Issa M. El-Nahhal

Synthesis, Characterization and Applications of Immobilized Iminodiacetic Acid-Modified Silica

Porous immobilized iminodiacetic acid modified silica of the general formula S—(CH2)3—N(CH2COOH)2, (where S represents [Si—O]n siloxane network) has been prepared by replacement of the iodide in 3-iodopropyl modified silica with diethyliminodiacetate. The immobilized-diethyliminodiacetate ligand system (S-DIDA) was then hydrolyzed by hydrochloric acid to produce the immobilized iminodiacetic acid ligand system (S-IDA). The iodo functionalized modified silica (S-I) was prepared by polycondensation of Si(OEt)4 and (MeO)3Si(CH2)3I. The XPS and CP/MAS 13C NMR spectra showed that not all iodine atoms are replaced and that the hydrolysis of ethyl acetate groups are incomplete upon treatment with HCl. The immobilized iminodiacetic acid ligand system exhibits high potential for the uptake of various di- and trivalent metal ions such as (Mn2+, Fe3+, Co2+, Ni2+, Cu2+ and Zn2+). Complexation of the iminodiacetate ligand system for the metal ions at the optimum conditions was found in the order: Cu2+ > Fe3+ > Ni2+ > Co2+ > Mn2+ > Zn2+. Stability studies of the iminodiacetate ligand system showed that a degradation of the siloxane network and leaching of some species occurred upon treatment with strong acid and base aqueous solutions.

Nanostructured copper oxide-cotton fibers: synthesis, characterization, and applications

Copper oxide nanoparticles were prepared and subsequently deposited onto surface of the cotton fibers by ultrasonic irradiation. The structure and morphology of the coated and un-coated cottons were examined by X-ray diffraction and scanning electron microscopy/energy dispersive X-ray analysis. These methods revealed that of CuO nanoparticles are crystalline and corresponds to monoclinic phase, and that these nanoparticles are physically adsorbed onto the cotton fiber surface. They have an average crystallite size of 10 nm; the physical and chemical properties of the treated cotton fibers are markedly different from those of the untreated cotton fibers. The CuO-cotton fiber nanocomposites were tested against Escherichia coli (Gram negative) and Staphylococcus aureus (Gram positive) cultures and showed a significant antimicrobial activity; whereas its analogous CuS-coated cotton material formed by the reaction CuO-coated cotton fibers with H2S showed no activity.

Encapsulation of Phenolphthalein pH-Indicator into a Sol-Gel Matrix

Transparent monolithic silica doping with phenolphthalein has been prepared via the acid-catalyzed sol-gel reactions of tetraethylorthosilicate in the presence of phenolphthalein. The immobilized phenolphthalein pH-indicator shows similar behavior as its solution counterpart. The UV/Vis spectra indicate that the phenolphthalein retains its structure during the sol-gel reactions in terms of response to pH. The phenolphthalein can be regarded as uniformly distributed in the silica matrix. This observation has been confirmed using polarized microscopy.

Uptake of Divalent Metal Ions (Cu2+, Zn2+ and Cd2+) by Polysiloxane Immobilized Monoamine Ligand System

ABSTRACT Porous solid siloxane polymers carrying a monoamine functional group of formula P-(CH2)3NH2 (Where P- represents a siloxane framework silica like ) has been prepared by polycondensation of Si(OEt)4 and (MeO)3Si(CH2)3-NH2. Treatment of aqueous solutions of divalent metal ions with the polysiloxane monoamine ligand system demonstrates that this material has high potential for preconcentration of metal ions (Cu2+, Zn2+ and Cd2+). The tendency of these divalent metal ions to chemisorb by the monoamine ligand system at the optimum conditions increases in the order: Cd2+ <Zn2+ <Cu2+. The optimum pH is 5.5 for copper and 6-7 for zinc and cadmium. The ammonia/ ammonium chloride buffer solution gave maximum uptake for all metal ions. It is also found that the uptake of copper ions is concentration dependent and is independent of the presence of other competing ions. The monoamine ligand system suffers from leaching of ligand containing groups upon treatment with acidic solutions. The highest leaching occurs at low pH.

UPTAKE OF DIVALENT METAL IONS (CU2+, NI2+, AND CO2+) BY POLYSILOXANE IMMOBILIZED TRIAMINE-THIOL AND THIOL-ACETATE LIGAND SYSTEM

Insoluble porous solid polysiloxanes-immobilized ligand systems bearing hybrid mixture of triamine-thiol ligand and thiol-acetate ligand as chelating functional groups of the general formula P-(CH2)3-X(Y) (Where P represents a silica like siloxane framework and X represents a mixture of triamine and thiol, -NHCH2)2NH-(CH2)2-NH2 and –SH, and Y represents a thiol-acetate -SCH2COOH functional groups) has been prepared. The immobilized triamine-thiol ligand system was prepared through the sol-gel process by hydrolytic polycondensation of Si(OEt)4 and a mixture of 3-mercaptopropyltrimethoxysilane and 3-diethylenetriaminepropyltrimethoxysilane coupling agents. The immobilized thiol-acetate ligand system was prepared by the reaction of polysiloxane immobilized thiol ligand with ethylchloroacetate. These ligand systems exhibit high potential for extraction and preconcentration of divalent metal ions (Co2+, Ni2+ and Cu2+). The results indicate that the triamine-thiol ligand seems to form 1:1 metal to ligand complexes, where there is no clear stoichiometry structure in the case of the thiol-acetate ligand.

