Synthesis, Fabrication of Graphene Oxide Membranes, and Controlling Their Diffusion by Thermal Reduction

Graphene and graphene oxide have many applications in different fields such as electronic devices, electrochemical energy storage, catalysis, polymer composite, and liquid crystal devices. Oxidation of graphite to graphite oxide permits the separation of its newly formed graphene oxide molecular layers. Graphene oxide, easily deposited in the form of a film through vacuum filtration, can be partially reduced by various methods to imperfectly restore the π-network system of graphene. Reduced graphene oxide (rGO) films possess functional properties with practical applications. The main objective of this research is to carry out controlled extents of thermal reduction of graphene oxide to manipulate the d-spacing of the layers within the partially reduced films to optimize their characteristics with respect to metal ion diffusion across the films. In addition to this main objective, several other features of rGO were explored, including mechanical properties and electrical conductivity. Since GO is an electrical insulator, thermal or chemical reduction methods must be utilized in order to make it electrically conducting. Both of these methods have been used in this thesis. In the first project, the primary aim of this work, reduction of GO films was done via thermal treatment (60, 180, 200, 225, 250, and 300 °C) and also by ascorbic acid as well as hydrazine vapour. Chemical cross-linking (Na+, Mg2+, Ba2+, Fe2+, Fe3+) was performed to explore the reduction in the d-spacing between reduced GO layers. Tensile strength test was conducted on non-reduced and the GO films reduced at different temperatures to investigate their strength. In the second project, thermally reduced GO films were used in diffusion studies of 100 mM NaCl and 100 mM CaCl2. Current-voltage measurements were also conducted on these films to investigate the impact of the change in the d-spacing by thermal treatment on their electrical conductivity. In the third project, ZnO nanorods were grown on GO film by hydrothermal method and colloidal ZnO as well as GO-ZnO composite were prepared and then used in photodegradation of methylene blue as organic pollutant. In the forth project, ZnO nanorods were incorporated between reduced GO layers so that they would segregate the reduced GO layers to provide a large surface area, after which manganese divalent ions were added to form manganese dioxide so that greater charge can be stored, hence increasing the capacitance of these films for energy storage. Finally, surface potential was applied to these films to explore its influence on the diffusion of 100 mM CaCl2 through different thermally reduced GO films. Based on the results, the d-spacing for GO films was reduced from 7.36 to 4.59 Å on increasing the temperature of thermal reduction from 60 °C to 250 °C. This impacts both the in-plane and out of plane electrical conductivity of the GO films and also their diffusion characteristics. The in-plane electrical conductivity increases by over seven orders of magnitude between 60 °C and 250 °C, and the out-of-plane electrical conductivity also increases by over six orders of magnitude. Similarly, the diffusional resistance for NaCl increases by over 500 times and that of CaCl2 by over 60 times. Powder XRD, SEM, FTIR spectroscopy, Raman spectroscopy, XPS, UV-vis spectroscopy, and TGA were conducted to confirm the phase, morphology, reduction, and thermal stability of these films

Experimental study of natural convective heat transfer from an inclined isothermal cylinder with an exposed top surface mounted on a flat adiabatic base

Paper presented at the 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Mauritius, 11-13 July, 2011.Natural convective heat transfer rates from inclined cylinders with a circular cross-section and which have an exposed top surface have been experimentally measured. The cylinder is mounted on a large flat essentially adiabatic surface with the other cylinder surfaces exposed to the surrounding air and with the cylinder, in general, inclined to the vertical at angles between vertically upwards and vertically downwards. The diameter-to-height ratio of the cylinders used in the present study was comparatively small, diameter-to-height ratios of between 1 and 0.25 being used. The main aim of the present work was to determine how the diameter-to-height ratio of the cylinder, i.e., D/h, influences the mean heat transfer rate from the cylinder at various angles of inclination. The heat transfer rates were determined by a transient method, which basically involving heating the model and then measuring its temperature-time variation while it cooled. Tests were carried out in air with all models at various angles of inclination to the vertical of between 0o and 180o. The Rayleigh number, Ra, based on the cylinder height, h, was between approximately 2E4 and 4E6. The experimental results have been compared with the results obtained in an earlier numerical study.pm201

Physicochemical properties of pseudobrookite Fe2TiO5 synthesized from ilmenite ore by co-precipitation route

