co-doped MoS2, starting from 0.03939 min-1 to 0.18204 min-1.
Manganese (Mn) substituted molybdenum disulfide Mo1-xMnxS2 (0 ≤ x ≤ 0.015) nanostructures were synthesized using the hydrothermal method for photocatalytic activity by taking ammonium molybdate tetrahydrate, thiourea, and manganese (II) acetate tetrahydrate as precursors. The effect of Mn incorporation on the morphological, structural, optical, and photocatalytic properties of pristine MoS2 was examined. Field emission SEM was used to study the morphology of the as-synthesized samples, and the recorded images showed an aggregated nanoflower-like structure. XRD technique was carried out in order to examine the crystal structure of pure and Mn-doped MoS2 samples, and the results confirmed that Mn is completely doped into the lattice of the 2H-MoS2 polytype, with a decrease in the average particle size by increasing the dopant ratio. Also, further investigation of the structure was detected using FTIR spectroscopy, which collects data about the functional groups and chemical bonds existing in the prepared samples, confirming the presence of the Mo-S characteristic band. The elemental composition of pure and Mn-doped MoS2 NFs was confirmed by EDX spectroscopy. The optical properties were observed through optical UV-vis spectroscopy, demonstrating allowed direct transitions with an optical energy band gap that decreased with increasing the Mn doping ratio. Doping of transition metal ions in MoS2 nanosheets is a recognized approach for improving their catalytic efficiency for the reduction of organic pollutants; therefore, the photocatalytic performance of undoped and Mn-doped MoS2 NFs was evaluated by the degradation of MB dye under visible light irradiation (150-watt halogen lamp). This part of this thesis is the first work on the Mo1-xMnxS2 nanostructure with small x values that demonstrate its effectiveness as a photocatalyst for MB degradation. The obtained results indicated that 1.5% Mn-doped MoS2 achieves a maximal photocatalytic degradation of 96% MB in 60 minutes, compared to 78% for pure MoS2 photocatalyst. In addition, the estimated degradation rate constant was 0.022 min-1 for pure MoS2 and increased with increasing the Mn-dopant ratio up to 0.051 min-1 for 1.5% Mn-doped MoS2.
Iron-substituted molybdenum disulfide Mo1-xFexS2 (0 ≤ x ≤ 0.1) nanostructures were synthesized for photocatalytic activity utilizing the hydrothermal process, with precursors including ammonium molybdate tetrahydrate, thiourea, and ferric nitrate nonahydrate. Several characterization approaches were used to investigate the influence of Fe incorporation on the morphological, structural, optical, and photocatalytic characteristics of pure MoS2. Field emission SEM was utilized to investigate the morphology of the as-synthesized samples, and the pictures revealed an aggregated nanoflower structure. The XRD findings revealed that Fe is entirely doped into the lattice of the 2H-MoS2 polytype, with an increase in average particle size as the dopant ratio increased. Furthermore, FTIR analysis, which gathers data on the functional groups and chemical bonds present in the produced samples, confirmed the existence of Mo-O and Fe-O characteristic peaks. A decrease in the optical energy band gap was observed by increasing the Fe concentration, from 1.9 eV for pure MoS2 to 1.45 eV for 10% Fe-doped MoS2. This observation was made through optical UV-vis spectroscopy. Fe-doped MoS2 nanoflowers’ photocatalytic activity was assessed by the degradation of MB dye under UV light irradiation (8-watt with 365 nm wavelength). The photocatalytic activity has steadily decreased as the Fe dopant ratio has increased. It reduced from 75.9% for pure MoS2 to 73.99%, 55.38%, 44.68%, 34.19%, and 18.80% for 2%, 4%, 6%, 8%, and 10% Fe-doped MoS2, respectively.