Nitric acid treatments

Nitric acid treatment lowered the methane uptake by about ten percent. This could be due to oxygen occupying sites within pores, but may be the result of weaker interaction between methane and an oxide surface as is observed for silica. Reduction of these treated carbons with hydrogen restored their original methane uptake. Clearly for methane storage, there is no advantage in modifying the carbon surface by nitric acid treatment. 

The photolysis of nitrite esters has been found to be of considerable synthetic utility, particularly in functionalizing steroid methyl groups. The most spectacular application of this reaction has been a three-step synthesis of aldosterone.<59) Irradiation of corticosterone-11-nitrite (30) followed by nitric acid treatment gave aldosterone (32) in a 15% overall yield ... 

Boron trifluoride in aqueous dioxane was being evaporated with nitric acid treatment (3 portions) for analysis. Final addition of perchloric acid with continued heating led to an explosion while unattended. Ring scission of dioxane to diethylene glycol and formation of diethylene glycol nitrate and/or perchlorate may have been involved. 

An important route to solubilization of carbon nanotubes is to functionalize their surface to form groups that are more soluble in the desired solvent environment. It has been shown that acid treatment of nanotube bundles, particularly with HC1 or HNO3 at elevated temperatures, opens up the aggregate structure, reduces nanotube length, and facilitates dispersion (An et al., 2004 Kordas et al., 2006). Nitric acid treatment oxidizes the nanotubes at the defect sites of the outer graphene sheet, especially at the open ends (Hirsch, 2002 Alvaro et al., 2004), and creates carbonyl, carboxyl, and hydroxyl groups, which aid in their solubility in polar solvents. 

The process must be developed and tested for die efficacy of submerged-bath dilute nitric acid treatment for metals parts, including die effects of agitation and temperature. 

The filtrate from the nitric acid treatment contains the nitrates of Pb, Bi, Cu, and Cd. Dilute H2S04 precipitates Pb as PbS04, leaving the other metals (which form soluble sulphates) in solution. 

It must be remembered that arsenite may be partially oxidized by the dilute nitric acid treatment and also by other oxidizing anions which may be present. Arsenite is, however, readily detected in the analysis for cations (cf. Section III.12, reaction 1). 

Yates group [67] used IR spectroscopy, temperature-programmed desorption, and mass spectrometry to study Xe adsorption on purified and cut SWNTs. The nanotubes were cut by subjecting them to a mixture of sulfuric and nitric acid treatment, followed by sonication with sulfuric acid and peroxide. Infrared (IR) measurements determined the presence of carboxylic acid and quinone groups on the treated tubes. Mass spectrometry of treated tubes heated under vacuum determined the evolution of different groups from the tubes as the temperature increased (CH4, CO, H2, and CO2). 

Table 4 shows the atomic ratios obtained from XPS measurements. The nitric acid treatment produces an important removal of of P and Cl, and an inqrartant increase of N and 0. The esterification produces an increase of P, N and Cl, and there are no significant changes when the complex is supported (sample Rh(COD)/GF-ONP). Sanqtle Rh(HONP)/GF-Cl showed a lower amoimt of P, Cl and N than Rh(COD)/GF-ONP, but higher than its precursor GF-N. These results suggest that the esterification has been made. 

Conventional conductivity detector cells where the electrolyte is in contact with the electrodes are likely to use electrodes made from 316 stainless steel. A new cell should be treated with 1 N nitric add for about 60 min to deactivate or passivate the cell and stabilize the signal. In fact, such nitric acid treatment is a good idea for all parts of a stainless steel IC system. 

Fig 4 compares kinetics in the presence of the catalyst and the support treated separately with HNOj 0.25 M with the curve obtained under the same experimental conditions with the catalyst directly treated with HNO3 0.25 M. However, this nitric acid treatment of the catalysts could result in a dissolution of the metal, and a modification of the metallic dispersion. ICP measurement shows that the metal loading remains unchanged after treatment, while dispersion decreased from 12% to 8%. As shown in fig 4, this lower dispersion is surprisingly accompanied by an increase in activity. The easiest explanation of this experimental fact, confirmed by the results obtained with a mechanical mixture of carbon and catalyst, consists in the catalytic role of the support. 

