Abdullah Y. Obaid

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.

Co-circulation of three camel coronavirus species and recombination of MERS-CoVs in Saudi Arabia

Coronaviruses in the Middle East Middle East respiratory syndrome coronavirus (MERS-CoV) causes severe acute respiratory illness and kills about a third of people infected. The virus is common in dromedary camels, which can be a source of human infections. In a survey for MERSCoV in over 1300 Saudi Arabian camels, Sabir et al. found that dromedaries share three coronavirus species with humans. Diverse MERS lineages in camels have caused human infections, which suggests that transfer among host species occurs quite easily. Haagmans et al. made a MERS-CoV vaccine for use in camels, using poxvirus as a vehicle. The vaccine significantly reduced virus excretion, which should help reduce the potential for transmission to humans, and conferred cross-immunity to camelpox infections. Science, this issue p. 81, p. 77 Several camel coronaviruses occur in the Middle East, and a recombinant lineage is linked to the recent human outbreaks of MERS. Outbreaks of Middle East respiratory syndrome (MERS) raise questions about the prevalence and evolution of the MERS coronavirus (CoV) in its animal reservoir. Our surveillance in Saudi Arabia in 2014 and 2015 showed that viruses of the MERS-CoV species and a human CoV 229E–related lineage co-circulated at high prevalence, with frequent co-infections in the upper respiratory tract of dromedary camels. viruses of the betacoronavirus 1 species, we found that dromedary camels share three CoV species with humans. Several MERS-CoV lineages were present in camels, including a recombinant lineage that has been dominant since December 2014 and that subsequently led to the human outbreaks in 2015. Camels therefore serve as an important reservoir for the maintenance and diversification of the MERS-CoVs and are the source of human infections with this virus.

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.

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.

Studies on the kinetics of growth of silver nanoparticles in different surfactant solutions

Silver nanoparticles were prepared in aqueous silver nitrate solution using hydrazine as reducing agents in presence of two ionic surfactants (cetyltrimethylammonium bromide; CTAB and sodium dodecyl sulfate; SDS) and one non-ionic surfactant (Triton X-100). The reaction rate was determined spectrophotometrically. The nature of the head group of these surfactants is responsible for the formation of stable, yellow and transparent silver sol. For a certain reaction time, i.e., 20 min, the absorbance of reaction mixture first increased until it reached a maximum, then decreased with [hydrazine]. The reaction follows first-order kinetics with respect to each in [hydrazine] and [Ag(+)]. The results suggest formation of a complex between silver(I) and hydrazine, decomposes in a rate-determining step, leading in the formation of a free radical, which again reacts with the silver(I) in a subsequent fast step to yield the products. The transmission electron microscopic (TEM) images show that CTAB stabilized silver nanoparticles are spherical and of uniform particle size, and the average particle size is about 15 nm.

Aerosol assisted chemical vapour deposition of hydrophobic TiO2–SnO2 composite film with novel microstructure and enhanced photocatalytic activity

Aerosol assisted chemical vapour deposition (AACVD) was used to synthesise a TiO2–SnO2 composite film onto a glass substrate. For comparison a TiO2 film and a SnO2 film were also prepared. All films were characterised by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and wavelength dispersive X-ray spectroscopy (WDX). XPS and WDX of the composite film revealed a TiO2 rich film with a high level of SnO2 segregation at the surface. Highly structured pyramid-like features gave rise to hydrophobic films with static water contact angles of 134°. Photocatalytic activities were determined by monitoring the degradation of intelligent ink (containing Resazurin redox dye) via UV-visible spectroscopy. Under UVA irradiation, the TiO2 film only began to degrade the dye after being irradiated in excess of 100 minutes, whereas the composite TiO2–SnO2 film required only 6 minutes of irradiation before degradation was observed. The formal quantum efficiency (FQE) for the TiO2–SnO2 composite was determined to be 1.01 × 10−2 molecules per incident photon and the formal quantum yield (FQY) was 1.17 × 10−2 molecules per absorbed photon. This is an order of magnitude superior to Pilkington Activ™ self-cleaning glass a commercial self-cleaning TiO2 coating on glass. This improved photocatalytic activity is attributed to the presence of electron scavenging SnO2 sites that increase charge separation and the increased surface area due to the highly structured morphology.

Combinatorial Atmospheric Pressure Chemical Vapor Deposition of Graded TiO2–VO2 Mixed-Phase Composites and Their Dual Functional Property as Self-Cleaning and Photochromic Window Coatings

A combinatorial film with a phase gradient from V:TiO₂ (V: Ti ≥ 0.08), through a range of TiO₂-VO₂ composites, to a vanadium-rich composite (V: Ti = 1.81) was grown by combinatorial atmospheric pressure chemical vapor deposition (cAPCVD). The film was grown from the reaction of TiCl₄, VCl₄, ethyl acetate (EtAc), and H₂O at 550 °C on glass. The gradient in gas mixtures across the reactor induced compositional film growth, producing a single film with numerous phases and compositions at different positions. Seventeen unique positions distributed evenly along a central horizontal strip were investigated. The physical properties were characterized by wavelength dispersive X-ray (WDX) analysis, X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and UV-visible spectroscopy. The functional properties examined included the degree of photoinduced hydrophilicity (PIH), UVC-photocatalysis, and thermochromism. Superhydrophilic contact angles could be achieved at all positions, even within a highly VO₂-rich composite (V: Ti = 1.81). A maximum level of UVC photocatalysis was observed at a position bordering the solubility limit of V:TiO₂ (V: Ti ≈ 0.21) and fragmentation into a mixed-phase composite. Within the mixed-phase TiO₂: VO₂ composition region (V: Ti = 1.09 to 1.81) a decrease in the semiconductor-to-metal transition temperature of VO₂ from 68 to 51 °C was observed.

Aerosol assisted chemical vapor deposition of conductive and photocatalytically active tantalum doped titanium dioxide films

This paper shows the aerosol assisted chemical vapour deposition of transparent, blue coloured and conductive tantalum doped titanium dioxide films from the CVD reaction of Ti(OEt)4 and Ta(OEt)5. Hall effect measurements showed the doped films to have excellent n-type electrical conductivity showing, to the best of our knowledge, the lowest reported sheet resistance ever recorded for Ta-doped TiO2 of 14 Ω sq−1. The Ta 6 atom% doped TiO2 film also showed the best electrical results with a charge carrier concentration of 1.60 × 1021 cm−3 and mobility of 1.44 cm2 V−1 s−1 making it a suitable electrode in photovoltaic devices. The doped films were multifunctional, showing good photocatalytic activity under UV-light illumination. XPS and XRD studies gave strong evidence that the Ta was entering the TiO2 lattice as Ta5+ and that a reduction of some Ti4+ to Ti3+ was observed.

Carbon nanofiber-templated mesoporous TiO2 nanotubes as a high-capacity anode material for lithium-ion batteries

The present communication demonstrates the synthesis of uniform mesoporous TiO2 nanotubes via hydrolysis and condensation of tetrabutyl titanate (TBOT) using carbon nanofibers as templates followed by calcination under air. We further demonstrate the use of such TiO2 nanotubes as an anode material for rechargeable lithium-ion batteries (LIBs) with high discharge capacity, good rate capability and excellent cycling performance. They deliver a high discharge capacity of 209.6 mA h g−1 at a current density of 0.2 C in the voltage range 1.0–3.0 V. They can still deliver a discharge capacity of 108.1 and 88.8 mA h g−1 with 100 and 93.2% capacity retention after 500 charge–discharge cycles under current densities of 2 and 4 C, respectively.