Siham Y. AlQaradawi

Photocatalytic degradation of methyl orange as a model compound

Titanium dioxide (TiO 2 ) was used as a photocatalyst for the detoxification of water containing methyl orange (MO), which was used as a model compound. Solar radiation was used as an irradiation source. It was found that there was no degradation for the MO in the dark and in the presence of TiO 2 . Also no degradation was observed for MO when the solution placed under solar radiation but without TiO 2 . Several experiments were used to optimize the experimental parameters. In the first set of experiments variable amounts of TiO 2 were used with a fixed concentration of MO. It was found that 0.4% of TiO 2 gave the highest degradation rate constant, 0.619 h -1 . In the second set of experiments TiO 2 concentration was fixed at 0.4% and the MO concentration was varied, the highest rate constants was obtained when the concentration of MO was 4 x 10 -5 M and it was found to be 0.639h - The degradation became negligible in the presence of high concentrations of MO. The highest degradation rate was obtained at pH = 3 with a rate constant K = 2.6683h -1 , followed by that at pH = 9 where the calculated K = 0.7585 h -1 .

Dynamic Cross-Linking of Polymeric Binders Based on Host–Guest Interactions for Silicon Anodes in Lithium Ion Batteries

We report supramolecular cross-linking of polymer binders via dynamic host-guest interactions between hyperbranched β-cyclodextrin polymer and a dendritic gallic acid cross-linker incorporating six adamantane units for high-capacity silicon anodes. Calorimetric analysis in the solution phase indicates that the given host-guest complexation is a highly spontaneous and enthalpically driven process. These findings are further verified by carrying out gelation experiments in both aqueous and organic media. The dynamic cross-linking process enables intimate silicon-binder interaction, structural stability of electrode film, and controlled electrode-electrolyte interface, yielding enhanced cycling performance. Control experiments using both α, γ-CDp with different cavity sizes and a guest molecule incorporating a single adamantane unit verified that the enhanced cycle life originates from the host-guest interaction between β-cyclodextrin and adamantane. The impact of the dynamic cross-linking is maximized at an optimal stoichiometry between the two components. Importantly, the present investigation proves that the molecular-level tuning of the host-guest interactions can be translated directly to the cycling performance of silicon anodes.

Synthesis, spectroscopic and thermal investigations of solid charge-transfer complexes of 1,4,7-trimethyl-1,4,7-triazacyclononane and the acceptors iodine, TCNE, TCNQ and chloranil

The solid charge-transfer complexes formed in the reaction of the electron donor 1,4,7-trimethyl-1,4,7-triazacyclononane (TMTACN) with the acceptors iodine, tetracyanoethylene (TCNE) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) have been isolated. These were characterized through electronic and infrared spectra as well as thermal and elemental analysis. The results show that the formed solid CT-complexes have the formulas [(TMTACN)I]I3, [(TMTACN)(TCNE)5] and [(TMTACN)(TCNQ)3] in full agreement with the known reaction stoichiometries in solution. The chloranil CT-solid complex cannot be isolated in pure form.

Synthesis and Spectroscopic Studies of the Charge‐Transfer Complexes of 2,3‐Diaminopyridine and π‐Electron Acceptors

Abstract The spectrophotometric properties of the charge transfer (CT)‐complexes formed between 2,3‐diaminopyridine (DAPY) and π‐acceptors tetrachloro‐p‐benzoquinone (chloranil) and tetracyanoethylene (TCNE) have been studied in chloroform. The stoichiometry of these CT‐complexes is shown to be 1:1, (DAPY:chloranil) and 1:3 (DAPY:TCNE) forming complexes with the general formula [(DAPY)(chloranil)] and [(DAPY)(TCNE)3]. The two complexes were isolated as solids and further characterized by elemental analysis and infrared measurements.

Self-assembled zirconia nanotube arrays: fabrication mechanism, energy consideration and optical activity†

We present a comprehensive roadmap for the precise control of the dimensions and optical properties of anodically fabricated zirconia nanotubes. The effects of anodization time, applied voltage, solvent composition, as well as fluoride and water content are investigated. The length of the resulting nanotubes showed a strong dependence on the concentration and mobility of F− ions, whilst O2− ion content was found to play a key role in controlling the nanotube wall thickness. A new insight into the formation of Zirconia nanotubes is introduced and discussed based on the Point Defect Model (PDM). Also, the energy consumption in the fabrication process of the nanostructured electrodes is modelled based on the involved thermodynamics and kinetic aspects. The effect of the dimensions of the nanotubes on the optical characteristics of the arrays was studied using Finite Difference Time Domain (FDTD). The results show a decrease in transmittance with increasing length and wall thickness, and decreasing pore size of the nanotubes. The reported results provide deep insight into the structure–property relationships of ZrO2 nanotubes, which will be of great help in large-scale industrial applications.

