Acid-treated samples

Fig. 4 shows the SEM images of SWNTs purified by the thermal oxidation and acid-treated. Fig. 4(a) shows a SEM image of the raw soot. In addition to the bundle of SWNTs, carbonaceous particles are shown in the figure. These stractural features mi t be causal by various in the arcing process because of an inhomogeneous distribution of catalysts in the anodes [7]. It can be seen that the appearance of SWNTs was curled and quite different fiom that of MWNTs. Fig. 4(b) shows a decrease of amorphous carbons after oxidation. The basic idea of the selective etching is that amorphous carbons can be etched away more easily than SWNTs due to the faster oxidation reaction rate [2]. Since the CNTs are etched away at the same time, the yield is usually low. The transition metals can be etched away by an add treatment. Fig. 4(c) shows the SEM image of the acid-treated sample, where the annealed sample was immersed in 10 % HCl. 

Both 1st- and 2nd-order rate expressions gave statistically good fits for the control samples, while the treated samples were statistically best analyzed by 2nd-order kinetics. The rate constants, lst-order activation parameters, and char/residue yields for the untreated samples were related to cellulose crystallinity. In addition, AS+ values for the control samples suggested that the pyrolytic reaction proceeds through an ordered transition state. The mass loss rates and activation parameters for the phosphoric acid-treated samples implied that the mass loss mechanism was different from that for the control untreated samples. The higher rates of mass loss and... 

This conclusion is based on a high char yield and similar rates of mass loss at 300°C for untreated and boric acid treated samples. Boric acid samples also had much higher AH+ s and, consequently, higher Ea s. Our results suggest that certain thermally-stable, weak polybasic acids which can complex with polysaccharides may provide fire-resistant properties to lignocellulosics. The results and conclusions were strongly influenced by the technique used to analyze the TGA data. 

The 2nd-order 300°C rates determined by the Arrhenius equation (Table VI) show that the rates are extremely high compared to the control or boric acid treated samples. In addition, the rate of mass loss appears to be unaffected by crystallinity. Ea values were lowered relative to the untreated control samples, except for the amorphous sample, and also appeared to be unaffected by... 

Other samples were treated with 10% sodium hydroxide solution, distilled, and subsequently handled in the same way as the acid-treated samples. 

For samples prepared without boric acid, the Mossbauer spectra show the presence of iodide ion, both before and after stretching. However, the stretching causes a colour change from brown to blue, and close observation of the Mossbauer spectrum reveals the presence of very small peaks in positions close to those for the boric-acid-treated samples. These presumably represent small amounts of I3 and/or I5, but the weakness of the signals... 

The Hb NMR spectrum of this sample contains a single narrow resonance centered at -3.2 ppm, which is characteristic of boron in a tetrahedral coordination environment in the framework structure. The Si nmr spectra of a synthetically prepared siliceous mordenite with the same Si/Al ratio is shown in Figure 8. No CP resonances are present, Which indicates that hydroxyl nest concentration in this material is very low compared to the acid treated sample. These data confirm that hydroxyl nests, generated by the removal of A1 from the zeolite structure, are reactive sites for isomorphous substitution. Aluminum deficient, preformed zeolites which do not contain hydroxyl nests, i.e. synthetically prepared samples, do not undergo isomorphous substitution when treated in a similar fashion. 

For such treated samples it is not easy to discriminate between two possible effects of dealumination, namely, the removal of some acid sites and the decrease in microporosity due to the deposition of aluminum-containing debris in the pores. Thus, hydrothermally dealuminated FER, hydro thermally dealuminated acid-washed FER. acid-washed FER, and CsFER were compared under the same experimental conditions (62). The results indicate the following order of isobutylene selectivities untreated FER < acid-treated FER < hydrothermally treated FER < hydrothermally acid-treated FER < CsFER 61). These results, obtained with noncoked catalysts, reinforce the interpretation in terms of shape selectivity. The hydrothermally acid-treated sample has acid sites located only in the micropores, and the aluminium debris in the micropores creates an additional constraint playing a role identical to that of Cs" in FER. 

In the present studies, a-alumina, a non porous alumina, has been used as a standard. The surface area of this sample is 9 m /g and monolayer volume is 2 cc/g.It can be concluded from the Figure 2 that v-a plot for AD-101 is almost a straight line passing origin. Treatment of AD-101 with alkali shows an upward deviation from straight line which shows an increase in mesopore. However, the upward deviation is minimised in the acid treated sample which is in agreement with the pore size distribution for these samples. ... 

The SAXS spectra for the set of acid-treated samples are shown in Fig. 4. For V, H3SEN and H6SEN, the X-ray responses are similar, with small but systematic differences. Sample M3SEN is, however, significantly different from the others. The entire low- region has slope -A, characteristic of smooth surfaces [7]. The absence of any curvature at low q makes it difficult to define with confidence the numerical value of the specific surface area. However, on the basis of a plausible assumption about the lower cutoff limit, it is found to be of the same order as in the other samples. 

To the remaining sample and standard solutions add, in order, 15 ml of buffer solution pH 7 5, 2 ml of 10 per cent sodium bisulphite and 3 ml of 0-4N sodium hydroxide. Place the flasks in boiling water for exactly five minutes, add 12 ml of 5N hydrochloric acid, mix and continue heating for a further two minutes. Cool the flasks immediately. Dilute all solutions to volume with water and measure the extinctions of the acid-treated sample and standard solutions at 445 mju in a 1-cm... 

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