Patrick G. Ndungu

Multiwalled Carbon Nanotube-titania Nanocomposites: Understanding Nano-Structural Parameters and Functionality in Dye-sensitized Solar Cells

Nanocomposites consisting of multiwalled carbon nanotubes and titania were synthesized by two methods, namely, sol-gel and chemical vapour deposition (CVD) methods. The work takes advantage of the bridging ability of nanotechnology between macromolecules and the solid state process in engineering alternative nanomaterials for various applications including solar cell fabrication. Physical and chemical characterization of the mesoporous nanocomposites from the two synthetic methods were investigated using Raman spectroscopy, thermogravimetric analysis, Fourier transformation infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, surface characterization and X-ray diffraction analysis. Physicochemical properties in the nanocomposites such as thermal stability, pore volume, crystallinity and surface area were observed to be a subject of MWCNT: titania ratios and synthetic methods. From the CVD synthetic method, observed attributes include more uniform and smoother coating; better crystallinity and larger pore width than sol-gel method. On the other hand, nanocomposites from sol-gel synthetic method had larger surface areas, were more defective and less thermally stable than those from CVD. Nanocomposites by the CVD method performed 39.2 % more efficient than those from sol-gel in light-harvesting experiments. The study shows that the nanocomposites synthesized were more effective than titania alone when the cheaper natural dye, Eosin B, was used. This highlights the great potential of typical nanomaterials in improving the performances of titania in DSSCs as well as lowering the cost of the ultimate devices.

Oxyhalogen-sulfur chemistry: kinetics and mechanism of oxidation of captopril by acidified bromate and aqueous bromine.

By nature of their nucleophilicity, all thiol-based drugs are oxidatively metabolized in the physiological environment. The key to understanding the physiological role of a hypertension drug, (2S)-1-[(2S)-2-methyl-3-sulfanylpropanoyl]pyrrolidine-2-carboxylic acid, medically known as captopril is through studying its oxidation pathway: its reactive intermediates and oxidation products. The oxidation of captopril by aqueous bromine and acidified bromate has been studied by spectrophotometric and electrospray ionization techniques. The stoichiometry for the reaction of acidic bromate with captopril is 1:1, BrO3(-) + (C4H6N)(COOH)(COCHCH3CH2)-SH → (C4H6N)(COOH)(COCHCH3CH2)-SO3H + Br(-), with reaction occurring only at the thiol center. For the direct reaction of bromine with captopril, the ratio is 3:1; 3Br2 + (C4H6N)(COOH)(COCHCH3CH2)-SH + 3H2O → (C4H6N)(COOH)(COCHCH3CH2)-SO3H + 6HBr. In excess acidic bromate conditions the reaction displays an initial induction period followed by a sharp rise in absorbance at 390 nm due to rapid formation of bromine. The direct reaction of aqueous bromine with captopril was much faster than oxidation of the thiol by acidified bromate, with a bimolecular rate constant of (1.046 (±0.08) × 10(5) M(-1) s(-1). The detection of thiyl radicals confirms the involvement of radicals as intermediates in the oxidation of Captopril by acidified BrO3(-). The involvement of thiyl radicals in oxidation of captopril competes with a nonradical pathway involving 2-electron oxidations of the sulfur center. The oxidation product of captopril under these strong oxidizing conditions is a sulfonic acid as confirmed by electrospray ionization mass spectrometry (ESI-MS), iodometric titrations, and proton nuclear magnetic resonance ((1)H NMR) results. There was no evidence from ESI-MS for the formation of the sulfenic and sulfinic acids in the oxidation pathway as the thiol group is rapidly oxidized to the sulfonic acid. A computer simulation analysis of this mechanism gave a reasonably good fit to the experimental data.

