*3.1. Analysis of AGO*

SEM was performed to characterize the microscopic morphology of AGO. Figure 1a shows that AGO was stacked together to form a multilayer sheet structure, which is consistent with the reported of Ramanathan et al. [20–22]. Compared with GO, Figure 1b shows TEM images, further showing a transparent yarn-like structure with fewer wrinkles and smoother surface of AGO [15,20]. It was attributed to the partial reduction of GO by EDA and the interaction between the AGO plates, which together led to decrimping and blurring of the edges [14,15,23].

The FTIR spectra of AGO are shown in Figure 1c. The obvious disappearance of stretching peaks of O−H (3430 cm<sup>−</sup>1) and C=O (1729 cm−1), and the appearance of stretching peaks of N−H (3260 cm−1) and C−H (3050, 2885 cm−1) both indicate the partial modification of GO by EDA [23,24]. Moreover, for AGO, three new peaks appear at 1665, 1536, and 1440 cm<sup>−</sup>1, which are assigned to the C=O stretching of the amide I band and the combined absorption caused by N−H bending and C–N stretching in the amide II band, respectively. It is attributed to the amidation reaction or the substitution reaction between EDA and GO, which is consistent with the XRD results (Figure 1d).

The Raman spectra of GO and AGO are shown in Figure 1e. A Raman D-band and a G-band of GO are observed at 1354 and 1600 cm−1, corresponding to the structure defects on the graphene sheets and the sp<sup>2</sup> hybridization of the hexagonal carbon structure, respectively. Compared to the Raman spectra of GO, the D-band and G-band of the AGO shift to 1340 and 1595 cm−1, respectively. In general, the relative intensity of the ID/IG ratio partly indicates the quality of grapheme [25]. Herein, the ID/IG ratio of GO (1.41) was lower than that of AGO (1.60), indicating a slight reduction of GO, which was attributed to the conversion of carbon atoms from the sp3 to the sp2 state [26].

The composition and chemical state of elements of AGO were further researched by XPS. Figure 1f, demonstrates that the full spectrum of AGO shows a significant decrease in O1s and an increase in C1s, accompanied by the generation of a new peak N1s, indicating the successful modification of GO. Through further analysis, it was found that the changes in the intensity of O1s component in Figure 1f were attributed to the disappearance or the decrease of the intensity of the C–OH group (285.2 eV), C–O–C group (286.8 eV), and O=C–O (288.9 eV) group in Figure 1f-1. The new peak at the binding energy of 285.9 eV of C1s component in Figure 1f-4 corresponded to the C–N group, which was proved by the three main Gaussian peaks at binding energies of 399.0, 400.0, and 401.5 eV of N1s component in Figure 1f-3, assigned to –NH2, C–N, and –CO–NH groups, respectively. Furthermore, the O1 spectrum of AGO shown in Figure 1f-5 also indicates the decrease in the strength of the oxygen-containing groups to varying degrees, which further reveals that the amidation reaction between EDA and GO is mainly caused by amino groups and oxygen-containing groups [23,27].

**Figure 1.** Characterization of amidated graphene oxide (AGO). (**a**) SEM, (**b**) TEM, (**c**) FTIR spectra, (**d**) XRD pattern, (**e**) Raman spectra, (**f**) XPS survey spectra, (**f-1**) C1s spectra of GO, (**f-2**) O1s spectra of GO, (**f-3**) N1s spectra of AGO, (**f-4**) C1s spectra of AGO, and (**f-5**) O1s spectra of AGO.
