Mohamed A. Salem

Kinetics of degradation of allura red, ponceau 4R and carmosine dyes with potassium ferrioxalate complex in the presence of H2O2

The degradation of title dyes with ferrioxalate and H(2)O(2) couple has been investigated spectrophotometrically. In the absence of either one of the oxidizing agents no degradation occurred. The reaction rate was proportional to moderate concentrations of the dye and H(2)O(2). At high concentration of the dye and H(2)O(2) the reaction rate decreased. With regard to the concentration of the ferrioxalate complex the rate of reaction increased even over a wide range of complex concentration. Degradation of dyes does not occur in acidic medium. It is slow in neutral but thoroughly fast in alkaline medium. The reaction rate reaches a maximum value at pH 11.5. This behavior was again observed if HCl or NaOH were added. With HCl the reaction rate decreases with increasing acid concentration but greatly increases with NaOH concentration. Isopropanol showed inhibiting effect due to scavenging the in situ generated hydroxyl radical (()OH). Oxalate ion enhanced the rate, confirming an outer sphere mechanism. The activation parameters of the reaction are estimated and a possible mechanism is proposed. The mechanism is well confirmed with data simulation procedure.

Kinetics of heterogeneous decomposition of hydrogen peroxide with some transition metal complexes supported on silica-alumina in aqueous medium

Abstract Silica-alumina in the form of diethylamine (deam)-, dimethylamine (dmam)-, ethylamine (eam)-, ammonia (amm)- and aniline (an) -copper(II) complexes as well as deam-cobalt (II) complex have been used as potentially active catalysts for H2O2 decomposition in an aqueous medium. The reaction was first order with respect to the H2O2 concentration and the rate constants (per g of dry silica-alumina) were determined. A coloured compound, a peroxo-metal complex, which formed at the beginning of the reaction in each case, was found to contain the catalytically active species. The activation energy and the change in the entropy of activation increased with the basicity of the ligands in the following order: an

Pt@Ag and Pd@Ag core/shell nanoparticles for catalytic degradation of Congo red in aqueous solution

Platinum/silver (Pt@Ag) and palladium/silver (Pd@Ag) core/shell NPs have been synthesized in two steps reaction using the citrate method. The progress of nanoparticle formation was followed by the UV/Vis spectroscopy. Transmission electron microscopy revealed spherical shaped core/shell nanoparticles with average particle diameter 32.17nm for Pt@Ag and 8.8nm for Pd@Ag. The core/shell NPs were further characterized by FT-IR and XRD. Reductive degradation of the Congo red dye was chosen to demonstrate the excellent catalytic activity of these core/shell nanostructures. The nanocatalysts act as electron mediators for the transfer of electrons from the reducing agent (NaBH4) to the dye molecules. Effect of reaction parameters such as nanocatalyst dose, dye and NaBH4 concentrations on the dye degradation was investigated. A comparison between the catalytic activities of both nanocatalysts was made to realize which of them the best in catalytic performance. Pd@Ag was the higher in catalytic activity over Pt@Ag. Such greater activity is originated from the smaller particle size and larger surface area. Pd@Ag nanocatalyst was catalytically stable through four subsequent reaction runs under the utilized reaction conditions. These findings can thus be considered as possible economical alternative for environmental safety against water pollution by dyes.

Kinetics and Mechanism of Oxidation of 4-(phenylazo)diphenylamine with Peroxydisulphate

Oxidation of 4-(phenylazo)diphenylamine (PDA) by peroxydisulphate is first order in each one of the reactants. With Ag* as catalyst, it is first order in the oxidant and catalyst, and zero order in the substrate concentration. In the presence of anionic micelles of sodium dodecylsulphate the reaction rate is enhanced and then inhibited. In a medium containing mixed anionic and cationic (cetyltrimethyl ammonium bromide-) micelles a depression in the oxidation rate occurs. The effects of radical scavenger and ionic strength are examined, and mechanisms account for the reaction are discussed.

Catalytic conversion of n-pentanol to 1,1-dialkyl ether by aluminium and iron exchanged montmorillonite catalyst

Abstract Heterogeneous catalytic conversion of n-pentanol to 1,1-dialkyl ether by Fe 3+ - and Al 3+ -exchanged montmorillonite catalyst was studied under different conditions. The catalyst was first heated in the presence of air or hydrogen at temperatures ranging from 80°C to 300°C and X-ray diffractometry, TGA, cation exchange capacity were performed. The final products were analysed by gas chromatography. It was found that Al 3+ -exchanged ions are more efficient as a catalyst than the corresponding Fe 3+ -exchanged ones under the same conditions.

Effect of medium acidity on the spectral behaviour of some pyrazinyl diolefinic laser dyes

Abstract The spectral behaviour of the diolefinic dyes, 2,5-distyrylpyrazine (DSP) and 1,4-bis(β-pyrazinyl-2-vinyl) benzene (BPVB) have been studied in different media. The electronic absorption and emission spectra of the two dyes are bathochromically shifted with increase in medium acidity. A solution of each dye in 98% sulphuric acid acquired a deep blue colouration which changes through orange to a pale yellow upon dilution with water. The deep blue colour observed is responsible for the appearance of a new absorption peak at 550 nm, indicating the presence of a charge-transfer species being formed by the protonation of nitrogen heteroatoms of the pyrazinyl rings. The excimeric emission and excitation spectra of DSP and BPVB adsorbed from toluene onto the surface of silica-alumina ( ∼ 13% Al 2 O 3 ) catalyst (activated at 650°C in air) are broad, structurless and substantially bathochromically shifted by ∼ 110 nm compared with the corresponding peaks obtained for dilute solutions containing no catalyst. Poly-DSP undergoes monomerization upon adsorption on the surface of the activated silica-alumina catalyst. The depolymerization process is believed to be via cyclobutane ring rupture.

THE DEOXYGENATION KINETICS OF NEW OXOVANADIUM(IV) COMPLEXES

SummaryThe deoxygenation reaction kinetics of some monomeric, dimeric and polymeric oxovanadium(IV) complexes with SOCl2 have been studied by the stopped-flow technique in DMF. The reaction is bimolecular and obeys second-order kinetics; first-order in both SOCl2 and complex. The polymeric halogeno product decays with time, but at a rate much slower compared to the rate of its formation. The correlation observed between the structure of these complexes and their reactivities is discussed.

Some sorption properties of Nile silt

Abstract The sorption properties of heat-treated Nile silt were investigated using thermoanalytical, X-ray diffraction, and spectroscopic techniques. After heat treatment at 650°C, the silt shows remarkable sorption properties for both organic, e.g. 3,6-bis-dimethyl-amino acridine hydrochloride, and inorganic, e.g. Cu 2+ , cations. The cation uptake from chloroform and dichloromethane solvents is highly efficient but from protic solvents such as methanol or water it is insignificant. There is also a slight uptake of crude oil by the silt, a fact which may be useful in the fight against oil pollution. The purity of the chloroform and dichloromethane was improved enormously after passing through columns of the heat-treated silt and this could be of industrial significance. The basicity of the silt makes it a cheap and safe alternative for reducing the acidity of water resources.