Oxidative pretreatments

The effect of oxidation pretreatment and oxidative reaction on the graphitic structure of all CNF or CNF based catalysts has been studied by XRD and HRTEM. From the diffraction patterns as shown in Fig. 2(a), it can be observed the subsequent treatment do not affect the integrity of graphite-like structure. TEM examination on the tested K(0.5)-Fe(5)/CNF catalysts as presented in Fig.2(b), also indicates that the graphitic structure of CNF is still intact. The XRD and TEM results are in agreement with TGA profiles of fi-esh and tested catalyst there is no obviously different stability in the carbon dioxide atmosphere (profiles are not shown). Moreover, TEM image as shown in Fig. 2(b) indicates that the iron oxide particle deposited on the surface of carbon nanofibcr are mostly less than less than 10 nm. 

This hematite is not soluble in the cyanide solution. The oxidative pretreatment of gold ores thus reduces the cyanide consumption. Some impurity elements inhibit leaching reactions, examples include elements, carbon, sulfur and arsenic in gold ores are such impurities, but these can be removed by heating in air. 

Nyavor, K. Egiebor, N. O. Application of pressure oxidation pretreatment to a double-refractory gold concentrate. CIM Bull. 1992, 85, 84-96. 

The first instance of successful application was in the examination of some supported chromia catalysts. A pronounced variation in catalyst performance, caused by certain oxidative pretreatments, was found to correlate with variations in absorption edge spectra. Spectra involved were... 

Among the surface-modified CNTs materials, a bulk-modified CNT paste (CNTP) has also been reported [126]. The new composite electrode combined the ability of CNTs to promote adsorption and electron-transfer reactions with the attractive properties of the composite materials. The CNTP was prepared by mixing MWCNTs powder (diameter 20-50 nm, length 1-5 jim) and mineral oil in a 60 30 ratio. The oxidation pretreatment [performed in ABS (pH 5.0) for 20 s at 1.30 V, vs Ag/AgCl] proved to be critical in the state of the CNTP surface. Pretreatments improved the adsorption and electrooxidation of both DNA and DNA bases, probably due to the increase in the density of oxygenated groups. 

It has been presumed that there are two possible causes for the poor recoveries of cyst(e)ine as cysteic acid. The first is the incomplete conversion of cyst(e)ine to cysteic acid by the per-formic acid oxidation. The second is the oxidative destruction of cysteic acid during the HC1 digestion due primarily to the presence of residual performic acid at elevated temperatures. In response to this possibility, many studies have employed the addition of HBr after the oxidative pretreatment to consume excess/residual peroxide. An interesting collaborative study reported by Llames and Fontaine (84) compares the use of HBr vs. metabisulfite for the purpose of scavenging leftover peroxide. It appears the use of hydrobromic acid yields slightly better results. 

RG Elkin, JE Griffith. Hydrolysate preparation for analysis of amino acids in sorghum grains effect of oxidative pretreatment. J Assoc Off Anal Chem 68 1117-1121, 1985. 

In view of the above considerations, the oxidation state of Pd has a significant effect and it was demonstrated that an oxidative pretreatment of the catalyst enhances... 

The preparation of real supported catalysts will involve the deposition of a precursor salt followed by decomposition and/or reduction to the final metallic state. We shall consider the influence of the precursors and the effect of oxidative pretreatments later. First, we consider how the shapes of supported metal particles will vary with time under reducing conditions, since this represents the working condition for most metal catalysts. A comprehensive review of sintering and redispersion in supported metals has been presented by Ruckenstein and Dadyburjor.232... 

Based on the creation of naphthenic structures in the condensation reaction, the modification by aluminum chloride increased carbon yield and improved the potential for anisotropic development. Oxidative pretreatment usually impairs anisotropic development although it increases carbon yield. The oxidized pitch is also modified by aluminum chloride (34) this may be used to prepare additives (38) and mesophase pitches (39). It should be noted that these processes allow the catalyst to be readily separated (in contrast to catalytic carbonization) since the modified product is still either soluble in some solvents or fusible. 

Hall, E.D. (1987) Intensive anti-oxidant pretreatment retards motor nerve degeneration, Brain Res. 413, 175-178. 

Many authors pointed out that an oxidative pretreatment of the carbon surfaces is necessary to enhance the adsorptive accumulation of DNA [ 15,16,23]. The enhanced adsorptive accumulation is attributed to increased surface roughness and hydrophilicity following such treatment. This pre-treatment consists of the application of + 1.6 V/ + 1.8 V for a short period of time (1-3 min) in acidic media. The application of high potentials in acidic media (e.g. acetate buffer pH 4.7) seems to increase the hydrophilic properties of the electrode surface through the introduction of oxygenated functionalities accomplished with an oxidative cleaning [31]. 

Scheme 2. Fabrication and oxidative pretreatment of carbon nanoelectrode arrays for functionalization. From reference 69.

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