Oxidative Purification Research Articles

The role of vacancy defects and holes in the fracture of carbon nanotubes

We present quantum mechanical calculations using density functional theory and semiempirical methods, and molecular mechanics (MM) calculations with a Tersoff–Brenner potential that explore the role of vacancy defects in the fracture of carbon nanotubes under axial tension. These methods show reasonable agreement, although the MM scheme systematically underestimates fracture strengths. One- and two-atom vacancy defects are observed to reduce failure stresses by as much as ∼26% and markedly reduce failure strains. Large holes – such as might be introduced via oxidative purification processes – greatly reduce strength, and this provides an explanation for the extant theoretical–experimental discrepancies.

Space durable polymer/carbon nanotube films for electrostatic charge mitigation

Low color, flexible, space environmentally durable polymeric materials possessing sufficient surface resistivity (10 6 –10 10 Ω/square) for electrostatic charge (ESC) mitigation are of interest for potential applications on Gossamer spacecraft as thin film membranes on antennas, large lightweight space optics, and second surface mirrors. One method of incorporating intrinsic ESC mitigation while maintaining low color, flexibility, and optical clarity is through the utilization of single-walled carbon nanotubes (SWNTs). However, SWNTs are difficult to uniformly disperse in the polymer matrix. The approach reported herein employed amide acid polymers endcapped with alkoxysilane groups that could condense with oxygen containing functionalities that were present on the ends of SWNTs as a result of the oxidative purification treatment. These SWNTs were combined with the endcapped amide acid polymers in solution and subsequently cast as unoriented thin films. Two examples possessed electrical conductivity (measured as surface resistance and surface resistivity) sufficient for ESC mitigation at loading levels of ≤0.08 wt% SWNT as well as good retention of thermo-optical properties. The percolation threshold was determined to lie between 0.03 and 0.04 wt% SWNT loading. Electrical conductivity of the film remained unaffected even after harsh mechanical manipulation.

Electron spin resonance of carbon nanotubes under hydrogen adsorption

Carbon nanotubes provided by different manufacturers and synthesized by a variety of methods were subjected to the same oxidative purification procedure. Electron spin resonance (ESR) was used to investigate changes in the electronic structure before and after purification and exposure to hydrogen gas at a pressure of 136 kPa. The ESR signal in single-wall carbon nanotubes was due to paramagnetic impurities and diminished in intensity upon hydrogen adsorption. The conduction electrons of multiwall carbon nanotubes gave rise to signals with Dysonian line shapes. Here, the signal intensity increased upon hydrogen adsorption and the asymmetry parameter as well as the g factor were affected, suggesting a decrease in band gap. In samples with large metal content a ferromagnetic resonance was observable which disappeared upon purification. Some samples yielded no observable ESR signal due to an increased relaxation time of the electrons upon interaction with residual metal catalyst particles and possibly a large proportion of semiconducting nanotubes.

Physical Aspects of Process Control in Selective Laser Sintering of Metals

AbstractDirect selective laser sintering (SLS) is a layered manufacturing technique that can produce fully dense, functional components in high performance metals. In this review paper, a first step is taken towards identifying and understanding some of the important physical mechanisms in direct SLS. This study not only provides an insight into phenomena observed during direct SLS processing of a variety of metallic materials but also helps in selecting those materials that are most amenable to direct SLS processing. The physical mechanisms discussed include oxidation, non‐equilibrium wetting, epitaxial solidification, metal vaporization, and oxide purification. Understanding these mechanisms is crucial for the design of direct SLS machines, process development, and process control.

Relationship between Shape Characteristics of Contact Media Used in Biofilm Oxidation Processes and Purification Capability in Rivers and Streams

The present study is aimed at clearly understanding the relationship among the arrangement of the gravel, the flow rate, and the porosity of the contact media, and the purification capability, which should be effective for a multi-natural type river restoration. Experimental studies were carried out by filling a linear circulation water passage (rated at a grade of 1/830, 30m long, 24cm wide, and 9cm deep, with a Stone type contact media or a net type contact media, whereby the biofilm attachment capability, the filling conditions and the flow rate were varied.The organic material removal capability differed depending upon the roughness coefficient of the flow passage; the greater the contact provided for the contact media, the higher the purification capability on contact with the biofilm; but it was found that the purification velocity would not improve, even when the amount of attached biofilm per unit contact media was increased to an extremely high level. This means that as the biofilm thickness increases, the porosity decreases so as to cause the decrease of the flow rate through the filled layer. In order to improve nitrification capability, it is necessary to establish the critical flow rate through the filled layer at above 5cm⋅s-1. On the other hand, for the nutrient removal (denitrification), it is important to have a greater amount of biofilm and to keep an anaerobic condition inside the biofilm. Therefore, it is important to make the proper combination of the rapids and pools in the biofilm processes in the rivers and streams.

