## 3 Results and Discussion
### Micromorphology and Surface Chemical Composition Analysis
Besides, the perpendicular stretching and deformation banding vibration of Si-O-Al were obviously found at 757 cm\({}^{-1}\) and 537 cm\({}^{-1}\), respectively. These peaks were in common with the FTIR spectra of HNTs investigated by [PERSON] et al. [46], indicating that the typical structures and chemical groups of HNTs were retained after the purification of acid treatment. After being treated by PDA, there remained little changed in the characteristic peaks of pure HNTs. The new peaks at 3422 cm\({}^{-1}\), 2940 cm\({}^{-1}\)/2875 cm\({}^{-1}\), and 1650 cm\({}^{-1}\) that were found in PDA-HNTs were attributed to the stretching vibrations of -OH groups, non-symmetric/symmetric stretching vibrations of -CH\({}_{2}\) groups, and the stretching vibrations of aromatic C=C groups, respectively, which proved that PDA had been successfully decorated on the HNTs surfaces [32; 47]. In comparison to the spectra of PDA-HNTs, the absorption peaks at 2940 cm\({}^{-1}\) and 2875 cm\({}^{-1}\) in ODA-HNTs were enhanced, which was ascribed to the secondary reaction of grafting long chain alkyl amine in PDA platforms. Excitingly, although VM was added to the reaction system, the location and intensity of characteristic peaks in VM/ODA-HNTs were almost identical to those in ODA-HNTs, indicating that VM simply acted as a promoter instead of reacting with PDA and HNTs. Figure 3: X-ray diffraction (XRD) patterns of P-HNTs, PDA-HNTs, ODA-HNTs, and VM/ODA-HNTs. Figure 2: Transmission electron microscopy (TEM) images of the (**a**) P-HNTs; **(b**) PDA-HNTs; and (c) ODA-HNTs. The surface chemical changes of HNTs after mussel inspired modification were determined by investigating the XPS spectra of nanotube surfaces. Figure 5a presents the low resolution XPS wide scan spectra of PDA-HNTs and ODA-HNTs. As shown in Figure 5a, the characteristic peaks of O 1s, Si 2p/2s, and Al 2p/2s were all observed in these two samples, which were attributed to the elements O, Si, and Al in HNTs. In the case of unmodified P-HNTs, carbon impurity (C 1s peak) was detected on the nanoclay surfaces as shown in Figure S1, which could be assigned to the contamination of the oxide surface deriving from the atmosphere or in the wet process [48]. Excitingly, the signals of N appeared in the curve of PDA-HNTs, indicating that the PDA layer was successfully decorated on the HNTs surfaces. When compared with PDA-HNTs, the higher at. % of elements C (26.45%) and N (1.57%) were found in ODA-HNTs (Table S1), which was ascribed to the long-chain alkylamine grafting onto the PDA-coated HNTs. Figure 5b shows the high resolution XPS spectra of C 1s core-level spectra of PDA-HNTs. This C1 core-level spectra can be curved-fitted to three peak components corresponding to binding energy (BE) at 284.4 eV for C-C, C=C, and C-NH\({}_{2}\) species, at 285.7 eV for C-O and C-N species, and at 287.7 eV for C=O species, respectively, which were in well accordance with reported functional groups species of polydopamine [47]. Interestingly, the contents of C=O species were much lower than that of polydopamine coating on other substrates (>10%) [49], only 1.83% in PDA-HNTs (Table S2). This may be due to the high surface area of HNTs that can inhibit the change of dopamine from phenol to quinone [31]. Figure 5c,d exhibit the N 1s core-level spectra of the PDA-HNTs and ODA-HNTs. The N 1s core-level of PDA-HNTs was peak-fitted into three components, including primary amine species (R-NH\({}_{2}\), 401.8 eV), secondary amine species (R\({}_{1}\)-NH-R\({}_{2}\), 399.9 eV), and tertiary or aromatic amine species (C=NR, 398.6 eV), respectively [32; 50]. As for ODA-HNTs, the contents of secondary (36.31%) and tertiary/aromatic amine (22.20%) species spectrum were enhanced (Table S3) due to octadecylamine grafting onto PDA-HNTs surface via Michael addition or Schiff base reactions, resulting in two different kinds of resultant products, as illustrated in Scheme 1.