Charles U. Pittman

Surface characterization of electrochemically oxidized carbon fibers

High strength PAN-based carbon fibers were continuously electrochemically oxidized by applying current to the fibers serving as an anode in 1% wt aqueous KNO3. Progressive fiber weight loss occurred with increasing extents of electrochemical oxidation. XPS studies (C 1s and O 1s) indicated that the oxygen/carbon atomic ratio rose rapidly to 0.24 as the extent of electrochemical oxidation was increased from 0 to 133 C/g and then remained almost constant as the extent of electrochemical oxidation rose to 10 600 C/g. Fitting the C 1s spectra demonstrated that the rise in surface oxygenated functional groups was mainly due to an increase in carboxyl (COOH) or ester (COOR) groups. An increase in the intensity of the O 1s peak (534.6–535.4 eV) after electrochemical oxidation corresponded to chemisorbed oxygen and/or adsorbed water. Electrochemical oxidation increased surface activity by generating more surface area via the formation of ultramicropores, and by introducing polar oxygen-containing groups over this extended porous surface. FT-IR spectra showed a broad peak at about 1727 cm−1 from C=O stretching vibrations of carboxyl and/or ketone groups, the relative intensity of which increased significantly with the extent of electrochemical oxidation. Post-oxidation heat-treatments in flowing nitrogen at 550°C for 30 min. caused further weight losses due to decarboxylation of carboxyl groups and other reactions in which oxygenated functions decomposed. These weight losses increased with the extent of electrochemical oxidation. This demonstrated that more oxygenated groups formed on the internal pore surfaces as pores increasingly penetrated deeper into the fibers with increased electrochemical treatment. Weight loss depended on the heat treatment temperature since different types of carbon–oxygen surface groups were formed during the electrochemical oxidations. Different functions have different abilities to decarboxylate or decarbonylate. The amount of Ag+ and NaOH uptake by electrochemically oxidized fibers rapidly decreased as the temperature of the post heat treatment increased to 550°C. Beyond 550°C the progressive decrease in Ag+ adsorption and NaOH uptake continued at a slower rate and approached 0 μmol/g after heating to 850°C. Conversely, after heat treatment I2 adsorption showed a marked increase as the treatment temperature was raised. Thermal decomposition of carbon–oxygen complexes within the pore structure leads to a lower hydrophilicity of the pore surface. The extensive micropore surface area generated by electrochemical oxidation becomes more accessible to I2 as CO2 and CO evolve. Very narrow pores (<10 A diameter) blocked by hydrogen bonding and oxygenated functions become more open. XPS analyses illustrated that the surface oxygen content decreased significantly after heat-treating to 550 or 850°C and was lowest after the 850°C treatment.

Chemical modification of carbon fiber surfaces by nitric acid oxidation followed by reaction with tetraethylenepentamine

Amino groups react rapidly with both isocyanates and epoxides. Thus, to prepare carbon fibers which might exhibit enhanced adhesion to both polyurethanes and epoxy resin matrices, attempts were made to introduce a high surface amine concentration onto high-strength carbon fibers (derived from PAN) by nitric acid oxidation followed by reaction with excess tetraethylenepentamine (TEPA). Fibers were oxidized with concentrated (70%) nitric acid at 115 °C (20, 40, 60 and 90 minutes) to generate surface acidic functions, primarily carboxyl and phenolic hydroxyl groups. These oxidized fibers were then reacted with TEPA at 190–200 °C to introduce surface-bound amino functions onto the surface via amide functions. The amide functions formed at the surface to graft TEPA to the surface. TEPA does not react with hydroxyl functions so hydroxyls remain on the surface. Decarboxylation of surface carboxyl groups was minor during the TEPA grafting. The quantity of surface-bound acidic and basic functions on these modified fiber surfaces was measured by NaOH and HCl uptake experiments. Then, methylene blue and metanil yellow dye adsorption experiments were employed to provide a measure of the surface area and both the surface density and steric availability of surface acidic and basic functions. The dye adsorption gave lower values of acidic and basic functional group surface concentrations than did NaOH/HCl uptake measurements. The number of acidic groups increased continuously with increasing oxidation times but after an initial jump in acidic groups per 100 A2 at the start of the oxidation, the density of the surface acidic was approximately constant. Instead, the surface area increased, which accounted for the increase in total acidic groups. Nitrogen BET measurements were also performed and the BET surface areas were compared to those derived from dye adsorption experiments. Similarly, both HCl and metanil yellow adsorption measurements led to a value of 5.6 basic (amine) groups per 100 A2 after reaction with TEPA. The results were consistent with an increase in surface area during nitric acid oxidation. About 52% of the surface acidic functions, which were generated during nitric acid oxidations of 20–60 minutes, had reacted with TEPA. An average of 2.6 amino groups were introduced for each carboxyl group consumed in the reaction with TEPA. Thus substantial looping of TEPA occurs where more than one amino function of TEPA has formed an amide bond at the surface. The average ratio of the total amino groups introduced to the total amount of acidic groups present after nitric acid oxidation was about 1.35.