Characterization of the surfaces of single-walled carbon nanotubes using alcohols and hydrocarbons: a pulse adsorption technique

A pulse mass analyzer was used to study the vapor phase adsorption of organic compounds on single-walled carbon nanotubes and chemically modified/oxidized SWCNTs. The change in mass of a packed bed of adsorbent held at 200 °C was observed following the injection of a pulse of an organic compound from the series: ethanol, iso-propanol, cyclohexane, cyclohexene, benzene, or n-hexane. The relative strength of adsorption was obtained by the mass increase resulting from injection of the pulse and by the time required for desorption. This time was broken into the transit time to reach the end of the bed and the half-time for return from peak to baseline. Hexane was the most strongly held compound of the organic sequence. Oxidative purification of a raw nanotube sample produced a less hydrophobic surface. The effect of the purification was reversed by thermolysis at 700 °C, which removed oxygenated functional groups and increased the affinity for hydrocarbons. The amorphous carbon associated with the raw nanotube sample is a strong adsorbent for hydrocarbons. By comparison, an activated carbon had a greater affinity for hydrocarbons than any of the nanotube samples.

Investigation of the Pore Structure of As-Prepared and Purified HiPco Single-Walled Carbon Nanotubes by N2/Ar AdsorptionImplication for H2 Storage

Open single-walled carbon nanotubes (SWNTs) are attractive as potential storage media for hydrogen gas. The present paper investigates the micropore structure of HiPco SWNTs samples, as studied by nitrogen and argon adsorption technique at low pressures. The proportion of open SWNT is estimated with the Horvath−Kawazoe method. The results show that as-prepared samples may contain as much as 40% open SWNTs, whereas the oxidative purification process reduces this amount significantly. X-ray diffraction and Raman spectroscopy show that the Horvath−Kawazoe method is reliable for estimating the diameter of open SWNTs. In addition, the Horvath−Kawazoe method appears to be sensitive to species adsorbed in the outer grooves.

Determination of thermo-oxidation products of plant sterols

Plant sterols are subjected to oxidation when exposed to air and, especially, when heated at high temperatures. We developed a method to study thermo-oxidation of plant sterols. The method consisted of cold saponification, purification of oxides by solid-phase extraction and gas chromatography analysis. To compensate for losses during the procedure, an internal standard was added before saponification. The method showed good recovery of added cholesterol oxides, separation of plant sterol oxides and reproducibility in detecting thermo-oxidation products of stigmasterol and rapeseed oil. Based on this study, the major products are 7-hydroxy, 5,6-epoxy and 7-keto compounds and oxides are formed faster in bulk stigmasterol than in rapeseed oil.

Reactivity of different kinds of carbon during oxidative purification of catalytically prepared carbon nanotubes

In the purification procedure of catalytically prepared carbon nanotube samples, the oxidative removal of amorphous carbon was investigated. Oxidation was carried out by KMnO4, H2O2, O3 or HClO4. The selectivity of the amorphous carbon burning reaction was studied as a function of the reaction temperature by transmission electron microscopy. The advantages of the different methods are as follows: although oxidation by KMnO4 in an acidic suspension provides nanotubes free of amorphous carbon, and can easily be controlled, it must be followed by filtration and cc HCl treatment in order to dissolve the MnO2 formed during the reaction. Oxidation with hydrogen peroxide does not give undissolved residue on the surface of the tubes. Ozone treatment produces gaseous by-products, but requires higher reaction temperature. This method is more difficult to control. During oxidation, competitive oxidation always takes place: carbon nanotubes and amorphous carbon react simultaneously. While amorphous carbon can be attacked from any direction, carbon nanotubes can be oxidized only from the ends.

Some comments on the paper by Edward S Fry on the visible and near-ultraviolet absorption spectrum of liquid water

It is contended that the most comprehensive collection of data on the visible and near-ultraviolet spectrum of pure liquid water can still be found [Appl. Opt. 38, 1216 (1999)]. The data produced [Appl. Opt. 36, 8710 (1997)] from the integrated light loss in a light-scattering cavity containing water produces a useful set of data, although the error bars presented are underestimated. Furthermore, an oxidative purification step was not incorporated into the water purification procedure to remove residual traces of light-absorbing organic impurities.

The CrIIL reduction of [2Fe-2S] ferredoxins and site of attachment of CrIII using 1H NMR and site-directed mutagenesis.

