# Superhydrophobic Polypyrrole-Coated Cigarette Filters for Effective Oil/Water Separation
## 3 Results and Discussion  
### Surface Morphology and Characterization of Superhydrophobic Cigarette Filters  
A SEM image of the original cigarette filter surface is shown in Figure 1a. The experimental sample revealed porous fiber structures, which benefited oil absorption. The fiber surface presented smooth and flat topography, as shown in the inset of Figure 1a. Figure 1b shows images of a Ppy-coated cigarette filter surface with 0.2 mol/L pyrrole under low and high magnification. After the polymerization of pyrrole, the fiber surface became rough. Ppy nanoparticles were spherical in structure and evenlydistributed, and the sizes of the particles were about 400 nm. The nanoparticles did not completely cover the fiber surface. Moreover, some Pyy nanoparticles aggregated into microparticles, as shown in the inset of Figure 1b. With increasing pyrrole concentration, the surface became increasingly rougher with micro-nano hierarchical structures, as shown in Figure 1c. The Pyy particles were in an obvious aggregation state, and the average particle size increased to 1 \(\upmu\)m. Thus, Pyy nanoparticles uniformly covered the cigarette filter surface, and the roughness of the fiber surface could be easily controlled by the pyrrole concentration. The FTIR spectrum for a superhydrophobic cigarette filter is shown in Figure 2. The characteristic peaks at 2921 cm\({}^{-1}\) and 2851 cm\({}^{-1}\) were attributed to C\(-\)H stretching vibration of \(-\)CH\({}_{3}\) and \(-\)CH\({}_{2}-\). Moreover, there were no obvious S-H characteristic peaks at 2570 cm\({}^{-1}\). Combined with the existence of \(-\)CH\({}_{3}\) and \(-\)CH\({}_{2}-\), this confirmed that S\(-\)H is broken, and n-dodecanethiol is grafted on the Pyy particle surface via chemical interaction [29]. The C=C stretching vibration was located at 1550 cm\({}^{-1}\). The deformation vibration absorption peak of C\(-\)H was located at 1463 cm\({}^{-1}\). The C-N stretching vibration peaks were located at 1200 cm\({}^{-1}\) and 1037 cm\({}^{-1}\). The =C-N plane vibration was located at 898 cm\({}^{-1}\)[30]. A stretching vibration peak of C=O was located at 1717 cm\({}^{-1}\), owing to powder oxidization in the air [31]. Consequently, it could be concluded that the cigarette filter was covered by Pyy particles, and n-dodecanethiol was successfully modified on the surface of Pyy particles. Figure 1: SEM images of Pyy-coated cigarette filters with different pyrrole concentrations: (**a**) Ordinary sample; (**b**) 0.2 mol/L pyrrole; (**c**) 1.0 mol/L pyrrole. Figure 2: FTIR spectrum of an as-prepared superhydrophobic cigarette filter. XPS was used to investigate the surface chemical composition and valence state. In order to further analyze the polymerization mechanism of pyrrole and the reaction mechanism of n-dodecanethiol grafting, typical XPS survey spectra of Ppy particles before and after modification with n-dodecanethiol are shown in Figure 3a. Both samples exhibited a C1s peak at 284.8 eV, O1s peak at 531.9 eV, and N1s peak at 399.9 eV. After n-dodecanethiol modification, two new peaks appeared in the spectrum of Ppy particles at 163.84 eV and 197.84 eV, which were the binding energy peaks of S2p and S2s, respectively. As shown in Figure 3b, the C1s spectrum of Ppy particles showed four different peaks at 283.85 eV, 284.8 eV, 286.0 eV, and 287.3 eV, which corresponded to the characteristic peaks of C-H, C-C, C=C, and C-N, respectively [32]. Figure 3c shows the N1s spectrum of Ppy particles. The characteristic peaks at 399.5 eV, 399.8 eV, and 401.0 eV corresponded to C-N, N-H, and NH\({}_{4}^{+}\) groups, respectively [33]. The characteristic peaks of C1s and N1s in the XPS spectra were highly consistent with the FTIR spectrum, which further proved that Ppy particles were indeed generated on the cigarette filter surface. Figure 3d shows the O1s spectrum of Ppy particles. The XPS O1s peaks could be fitted to two peaks, located at 532.1 and 534.9 eV, which were attributed to the hydroxyl and surface-adsorbed oxygen species [34].