Adsorption properties of gold onto a chitosan derivative.

In order to find a material which can be used for the recovery of Au(III), a chitosan derivative was synthesized by carboxymethylation and grafting sulfur groups onto cross-linked chitosan backbone. Adsorption studies were carried out at different pH values to optimize the pH condition. Batch method was conducted to study the effects of parameters such as reaction time, initial metal concentration and temperature on Au(III) sorption. The maximum adsorption affinity for Au(III) was found to be 8.32 mmol/g at pH 4.0, 25 °C. The results of kinetic study showed that the adsorption reaction followed the pseudo second order model. The derivative showed high adsorption ability and reusability toward Au(III). All results suggested that the chitosan derivative had potential to be utilized in the recovery of Au(III) from aqueous medium.

Surface area measurement of functionalized single-walled carbon nanotubes.

Single-walled carbon nanotubes have been functionalized and the specific surface areas of the functionalized nanotubes measured. Contrary to expectations, functionalization leads to a decrease in specific surface area compared to that of the unfunctionalized nanotubes. Treatment with a concentrated 1:1 nitric/sulfuric acid mixture followed by high-temperature baking at 1000 degrees C was found to increase the specific surface area of the nanotubes. For the unfunctionalized SWNTs, this treatment increases the specific surface area (SSA) by 20%. In the case of SWNTs functionalized by n-butyl groups the increase in the SSA was nearly 2-fold with the value increasing from 410 (drying at 110 degrees C) to 770 m2/gm (acid and bake treatment followed by drying at 110 degrees C). For the ozonized SWNTs, the SSA increases more than 3-fold from 381 (drying at 110 degrees C) to 1068 m2/gm (acid and bake treatment followed by drying at 110 degrees C). SEM images indicate that the nanotubes rebundle in the solid state with an average bundle size of 10-30 nm. AFM studies show that the ozonized tubes have been cut to short bundles after ozonolysis. Hydrogen uptake studies carried out on the baked ozonized tubes led to a 3 wt % hydrogen uptake at 77 K and 30 bar.

Dielectrophoresis field flow fractionation of single-walled carbon nanotubes.

We report a study on Dielectrophoresis Field Flow Fractionation of Single-Wall Carbon Nanotubes (SWNTs). SWNTs, individually suspended in 1% SDBS solution, were separated by type when they passed a dielectrophoresis field flow fractionation device where 1 MHz AC voltage was supplied and the field strength was well below 1 V per mum. Furthermore, we uniquely observed enrichment of semiconductive SWNTs based on their band gap. In addition to Raman spectrum, UV-vis absorption and NIR fluorescence spectra were used for solution samples for characterization.

Thermolysis of fluorinated single-walled carbon nanotubes: identification of gaseous decomposition products by matrix isolation infrared spectroscopy.

The thermal decomposition of fluorinated single-walled carbon nanotubes (F-SWNTs), known to result in pristine SWNTs, has been investigated by freezing the gaseous products formed at temperatures between 50 and 500 degrees C under high vacuum in an argon matrix at 10-20 K and analyzing the trapped species by IR spectroscopy. The major products of F-SWNT decomposition are carbonyl fluoride (COF2) below 300 degrees C and CF4 above 300 degrees C. For comparison, graphite fluoride is stable thermally up to 300 degrees C under these conditions, and the major gas-phase species at temperatures below 500 degrees C are CF4 and the CF3 radical. F-SWNTs are thermally less stable than graphite fluoride, and etching of the nanotubes is observed at lower thermolysis temperatures.

A model for nucleation and growth of single wall carbon nanotubes via the HiPcO process: a catalyst concentration study.

Using the High Pressure carbon monoxide (HiPco) reactor we conducted an experiment on the effects of changing the catalyst concentration. With each catalyst concentration tested the resulting raw HiPco material was characterized for average SWNT lengths, SWNT diameters, residual iron particle size, and large fullerene content. We were able to determine trends in each of these characteristics as the catalyst concentration was changed. As the catalyst concentration was decreased SWNT lengths increased, SWNT diameters increased, the residual iron particle size increased, and the large fullerene content decreased. From these trends we have developed a Competitive Growth model for nucleation and growth of SWNTs via the HiPco process.

