Lysine-modulated synthesis of enzyme-embedded hydrogen-bonded organic frameworks for efficient carbon dioxide fixation

Abstract

Carbonic anhydrase (CA) is an important carbon fixation enzyme. Immobilization of CA can expand its application in the realm of adsorption, catalysis, and so on. As a typical metal-free framework, hydrogen-bonded organic frameworks (HOFs) featuring mild synthesis process, exquisite framework structure and good enzyme compatibility have been used for enzyme embedding. However, the catalytic performance of CA-embedded HOFs (CA@HOFs) is limited by the micropore size of HOFs and the slow adsorption of CO2. Herein, CA@Lys-HOF-1 was synthesized by introducing lysine (Lys), a basic amino acid, during the coprecipitation of CA and HOFs for CO2 fixation. The addition of Lys enlarged the average pore size of HOF-1 from 1.8 to 3.2 nm, whereas the introduced -NH2 groups increased the initial adsorption of CO2 from 0.55 to 1.21 cm3 g-1. Compared to CA@HOF-1, the activity of CA@Lys-HOF-1 was enhanced by 71.25%, and the corresponding production of CaCO3 was enhanced by 12.7%. After eight reaction cycles, CA@Lys-HOF-1 still maintained an output of 9.97 mg of CaCO3 every 5 min, 83.7% of the initial production. It is hoped that the CA@Lys-HOF-1 reported offers a platform for efficient and continuous fixation of CO2.