3.1.3. Porous Texture

Figure 7a shows nitrogen adsorption/desorption isotherms of bare ACC and representative PAni-ACC composite samples. The evolution of the BET specific surface area and that of different pore volumes with the electropolymerization time is plotted in Figure 7b,c respectively. A detailed list of these parameters can be found in Table 1. The shape of the N2 adsorption curve of the unmodified ACC (Figure 7a) corresponds to type IV isotherms, with a H4 adsorption/desorption hysteresis loop [49]. This form is typical of solids possessing mesopores embedded in a microporous matrix, where the adsorptive uptake proceeds via multilayer adsorption followed by capillary condensation [49]. The shape of the isotherm is similar to those reported for other cellulose-based commercial activated carbon fibers [23,39]. The growth of PAni layers leads to a general decrease in the N2 uptake, but the isotherm shape remains unchanged for composite textiles obtained at short to intermediate electropolymerization time. However, when the amount of charge passed is sufficiently high to produce thick PAni films, there is a dramatic loss in the N2 adsorption capacity and the hysteresis does not close at lower pressures. This may be due to diffusional restrictions to gas adsorption/desorption associated to pore narrowing and/or occlusion induced by the grown polymer.

**Figure 7.** Porous texture characterization of untreated ACC and hybrid Pani-ACC composites synthesized after different electropolymerization times: (**a**) N2 adsorption–desorption isotherms; (**b**) Brunauer-Emmett-Teller (BET) surface area; (**c**) Pore volume distribution: micropore volume (open circles), ultramicropore volume (open diamonds), mesopore volume (open triangles).

**Table 1.** Porous texture analysis of as-received ACC and hybrid PAni-ACC composites synthesized after different electropolymerization times.


1 Volume of micropores. 2 Volume of ultramicropores.

The commercial ACC has a high apparent BET surface area of 1424 m<sup>2</sup>/g and exhibits both a micropore and mesopore structure (Table 1). In accordance to what is observed in Figure 7a, microand mesopore volumes, and therefore the specific surface area, decrease by 20%–25% whenever PAni grows as a uniform thin and dense film at short-to-moderate electropolymerization time (10–60 min, Figure 7b,c). Within this time interval, these parameters remain constant, but they drop pronouncedly in the hybrid composites with thick PAni layers. In contrast, the volume of the narrower micropores (ultramicropores) barely changes with PAni loading, except at long electropolymerization time, when a clear decrease is also observed (Figure 7c).
