Saudi Cultural Missions Theses & Dissertations
Permanent URI for this communityhttps://drepo.sdl.edu.sa/handle/20.500.14154/10
Browse
3 results
Search Results
Item Restricted Microwave Assisted Synthesis of Au/TiO2 Catalyst for Photocatalysis and Oxidation Processes(Cardiff University, 2024) Alazmi, Abdullah Mubarak S; Edwards, JenniferHeterogeneous catalysis using supported metal nanoparticles has attracted tremendous interest for applications including photocatalysis and selective oxidations. This work focuses on synthesis and characterization of Au nanoparticles supported on TiO2 (Au/TiO2), which exhibits unique photocatalytic and catalytic properties arising from quantum and plasmonic effects of Au as well as strong metal-support interactions. A facile microwave-assisted polyol approach was used to prepare Au/TiO2 with 0.1-3 wt% Au loading. Structural characterization by XRD revealed anatase TiO2 support was retained after Au deposition. Au particle size increased from sub nm clusters at 0.1 wt% to 13.5 nm nanoparticles at 3 wt% loading, demonstrating tunable nanoparticle dimensions. CO oxidation testing showed highest mass activity for 0.5 wt% Au/TiO2, with declining performance at higher loadings attributed to loss of low-coordination sites through agglomeration. Photocatalytic degradation of methyl orange dye was most efficient with 0.5 wt% Au/TiO2 under simulated solar irradiation. The higher photoactivity is ascribed to improved visible light harvesting and minimized charge recombination from uniform deposition of small plasmonic Au nanoparticles. The results demonstrate optimized Au loading and dispersion governs both catalytic and photocatalytic efficiency of Au/TiO2 synthesized via microwave polyol method.29 0Item Restricted Structure and Physical Properties of Mixed-Metal Chalcogenides for Energy Applications(University of Reading, 2024-03-08) Aldowiesh, Alaa; Powell, AnthonyThermoelectricity offers a promising solution to help address the ongoing energy crisis by utilizing waste heat and reducing the reliance on conventional energy sources thereby contributing to a more sustainable and environmentally friendly energy future. A thermoelectric device allows for the direct conversion of thermal energy to electrical energy or vice versa through several principles. The structural and thermoelectric properties have been investigated for three families of mixed-metal chalcogenides materials. Chemical substitution approaches have been used on all the prepared materials as a method to enhance the thermoelectric performance. Focusing on Cu2BGeSe4 (B = Fe, Mn and Co), the influence of magnetic ions on crystal structure and thermoelectric properties was explored. Different crystal structures are adopted based on the magnetic ion present, with Cu2FeGeSe4 and Cu2MnGeSe4 exhibiting structural phase transitions at ~ 500 K affecting their electrical properties. The phase Cu2CoGeSe4, which was characterised by the increased tetragonal distortion parameter, achieved a maximum figure of merit ZT of 0.52 at 875 K. Magnetic studies uncovered antiferromagnetic order in Cu2MnGeSe4. Neutron diffraction data revealed magnetic scattering in Cu2MnGeSe4 phase, while Cu2FeGeSe4 showed no evidence of long-range magnetic ordering which indicates a spinglass transition. The magnetic unit-cell of Cu2MnGeSe4 is doubled in the a and c directions and is defined by the propagation vector k = [1/2, 0, 1/2] with an ordered magnetic moment of μ = 3.950(2) μB at 5 K. The room-temperature analysis of neutron diffraction data for Cu2FeGeSe4 shows an antisite cation disorder at the 4d and 2a sites. Investigations of the effect of magnetic ions on the thermoelectric properties were extended to the mixed derivatives, Cu2Fe1-xMxGeSe4 (M=Mn and Co) (0 ≤ x ≤ 1), in which improvements in figure of merit and the average figure of merit were observed, with Cu2Fe0.925Co0.075GeSe4 achieving the maximum ZT = 0.53 at 800 K. Tunning the carrier concentration through electron doping was investigated in the series Cu2FeGeSe4-x (0 ≤ x ≤ 0.3). Reducing the Se content increases the figure of merit reaching ZT = 0.47 at 875 K for Cu2FeGeSe3.90 in comparison with the end-member phase. The new kiddcreekite-type materials have been investigated as a potential TE materials. The materials are of interest for their complex crystal structure, large unit-cell and the presence of heavy atoms. X-ray powder diffraction coupled with Rietveld refinements