Activated carbon Boehm titration method

The importance of basicity was also shown when the density of basic groups on the surface determined using Boehm titration method was linked to the MM removal ctpachy. The majority of carbons used for that research followed the linear trend. The discrepancy in some case was caused by the differences in the content of catalytically active phase, iron oxide, which will be addressed later in this section. 

Oxidation and incorporation of nitrogen usually affect the surface chemistry of carbons [12, 20, 24]. The types and numbers of basic and acidic groups evaluated using Boehm titration [3, 4]. are collected in Table 2. The data reported indicate that the initial carbons differ in their acidity as a result of the activation method and the type of an organic precursor [1]. BAX is more acidic than BPL. This is expected for a phosphoric acid activated carbon [25]. After modification with urea and heat treatment at 723 and 1223 K, the overall surface chemistry... 

Boehm and Johnson Matthey titrations. Both titrations give information on the acidic or basic character. The procedures are described in [13] and [14]. Boehm method classifies the surface acidic sites in three types (called phenolic, lactonic, carboxylic), by growing strength of acidity. However, this arbitrary classification fails to attribute one surface acidic group to one type of acidity. Moreover, this method does not give very accurate results with solids containing few acidic sites. Nevertheless, it appears for our active carbon that "phenolic" sites are a majority. The amount of each type of acidic sites does not change very much with the nitric treatment. 

A quantitative comparison between direct potentiometric titration and the classical Boehm method for characterization of the acidity of activated carbons has been drawn by various researchers [85,215,218], Although a rather acceptable agreement is generally accomplished for both methods, when applied to a carbon snrface where oxygen is the major constituent, some discrepancies exist. Figure 2.7 shows a correlation between the total acidic groups detected on an activated carbon using both Boehm and potentiometric titrations. 

Thirdly, in order to improve the dispersion of platinum catalysts deposited on carbon materials, the effects of surface plasma treatment of carbon blacks (CBs) were investigated. The surface characteristics of the CBs were determined by fourier transformed-infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), and Boehm s titration method. The electrochemical properties of the plasma-treated CBs-supported Pt (Pt/CBs) catalysts were analyzed by linear sweep voltammetry (LSV) experiments. From the results of FT-IR and acid-base values, N2-plasma treatment of the CBs at 300 W intensity led to a formation of a free radical on the CBs. The peak intensity increased with increase of the treatment time, due to the formation of new basic functional groups (such as C-N, C=N, -NHs, -NH, and =NH) by the free radical on the CBs. Accordingly, the basic values were enhanced by the basic functional groups. However, after a specific reaction time, Nz-plasma treatment could hardly influence on change of the surface functional groups of CBs, due to the disappearance of free radical. Consequently, it was found that optimal treatment time was 30 second for the best electro activity of Pt/CBs catalysts and the N2-plasma treated Pt/CBs possessed the better electrochemical properties than the pristine Pt/CBs. 

It is seen that the ZCP is strongly dependent on acid treatment. The results of titration by using Boehm s method are also given in Table 5.5. The untreated sample of this particular activated carbon (North American carbon, low ash , <2%) is basic, with ZCP = 10. Carboxyl is the most abundant group on aU acid treated carbons. The approximate distribution of different add groups is seen from the titration results. 

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