Oxygen plasma and isobutylene plasma treatments of carbon fibers: Determination of surface functionality and effects on composite properties

High strength, PAN-based carbon fibers were treated with oxygen plasmas and isobutylene plasmas. The effects of exposure time, plasma power and gas pressure on the quantity of acidic functional groups introduced onto the fiber surfaces were examined. NaOH uptake measurements provided a quantitative determination of the surface acidic functions. Plasma treatments were able to generate a three-to-five-fold increase in the number of acidic functional groups per 100 A2. Methylene blue (MB) adsorption measurements, when used with NaOH uptake values, provided an estimate of the surface density of the acidic functions (functions/100 A2) that was independent of direct surface area measurements. This method was compared to the direct use of NaOH uptake values with nitrogen BET measurements of the surface area to give the number of acidic functions per 100 A2. These methods were compared for both oxygen plasma-oxidized and nitric acid-oxidized carbon fibers. The largest quantity of acid functions (16 μeq/g fiber) was obtained after 4 minutes in an oxygen plasma at 50 W. MB adsorption decreased while NaOH uptake increased as exposure time to oxygen plasma increased implying some decrease in surface area occurred. Surface area measurements (BET), however, showed no change in surface area over a 10 minute exposure to a 200 W oxygen plasma (all surface areas were in the range of 0.62 to 0.75 m2 g−1). These results are discussed in terms of possible effects of surface roughness, dye configuration or multiple dye layers. The rate of depositing polyisobutylene polymer residues on a flat glass surface was greater than that achieved on carbon fiber surfaces where shadowing effects could have existed within a tow. Oxygen plasma treatment improved the interfacial shear strength (determined by single filament fragmentation tests using an epoxy resin). The interlaminar shear strength (three-point bending) of carbon fiber/epoxy composites (Vf = 0.57) increased 28–29% using oxygen plasma-treated fibers while the Izod impact strength was unchanged. Plasma-polyisobutylene coated fibers (~ 650 A thick coating) exhibited a 37% increase in Izod impact strength when incorporated into epoxy matrix composites but the interlaminar shear strength decreased by 21% versus composites prepared with as-received fibers.

Heavy metals [chromium (VI) and lead (II)] removal from water using mesoporous magnetite (Fe3O4) nanospheres