confirmed the cubic structure with the space group F4̅ 3m and lattice parameters a = 10.8328(1) Å and a = 11.2781(2) Å for Cu6SnWS8 and Cu6SnWSe8 respectively. Cu6SnWS8 outperformed Cu6SnWSe8 in the figure of merit due to its lower electrical resistivity and enhanced Seebeck coefficient, attributed Alaa Aldowiesh VII to point-defects and off-stoichiometry that altered the electronic band structure. The maximum figure of merit reached ZT = 2.3 × 10-4 at 575 K for Cu6SnWSe8 and ZT = 0.021 at 675 K for Cu6SnWS8. Substituting components at different sites within the kiddcreekite materials (24f , 4c, 4a and 16e) through electron, hole, and isovalent substitution shows limited effectiveness in improving ZT, as the substitution negatively impacted the electrical transport properties. Work on p-type two-dimensional materials demonstrated that Cr2-xInxGe2Te6 (x = 0, 1, 2) based compounds are good candidates for thermoelectric applications. The phases Cr2Ge2Te6 and In2Ge2Te6 crystallise in the trigonal space group R3̅ , whereas the phase CrInGe2Te6 crystallises in the trigonal space group P3̅ 1c. Replacing one Cr3+ with In3+ increased the figure of merit reaching ZT⊥ = 0.18 at 730 K in CrInGe2Te6. However, the power factor in the undoped material, CrInGe2Te6, is lower than that of conventional thermoelectric materials. This indicates that further enhancement of the electrical properties can be achieved through chemical substitution. The thermoelectric performance is greatly enhanced in the two series Cr1-xMnxInGe2Te6 and CrIn1-xMnxGe2Te6 (0 ≤ x ≤ 0.1). The substitution reduced the electrical resistivity, ρ, and this reduction offset the insignificant increase in the thermal conductivity. Hole doping enhanced the thermoelectric performance by up to 67% and 60% in Cr0.92Mn0.08InGe2Te6 and CrIn0.92Mn0.08Ge2Te6 ,respectively, reaching ZT⊥ = 0.52 and ZT⊥ = 0.42 at 730 K.16 0Item Restricted Solvation Dynamics of Choline Halide-Based Deep Eutectic Solvents(2023) Alfurayj, Ibrahim Ahmed; Burda, ClemensThe intermittent nature of renewable energy sources requires reliable and cheap long-term energy storage technologies. Redox flow batteries (RFBs) are reliable, scalable, and cost-efficient. Electrolytes are crucial for RFB's performance. Deep eutectic solvents (DESs) are a new class of ionic liquids with relatively cheap and easy synthesis. In addition, their properties are tunable, making DES an excellent candidate for many energy and industry applications. A DES mixture is created by combining hydrogen-bond acceptor (HBA) and donor (HBD) in a specified ratio, producing a mixture with a lower melting point than its constituent components. Varying the type and ratio of HBA results in tunning DES properties. Also, adding co-solvents, such as water, can provide further tunning to DES mixtures. This dissertation aims to study the potential of water addition, HBA choice, and the compositional variation to optimize the solvation dynamics and physicochemical properties of choline halide-based DESs. Besides the most famous Ethaline (choline chloride ChCl): ethylene glycol (EG), 1:2), we reported the first choline fluoride (ChF) and EG-based DES mixture preparation with 1:2 molar ratio. We studied physical properties upon water addition by conductivity, density, viscosity, and ET(30) polarity. NMR, FT-IR, and Raman spectroscopies were used to characterize their structures. Femtosecond transient-absorption spectroscopy (fs-TSA) and NMR-diffusometry were used to study solvation dynamics, providing a powerful tool for studying charge transport properties. Volumetric properties were used to study the effect of water in EthalineF/water and Ethaline/water mixtures. This work also investigated the eutectic enhancement of dynamics and charge transport in Ethaline. We provided excellent tools, such as using B30 as a probe molecule in time-resolved spectroscopy to study solvation dynamics and correlating DES-DES self-interactions to experimental conductivities. Also, proved that water (>1 wt.%) can accelerate charge transport and enhance physical properties. The vibrational spectroscopies indicate that EthalineF has stronger hydrogen bond interactions than Ethaline. In addition, we reported the effect of the solvodynamic radius on the observed lower conductivity in EthalineF compared to Ethaline. Furthermore, based on the NMR diffusion measurements, we assigned the two F-NMR peaks to be EG and choline associated fluorides.17 0