Nonporous and porous silica-polyethylene composite membrane attached FDH for carbon dioxide conversion to formate and its application in a photo-enzyme coupled system

Enzymatic conversion of CO2 to formate represents a highly efficient pathway for CO2 utilization, however, the susceptibility and solubility of enzyme require immobilization to improve their stability and recyclability. By combining particles with polymer membrane as the carrier, the loss of particles can be avoided and a larger surface area and higher catalytic activity can be obtained. Herein, polyethyleneimine (PEI) modified SiO2 or mesoporous silica (mSiO(2)) was attached to the surface of carboxylated polyethylene (PE) hollow fiber membrane to prepare PE-SiO2 and PE-mSiO(2) composite membrane for the immobilization of formate dehydrogenase (FDH). The preparation conditions were optimized, and the effects of SiO2 particle size and the structure of mSiO(2) varied with etching conditions on the catalytic properties of FDH immobilized on composite membrane were investigated for the first time. The results show that with the appropriate concentrations of the activators and PEI, PE-SiO2-FDH prepared from SiO2 with the size of 340 nm (SiO2(340)) manifested the best catalytic performance in the range of 160 similar to 410 nm, with the enzyme activity recovery rate of 240 %. The relative activity was 86.7 % after 5 cycles and 52.8 % after incubation at 60 degrees C for 6 h. After the etching conditions were optimized, PE-mSiO(2(340))-FDH with the protection of mesoporous structure exhibited a higher enzyme activity recovery rate (320 %), reusability (88.2 %) and the thermal stability (64.4 %) than PE-SiO2(340)-FDH. In addition to segments, the application performance of PE-SiO2-FDH and PE-mSiO(2)-FDH module in a photo-enzyme coupled system (PECS) with cofactor regeneration was also investigated. The turnover number of cofactor reached 0.482 and 0.503 after 5 h with 2 mM cofactor. PE-mSiO(2)-FDH module exhibited an outstanding continuous operation performance and a high TON of 1849.2 after 96 h was obtained with the initial addition of 0.01 mM cofactor.