2.3.3 FT-IR analysis
The vibrations of molecules and polar bonds among different atoms were studied by FT-IR spectra (iD1 Transmission Nicolet iS5, Thermo Fisher, USA), with recorded frequencies ranging from 4,000 to 500 cm-1 (Yu & Irudayaraj, 2005). FT-IR measurements were performed for each sample, which were mixed with dried KBr powder and then compressed into salt discs.