Reversing adsorption and separation of 1-phenylethanol and acetophenone in organic phase via β-ketoenamine-linked covalent organic frameworks

Abstract

Adsorption is considered as a promising method to purify the mixed acetophenone (AP) and 1-phenylethanol (1-PE) that are generally difficult to separate. Many efforts have been made to improve the preferential uptake of AP over 1-PE in aqueous phase, but there exists a practical bottleneck associated with their limited aqueous solubility. Herein, we demonstrate unprecedented reversal of selectivity in the organic medium enabled by β-ketoenamine-linked covalent organic frameworks (COFs), which were fabricated successfully by polycondensation between 1,3,5-triformylphloroglucinol (Tp) and diamines. The dependence of selective adsorption ability toward 1-PE on pore size was firstly investigated experimentally, indicating that TpBZ-COF with moderate pore size outperformed other analogues. The adsorption behaviors of 1-PE and AP onto TpBZ-COF were examined systematically. The evaluation results revealed a strong affinity toward 1-PE versus AP as well as excellent stability in recycling experiments. Further, the dynamic breakthrough experiments confirmed the practical application potential and remarkable recyclability. To probe the mechanism and structure–activity relationship, an imine-linked COF possessing similar porous structure was used as a reference for comparison of separation performance both experimentally and theoretically. The occurrence of hydrogen bonding between the hydroxyl of 1-PE and β-ketoenamine-linkage as H-bond acceptor in suitable pore spaces endows TpBZ-COF a fantastic candidate for purifying 1-PE and AP from petrochemical by-products.