Mohamed A. Mekewi

Catalytic Polymerization of Methyl Methacrylate in Different Media Using Supported Metal Phthalocyanines, 1. Bulk Polymerization in Relation to the Microcrystalline Structure of Supported Metal Phthalocyanines

Different catalyst samples of nickel(II) and copper(II) phthalocyanines supported over bentonite clay (Indian type) were prepared with complex loadings ranging between 0.2 and 2.2 wt.-%. Catalyst activities were investigated in the bulk polymerization of methyl methacrylate (MMA) at 80°C in the absence and in the presence of sodium bisulfite as a cocatalyst. In all cases, the catalyst efficiency was evaluated in terms of conversion yield (%), polydispersity index (M w /M n ) was determined via GPC analysis in toluene. The stereotacticity was determined from 1 H NMR spectra. Optimum polymerization conditions were determined for both catalyst systems. Samples with metal phthalocyanines loadings of 1.8% were the most active ones. The polymers produced have controlled molecular weights, which are nearly proportional to conversion, show narrow molecular weight distributions and syndiotactic-rich steric structures. Nickel phthalocyanine seemed to have more stereoregulating effect while copper phthalocyanine had a more enhancing effect for the living polymerization process. The microstructure of solid catalysts was investigated by means of scanning electron microscopy and were correlated with activity data.

Erratum to: Facile one-step process for synthesis of vertically aligned cobalt oxide doped TiO2 nanotube arrays for solar energy conversion

Vertically aligned cobalt oxide doped TiO2 nanotube arrays (Co.-oxide TNTAs) were synthesized via one pot-anodic oxidation of pure titanium substrate in the presence of ammonium fluoride and cobalt salt. After subsequent annealing in air the produced arrays were in the tubular structure and doped with Co.-oxide. The designed TNTAs and Co.-oxide TNTAs were tested as photoanode electrodes in a photoelectrochemical cell. Energy dispersive X-ray (EDX) spectroscopy confirms the incorporation of Co. in the doped TNTAs. The Tauc plots estimated from UV–Vis diffuse reflectance spectra displayed that the insertion of the optimum amount of Co.-oxide leads to a decrease in the band gap of TiO2 from 3.2 to 2.9 eV. The influences of various cobalt salt concentrations in the electrolyte solution (5, 10, 15, 20 and 25 mM) on the morphology were studied. The evaluation of the photocurrent and photoconversion efficiency was performed for all the fabricated electrodes. Morphological studies illustrated that the addition of cobalt salt with small concentration has no an obvious effect on the ordered tubular structure of TNTAs, whereas, at higher concentrations the tubular structure was partially collapsed. Co.-oxide enhanced the photoconversion efficiency of TNTA electrode by 30 % at optimum concentration under 110 mW/cm2 solar simulator illumination.

Nonionic surfactants from poly(ethylene terephthalate) waste: I. Influence of structural variations on the surface activity

Poly(ethylene terephthalate), PET, waste was depolymerized with propylene glycol (PG) to an oligoester (OE). The hydroxyl value of the glycolized product before and after removing the free glycol were determined. The glycolized product was reacted with polyethylene glycol (PEG) of different molecular weights, namely, 600, 1000 and 4000 to form compounds having different hydrophil-lipophil balance (HLB) and hence different surface activities. The interfacial tension at the aqueous/benzene interface was determined. It was found that the demulsifiers concentrations required to cause minimum interfacial tension are always less than that inducing maximum demulsification efficiency. The demulsification efficiency of the prepared surfactants in breaking synthetic water-in-benzene emulsions stabilized by petroleum asphaltenes was evaluated. The data revealed that the demulsification efficiency increases with increasing the demulsifiers concentration, contact time and hydrophilicity.

Sustainable removal of Cu2+, Ni2+ and Zn2+ ions from severe contaminated water using kaolin/poly(glycine) composites, characterization and uptake studies

AbstractKaolinite clay of Saint Catharine, Sinai, was treated by glycine molecules and then modified by various diamino-compounds like ethylenediamine, phenyl hydrazine and polyoxypropylenediamine. The native and modified clays were structurally and texturally characterized by XRD, FTIR, XRF, BET, pore size distribution and SEM in addition to exchange capacity parameters. Phenyl hydrazine and polyoxypropylenediamine organo-modifiers proved superior in function compared to ethylenediamine with regard to in situ glycine polymerization forming large fragments of ordered polypeptides which acted as super clay sheet binders. Adsorption of Cu(II), Ni(II) and Zn(II) ions by the modified kaolinite under variable concentrations of metal ions and interacting time were studied. Adsorption isotherm investigation indicated that Freundlich equation was a better fit than Langmuir model reflecting surfaces of various accommodated active sites with analogue sites distribution. The adsorption rate constants sequence for al...

Effect of thermal treatment on various characteristics of undoped and V2O5-doped Co3O4/TiO2 catalysts

The thermal treatment of undoped and V2O5-doped Co3O4/TiO2 catalysts was studied in the temperature range, 330–600° C both in vacuum and in air. The wide difference in the catalytic behaviour of the two catalysts could be attributed to surface as well as bulk diffusion of the active cobalt oxide particles. Although in both cases the total Co3+ ions of various energy states were considered to be the active species for the given reaction, the distribution of various cobalt species, namely Co-t and Co-o, occupying tetrahedral and octahedral sites in the support-defective structure, seemed to be seriously affected by doping with V2O5. This dopant was supposed to have two-fold effect: part is incorporated into the surface Co3O4 crystallites leading to smaller more mobile particles, easily reducible and more dispersed, and another part diffuses a few atomic layers deeper in the support causing the redistribution of cobalt species. Upon heating, the increased mobility and the increased availability of the support tetrahedral sites may be responsible for the deactivation behaviour. The bulk diffusion enhanced by doping might cause some modification in the porosity characteristics of the titania support.

