*2.4. Fourier Transform Infrared Spectroscopy Test*

The prepared samples were tested with a Fourier transform infrared spectrometer (Bruker Scientific Technology Co., Ltd., Beijing, China). The detection mode was ATR, the resolution was 4 cm<sup>−</sup>1, the test wavenumber range was 400–4000 cm−1, and the number of scans was 16.