Controlled multistep purification of single-walled carbon nanotubes.

A controlled and scalable multistep purification method has been developed to remove iron impurity and nonnanotube carbon materials from raw single-walled carbon nanotubes (SWNTs) produced in the HiPco (high-pressure CO) process. In this study, iron nanoparticles, coated by carbon, are exposed and oxidized by multiple step oxidation at increasing temperatures. To avoid catalytic oxidation by iron oxide of carbon nanotubes, the exposed and oxidized iron oxide is deactivated by reaction with C(2)H(2)F(4) or SF(6). The iron fluorides are removed by a Soxhlet extraction with a 6 M HCl solution. The purity and quality of each sample were determined by thermogravimetric analysis (TGA), Raman spectrometry, ultraviolet-visible-near-IR (UV-vis-near-IR) spectrometry, fluorescence spectrometry, and transmission electron microscope (TEM) spectroscopy. The purity and yield of SWNTs are improved due to reduced catalytic activity of the iron oxide. Greater iron oxide removal also resulted from oxidation at higher temperatures.

Controlled oxidative cutting of single-walled carbon nanotubes.

The oxidation reaction of piranha solutions with purified HiPco carbon nanotubes was measured as a function of temperature. At high temperatures, piranha is capable of attacking existing damage sites, generating vacancies in the graphene sidewall, and consuming the oxidized vacancies to yield short, cut nanotubes. Increased reaction time results in increasingly shorter nanotubes. However, significant sidewall damage occurs as well as selective etching of the smaller diameter nanotubes. On the other hand, room-temperature piranha treatments show the capability of cutting existing damage sites with minimal carbon loss, slow etch rates, and little sidewall damage. Combined with a method of introducing controlled amounts of damage sites, these room-temperature piranha solutions have the potential to yield an efficient means of creating short, cut nanotubes.

MALDI matrices for biomolecular analysis based on functionalized carbon nanomaterials.

When used in small molar ratios of matrix to analyte, derivatized fullerenes and single wall nanotubes are shown to be efficient matrices for matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. The mixing of an acidic functionalized fullerene with a solution of bioanalyte, depositing a dried droplet, and irradiating with a pulsed nitrogen laser yields protonated or cationized molecular ions. Derivatized fullerenes could offer several advantages over conventional MALDI matrices: a high analyte ionization efficiency, a small molar ratios (less than 1) of matrix/analyte, and a broader optical absorption spectrum, which should obviate specific wavelength lasers for MALDI acquisitions. The major disadvantage to the use of fullerenes is the isobaric interference between matrix and analyte ions; however, it is overcome by using MALDI-ion mobility time-of-flight (IM-oTOF) mass spectrometry to preseparate carbon cluster ions from bioanalyte ions prior to TOF mass analysis. However, an alternative to the dried droplet preparation of fullerene MALDI samples is the aerosolization of matrix-analyte solutions (or slurries) followed by impacting the aerosol onto a stainless surface. We also demonstrate that the fullerene matrices can be used to acquire spectra from rat brain tissue.

Macroscopic, neat, single-walled carbon nanotube fibers.

Well-aligned macroscopic fibers composed solely of single-walled carbon nanotubes (SWNTs) were produced by conventional spinning. Fuming sulfuric acid charges SWNTs and promotes their ordering into an aligned phase of individual mobile SWNTs surrounded by acid anions. This ordered dispersion was extruded via solution spinning into continuous lengths of macroscopic neat SWNT fibers. Such fibers possess interesting structural composition and physical properties.

Sidewall carboxylic acid functionalization of single-walled carbon nanotubes.

