Doping adsorption isotherms

Fig. Zll a The formation process of ordered N-doped mesoporous carbon from a one-pot assembly method using dicyandiamide (DCDA) as a nitrogen source, b CO2 and N2 adsorption isotherms at 25 °C for the N-doped mesoporous carbon H-NMC-2.5. c CO2 adsorption isotherms at different temperature for A-NMC after activation by KOH. Reproduced from Ref. [56] by permission of John WUey Sons Ltd...

Nitrogen adsorption isotherm on a pure silica sample after drying and calcination is shown in Fig.2. It is of type I, characteristics of microporous materials [47]. The corresponding pore size distribution of this sample is given in Fig.3. As shown, the sol-gel derived silica sample contains microporous (< 2 nm) pores, with an average pore diameter of about 0.6 nm. The pore structure of the pure and alumina doped silica samples is summarized in Table 3. The surface area of sol-gel derived silica is much larger than the sol-gel derived crystalline samples, described in Section 2.1. 

In relation to the electrolyte concentration Cq in the doping solution, the following domains can be distinguished in the adsorption isotherms (see Fig. 8.9). 

Fig. 8.10 Adsorption isotherms of m-PBI (25 °C), AB-PBI (25 °C) and Fumapem AM-55 (110 °C) doped with various protic electrolytes H A. The curves are fitted by non-linear regression using (8.22). The...

Fig. 8.11 FT-Raman spectra (left) of pristine m-PBI bottom) and doped with H3PO4 at different doping degrees 6 (25 °C), taken from Daletou et al. [81]. In the rectangle at 910 cm the Raman signal of buLk-Iike H3PO4 is marked by an up arrow. Adsorption isotherm right) for H3PO4 by m-PBI (25 °C, see also Fig. 8.10).

The thermodynamic data from the adsorption isotherms can be combined successfully with spectroscopic data from Raman investigations. From the changes of characteristic Raman bands as a function of doping degree 6, two distinguishable stages of protic electrolyte (phosphoric acid) uptake can be identified ... 

The isotherms of Al-PILC and Zr-PILC are of type I, indicating the small dimensions of the pillars. The shape of the adsorption isotherm of Fe-PILC resembles a type II isotherm (nonporous). The isotherm of Ti-PILC is close to type IV, but with a distortion in the relative pressure range 0.05-0.5 followed by capillary condensation. The distortion is due to the presence of pores on the border region between micro- and mesopores (1.5-3.5 nm). Isotherms of intermediate shape can also be observed, for example, alumina PILC doped with lanthania (LaAl-PILC) (31). For some PILC materials, the presence of a large hysteresis loop in the isotherm might be observed, indicating the importance of mesopores in the structure. From the adsorption isotherm data, several parameters describing the porosity can be quantitatively derived. 

Figure 1. N2 adsorption (filled) and desorption (open symbols) isotherms for a) pure and Fe-modified SBA-15 and their N-doped carbon replicas b) pure and Fe-modified MLV-0.75 and their N-doped replicas (for clarity, the relevant isotherms are shifted up by 200 or 600 cm3g 1). Pore size distributions calculated from the desorption isotherms with the modified BJH method for c) pure and Fe-modified SBA-15 and CMK-3 carbons d) pure and Fe-modified MLV-0.75 and OCM carbons.

FIGURE 3.22 H20 adsorption-desorption isotherms at 25°C for the undoped and N-doped carbons. 

N-doping has already been reported for ACF and activated carbon [150,152], It is well known that the uptake pressure and the shape of the H20 isotherm are functions of both micropore size and surface chemical properties. In this case, however, the influence of micropore size can almost be excluded and the observed difference in the uptake pressure be attributed solely to carbon surface chemistry. It is therefore reasonable to conclude that the inner pore surface of the N-doped carbon is more hydrophilic than that of the undoped one. Since the O content of the former carbon is lower than that of the latter, the above results indicate that in this case the presence of N groups is more effective for H20 adsorption. 

Figure 22.9 Examples of molecular engineering of carbon surface (a) isotherms for adsorption of HjO vapor on various chemically modified carbons, (b) gas drying characteristics of the modified selective surface membrane (SSF) membrane, (c) high-temperature chemisorption of CO2 on MgO-doped activated carhon.

Fig. 43. N2 adsorption-desoption isotherms at 77 K on three carbon aerogels, witliout (a) or with metal doping (b). Courtesy of Phof. K. Kaneko of Chiba Univ.

Doping dodecyl benzene sulfonic acid (DBSA) into PANI/carbon nanotube composite can fabricate PANI/carbon nanotube-DBSA nanocomposite [56]. The preparation, as well as the adsorption to Cr(VI), is depicted in Figure 11.11 with the pseudo-second-order kinetics and Freundlich isotherm model with maximum monolayer adsorption capacity of 55.55 mg/g. Electrostatic interactions between PANI and Cr(VI) anions are the predominant driving forces for this adsorption process. 

FIGURE 16 Adsorption-desorption isotherms of p- and w-xylene on Al-PILC doped with various amounts of Na ions. The pH value of the dispersion for loading the Na into the PILC structure is given on top of the plots. (From Ref. 89.)... 

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