Effect of graphite/sodium nitrate ratio and reaction time on the physicochemical properties of graphene oxide

Abstract Graphene oxide (GO) was synthesized by the reaction of graphite with sodium nitrate and the graphite/sodium nitrate mass ratio and the reaction time were varied in order to obtain the highest oxygen content. The GO was characterized by TEM, SEM, AFM, XRD, FT-IR, TGA, elemental analysis, and UV-vis and Raman spectroscopy. The effect of oxygen content on the physicochemical properties of GO was investigated. Results indicate that increasing the graphite to sodium nitrate ratio increases the oxygen content, BET surface area, pore volume and pore size but reduces the crystallite size of the GO samples. However, the oxygen content of GO is not directly related to the reaction time. Physicochemical properties such as d-spacing and defect density increase with increasing oxygen content while the thermal stability decreases. The physicochemical properties such as oxygen content, crystallinity, thermal stability and structure can be tailored by varying the graphite/sodium nitrate ratio and reaction time.

Synthesis and characterization of Ce 0.6 Sr 0.4 Fe 0.8 Co 0.2 O 3– δ perovskite material: Potential cathode material for low temperature SOFCs

Abstract A sol-gel method and a modified chemical vapour deposition technique were used to produce nanostructured Ce 0.6 Sr 0.4 Fe 0.8 Co 0.2 O 3– δ materials at temperatures as low as 400 °C. Powders were characterized using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, thermo gravimetric analysis, powder X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy, high resolution transmission electron microscopy (HRTEM), and nitrogen sorption at 77 K. FTIR spectra showed that the sol-gel method resulted in residual carbon groups on the materials after calcination, while the Raman and XRD analysis confirmed that both synthesis methods resulted in cubic perovskite structure. However, the chemical vapour deposition (CVD) method resulted in materials with a smaller crystallite size when compared to those prepared via the sol-gel route. The overall morphology of the powders was irregularly shaped aggregated particles as observed by SEM and HRTEM. In addition, HRTEM analysis showed that the materials were highly crystalline. Textural analysis revealed the powders had some mesoporosity, and the surface areas were 76.69 and 65.90 m 2 /g for materials synthesized using the CVD and sol-gel methods, respectively. The synthesized perovskite powders were used to fabricate button cells employing samarium doped ceria (SDC) as the electrolyte and NiO/SDC as the anode materials. As cathode materials, the maximum power density observed was 308.4 mW/cm 2 at 500 °C.

Theoretical and experimental adsorption studies of sulfamethoxazole and ketoprofen on synthesized ionic liquids modified CNTs

The adsorption of sulfamethoxazole (SMZ) and ketoprofen (KET) using carbon nanotubes (CNTs) and CNTs modified with ionic liquids (ILs) was investigated. Two ionic liquids (1-benzyl, 3-hexyl imidazolium, IL1 and 1-benzyl, 3-decahexyl imidazolium, IL2) were synthesized, and characterized by nuclear magnetic resonance (1H and 13C NMR) and high resolution-mass spectrometry (HR-MS). CNTs and modified CNTs were characterized using FT-IR, X-ray diffraction (XRD), surface area and porosity analysis, thermal gravimetric analysis (TGA), Zeta potential, Raman and scanning electron microscopy (SEM). Kinetics, isotherm and computational studies were carried out to determine the efficiency and adsorption mechanism of SMZ and KET on modified CNTs. A density functional theory (DFT) method was applied to shed more light on the interactions between the pharmaceutical compounds and the adsorbents at the molecular level. The effects of adsorbent dosage, concentration, solution pH, energetics and contact time of SMZ and KET on the adsorption process were investigated. The adsorption of SMZ and KET on CNTs and modified CNTs were pH dependent, and adsorption was best described by pseudo-second-order kinetics and the Freundlich adsorption isotherm. Ionic liquid modified CNTs showed improved adsorption capacities compared to the unmodified ones for both SMZ and KET, which is in line with the computational results showing performance order; CNT+KET/SMZ < CNT-ILs+SMZ < CNT-ILs+KET.

Recent advances in titanium dioxide/graphene photocatalyst materials as potentials of energy generation

The properties of titanium dioxide (

Supporting titanium on silica, graphene, epoxy graphene and carbon nanotubes: A first-principles study

\hbox {TiO}_{2})

Photocatalytic degradation of 4-chloro-2-methylphenoxyacetic acid using W-doped TiO2

TiO2)/graphene/graphene oxides (GO) are examined in this study. These views summarize the recent theoretical and experimental novel approaches in the catalytic activity of