Covalent organic framework adsorption separation of the mother liquor sugars from industrial steviol: A combination of experimental and theoretical analysis

Mother liquor sugar (MLS) is considered a by-product of the industrial production of stevia glycosides. In this work, an efficient purification strategy for separating Steviol glycosides (SvGls) from MLS was developed. A β-ketenamine covalent organic framework (TPAQ-COFs) was prepared by a surfactant (sodium dodecyl sulfate (SDS)) assisted Schiff base reaction. The adsorption capacity for Rebaudioside A (RA), Rebaudioside D (RD), and Stevioside (ST) was studied. The research indicated that after adding SDS, the aggregation phenomenon of TPAQ-COFs was reduced, and the total adsorption of RA, RD, and ST increased by 338.94 mg/g. According to Langmuir model, the adsorption of RA, RD, and ST by TPAQ-COFs were 423.73, 253.16, and 381.68 mg/g, respectively. In addition, density functional theory and electrostatic potential elucidate the adsorption mechanism of SvGls on TPAQ-COFs. In TPAQ-COFs molecules β-ketenamine forms hydrogen bonds with SvGls, as well as abundant Π-Π interaction site is the main reason for its efficient adsorption of SvGls. After 9 cycles, the reuse rates of ST, RA, and RD in TPAQ-COFs were 96.26 %, 96.90 %, and 94.77 %, respectively, demonstrating high reusability and stability. This study lays the foundation for the practical application of a covalent organic framework in the separation and purification of MLS.