The recently reported NMR solution structure of FeIIIFeIII parsley FdI has made possible 2D NOESY NMR studies to determine the point of attachment of CrIIIL in FeIIIFeIII...CrIIIL. The latter Cr-modified product was obtained by reduction of FeIIIFeIII parsley and spinach FdI forms with [Cr(15-aneN4) (H2O)2]2+ (15-aneN4 = 1,4,8,12-tetraazacyclopentadecane), referred to here as CrIIL, followed by air oxidation and chromatographic purification. From a comparison of NMR cross-peak intensities of native and Cr-modified proteins, two surface sites designated A and B, giving large paramagnetic CrIIIL broadening of a number of amino acid peaks, have been identified. The effects at site A (residues 19-22, 27, and 30) are greater than those at site B (residues 92-94 and 96), which is on the opposite side of the protein. From metal (ICP-AES) and electrospray ionization mass spectrometry (EIMS) analyses on the Cr-modified protein, attachment of a single CrIIIL only is confirmed for both parsley and spinach FdI and FdII proteins. Electrostatic interaction of the 3+ CrIIIL center covalently attached to one protein molecule (charge approximately -18) with a second (like) molecule provides an explanation for the involvement of two regions. Thus for 3-4 mM FeIIIFeIII...CrIIIL solutions used in NMR studies (CrIIIL attached at A), broadening effects due to electrostatic interactions at B on a second molecule are observed. Experiments with the Cys18Ala spinach FdI variant have confirmed that the previously suggested Cys-18 at site A is not the site of CrIIIL attachment. Line broadening at Val-22 of A gives the largest effect, and CrIIIL attachment at one or more adjacent (conserved) acidic residues in this region is indicated. The ability of CrIIL to bind in some (parsley and spinach) but not all cases (Anabaena variabilis) suggests that intramolecular H-bonding of acidic residues at A is relevant. The parsley and spinach FeIIFeIII...CrIIIL products undergo a second stage of reduction with the formation of FeIIFeII...CrIIIL. However, the spinach Glu92Ala (site B) variant undergoes only the first stage of reduction, and it appears that Glu-92 is required for the second stage of reduction to occur. A sample of CrIIIL-modified parsley FeIIIFeIII Fd is fully active as an electron carrier in the NADPH-cytochrome c reductase reaction catalyzed by ferredoxin-NADP+ reductase.

Purification of refractory metal powders and oxides by magnetic means: B.D.Bryskin et al. (Rhenium Alloys Inc, USA.)

Purification of refractory metal powders and oxides by magnetic means: B.D.Bryskin et al. (Rhenium Alloys Inc, USA.)

亜鉛浸出残さの脱鉄処理で得られる酸化鉄の精製と磁化特性に及ぼす事前水洗とＮａ２Ｂ４Ｏ７フラックス添加量低減の影響

The purification of raw iron oxide obtained from iron precipitation of the zinc leach residue using the recrystallization method with Na2B4O7 flux and their magnetic properties has been investigated. The main purpose of present study are to examine the effect of the prior water washing and decrease of amounts of Na2B4O7 flux on the purification of raw material. As a result, it was recognized that the prior water washing of raw material are undesirable, because of decrease of desulfurization in the purification by the sub-sequent recrystallization method,and the elimination of Zn, S and As in raw material is the best, when raw material/flux ratio is 70/30 and the prior water washing is not carried out. The magnetic properties is similar to that of α-Fe2O3 single crystal. The synthesis and magnetic properties of Mn-Zn ferrite from purified iron oxide were also examined.

Determination of platinum group elements by inductively coupled plasma-mass spectrometry combined with nickel sulfide fire assay and tellurium coprecipitation

A method was developed for the determination of trace platinum group elements (PGEs) by nickel sulfide fire assay inductively coupled plasma-mass spectrometry (ICP-MS). With isotope dilution, the improved technique gives precise Os content data. Through the purification of the reagent nickel oxide, reagent blank was greatly reduced. Results obtained for the standard reference materials (SRM) GPt-1-GPt-7(GBW 07288-07294, China), DZ Σ-2 (GBW 07102, China) and Guilin Cu–Ni Ore are in good agreement with the recommended values for platinum group elements. The detection limits ranged from 0.01 to 0.39 ng/g. The relative standard deviations for Ru, Rh, Pd and Ir were less than 5%, for Os less than 1%, and Pt less than 8% for SRM GPt-6.

Extraction and Purification of Dimeric Fullerene Oxides from Fullerene Soot

In this paper, a novel method called hydrothermally initiated dynamic extraction (HIDE) is proposed for the extraction of dimeric fullerene oxides such as C120O and C130O in the fullerene soot. In this method, the soot is hydrothermally treated prior to the extraction by organic solvent. As a result, a few types of dimeric fullerene oxides were efficiently extracted from the soot for the first time. The extraction efficiency was 40 times more than that of the Soxhlet extraction with organic solvents, and several dimeric fullerene oxides were obtained in milligram quantities. Furthermore, the analyses strongly indicated that the extract contains not only dimeric fullerene oxides but also higher fullerene oxides. The detailed purification procedures for each dimeric fullerene oxide are also presented in this report.