Johnson Matthey method gives information on the acidity and on the basicity of the solids but does not give any information on different type of acidity or basicity. The results show that the effect of the carbon modification is mainly observed in the basic part of the curve (fig 5). It means that the nitric acid treatment does not create supplementary acidic sites on the surface, but suppresses basic sites, those ones that are probably responsible for the coupling reactions. The nitric treatment of the active carbon probably decrease the formation of heavy products. 

Finally, a more precise method for the characterization of the acidity and the basicity of the active carbon sites is needed. TPD of weak acids and bases may contribute. Basidty is probably more important, since we have shown that i) global surface basicity is more affected by nitric acid treatment than surface acidity, and ii) the amount of the different surface acidic sites is not directly related to the catalytic effects. 

A similar transformation of 1,9,10-anthyridines is also described. 7-Nit-roanthydrine-2,6-dione 344 or 3,7-dinitroanthyridine-2,6-dione 345 can be prepared by nitration of anthydrine-2,6-dione 346 with various amounts of a mixture of concentrated sulfuric and nitric acids. Treatment of nitro derivative 344 with sodium... 

Moderate heat treatment of the MCB silica gel at 450 °C for 24 h, a temperature below the sintering temperature, alters the surface such that the fluorescence spectra of 1-AP adsorbed on this surface have characteristics of both 1-AP and 1-APH+ a heating temperature of 650 °C yielded an adsorbed 1-AP spectrum identical to that of 1-AP adsorbed on FS-662. A several-hour concentrated nitric acid treatment of the FS-662 silica, followed by washing with water until the wash maintained a neutral pH and drying, alters the surface such that the fluorescence spectrum of 1-AP adsorbed to this surface resembles that obtained from the MCB surface. 

A detailed analytical study of fhe acfivity of some solid acid catalysts, including mesoporous silica-supported Nation, in the acylation of anisole with AAN allows the conclusion that catalyst deactivation is caused by the primary ketone product and/or multiple acetylated products in the micropores of Nation catalyst aggregates. i Experiments were performed with a commercially available silica-supported Nation catalyst in a continuous-mode slurry operation by using carbon-dioxide-expanded liquids (nitromethane or nitrobenzene) as solvents. At 90°C, 80% AAN conversion is observed with a TOS of 2 h, but the catalyst rapidly deactivates, and 27% conversion is evaluated after 6 h TOS with a TON value of about 400. The catalyst can, however, be completely regenerated upon nitric acid treatment. These results confirm that silica-supported Nation catalysts are promising alternatives for the traditional aluminum chloride homogeneous Lewis acid catalyst. 

The adventitious layer of salts on Mg/, does not contain significant O2- unless il is baked. The anions arc almost entirely Oil with some HCOi in the outer layers. Aqueous nitric acid treatments leave reconstituted MgtOHh layers, perhaps with fewer defects, but it does not leave exposed metallic surfaces. 

Basically the same reasoning applies to the shear deformation of fibrils. The much longer microfibrils are less easily displaced in a shear mode. Hence, the increase in the fraction of interfibrillar tie molecules per amorphous layer is substantially smaller in linear polyethylene than in nylon 6. At a total draw ratio of 15-20, the total fraction of taut tie molecules seems to reach saturation, as is demonstrated by nitric acid treatment of highly drawn polyethylene fibers (23). 

Biniak and co-workers reported that nitric acid treatment of carbon materials results in the formation of pyridine structures and pyridine-N-oxide species at the expense of pyrrolitic moieties [105]. An increase in the intensity of the bands at 1330 and 880 cm respectively, characteristic of pyridine, pyridine-N-oxide, or pyridone structures suggested that the ammonia treatment incorporated nitrogen into the carbon aromatic lattice with the formation of pyridinelike structures. The assigmnent of other nitrogen-containing bonds that can be found on the carbon surface is presented in Table 2.4. 

Besides the classical nitric acid treatments, other oxidative agents have been used to prepare functionalized CNTs. Rao et al. [170] have compared the effects of concentrated nitric acid, aqua regia, HF-BF3, aqueous OSO4, and KMn04 (acid/alkali) solutions on MWCNT structures [170]. Indeed, all these oxidants... 

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