Boric acid modified macroporous adsorption resin and its adsorption properties for catechol compounds

Abstract

Resins have been modified with many functional groups by Friedal − Crafts alkylation reaction. In this research, a Friedal − Crafts acylation reaction in combination with commercial BNKX − 5 was first used to synthesize the boric acid − based macroporous resin named BNKX − 5−BA. The adsorption results of the experiments showed that the adsorption capacities of BNKX − 5 and BNKX − 5−BA were all affected by pH, and the adsorption capacities of all target compounds on BNKX − 5−BA increased as the pH value increase, meanwhile opposite results observed for BNKX − 5. Furthermore, the polymers had larger adsorption capacity for larger molecular weight compounds. Adsorption isotherms of taxifolin on BNKX − 5−BA were fitted better to Freundlich model and adsorption kinetic process followed the pseudo–first–order equation. The boric acid affinity, hydrogen bonding, π−π interactions and molecular sieving effect may have been the possible adsorption driving forces. The resin could be absolutely desorbed by 50 %, pH < 4 ethanol solution and after five adsorption − desorption cycles only 5.41 % loss in adsorption capacity. The results provide a method to modify MARs with boric acid to separate and purify catechol compounds from herbal plants.