Magnetite nanospheres with hollow interiors were synthesized using a simple, one-pot, and template free solvothermal method with ferric chloride as the iron precursor. The composition, surface properties and morphology were studied using X-ray powder diffraction (XRD), energy dispersive X-ray fluorescence (EDXRF), Fourier transform infrared spectroscopy (FTIR), surface area analysis, point of zero charge (pHpzc), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and magnetic moment determination. These mesoporous nanospheres have a SBET=11.3m(2)/g and a high saturation magnetization of 77.5emu/g. These magnetite nanospheres successfully remediated Cr(6+) and Pb(2+) from water. The optimum pHs for Cr(6+) and Pb(2+) adsorption were 4.0 and 5.0, respectively. Adsorption was carried out at 25, 35 and 45°C. The sorption data were fitted using Freundlich, Langmuir, Redlich-Peterson, Sips, Koble-Corrigan, Radke and Prausnitz and Toth adsorption models. The pseudo-second order model better fitted the kinetics data. The Langmuir adsorption capacities of magnetic nanospheres were ∼9 and ∼19mg/g for Cr(6+) and Pb(2)(+), respectively. Magnetic collection of these magnetite nanospheres can be used to isolate and regenerate the used adsorbent.

Synthetic and catalytic studies of polymer-bound metal carbonyls☆

Abstract The reactions of polymeric analogs of benzyl-diphenylphosphine and -triphenylphosphine with a variety of metal carbonyls have been examined using both thermal and photochemical techniques. Metal derivatives of both linear polymers and swellable cross-linked resins have been synthesized in this manner. The catalysis of hydroformylation and isomerization reactions have been studied using a polymeric derivative of dicobalt hexacarbonyl. The catalyst could be very easily recycled and gave product yields in the hydroformylation of pentenes quite similar to those reported earlier using the corresponding homogeneous species. The cyclization of ethyl propiolate has also been carried out using a new polymeric nickel complex. Benzene isomers are isolated during the initial use of this catalyst whereas cyclooctatetraene isomers, in addition, are observed using the recycled catalyst.

Removal of Molecular Adsorbates on Gold Nanoparticles Using Sodium Borohydride in Water

The mechanism of sodium borohydride removal of organothiols from gold nanoparticles (AuNPs) was studied using an experimental investigation and computational modeling. Organothiols and other AuNP surface adsorbates such as thiophene, adenine, rhodamine, small anions (Br(-) and I(-)), and a polymer (PVP, poly(N-vinylpyrrolidone)) can all be rapidly and completely removed from the AuNP surfaces. A computational study showed that hydride derived from sodium borohydride has a higher binding affinity to AuNPs than organothiols. Thus, it can displace organothiols and all the other adsorbates tested from AuNPs. Sodium borohydride may be used as a hazard-free, general-purpose detergent that should find utility in a variety of AuNP applications including catalysis, biosensing, surface enhanced Raman spectroscopy, and AuNP recycle and reuse.

Adsorption of precious metal ions onto electrochemically oxidized carbon fibers

Electrochemically oxidized carbon fibers (ECF) adsorbed a prodigious amount of Ag+ in contrast to oxygen plasma and nitric acid treated carbon fibers. The amount of adsorbed Ag+ reached 3700 μmol/g after 5652 C/g of electrochemical oxidation. This value approaches the 4050 μmol/g of Ag+ which adsorbed onto steam-activated Kenaf-based carbon (with a surface area of 1284 m2/g determined by N2/BET) under the same adsorption conditions. ECF oxidized to 9540 C/g adsorbed more than its own weight of Ag+ (12 608 μmol/g). These fibers exhibited a surface area of 115 m2/g (CO2–DR). Two different reactions occurred during Ag+ adsorption. These reactions were ion exchange adsorption between Ag+ and acidic functions (carboxyl) and redox adsorption between Ag+ and reducing functions such as catechol groups on these electrochemically oxidized fibers (ECF). The redox capability was expressed by the reaction electric potential (E) using the Nernst equation. High resolution XPS C 1s spectra of ECFs (level of oxidation 5300 C/g), before and after Ag+ adsorption, showed that the carbon atoms present in phenolic, alcohol or ether groups and those present in carbonyl or quinone groups increased after Ag+ adsorption. X-ray diffraction and X-ray photoelectron spectroscopy (XPS) Ag 3d spectra of the ECF showed that adsorbed Ag+ was reduced to Ag0 after both Ag+ adsorption and subsequent post-heat treatment of the fibers under N2 at 550°C for 30 min. Only about one-third as much Au3+ adsorption occurred versus the extent of electrochemical oxidation as was observed for Ag+. This ratio matches the requirement that three electrons are required to convert Au3+ to Au0 versus one to convert Ag+ to Ag. High resolution angle resolved XPS (ARXPS) Pd 3d and Pt 4f spectra show that there are two different Pd oxidation states and three different Pt oxidation states present after adsorption of Pd2+ and Pt2+ onto ECF. The peak areas as a function of take off angle showed that substantial amounts of Pd0 and Pt0 are present in addition to Pd2+ and Pt2+ and Pt4+ on the outermost surface regions of oxidized fibers.

