Preparation and characterization of some molecular and glassy semiconductors.

This work concerns mainly the characterization of oxonol dyes, cyanine dyes and their complexes, especially with tetrathiafulvalene (TTF). Some work has also been done on titanium (IV) doped iron (III) oxide. Cyclic voltammetry shows that TTF and its derivative dibenzo TTF can be reversibly oxidized to its radical cation and dication in non-aqueous solution. The equilibrium potentials for two one-electron oxidation steps in acetonitrile/tetrabutylammonium perchlorate (TBAP) were measured and found to be E(0,+.) = 0.302V and E(+.,++) = 0.770V for TTF and E(0,+.) = 0.540V and E(+.,++) = 0.900V for dibenzo TTF. Unlike cyanine dyes, oxonols are irreversibly oxidized and equilibrium potentials were measured by extrapolation of potential-sweep rate curves. Also using cyclic voltammetry, the rates of electron-transfer were calculated for TTF and dibenzo TTF as well as an electrochemical reduction series for some charge-transfer compounds relative to hydrogen reduction potential.The complex TTF/oxonol dye was prepared electrochemically at the optimum conditions. Its solubility and sensitivity towards pH changes were measured. Cyclic voltammetry shows that the complex is irreversibly oxidized and at lower voltages compared to its constituents TTF and oxonol dye. Electrical measurements show that the complex is a semiconductor and the energy gap is 0.516 eV. First ionization potentials measured by photoelectron spectroscopy for TTF, dibenzo TTF and TTF-oxonol dye complex give approximately the same value which suggests that, the solution chemistry of these conpounds is different from their gaseous state behaviour. MNDOcalculations were used for geometry optimization, charge-density distribution, heats of formation and ionization potentials. Coupling constants and g-factors were calculated for TTF, its dibenzo derivative and its dye complexes using esr spectroscopy. Charge-transfer couplexes, particularly TTF/TCNQ show some degree of response towards polluting gases such as sulphur dioxide and carbon monoxide as determined by their conductivity changes when the gases were passed over the surface. They may therefore be used as gas sensors if certain modifications in structure or electrode design could be made.Titanium (IV) Iron (III) oxide mixture shows a reasonable conductivity of 1.4 x 10 ft cm but unfortunately a compressed pellet electrode is not mechanically stable. This problem can be solved by sintering the oxides with glass powder which resulted in a high resistance electrode in which some pH/voltage measurements have been done.<p

Surface Functionalization of Mesoporous Carbon for the Enhanced Removal of Strontium and Cesium Radionuclides

Mesoporous carbons (MPC) and modified mesoporous carbons (MMPC) were prepared from asphalt for the adsorption of several metal ions from the aqueous solution. In this study, we investigated the adsorption efficiency of Cesium (Cs+) and Strontium (Sr2+) ions using mesoporous and modified mesoporous carbons. The optimum conditions for the removal of Cs+ and Sr2+ were at 10.0 pH, 1.00 ppm (1000.0 &micro;g/L) concentration, 20.0 min contact time, 0.20 g/L adsorbent dose, 25.0 &deg;C temperature with more than 95.0% removal of Cs+ and Sr2+ ions using MMPC. The limit of detection (LOD) was found to be 0.030 ppb and 10.00 ppb for Sr2+ and Cs+ metals ions, respectively, while the Limit of quantification (LOQ) was calculated to be 0.10 ppb for Sr2+ and 35.00 ppb for Cs+ metals ions. The functionalization of the MPC was performed using potassium permanganate to get MMPC, which were characterized by FT-IR spectroscopy. The nature of the X-ray diffraction peaks suggests that the MPC and MMPC carbons are amorphous and semi-crystalline materials. The scanning electron microscope (SEM) and transition electron microscope (TEM) studies showed the changes in the morphology due to the adsorption on the surface of the carbons. The TEM analysis clearly showed that the metal ions blocked most of the pores on the surface. The surface area, by N2 adsorption isotherm (BET), of MPC and MMPC were 937 and 667 m2&middot;g&minus;1, respectively. Among the adsorption isotherms, Langmuir isotherm showed the best linearity. The Langmuir isotherm indicates that the adsorption is monolayer and homogeneous with a finite number of ions. Adsorption kinetics showed better linearity with pseudo-second-order plots and obeys this order. This process indicates that the chemical interaction, such as covalent or ionic bonding, took place between the metal ions and the carbon adsorbents

Single-Walled Carbon Nanotube (SWCNT) Loaded Porous Reticulated Vitreous Carbon (RVC) Electrodes Used in a Capacitive Deionization (CDI) Cell for Effective Desalination

Acid-functionalized single-walled carbon nanotube (a-SWCNT)-coated reticulated vitreous carbon (RVC) composite electrodes have been prepared and the use of these electrodes in capacitive deionization (CDI) cells for water desalination has been the focus of this study. The performance of these electrodes was tested based on the applied voltage, flow rate, bias potential and a-SWCNT loadings, and then evaluated by electrosorption dynamics. The effect of the feed stream directly through the electrodes, between the electrodes, and the distance between the electrodes in the CDI system on the performance of the electrodes has been investigated. The interaction of ions with the electrodes was tested through Langmuir and Freundlich isotherm models. A new CDI cell was developed, which shows an increase of 23.96% in electrosorption capacity compared to the basic CDI cells. Moreover, a comparison of our results with the published results reveals that RVC/a-SWCNT electrodes produce 16 times more pure water compared to the ones produced using only CNT-based electrodes. Finally, it can be inferred that RVC/a-SWCNT composite electrodes in newly-developed CDI cells can be effectively used in desalination technology for water purification