The reactions of single-walled carbon nanotubes (SWNTs) with succinic or glutaric acid acyl peroxides in o-dichlorobenzene at 80-90 degrees C resulted in the addition of 2-carboxyethyl or 3-carboxypropyl groups, respectively, to the sidewalls of the SWNT. These acid-functionalized SWNTs were converted to acid chlorides by derivatization with SOCl(2) and then to amides with terminal diamines such as ethylenediamine, 4,4'-methylenebis(cyclohexylamine), and diethyltoluenediamine. The acid-functionalized SWNTs and the amide derivatives were characterized by a set of materials characterization methods including attenuated total reflectance (ATR) FTIR, Raman and solid state (13)C NMR spectroscopy, transmission electron microscopy (TEM), and thermal gravimetry-mass spectrometry (TG-MS). The degree of SWNT sidewall functionalization with the acid-terminated groups was estimated as 1 in 24 carbons on the basis of TG-MS data. In comparison with the pristine SWNTs, the acid-functionalized SWNTs show an improved solubility in polar solvents, for example, alcohols and water, which enables their processing for incorporation into polymer composite structures as well as for a variety of biomedical applications.

Oxidative properties and chemical stability of fluoronanotubes in matrixes of binary inorganic compounds.

The chemical stability of fluoronanotubes in selected solid inorganic matrixes has been studied by initially mixing and mechanically grinding the components and subsequently heating them at temperatures ranging from 35 to 600 degrees C. The inorganic compounds selected for matrixes included halides (KBr, KI, Lil, LiBr, LiCl, NaCl, Znl2), oxides (Li2O, Fe2O3, PbO, MnO), lithium peroxide (Li2O2), potassium superoxide (KO2), sulfides (Li2S and ZnS), zinc selenide (ZnSe), lithium nitride (Li3N), and aluminum phosphide (AIP). Solid products, resulting from the proceeding chemical reactions, were analyzed by X-ray diffraction, Raman spectroscopy, and SEM/EDX elemental analysis. Gaseous and volatile products were identified with the help of the TGA/MS technique. Experimental data presented in this paper provide clear evidence that fluoronanotubes are not chemically inert toward the solid matrixes studied and exhibit significant oxidative properties in the redox reactions occurring under various temperatures, depending on the nature of the inorganic compound.

Sidewall functionalization of single-walled carbon nanotubes with organic peroxides.

Single-wall carbon nanotubes (SWNTs) and their fluorinated derivatives (F-SWNTs) were reacted with organic peroxides including benzoyl and lauroyl peroxide to produce phenyl and undecyl sidewall functionalized SWNTs, respectively, which were characterized by Raman, FTIR, and UV-Vis-NIR spectra as well as TGA/MS, TGA/FTIR, and TEM data.

Covalent sidewall functionalization of single wall carbon nanotubes.

Alkyllithium reagents may be used to attach alkyl groups to the sidewalls of fluoro nanotubes. Thermal gravimetric analysis combined with UV-vis-Nir spectroscopy has been used to provide a quantitative measure of the degree of functionalization. SWNTs prepared using the HiPco process exhibit a higher degree of alkylation than SWNTs from the laser-oven method, indicating that the smaller diameter fluoro tubes are alkylated more readily. The spectral signature of the pristine SWNTs can be regenerated when the alkylated SWNTs are heated in Ar at 500 degrees C, demonstrating that dealkylation occurs at this temperature. TGA-MS analysis using a sample of n-butylated h-SWNTs showed that 1-butene and n-butane are formed during thermolysis.

Response of Ceriodaphnia dubia to ionic silver: discrepancies among model predictions, measured concentrations and mortality.

Silver thiosulfate, often a waste product of photoprocessing, is less bioavailable or toxic to aquatic organisms than is ionic silver. We conducted duplicate 48-h Ceriodaphnia dubia tests in reconstituted laboratory water using treatments of 92.7 nM Ag+ with various concentrations of thiosulfate. Expected Ag+ concentrations were generated for thiosulfate treatment levels using MINEQL + chemical equilibrium modeling. Ag+ concentrations in treatments were determined using a novel silicon-based sensor. Based on predicted Ag+ and published 48-h LC50 values for C. dubia, we did not expect to observe adverse effects. Yet, 100% mortality was observed at low thiosulfate treatments, whereas > 85% and > 95% survival was observed at higher thiosulfate treatment levels, respectively. Our results indicate that biotic responses match the sensor-based Ag+ concentrations. However, there is a discrepancy between these empirical results and responses expected to occur with Ag+ concentrations as predicted by MINEQL + chemical modeling. By correlating silicon sensor data with toxicity results obtained from our laboratory, our work clearly relates a specific chemical form (Ag+) to toxicity results.