Shaeel A. Al-Thabaiti

Preparation and characterization of silver nanoparticles by chemical reduction method.

Silver nanoparticles were prepared by the reduction of AgNO(3) with aniline in dilute aqueous solutions containing cetyltrimethlyammonium bromide, CTAB. Nanoparticles growth was assessed by UV-vis spectroscopy and the average particle size and the size distribution were determined from transmission electron microscopy, TEM. As the reaction proceeds, a typical plasmon absorption band at 390-450nm appears for the silver nanoparticles and the intensities increase with the time. Effects of [aniline], [CTAB] and [Ag(+)] on the particle formation rate were analyzed. The apparent rate constants for the formation of silver nanoparticles first increased until it reached a maximum then decreased with [aniline]. TEM photographs indicate that the silver sol consist of well dispersed agglomerates of spherical shape nanoparticles with particle size range from 10 to 30nm. Aniline concentrations have no significant effect on the shape, size and the size distribution of Ag-nanoparticles. Aniline acts as a reducing as well as adsorbing agent in the preparation of roughly spherical, agglomerated and face-centered-cubic silver nanoparticles.

Formation and characterization of surfactant stabilized silver nanoparticles: a kinetic study.

Kinetic data for the silver nitrate-ascorbic acid redox system in presence of three surfactants (cationic, anionic and nonionic) are reported. Conventional spectrophotometric method was used to monitor the formation of surfactant stabilized nanosize silver particles during the reduction of silver nitrate by ascorbic acid. The size of the particles was determined with the help of transmission electron microscope. It was found that formation of stable perfect transparent silver sol and size of the particles depend upon the nature of the head group of the surfactants, i.e., cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulphate (SDS) and Triton X-100. The silver nanoparticles are spherical and of uniform particle size, and the average particle size is about 10 and 50 nm, respectively, for SDS and CTAB. For a certain reaction time, i.e., 30 min, the absorbance of reaction mixture first increased until it reached a maximum, then decreased with [ascorbic acid]. The reaction follows a fractional-order kinetics with respect to [ascorbic acid] in presence of CTAB. On the basis of various observations, the most plausible mechanism is proposed for the formation of silver nanoparticles.

Two polymeric 36-metal pure lanthanide nanosize clusters

Two rarely seen 2D coordination polymers based on huge 36-metal pure lanthanide clusters, {[Gd36(NA)36(OH)49(O)6(NO3)6(N3)3(H2O)20]Cl2·28H2O}n (1) and {[Dy36(NA)36(OH)49(O)6(NO3)6(N3)3(H2O)20]Cl2·28H2O}n (2) (HNA = nicotinic acid), were synthesized and structurally characterized. The spherical Ln36 skeleton can be viewed as the aggregation of one cyclohexane chair-like Ln24 wheel and two identical tripod-like Ln6 units. The coordination of the carboxylic groups of the NA ligands with the Ln(III) cations results in a square layer. Additionally, compound 1 possesses a large MCE of 39.66 J kg−1 K−1 and compound 2 exhibits slow relaxation of the magnetization.

Photophysical studies of europium coordination polymers based on a tetracarboxylate ligand.

Reaction of europium sulfate octahydrate with p-terphenyl-3,3″,5,5″-tetracarboxylic acid (H4ptptc) in a mixed solvent system has afforded three new coordination polymers formulated as {[Eu(ptptc)0.75(H2O)2]·0.5DMF·1.5H2O}n (1), {[Me2H2N]2 [Eu2(ptptc)2(H2O)(DMF)]·1.5DMF·7H2O}n (2), and {[Eu(Hptptc)(H2O)4]·0.5DMF·H2O}n (3). Complex 1 exhibits a three-dimensional (3D) metal-organic framework based on {Eu2(μ2-COO)2(COO)4}n chains, complex 2 shows a 3D metal-organic framework constructed by [Eu2(μ2-COO)2(COO)6](2-) dimetallic subunits, and complex 3 features a 2D layer architecture assembling to 3D framework through π···π interactions. All complexes exhibit the characteristic red luminescence of Eu(III) ion. The triplet state of ligand H4ptptc matches well with the emission level of Eu(III) ion, which allows the preparation of new optical materials with enhanced luminescence properties. The luminescence properties of these complexes are further studied in terms of their emission quantum yields, emission lifetimes, and the radiative/nonradiative rates.

Starch-directed green synthesis, characterization and morphology of silver nanoparticles

Silver nanoparticles were prepared by a simple chemical reduction method using ascorbic acid and starch as reducing and stabilizing agents, respectively. The effect of starch, silver ions and ascorbic acid was studied on the morphology of the silver nano-particles using UV-visible spectrophotometry. The initial reaction time min and amount of starch were important parameters for the growth of Ag-nanoparticles. The morphology was evaluated from transmission electron microscopy (TEM). The truncated triangle nano-plates (from 17 to 30 nm), polyhedron, spherical with some irregular shaped Ag-nanoparticles were formed in presence of starch. Particles are aggregated in an irregular manner, leads to the formation of butterfly-like structures of silver. Starch acts as a stabilizing, shape-directing and capping agent during the growth processes. Silver nanoparticles adsorbed electrostatically on the outer OH groups of amylose left-handed helical conformation in solution.

