*2.1. Materials*

A viscose-based activated carbon cloth (CTex-20, knitted fabric, areal density: ~18 mg cm<sup>−</sup>2, mean fiber diameter: ~10 μm) was purchased from Mast Carbon International Ltd. (Hampshire, UK). The carbon fabric was cut in sheets of 45 mm × 55 mm. The untreated carbon samples were repeatedly washed with distilled water until constant pH. Then, they were dried in an oven at 80 ◦C overnight and finally allowed to cool down in a desiccator. Analytical reagent-grade aniline (≥99.0%) and sulfuric acid (98%) were supplied by Merck. Prior to use, aniline was distilled under vacuum and stored in the dark at 5 ◦C. Solutions of aniline (0.1 M) in aqueous H2SO4 electrolyte (0.5 M) were made up with distilled water. Background electrolyte solutions (0.5 M H2SO4) for cyclic voltammetry were prepared from Millipore Milli-Q water. The anionic monoazo dye Acid Red 27 (Colour Index no. 16185, empirical formula C20H11N2Na3O10S3) was purchased from Sigma-Aldrich (91 wt.% dye content) and used as received.

### *2.2. Preparation of Hybrid PAni-ACC Composites*

Polyaniline was polymerized on the carbon fabric substrate by galvanostatic treatment in an undivided home-made filter-press electrolyzer, designed for the electrochemical processing of textile-structured materials (Figure 1a) [30,31]. The cell was assembled in a flow-through parallel plate-and-frame configuration, with two identical stainless steel (SS) mesh electrodes separated by a 5-mm-thick plastic spacer, providing an interelectrode rectangular channel of 20 cm2. A dry ACC sheet (typically 0.4 g) was pressed against the anode SS mesh with a silicone rubber sealing gasket to leave an exposed geometric area of 20 cm2. The aniline-containing electrolyte was fed into the cell with the aid of a peristaltic pump (Dinko Instruments D-21V, Barcelona, Spain), until excess solution was collected at the outlet. As a pre-conditioning step, the system was left at open circuit for 30 min to allow carbon pore filling and facilitate aniline adsorption. Then, an input current of 100 mA (~14 mA cm<sup>−</sup><sup>2</sup> g<sup>−</sup>1) was passed through the cell for different processing times (10–120 min) at room temperature. The anode potential was measured against an Ag/AgCl reference electrode connected through a Luggin capillary drilled in the plastic spacer, and it was found to lie within the range 0.6–0.8 V. A schematic view of the electrochemical set-up is shown in Figure 1b. After the prescribed electropolymerization time, the modified carbon cloth was washed repeatedly with 0.5 M H2SO4 and subsequently with distilled water. The obtained PAni-ACC composite was dried at 40 ◦C under dynamic vacuum for 24 h and stored in a desiccator until further characterization studies.

**Figure 1.** (**a**) Cut-away view of the electrochemical filter-press cell; (**b**) Schematic diagram of the electropolymerization system.

## *2.3. Materials Characterization*

The morphology and micro-structure of the unmodified ACC and the PAni-ACC composites were examined by SEM. Secondary electron micrographs were obtained with a Phenom Microscope (FEI Co., Hillsboro, USA). X-Ray Photoelectron spectroscopy (XPS) was conducted in a K-ALPHA spectrometer (ThermoFisher Scientific) by using a microfocused monochromatized Al Kα radiation (1486.6 eV) of 400 μm spot size at 173 K and a base pressure below 5 × 10−<sup>10</sup> kPa. Photoelectrons were collected into a hemispherical analyzer operated in the constant energy mode at pass energy of 50 eV for narrow core-level and valence band spectra. Peak binding energies (BE) were referenced to the principal C1s line at 284.6 eV and given to an accuracy of ±0.2 eV. XPS data were analyzed with Thermo ScientificTM Avantage software. A smart correction function was used for background correction. Peak synthesis was done with mixed Gaussian (70%)/Lorentzian (30%) function lineshapes. Surface charging was compensated with a flood electron gun.

