The use of acrylic yarn modified with amidoxime and carboxylate-containing polymer for lead removal from drinking water.

Amidoxime and carboxylate-containing polymer adsorbents derived from acrylic yarn exhibit high adsorption capacity for lead(ii) (Pb2+) ions in water. The adsorption process follows pseudo-second-order kinetics and fits the extended Langmuir isotherm model with the maximum adsorption capacity of Pb2+ with 238 mg lead per gram of the fiber at room temperature. Endothermic (ΔH° = 20.3 kJ per mole), spontaneous, and with the increase in the entropy of Pb2+ adsorption was observed from the thermodynamic studies. Dynamic column adsorption experiments showed that the fiber can process 4.3 L of water spiked with 1 ppm of lead(ii) solution at a flow rate of 4.4 mL per min under the specified conditions. The selectivity of Pb2+ with the competitive metal ions showed varying results with highly selective for Pb2+ in a binary solution with sodium and calcium and varying degrees of competitiveness with transition metal ions. This efficient and easily prepared fiber adsorbent appears to be a promising new material for the remediation of lead-contaminated aquatic environments and potable waters.

A highly efficient uranium grabber derived from acrylic fiber for extracting uranium from seawater.

Acrylic fiber can be chemically converted to an amidoxime and carboxylate containing chelating adsorbent by a two-step synthesis method for extraction of uranium from seawater. A portion of the nitrile groups in the fiber is first converted to amidoxime using hydroxylamine followed by conversion of another portion of the nitrile groups to carboxylate with NaOH. At an optimized ratio of amidoxime/carboxylate (about 1 : 1), the chelating fiber in real seawater shows a higher uranium adsorption capacity and shorter saturation time compared with similar high-surface-area chelating fibers developed recently using a radiation-induced grafting method. The saturation capacity of uranium is estimated to be 7.73 grams per kilogram of the adsorbent at 20 °C and the half-saturation time is about 15.7 days. The fiber shows a vanadium/uranium ratio of about 1 in real seawater tests. The low vanadium adsorption capacity of the fiber is attributed to the branched-chain amidoxime groups formed by the specified amidoximation process. This simple and low-cost synthesis method can be scaled up to mass produce the chelating fiber for recovering metals from various aquatic environments including production of uranium from seawater.

Ultrasonic-assisted synthesis of Pd-Pt/carbon nanotubes nanocomposites for enhanced electro-oxidation of ethanol and methanol in alkaline medium.

Herein, a facile ultrasonic-assisted strategy was proposed to fabricate the Pd-Pt alloy/multi-walled carbon nanotubes (Pd-Pt/CNTs) nanocomposites. A good number of Pd-Pt alloy nanoparticles with an average of 3.4 ± 0.5 nm were supported on sidewalls of CNTs with uniform distribution. The composition of the Pd-Pt/CNTs nanocomposites could also be easily controlled, which provided a possible approach for the preparation of other architectures with anticipated properties. The Pd-Pt/CNTs nanocomposites were extensively studied by electron microscopy, induced coupled plasma atomic emission spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy, and applied for the ethanol and methanol electro-oxidation reaction in alkaline medium. The electrochemical results indicated that the nanocomposites had better electrocatalytic activities and stabilities, showing promising applications for fuel cells.

Carbonate-H2O2 leaching for sequestering uranium from seawater.

Uranium adsorbed on amidoxime-based polyethylene fiber in simulated seawater can be quantitatively eluted at room temperature using 1 M Na2CO3 containing 0.1 M H2O2. This efficient elution process is probably due to the formation of an extremely stable uranyl-peroxo-carbonato complex in the carbonate solution. After washing with water, the sorbent can be reused with minimal loss of uranium loading capacity. Possible existence of this stable uranyl species in ocean water is also discussed.

Surface-enhanced vibrational spectroscopy of adsorbates on microemulsion synthesized gold nanoparticles.

Very small (<10 nm) monodisperse gold nanoparticles (AuNPs) coated with a monolayer of decanethiol were prepared and their surface-enhanced infrared absorption (SEIRA) spectra were measured in the transmission mode. The AuNPs were prepared by the borohydride reduction of HAuCl(4) inside reverse micelles that were made by adding water to a hexane solution of sodium bis(2-ethylhexyl)sulfosuccinate (AOT). The gold nanoparticles were then stabilized by the addition of decanethiol. Subsequent addition of p-nitrothiophenol both facilitated the removal of excess AOT and showed that the gold surface was completely covered by the decanethiol. SEIRA spectra of decanethiol on gold particles prepared in AOT microemulsions were about twelve times more intense than corresponding layers on gold produced by electroless deposition and gave a significantly less noisy spectrum compared to the corresponding surface-enhanced Raman spectrum. The surface-enhanced Raman scattering (SERS) spectra of the same samples showed that the most intense spectrum was obtained from gold nanoparticles with a mean diameter of 2.5 nm. This result is in contrast to previous statements that SERS spectra could only be obtained from particles larger than 10 nm.

