Nanocomposite preparation

Figure 1B–E shows photographs during the reaction for the formation of the BP/PANI nanocomposite that is schematically summarized in Fig. 1F and described in detail in the following²¹. Firstly, 10 μL of aniline was added to the flask containing the BP dispersion, followed by the addition of 6.4 mg of ammonium persulfate (PSA) and 35.4 mg of benzenesulfonic acid (BSA). After around 20 min, a blue color appears, followed by a green color typical of emeraldine salt (ES), the conducting form of the polymer. Thus, by the end of 22 h of stirring (2500 rpm), a green solid was observed adhered to the flask wall, as indicated by the arrow in Fig. 1B. In the following, the acetonitrile (with very few solid remnants) was removed and discarded, and an interfacial system containing 20 mL of an aqueous solution of HCl (1 mol L⁻¹) and 10 mL of toluene was added to the same flask. Then, after the mixture stirred for 22 h (2500 rpm), the green solid migrated spontaneously from the flask wall to the L/L interface (see arrows in Fig. 1C,D), resulting in the formation of a self-assembled green film (Fig. 1E). The next steps of this process involved the solvents exchange, which was performed with the aid of a pipette, as depicted in Fig. 1F, in order to remove excess acidity and side products from the polymerization. The toluene present in the organic phase was repeatedly changed by consecutive removals followed by the additions of new portions of the solvent (three times). In the same manner, the aqueous phase was partially removed and a solution of HCl 10⁻³ mol L⁻¹ was added to the system, this process was consecutively repeated until pH 3. For the films deposition, a beaker (10 mL) containing the substrate of interest (glass, ZnSe crystal window, Si/SiO₂ or quartz) at the bottom was prepared with the same solvent system present in the flask. The stabilized film was transferred to the beaker with the aid of a pipette (see Fig. 1F), which promptly stabilizes at the new L/L interface. In the following, the substrate was pulled towards the interface, depositing the nanocomposite film (BP/PANI). The material was vacuum dried for 2 h at 60 °C. For comparison purposes, we obtained control samples of both neat PANI and BP that were synthesized separately. The synthesis of neat PANI was carried out without the presence of BP, following the same process described above that lead to a stable film of at the L/L interface. The production of a pure BP film, however, was unfeasible. Although the exfoliated BP mostly concentrated at the L/L interface, no film was formed. Thus, the neat BP control sample was obtained by collecting an aliquot of the BP dispersion from the interface and drying over the desired substrate (60 °C, air-free atmosphere).