Pseudobrookite (Fe2TiO5) is a semiconductor with numerous potential applications. Low-grade ilmenite ore has been used as an inexpensive source of Fe and Ti for preparation of Pseudobrookite. Ilmenite was first leached with 20% hydrochloric acid for 3 h at 70°C. Co-precipitation of soluble Fe and Ti from the rich filtrate was carried out at pH ≥ 9.1 followed by calcination at different temperatures (900-1300oC) for 2 h. X-ray diffraction patterns (XRD) showed that a single-phase nanocrystalline pseudobrookite powder was produced. The pH was a critical parameter for the evolution of formation the different sizes, structural morphology, and the magnetic properties of the product. Scanning electron microscope (SEM) images showed that particles synthesized at pH 11.2 contained more agglomerations and were more porous than those synthesized at pH 9.1. As the calcination temperature increases, the Fe2TiO5 changes from a small rod-like structure to an elongated rod-like structure, and finally to interconnected aggregated crystals. The magnetization of the synthesized Fe2TiO5 was measured using a vibrating sample magnetometer (VSM) and was found steadily increase with increasing calcination temperature from 1000 (≈9 emu/g) to 1300°C (16 emu/g). Such a large saturation of magnetization might be due to the high phase purity and well-defined crystallinity of Fe2TiO5

Synthesis, Spectroscopic, Structural and Molecular Docking Studies of Some New Nano-Sized Ferrocene-Based Imine Chelates as Antimicrobial and Anticancer Agents

The newly synthesized organometallic acetyl ferrocene imine ligand (HL) was obtained by the direct combination of 2-acetyl ferrocene with 2-aminothiophenol. The electronic and molecular structure of acetyl ferrocene imine ligand (HL) was refined theoretically and the chemical quantum factors were computed. Complexes of the acetyl ferrocene imine ligand with metal(II)/(III) ions (Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II)) were fabricated. They were inspected by thermal (DTG/TG), spectroscopic techniques (FT-IR, 1H NMR, mass, UV–Vis), molar conductivity, and CHNClM to explicate their structures. Studies using scanning electron microscope (SEM) were conducted on the free acetyl ferrocene imine ligand and its Cd(II) chelate to confirm their nano-structure. To collect an idea about the effect of metal ions on anti-pathogenic properties upon chelation, the newly synthesized acetyl ferrocene imine ligand and some of its metal chelates were tested against a variety of microorganisms, including Bacillus subtilis, Staphylococcus aureus, Salmonella typhimurium, Escherichia coli, Aspergillus fumigatus, and Candida albicans. The ligand and its metal chelate were tested for cytotoxic activity in human cancer (MCF-7 cell viability) and human melanocyte cell line HBF4. It was discovered that the Cd(II) chelate had the lowest IC50 of the three and thus had the prior activity. Molecular docking was utilized to investigate the interaction of acetyl ferrocene imine ligand (HL) with the receptors of the vascular endothelial growth factor receptor VEGFR (PDB ID: 1Y6a), human Topo IIA-bound G-segment DNA crystal structure (PDB ID: 2RGR), and Escherichia coli crystal structure (PDB ID: 3T88)

Cell Cycle Arrest and Apoptosis-Inducing Ability of Benzimidazole Derivatives: Design, Synthesis, Docking, and Biological Evaluation

In the current study, new benzimidazole-based 1,3,4-oxadiazole derivatives have been synthesized and characterized by NMR, IR, MS, and elemental analysis. The final compounds were screened for cytotoxicity against MDA-MB-231, SKOV3, and A549 cell lines and EGFR for inhibitory activities. Compounds 10 and 13 were found to be the most active against all the tested cell lines, comparable to doxorubicin, and exhibited significant inhibition on EGFR kinase, with IC50 0.33 and 0.38 μM, respectively, comparable to erlotinib (IC50 0.39 μM). Furthermore, these two compounds effectively suppressed cell cycle progression and induced cell apoptosis in MDA-MB-231, SKOV3, and A549 cell lines. The docking studies revealed that these compounds showed interactions similar to erlotinib at the EGFR site. It can be concluded that the synthesized molecules effectively inhibit EGFR, can arrest the cell cycle, and may trigger apoptosis and therefore, could be used as lead molecules in the development of new anticancer agents targeting EGFR kinase