2.5 Characterization
NMR spectra were carried out to analyze the chemical shift of multimer absorbent and complexes on a Bruker DPX 400 MHz spectrometer with CDCl3 in the capillary tube as an internal standard solvent. The viscosities were measured by Brookfield LVDV-II + Pro viscometer with a deviation of ±1%. The thermal stability of the multimer absorbent DBU-2EG and DBU-2EG-4H2S complexes were measured by thermal gravimetric analysis (TGA) using TGA thermogravimetric analyzer (Mettler Toledo) with the heating rate of 5℃/min in the nitrogen atmosphere.