*3.2. Characterization Analysis of AGO/SPEEK Films*

For any blending system, an important effect that should be addressed is the miscibility among different compounds as it determines structural stability and physicochemical properties of the blend. In this study, good miscibility between SPEEK and AGO resulted in the formation of transparent and homogeneous blending solutions and films. More obvious details were obtained based on the microstructure of the material. As shown in Figure 2a,b, there was a partial depressions on the GO/SPEEK films with no sheet structure, which is similar to the result of Dai et al. [12,28,29]. The surface of AGO/SPEEK films displayed a relatively rough morphology with a more obvious layered structure compared to GO/SPEEK films, consistent with the typical morphology of AGO [12,23]. Notably, most of the AGO was evenly dispersed in the SPEEK matrix, while small-scale accumulation gradually appeared with an increase in the AGO loading, indicating that the two compounds were homogeneous [28].

**Figure 2.** Characterization of films. (**a**) SEM of GO/SPEEK films, (**b**) SEM of AGO/SPEEK films, (**c**) FTIR spectra, (**d**) XRD pattern, (**e**) TGA curves, (**f**) XPS survey spectra, (**f-1**) O1s spectra and (**f-2**) N1s spectra of 0.5% (*w/w*) AGO/SPEEK films.

Numerous oxygen-containing functional groups, such as carbonyl (C=O), hydroxyl (–OH), carboxyl (–COOH), as well as amino groups, are present on both sides of AGO; therefore, the interfacial interactions between AGO and SPEEK matrices should be verified. Figure 2c shows the FTIR spectra of AGO/SPEEK films. The AGO/SPEEK film shows a characteristic broad peak corresponding to intermolecular hydrogen bonds, which is reflected in the shift of the −OH group band from 3440 to 3423 cm−1. The bands at 1080 and 1250 cm−<sup>1</sup> are associated with asymmetrical and symmetrical stretching vibrations of the O=S=O group, while for AGO/SPEEK film, the corresponding bands are shifted to 1070 and 1244 cm<sup>−</sup>1. The composition and chemical state of elements of AGO/SPEEK films were also researched by XPS (Figure 2f), which was found to be similar to the XPS results of AGO and revealed the blending mechanism between AGO and SPEEK. Figure 2d shows XRD results, clearly indicating the formation of hydrogen bonds between the sulfonated acid groups in SPEEK and polar or amino groups on AGO. Furthermore, TGA (Figure 2e) confirmed that the interface interaction caused by hydrogen bonds between AGO and

SPEEK matrix was stronger, leading to the shift in the TG curve toward high temperature, indicating the improvement of thermal stability [12,29].
