## 3 Results and Discussion  
### FTIR, XRD, and XPS Characterization  
The FTIR spectra of P(AA-co-AM) (a), GO (b), and GO/P(AA-co-AM) (c) were analyzed using an IFS 66v/S FTIR spectrometer, and the results are shown in Figure 1a-c. From the FTIR spectrum of P(AA-co-AM) (Figure 1a), it can be seen that the strong absorption bands of the amide group are present at 3462 and 3354 cm\({}^{-1}\), where the -NH\({}_{2}\) stretching vibration peak of acrylamide (AM) is present when acrylic acid (AA) is cross-linked with acrylamide (AM) to form P(AA-co-AM) [25]. The stretching vibration peak of C-H in the alkyl group is at 2984 cm\({}^{-1}\). The absorption peaks at 1650 and 1575 cm\({}^{-1}\) are the peaks of the C=O stretching vibration in the amide group (-CONH\({}_{2}\)) of acrylamide (AM) and the C=O stretching vibration in the carboxylate anion (-COO-) of acrylic acid (AA) when cross-linking with acrylamide (AM) to form P(AA-co-AM) [13; 26; 27]. Therefore, the results indicate that the P(AA-co-AM) hydrogel was successfully synthesized by the polymerization of acrylic acid (AA) with acrylamide (AM). The FTIR spectrum of GO in Figure 1b shows a strong hydroxyl (-OH) stretching vibration peak at 3461 cm\({}^{-1}\), which is the formation of intermolecular hydrogen bonds after the oxidation of graphite. At 1621 cm\({}^{-1}\), the stretching vibration peak of carbonyl C=O in the carboxyl group (-COOH) or the stretching vibration peak of the olefin group (C=C) formed after the oxidation of graphite is shown [28]. The presence of the monosubstituted olefin group (=CH-) at 997 cm\({}^{-1}\) in the infrared spectrum is not the only evidence of the presence of C=C in GO [29]. This result indicates that the graphite has been successfully oxidized to produce graphene oxide with inter-analytical hydrogen bonds and olefin groups. The FTIR spectrum of GO/P(AA-co-AM) in Figure 1c shows that the strong obtuse peak at 3440 cm\({}^{-1}\) is the stretching vibration peak of the hydroxyl-OH in the carboxylic acid group (-COO-) or the hydroxyl-OH in the graphene oxide are intermolecular hydrogen bonds, and at 1615 cm\({}^{-1}\) the stretching vibration peak of the carbonyl-C=O in the carboxylate anion (-COO-) in the acrylic acid (AA) at 1650 cm\({}^{-1}\) can be observed [13; 26; 27]. The stretching vibration peak moved to this point, thus indicating that graphene oxide (GO) was successfully cross-linked on the P(AA-co-AM) hydrogel to synthesize the GO/P(AA-co-AM) hydrogel, and a large number of intermolecular hydrogen bonds, including hydroxyl radicals and carboxyl radicals, were formed on the surface of the GO/P(AA-co-AM) hydrogel. The macroscopic XPS spectra of GO/P(AA-co-AM) and P(AA-co-AM) were analyzed using electronic energy spectroscopy, respectively, and the macroscopic XPS spectra are shown in Figure 2. Both GO/P(AA-co-AM) and P(AA-co-AM) detected C 1s (284.74 eV), N 1s (400.59 eV), O 1s (532.42 eV), and Na 1s (1071.54 eV) characteristic peaks. Since XPS analysis can be performed semi-quantitatively, the fractional heights and ratios of the characteristic peaks of C 1s and O 1s show that the carbon-oxygen ratio decreases significantly after cross-linking graphene oxide, and the content of oxygen-containing functional groups in the polymer increases significantly. From the XRD pattern of GO in Figure 1d, it can be determined that the characteristic peaks of the crystalline form of the oxides formed after the oxidation of graphite are similar to the characteristic peaks of organic substances that are polycarbonate and have hydroxyl and carboxyl groups, which indicates that graphite was successfully oxidized to graphene oxide. As shown in Figure 1e, a broad peak with an acute angle appears on the left side for the GO/P(AA-co-AM) sample, which indicates that graphene oxide was successfully cross-linked with acrylic acid and acrylamide to form the targeted graphene oxide hydrogel. Figure 1: FTIR spectra of (**a**) P(AA-co-AM), (**b**) GO, and (**c**) GO/P(AA-co-AM). XRD patterns of (**d**) GO and (**e**) GO/P(AA-co-AM).