Pt, Rh and Pt-Rh nanoparticles on modified single-walled carbon nanotubes for hydrogenation of benzene at room temperature.

Nanometer-sized Pt, Rh, and bimetallic Pt-Rh particles can be deposited on surface of phenylacetic acid functionalized single-walled carbon nanotubes (SWCNTs) by a microemulsion method. The SWCNT-supported metallic nanoparticles show much greater catalytic activities compared with commercially available carbon-supported Pt and Rh catalysts for hydrogenation of neat benzene under mild experimental conditions. The bimetallic Pt-Rh nanoparticle catalyst synthesized by this method shows an enhanced activity relative to individual SWCNT-supported Pt and Rh nanoparticle catalysts. The SWCNT-supported metal nanoparticle catalysts can be recycled and reused at least five times without losing their activity. The hydrogenation reactions performed under our experimental conditions would not affect the pi-pi stacking holding phenylacetic acid on SWCNT surface.

Kinetic study of hydrodechlorination of chlorobiphenyl with polymer-stabilized palladium nanoparticles in supercritical carbon dioxide.

Hydrodechlorination of 4-chlorobiphenyl in supercritical fluid carbon dioxide (SF-CO(2)) catalyzed by palladium nanoparticles stabilized in high-density polyethylene beads proceeds by consecutive reactions to the final product bicyclohexyl. Each step of the reaction sequence, that is, 4-chlorobiphenyl --> biphenyl --> cyclohexylbenzene --> bicyclohexyl, follows pseudo-first-order kinetics. Arrhenius parameters of each reaction step were determined separately in SF-CO(2) by in situ absorption spectroscopy using a high-pressure fiber-optic cell. A simulation of product distributions using the first-order consecutive reaction equations was performed and compared with the experimental results obtained by GC/MS analysis of the 4-chlorobiphenyl reaction system. The differences are explained in terms of adsorption/desorption behavior of the intermediates on the catalytic metal surface with respect to the stereostructures of the molecules generated by a molecular mechanics method.

Deposition of metal nanoparticles on carbon nanotubes via hexane modified water-in-CO2 microemulsion at room temperature.

Carbon nanotube-supported metallic nanoparticles (Pd, Rh, and bimetallic Pd-Rh) with diameters in the range 2-10 nm can be synthesized by hydrogen reduction of metal ions dissolved in the water core of a CO2 microemulsion in liquid CO2 at room temperature. The microemulsion is stabilized by sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and dissolved in liquid CO2 with the aid of hexane as a modifier. The metal nanoparticles synthesized in the microemulsion can be deposited on surfaces of multi-walled carbon nanotubes (MWCNTs) by stirring in the liquid CO2 phase. This simple method produces uniformly distributed metal nanoparticles on surfaces of the MWCNTs with high yields. The carbon nanotube-supported Pd/Rh bimetallic nanoparticles exhibit high catalytic activities for hydrogenation of aromatic compounds and can be reused without losing catalytic activity.

Deposition of platinum nanoparticles on carbon nanotubes by supercritical fluid method.

Carbon nanotube-supported platinum nanoparticles with a 5-15 nm diameter size range can be synthesized by hydrogen reduction of platinum(ll) acetylacetonate in methanol modified supercritical carbon dioxide. X-ray photoelectron spectroscopy and X-ray diffraction spectra indicate that the carbon nanotubes contain zero-valent platinum metal and high-resolution transmission electron microscopy images show that the visible lattice fringes of platinum nanoparticles are crystallites. Carbon nanotubes synthesized with 25% by weight of platinum nanoparticles exhibit a higher activity for hydrogenation of benzene compared with a commercial carbon black platinum catalyst. The carbon nanotube-supported platinum nanocatalyst can be reused at least six times for the hydrogenation reaction without losing activity. The carbon nanotube-supported platinum nanoparticles are also highly active for electrochemical oxidation of methanol and for reduction of oxygen suggesting their potential use as a new electrocatalyst for proton exchange membrane fuel cell applications.