Efficient photoelectrodes from anatase TiO2 nanotube arrays decorated with particles/rods/3D microflower rutile crystals for photoelectrochemical water splitting

Efficient photoanodes are designed of vertically aligned anatase TiO2 nanotube arrays (anatase TNTAs) decorated with different shaped rutile TiO2 structures (particles, 1D nanorods, 3D microflowers) to improve the photoelectrochemical water oxidation performance of pristine TNTAs. Anatase TNTAs were prepared by anodic oxidation of Ti substrate in NH4F electrolyte, and the rutile percent and shape are controlled by tuning the TiCl4 treatment time (20–120xa0min). The effects of treatment time on the morphology, crystal structure, band gap, photocurrent, and photoconversion efficiency are characterized by FESEM, HRTEM, XRD, UV–Vis diffuse reflectance spectroscopy, and photoelectrochemical measurements. XRD data confirmed that TiCl4 treatment induced the formation of the rutile phase of TiO2 over anatase TNTAs and the rutile amount in the TNTAs was increased upon increasing the treatment time. Additionally, the band gap of TNTAs was gradually decreased by increasing the rutile percent. The optimum treatment time is 80xa0min, which produces TiO2 photoanode array that possess the following characteristics: rutile/anatase mixed phase, nanorode/nanotube mixed morphology, 3.09xa0eV band gap, two times increase in photocurrent, and almost more than twofold enhancement in the photoconversion efficiency relative to pure TNTA.

Various characteristics of supported CoPc on Al2O3, SiO2 and SiO2-Al2O3 as selective catalysts in the oxidative dehydrogenation of cyclohexene

Abstract Various characteristics of CoPc supported on Al 2 O 3 , SiO 2 and SiO 2 -Al 2 O 3 ofvarying SiO 2 mole ratio were investigated. Different pore systems were found to exist depending on the support permitting entrance of CoPc molecules (SiO 2 and silica-rich samples) or not (Al 2 O 3 and alumina-rich samples). The major fraction of CoPc appeared as combined with the support surface was much less in silica and silica-rich samples. From chemisorption stoichiometries, CoPc molecules are proposed to lie flat on alumina and alumina-rich surfaces and inclined-edge oriented on silica and silica-rich surfaces. The studied catalysts exhibited good selectivities in the oxidative dehydrogenation of cyclohexene toward benzene. A mechanisms was suggested where the formation of an intermediate involving active oxygen species was considered the rate determining step.

Thermal properties of polystyrene/group IIB dithizonate films

The effect of group IIB metal dithizone complexes on the properties of polystyrene have been investigated by GPC, FTIR, X-ray diffraction, TGA and DSC. The results of GPC and X-ray diffraction analysis proved that an improvement in the polymer chain ordered was achieved due to the presence of these complexes during the bulk polymerization of styrene monomer if compared with that of pure sample. TGA thermograms showed that the thermal stability of polystyrene is enhanced with increasing complex concentration. However, mercury gives the best results followed by cadmium and zinc dithizonate. DSC scans for the different polymer samples provides a further support to the TGA data.

Synthesis and characterization of antioxidants and detergent dispersant based on some polyisobutylene copolymers

Abstract.Polyisobutylene succinic anhydride-urea/polyamines (PIBSA) copolymers were synthesized as potential antioxidants and detergent dispersant agents for lubricating oils samples (SAE-30). Homogeneity, thermal stability and dispersancy of the solutions were determined. Fully soluble oil compounds that are thermally stable up to 250xa0°C were achieved.The oxidation stability of lube oil samples in the presence of four designed PIBSA additives (varying in the number of amine groups) was determined for a time period of up to 72 hours. The dependence of the additive efficiency on its concentration was studied to achieve maximum stability. Some PIBSA additives at concentration 3.0 · 104xa0ppm exhibit the best results.Dispersivity values were measured at predetermined oxidation times. The results proved reliable dispersion capability as the nitrogen content of the additive is increased, i.e. the increase in the basic character of the additive leads to the increase in the neutralization capability. Moreover, the designed PIBSA additives retain their efficiency after long oxidation times, confirming their role as multifunctional nitrogen containing polymeric additive.

Salen Transition Metal Complexes as Catalysts for the Synthesis of Photostable Poly(methylmethacrylate)

ABSTRACT Polymethylmethacrylate (PMMA) was prepared in presence of Cr (III) and Ni (II) Salen complex compounds as catalysts for the controlled radical polymerization of the methylmethacrylate monomer. The PMMA structure was examined through FT-IR analysis in which characteristic bands of structural tacticity were observed. The PMMA order of tacticity was also identified using 1HNMR where clear indications of increased polymer tacticity and metal complex intervention with the PMMA growing chains were identified. PMMA samples, prepared in presence of Ni (II) and Cr (III) Salen complex compound, were subjected to various doses of UV light and significant resistance to degradation was noticed. The weight average molecular weight values, using GPC technique, were monitored as the measuring parameter for the PMMA photostability. The results of the present work strongly recommend the use of transition metal Salen complexes as promising catalysts for polymerization of PMMA due to their characteristic activity and the sound resistance toward UV photodegradation the polymer exhibited.