The porous texture was determined by physical adsorption of N2 (at 77 K) and CO2 (at 273 K) by using an automatic adsorption system (Autosorb-6, Quantachrome Instruments, Boynton Beach, USA). In order to remove moisture and adsorbed gases while avoiding thermal degradation of PAni, the samples were previously out-gassed under vacuum at 423 K for 4 h. The apparent specific surface area (SBET) and total micropore volume (d < 2 nm, <sup>V</sup>μ) were calculated from the N2 isotherm by applying the Brunauer-Emmett-Teller (BET) and the Dubinin-Radushkevich (DR) equations, respectively [30]. The DR theory was also applied to obtain the ultramicropore volume (d < 0.7 nm, Vultra μ) from the CO2 isotherm [30]. The good fitting of the N2 and CO2 adsorption data to the DR equation (*R*<sup>2</sup> > 0.99) validated the application of this method for the studied materials. The N2 uptake at a relative pressure near to capillary condensation (~0.97) was used to calculate the total pore volume (Vtp) [32]. The mesopore volume (2 nm < d < 50 nm, Vmeso) was estimated as the difference between total and micropore volumes.

The thermal stability of the samples was studied by thermogravimetric analysis (Mettler Toledo 851E/1600/LG) under a He stream at a flow rate of 100 mL min−1. About 10 mg of sample was placed in a 70 μL aluminum crucible and submitted to a two-stage heating protocol at a rate of 20 ◦C min−1. First, the samples were heated from 25 ◦C to 120 ◦C and kept at the latter temperature for 30 min for drying. Then, they were allowed to cool down to thermal equilibrium at 25 ◦C. In the second stage, the samples were heated up to 1000 ◦C.

### *2.4. Electrochemical and Sheet Resistance Measurements*

Cyclic voltammetry (CV) experiments were conducted in an all-Pyrex glass cell with provision for a standard three-electrode assembly. Round-shaped cut, dry ACC and PAni-ACC samples of approximately 1 cm<sup>2</sup> (10–13 mg) were weighed to an accuracy of ±0.001 mg. The samples were pressed at 20–25 kg cm<sup>−</sup><sup>2</sup> for 40 s in between a folded SS mesh, used as a current collector for the working electrode assembly. Prior to characterization, these electrodes were immersed in 0.5 M H2SO4 overnight to promote the material impregnation. A Pt wire was employed as a counter electrode. The working electrode potential was given with reference to a commercial Ag/AgCl/Cl− (3.5 M KCl) electrode. The measurements were carried out in a potentiostat system (VSP model, Bio-logic Science Instruments). The working solution was previously de-aerated by bubbling N2 and blanketed throughout all the experiments by a N2 stream flowing over it. Cyclic voltammograms were recorded at room temperature at a scan rate of 1 mV s<sup>−</sup><sup>1</sup> and presented as mass-normalized current (mA g<sup>−</sup>1) vs. potential plots. The gravimetric specific capacitance was evaluated from CV (Appendix A, Equation (A1)).

The conductivity of ACC and PAni-ACC composite fabrics was measured by the four-strip probe method [33]. Dry sample sheets (11 mm × 40 mm) were sputter coated with four Pd-Au thin strip probes (5 mm × 11 mm) in an EMITECH SC7620 Sputter coater (Quorum Technologies Ltd, Laughton, UK). The sputtered probes were 5 mm equally spaced across the length of the sample sheet. Copper wires were glued to the probes by conducting silver epoxy resin, and the contacts were secured with thin aluminum foils. A constant current, *I*, from a DC power supply (EP-613, Silver electronics) was passed through the two outermost probes and measured with a digital multimeter in series. The voltage drop, *V*, across the two inner probes was measured in a FLUKE 45 dual Display digital voltmeter. The electrical resistance, *R* (Ω), was obtained from the linear slope of *V* vs. *I* plots in the range 0–10 mA. The surface sheet resistance, *R*s (Ω -−1), was derived from the calculated electrical resistance according to Equation (A2) (see Appendix A) [34].

### *2.5. Dye Adsorption Measurements*

A synthetic stock amaranth solution was prepared by dissolving 1 g of dye in 1 L of distilled water. Working solutions of concentration in the range 25–200 mg L−<sup>1</sup> were obtained by proper dilution with distilled water. Dry ACC or PAni-ACC composites were cut in pieces of about 2 cm<sup>2</sup> and accurately weighed to ±0.1 mg (typical weights ~0.035–0.04 g). In a typical adsorption experiment, 50 mL of dye solution of known initial concentration were contacted with the adsorbent in 100 mL glass bottles with a screw cap, that were further sealed with Parafilm ®. The contact was made in a thermostatic water bath shaker (model WNE22, Memmert, Schwabach, Germany) at a constant temperature of 25 ◦C and at an agitation speed of 120 rpm, for the time necessary to reach equilibrium. After prescribed time intervals, the liquid-phase dye concentration was analyzed in a Thermo Scientific Helios γ UV-vis spectrophotometer at λmax = 520 nm.