Oriented MFI membranes by gel-less secondary growth of sub-100 nm MFI-nanosheet seed layers

A zeolite membrane fabrication process combining 2D-zeolite nanosheet seeding and gel-free secondary growth is described. This process produces selective molecular sieve films that are as thin as 100 nm and exhibit record high permeances for xylene- and butane-isomers.

Ultra-selective high-flux membranes from directly synthesized zeolite nanosheets

A zeolite with structure type MFI is an aluminosilicate or silicate material that has a three-dimensionally connected pore network, which enables molecular recognition in the size range 0.5–0.6 nm. These micropore dimensions are relevant for many valuable chemical intermediates, and therefore MFI-type zeolites are widely used in the chemical industry as selective catalysts or adsorbents. As with all zeolites, strategies to tailor them for specific applications include controlling their crystal size and shape. Nanometre-thick MFI crystals (nanosheets) have been introduced in pillared and self-pillared (intergrown) architectures, offering improved mass-transfer characteristics for certain adsorption and catalysis applications. Moreover, single (non-intergrown and non-layered) nanosheets have been used to prepare thin membranes that could be used to improve the energy efficiency of separation processes. However, until now, single MFI nanosheets have been prepared using a multi-step approach based on the exfoliation of layered MFI, followed by centrifugation to remove non-exfoliated particles. This top-down method is time-consuming, costly and low-yield and it produces fragmented nanosheets with submicrometre lateral dimensions. Alternatively, direct (bottom-up) synthesis could produce high-aspect-ratio zeolite nanosheets, with improved yield and at lower cost. Here we use a nanocrystal-seeded growth method triggered by a single rotational intergrowth to synthesize high-aspect-ratio MFI nanosheets with a thickness of 5 nanometres (2.5 unit cells). These high-aspect-ratio nanosheets allow the fabrication of thin and defect-free coatings that effectively cover porous substrates. These coatings can be intergrown to produce high-flux and ultra-selective MFI membranes that compare favourably with other MFI membranes prepared from existing MFI materials (such as exfoliated nanosheets or nanocrystals).

Layered double hydroxides supported on multi-walled carbon nanotubes: preparation and CO2 adsorption characteristics

Layered double hydroxides (LDHs) are promising materials for CO2 sorption, although improvements in performance are required for practical applications. In the current study, the CO2 sorption capacity and multi-cycle stability were both increased by introducing an open supporting framework of multi-walled carbon nanotubes (MWNTs). This nanostructured inert network provides a high surface area, maximizing the gas accessibility and minimizing coarsening effects. Specifically, LDH nanoparticles were precipitated directly onto MWNTs, initially oxidised to ensure a favourable electrostatic interaction and hence a good dispersion. The dependence of the structural and physical properties of the Mg–Al LDH grown on MWNT supports has been studied, using electron microscopy, X-ray diffraction, thermogravimetric analysis (TGA), and BET surface area, and correlated with the CO2 sorption capacity, established via TGA and temperature programmed desorption measurements. The use of a MWNT support was found to improve the absolute capacity and cycle stability of the hybrid adsorbent under dry conditions.

Tungsten Doped TiO2 with Enhanced Photocatalytic and Optoelectrical Properties via Aerosol Assisted Chemical Vapor Deposition.

Tungsten doped titanium dioxide films with both transparent conducting oxide (TCO) and photocatalytic properties were produced via aerosol-assisted chemical vapor deposition of titanium ethoxide and dopant concentrations of tungsten ethoxide at 500 °C from a toluene solution. The films were anatase TiO2, with good n-type electrical conductivities as determined via Hall effect measurements. The film doped with 2.25 at.% W showed the lowest resistivity at 0.034 Ω.cm and respectable charge carrier mobility (14.9 cm3/V.s) and concentration (×1019 cm−3). XPS indicated the presence of both W6+ and W4+ in the TiO2 matrix, with the substitutional doping of W4+ inducing an expansion of the anatase unit cell as determined by XRD. The films also showed good photocatalytic activity under UV-light illumination, with degradation of resazurin redox dye at a higher rate than with undoped TiO2.

Shape-directing role of cetyltrimethylammonium bromide in the preparation of silver nanoparticles

We report a simple chemical reduction method for the synthesis of different colored silver nanoparticles, AgNP, using tyrosine as a reducing agent. Effects of cetyltrimethylammonium bromide, CTAB, and tyrosine concentrations are analyzed by UV-visible measurements and scanning electron microscopy (SEM) to evaluate the mode of AgNP aggregation. The position and shape of the surface resonance plasmon absorption bands strongly depend on the reaction conditions, i.e., [CTAB], [tyrosine], and reaction time. Sub-, post-, and dilution-micellar effects are accountable for the fast and slow nucleation and growth processes. Spectrophotometric measurement also shows that the average size and the polydispersity of AgNP increase with [CTAB] in the solution. CTAB acted as a shape-directing agent.