Preparation of ethylenediaminetriacetic acid silica-gel immobilised ligand system and its application for trace metal analysis in aqueous samples

This article reports on the preparation of porous solid ethylenediaminetriacetic acid functionalised silica-gel (S-EDTA) of the general formula S-(CH2)3N(CH2COOH)-(CH2)2-N(CH2COOH)2 (where S represents [Si–O] n ). This was prepared by modification of 3-(2-aminoethylaminopropyl)trimethoxysilane with ethyl chloroacetate followed by polycondensation with tetraethylorthosilicate via the sol–gel process. The immobilised ethylenediaminetriacetic acid ligand system (S-EDTA) was characterised by FTIR, 13C CS-MAS NMR and XPS spectroscopic techniques. The resulting functionalised ligand system showed high potential to extract and separate Co2+, Ni2+ and Cu2+ metal ions from aqueous samples. The saturation sorption capacities of Co2+, Ni2+ and Cu2+ metal ions were 77.6, 89.1 and 99.4 mg g−1, respectively. The optimum separation pH values were 4.5 and 4 for Co(II) and Ni(II), respectively, while a solution of 0.1 mol L−1 HNO3 (pH = 1) was used to elute Cu(II).

Sol-Gel Thin Films Immobilized with Bromocresol Purple pH-Sensitive Indicator in Presence of Surfactants

Preparation of transparent sol-gel thin film immobilized with bromocresol purple (BCP) pH-sensitive indicator was made via the acid catalyzed sol-gel reaction of tetraethylorthosilicate and the bromocresol purple indicator (BCP). Different surfactants include cationic cetyl trimethyl ammonium bromide (CTAB), anionic sodium dodecyl sulfate (SDS), and nonionic Triton X-100 (TX-100) were used to improve the mesostructure of the host material and to increase its porosity. The color change behavior of the immobilized bromocresol purple indicator affected significantly in presence of SDS comparing with its free counterpart in aqueous solution. In presence of CTAB and Triton-X 100, the immobilized bromocresol purple indicator shows similar behavior as its free counterpart in aqueous solution. The BCP retains its structure during the sol-gel reactions in terms of response to pH. Different parameters including concentration of indicator and surfactant, temperature, number of layers, response time, life time, and the number of measurements were investigated. The pKa values of the different prepared BCP immobilized thin films were determined. The BCP thin film sensor showed stability, repeatability, reproducibility, fast response, and long life time behavior. The polarized light microscopy indicated that the bromocresol purple indicator molecules are distributed uniformly within the host silica network.

Encapsulation of Methyl Red pH‐Indicator into a Sol‐Gel Matrix

Encapsulation of methyl red pH indicator into transparent monolithic silica matrices was made via the acid‐catalyzed sol‐gel reaction of tetraethylorthosilicate and methyl red indicator. The immobilized methyl red shows behavior similar to its solution counterpart. It retains its structure during the sol‐gel reactions in terms of response to pH. Polarized light microscopy and the surface morphology indicated that methyl red molecules are strongly interacted within the host silica network.

Behaviour of phenol red pH-sensors in the presence of different surfactants using the sol-gel process

Phenol red was immobilised into a polysiloxane matrix using a sol-gel process to form pH optical sensors. The sol-gel was obtained by hydrolysis of tetraethoxysilane (TEOS) in the presence of phenol red (PR) and the appropriate surfactant. Different surfactants, namely cetyltrimethylammonium bromide (CTAB), dodecyldimetyl amino-oxide (GLA) and Triton X-100 (TX-100), were employed. Interestingly, the use of surfactants significantly improved the mesostructure of the silica and increased the porosity of the system. The two response pH ranges were shifted to pH 0.0–3.0 and pH 10.5–1.5M [OH−] compared with those of the free PR (pH 0.0–3.0 and pH 6.5–9.5). It is found that the pH response and the pKa shift of the phenol red were dependent, not only on the silica matrix but also on the ionic properties of surfactants. In the case of ionic surfactants such as CTAB or GLA, there was further shift to more acidic and more basic pH, whereas in the case of non-ionic surfactants such as TX-100 no significant change of the pH curve was observed.

Polysiloxane-Immobilized Triamine Ligand System, Synthesis and Applications

The polysiloxane-immobilized triamine ligand system of the formula P-(CH 2 ) 3 NH(CH 2 ) 2 NH(CH 2 ) 2 NH 2 (where P represents the siloxane network) has been prepared via the sol-gel process by hydrolytic polycondensation of (EtO) 4 Si and (MeO) 3 Si(CH 2 ) 3 NH(CH 2 ) 2 NH(CH 2 ) 2 NH 2 . An alternative method was used by the reaction of the iodopolysiloxane P-(CH 2 ) 3 -I and diethylenetriamine in the presence of triethylamine. The immobilized triamine ligand forms metal chelate complexes when treated with aqueous metal(II) ion solutions (Co 2+ , Ni 2+ , and Cu 2+ ). The elemental analysis and FTIR results suggest that this ligand system undergoes a substantial leaching of diethylenetriamine ligand moieties from the siloxane framework.