Sequential multistep reactions catalyzed by polymer-anchored homogeneous catalysts

Abstract : The first examples of sequential miltistep organic reactions carried out over polymer-anchored homogeneous catalysts are reported where two such catalysts are bound to the same crosslinked polymer. Also, sequential catalytic reactions where two catalysts, each anchored to a separate resin, are mixed together in the same reactor were conducted. Sequential cyclooligomerization of butadiene to 4-vinylcyclohexene, (Z,Z)-1,5-cyclooctadiene, and (E,E,E)-1,5,9-cyclododecatriene, followed by hydrogenation to ethylcyclohexane, cyclooctane, and cyclododecane, was accomplished using a single styrene-divinylbenzene resin to which (PPh3)2Ni(CO)2 and (PPh3)3RhCl had been anchored. The same reaction sequence was effected by a mixture of two resins to which (PPh3)2Ni(CO)2 and (PPh3)RhCl were individually attached.

Catalytic upgrading of bio-oil using 1-octene and 1-butanol over sulfonic acid resin catalysts.

Raw bio-oil from fast pyrolysis of biomass must be refined before it can be used as a transportation fuel, a petroleum refinery feed or for many other fuel uses. Raw bio-oil was upgraded with the neat model olefin, 1-octene, and with 1-octene/1-butanol mixtures over sulfonic acid resin catalysts from 80 to 150 °C in order to simultaneously lower water content and acidity and to increase hydrophobicity and heating value. Phase separation and coke formation were key factors limiting the reaction rate during upgrading with neat 1-octene, although octanols were formed by 1-octene hydration along with small amounts of octyl acetates and ethers. GC-MS analysis confirmed that olefin hydration, carboxylic acid esterification, acetal formation from aldehydes and ketones and O- and C-alkylations of phenolic compounds occurred simultaneously during upgrading with 1-octene/1-butanol mixtures. Addition of 1-butanol increased olefin conversion dramatically by reducing mass transfer restraints and serving as a cosolvent or emulsifying agent. It also reacted with carboxylic acids and aldehydes/ketones to form esters and acetals, respectively, while also serving to stabilize bio-oil during heating. 1-Butanol addition also protected the catalysts, increasing catalyst lifetime and reducing or eliminating coking. Upgrading sharply increased ester content and decreased the amounts of levoglucosan, polyhydric alcohols and organic acids. Upgrading lowered acidity (pH value rise from 2.5 to >3.0), removed the unpleasant odor and increased hydrocarbon solubility. Water content decreased from 37.2% to <7.5% dramatically and calorific value increased from 12.6 MJ kg−1 to about 30.0 MJ kg−1.

Cascade couplings of N-alkyl-N-methacryloyl benzamides with ethers and benzenesulfonohydrazides to generate isoquinoline-1,3(2H,4H)-dione derivatives.

Two radical-mediated cascade couplings of N-alkyl-N-methacryloylbenzamides with different ethers and arylsulfonohydrazides to generate ether- and arylsulfonyl-substituted isoquinoline-1,3(2H,4H)-dione derivatives were developed. Both casccades proceeded via initially triggered functionalization of the alkene functions of the N-alkyl-N-methacryloylbenzamides, followed by ortho radical cyclizations onto the aromatic ring to give isoquinoline-1,3(2H,4H)-dione derivatives in good yields. These highly functionalized drug-like molecules will be valuable in drug discovery in the future.