Ｚｎ浸出残さの脱鉄処理で得られた酸化鉄の高純度化とその磁化測定

Ｚｎ浸出残さの脱鉄処理で得られた酸化鉄の高純度化とその磁化測定

Advanced Oxidation Processes Against Phenolic Compounds In Wastewater Treatment

Abstract Experimental research into the oxidative treatment of aqueous solutions and wastewaters containing phenolic compounds was undertaken. Ozone, supported by short wavelength UV-irradiation, hydrogen peroxide and titanium dioxide catalyst, was selected as an oxidant in the following combinations: O3, O3/H2O2, O3/UV, O3/TiO2, O3/UV/H2O2 and O3/UV/TiO2. 5-Methylresorcinol was chosen as a model compound for the experiments with synthetic phenolic solutions. The results obtained from these experiments were compared with the results of oxidative purification of wastewaters produced from the thermal treatment of oil shale in Estonia.

Chemical oxidation of biologically treated phenolic effluents

Experimental research into the oxidative purification of biologically treated phenolic effluents of the Estonian oil shale chemical industry was undertaken. The main phenolic compounds identified in this wastewater were phenol, cresols, resorcinol and 5-methylresorcinols. For chemical oxidation of phenols different advanced oxidation methods (O 3, H 2O 2, UV, O 3/H 2O 2, O 3/UV, H 2O 2/UV, O 3/H 2O 2/UV) were tested. For tracking of the changes in the concentration of different phenols during the treatment process, HPLC and colorimetry were applied. It was shown that, in principle, phenols can be reduced almost by any oxidation method studied. Oxidation with molecular ozone has the most potential for practical application. Methods not including ozone (H 2O 2, UV, H 2O 2/UV) had, in general, lower efficiency for total phenols reduction than the methods combining ozone.

Studies on an artificial trypsin inhibitor peptide derived from the mung bean trypsin inhibitor: chemical synthesis, refolding, and crystallographic analysis of its complex with trypsin.

The active fragment with Lys at the reactive site of mung bean trypsin inhibitor (MBILF) is composed of two peptide chains, A1 of 26 residues and A2 of 9 residues linked via two disulfide bonds. In the present study, a peptide of 22 residue comprising the sequence of chain A1 from position 3 to 24 was synthesized by the solid-phase method. This synthetic peptide with six Cys residues contains a reactive site at position Lys11I-Ser12I (I denotes an inhibitor residue). Air oxidation and HPLC purification resulted in two antitrypsin active components, SPC1 and SPC2. Neither SPC1 nor SPC2 can stoichiometrically inhibit trypsin. The Ki values of SPC1 and SPC2 are 1.2 x 10(-7) and 4.0 x 10(-8) M, respectively. The complexes of SPC1 and SPC2 with bovine beta-trypsin (BTRY) were crystallized by ammonium sulphate precipitation at pH 6.4 and 6.0, respectively. The two crystals have the same crystal form with space group P2(1)2(1)2(1) and cell dimension of a = 63.2(2) A, b = 63.5(6) A, and c = 69.8(4) A. The crystal structure of one complex, SPC1-BTRY, was determined and refined at 2.2 A resolution to a final R-value of 19.2%. From the resulting electron density map, 9 residues of SPC1, from position 9I to 17I, were identified clearly and three-dimension atomic model of the 9-residue reactive loop formed by a disulfide bridge, Cys9I-Cys17I, was built. No electron density corresponding to the other 13 residues was observed in the present map.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxidative purification of wastewaters containing phenolic compounds from oil shale treatment

Abstract Experimental research into the oxidative purification of wastewaters produced from the thermal treatment of oil shale in Estonia was undertaken. The main toxic compounds of that wastewater were phenolic compounds, such as phenol, p‐cresol and 5‐methylresorcinol (5‐MR). Ozone and hydrogen peroxide were selected as oxidants and a literature review for both is presented. The optimum pH range for the ozonation of 5‐MR solutions and of a wastewater were determined, as well as the specific ozone consumption. It was shown that under conditions of competitive reactions the volatile phenols decompose faster than the non‐volatile ones. The treatment of phenolic solutions with hydrogen peroxide, in the presence of ferrous sulphate (Fenton's reagent), was found to be optimal in the pH range close to neutral. The catalyst, ferrous sulphate, is important for the oxidation rate but does not influence the process efficiency. The higher the initial concentration of the phenolic compounds the lower the specific oxidant consumption. The reactivity of the volatile phenols with hydrogen peroxide was also higher than that of the non ‐volatile phenols. The toxicity of the treated wastewater to Daphnia Magna decreased with increasing applied oxidant dose. The toxicity stabilizes after the complete decomposition of the phenolic compounds.