Ruthenium(III) mono (2,2′-bipyridine) complexes containing O,O-donor ligands and their oxidation properties for organic compounds

The new complexes [RuIIIbpyL2](PF6) and [RuIIIbpyL′Cl2] [bpy = 2,2′-bipyridine; HL = acetylacetone, trifluoroacetylacetone, benzoylacetone (Hbac), tropolone or maltol; HL′ = Hbac or dibenzoylmethane) have been prepared and characterized by spectroscopy. Their redox behaviour was studied by cyclic voltammetry. They effectively catalyze the oxidation of alcohols, alkanes and primary aromatic amines.

Rational design of porous binary Pt-based nanodendrites as efficient catalysts for direct glucose fuel cells over a wide pH range

The development of porous bi-metallic Pt-based nanocrystals (NCs) as efficient catalysts for the glucose oxidation reaction (GOR) over a wide pH range is still a grand challenge. Triggered by this challenge, we report the controlled synthesis of porous binary PtPd, PtCu, AuPt, and PtNi NCs with open dendritic frames as efficient catalysts for GOR. This was achieved by one-step reduction of their precursors in aqueous solutions of polyvinylpyrrolidone (PVP) under ultrasonic treatment at room temperature. Intriguingly, the porous AuPt and PtPd NCs exhibited the utmost enhancement in GOR activity relative to PtCu, PtNi, and commercial Pt/C catalysts under different pH conditions, which is ascribed to their porous structure and composition. Furthermore, the composition and synergetic effects of the binary metals plausibly generate an activity relationship that tune their catalytic activity and stability in different electrolytes.

Novel Mercaptopurine and Thioguanine Analogues: The Reaction of Dimethyl N‐Cyanodithioiminocarbonate with Oxo‐ and Amino‐diazoles

Abstract A novel and efficient method for the synthesis of a new variety of methylsulfanyl derivatives of azoloazines and azoloazoles by the reaction of dimethyl N‐cyanodithioiminocarbonate with diazoles containing oxo‐ and amino functions. The synthetic potential of the method is demonstrated.

Silver Nanoparticles-Decorated Titanium Oxynitride Nanotube Arrays for Enhanced Solar Fuel Generation

We demonstrate, for the first time, the synthesis of highly ordered titanium oxynitride nanotube arrays sensitized with Ag nanoparticles (Ag/TiON) as an attractive class of materials for visible-light-driven water splitting. The nanostructure topology of TiO2, TiON and Ag/TiON was investigated using FESEM and TEM. The X-ray photoelectron spectroscopy (XPS) and the energy dispersive X-ray spectroscopy (EDS) analyses confirm the formation of the oxynitride structure. Upon their use to split water photoelectrochemically under AM 1.5 G illumination (100 mW/cm2, 0.1 M KOH), the titanium oxynitride nanotube array films showed significant increase in the photocurrent (6 mA/cm2) compared to the TiO2 nanotubes counterpart (0.15 mA/cm2). Moreover, decorating the TiON nanotubes with Ag nanoparticles (13 ± 2 nm in size) resulted in exceptionally high photocurrent reaching 14 mA/cm2 at 1.0 VSCE. This enhancement in the photocurrent is related to the synergistic effects of Ag decoration, nitrogen doping, and the unique structural properties of the fabricated nanotube arrays.

Activation and stabilization of gallium arsenide anode in an aqueous photoelectrochemical cell

The formation of a porous layer on the surface of gallium arsenide anode, n-GaAs, increases photogenerated currents significantly. This layer was formed as a result of an anodic polarization of illuminated n-GaAs in acidified chloride electrolytes. The formation of the porous layer was confirmed by scanning electron microscopy micrographs. The porous layer increases the reflectivity of GaAs to light, thus enhances the photogenerated current density. In addition, the formation of the porous layer enriches GaAs surface with arsenic. As a result of this enrichment, the positions of the energy levels on the semiconductor surface might have been changed in favor of oxidizing the electrolyte rather than consuming electron–hole pairs in recombination processes within surface states. The n-GaAs with porous surface layer was employed as the working electrode in a photoelectrochemical cell with dimethylviologen as a reversible electrolyte. The rates of the anodic reaction, at GaAs, and cathodic reaction, at a Pt counter electrode, are about equal, only when the surface area of the Pt counter electrode is approximately 20 times greater than that of the n-GaAs. Equal rates of reduction and oxidation of the dimethlviologen redox couples reveals that the number of the photogenerated electrons and holes getting into the electrolyte are the same. Therefore, the photogenerated holes formed at GaAs surface are consumed totally as a result of the electrolyte oxidation rather than GaAs corrosion. The deposition of a thin layer of gold on the top of the porous surface doubles the magnitude of the photocurrent density due to suppressing electron–hole recombination process. � 2003 Elsevier B.V. All rights reserved.