*3.1. Characterization of m-LDH*

The FTIR spectra of Zn-Ti LDH, m-LDH, and SA are shown in Figure 1a. A broad absorption band between 3200 and 3400 cm−<sup>1</sup> of Zn-Ti LDH indicates the stretching mode of hydroxyl groups and physisorbed water in the interlayer of LDH. The bands at 1508, 1388, and 1047 cm−<sup>1</sup> are attributed to the interlayer CO<sup>3</sup> <sup>2</sup>−. In addition, the bands below 1000 cm−<sup>1</sup> are metal-oxygen (MO, O-M-O, or M-O-M) signals [15,23,24]. After the chemical modification with SA, the absorption bands at 2920, 2850, and 1462 cm−<sup>1</sup> are related to the CH<sup>2</sup> asymmetric vibrations, symmetric vibrations, and scissor mode of SA, respectively [31]. Notably, the bands attributed to the CO<sup>3</sup> <sup>2</sup><sup>−</sup> of Zn-Ti LDH and the band at 1701 cm−<sup>1</sup> attributed to the COOH group of SA disappeared or became weaker in the spectrum of m-LDH. At the same time, the clear absorption band at 1596 cm−<sup>1</sup> of m-LDH is due to COO− stretching vibrations, indicating that the SA was converted to stearate anion (from H3C(CH2)16COOH to H3C(CH2)16COO−) [23]. Figure 1b,c give the photographs of water droplets on the surface of Zn-Ti LDH and m-LDH, respectively. The wettability of Zn-Ti LDH changed with SA modification. Compared to Zn-Ti LDH, a larger water contact angle of m-LDH means lower hydrophilicity, which may result in a better dispersion in the PBSA matrix.

**Figure 1.** (**a**) The FTIR result of Zn-Ti LDH, m-LDH, and SA; the photographs of water contact angle on the surface of (**b**) Zn-Ti LDH and (**c**) m-LDH; (**d**) XRD result of Zn-Ti LDH and m-LDH.

Figure 1d shows the XRD patterns of Zn-Ti LDH and m-LDH. The diffraction peaks of Zn-Ti LDH at 2θ = 13.05◦ , 24.33◦ , 28.23◦ , 32.90◦ , 33.28◦ , 36.14◦ , and 38.70◦ correspond to the crystal planes of (003), (006), (012), (100), (101), (009), and (015), respectively [23,32]. The d-spacing of (003), (006), and (009) calculated by Bragg's law are 0.68, 0.37, and 0.25 nm,

respectively. After chemical modification using SA, the diffraction peaks of (003), (006), and (009) planes of LDH shifted to smaller angles at 2θ = 1.88◦ , 3.73◦ , and 5.64◦ , respectively. The d-spacing corresponding to (003), (006), and (009) planes of m-LDH increases to 4.69, 2.37, and 1.57 nm, respectively. The chemical modification can expand the interlayer distance of LDH, indicating that the ion exchange of SA was successful and consistent with the above FTIR results. In addition, the chain length of the stearate anion is about 2.25 nm [23]. From the increase in d-spacing from 0.68 nm of ZN-Ti LDH to 4.69 nm of m-LDH, we deduce that the intercalation of SA formed bilayer structures with an inclined angle of 63◦ .

The TGA curves of Zn-Ti LDH, m-LDH, and SA performed in the air environment are shown in Figure 2a. The 10% weight loss and Char yield weight percent at 600 ◦C of Zn-Ti LDH, m-LDH, and SA are shown in Table A1. The main thermal decomposition of Zn-Ti LDH occurs from 200 to 300 ◦C, which corresponded to the evaporation of carbonate anions [23]. After chemical modification using SA, there is no rapidly weight drop as same as Zn-Ti LDH at the temperature below 300 ◦C, and the residual weight of m-LDH is 46.9% at 600 ◦C. Combining the analysis results of FTIR, XRD and TGA, it can be seen that SA had been inserted into the Zn-Ti LDH laminates by ion exchange method. It can be seen from the change of contact angle that SA was also adsorbed on the surface of m-LDH.

**Figure 2.** (**a**) TGA and (**b**) UV-vis result of Zn-Ti LDH, m-LDH, and SA.

The UV–vis absorbance spectrum of Zn-Ti LDH, SA, and m-LDH are shown in Figure 2b. An absorption signal from 250 to 370 nm is observed for Zn-Ti LDH, which includes whole UV-B and most of the UV-A irradiation range. Simultaneously, no significant UV-absorbing character of SA is observed from 250 to 400 nm. After modification, the absorption intensity of m-LDH is lower than Zn-Ti LDH. However, the m-LDH still shows a significant absorption signal from 250 to 370 nm, which indicates a good application potential in UV irradiation protecting.
