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 beta-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 TPAQCOFs 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 beta-ketenamine forms hydrogen bonds with SvGls, as well as abundant Pi-Pi 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.