Controllable preparation of mesoporous silica and its application in enzyme-catalyzed CO2 reduction

Enzymatic conversion of CO2 to high-value chemicals is a significant route for the utilization of greenhouse gases in mild, high-selectivity and environment-friendly way, however, conversion efficiency is not yet satisfying. Here, mesoporous silica (mSiO2) nanoparticles with controllable structure were prepared and modified by polydopamine (PDA) and polyethyleneimine (PEI), which were then used in an integrated process for CO2 capture and conversion to formate for the first time. The effects of structure parameters of mSiO2 and modification conditions on its application properties were investigated. The results show that in a range of 230 ∼ 500 nm, SiO2 particles with smaller size exhibited better intensifying effect, while the optimal size was 410 nm for mSiO2 with the same etching extent, attributed to a higher specific surface area. mSiO2 itself was a robust CO2 adsorbent and the addition of 0.01 g mSiO2(410) enabled CO2 conversion to be accelerated 11.94 times compared to free enzyme. After modification, with 0.05 g PDA/PEI-mSiO2(340) and PDA/PEI-mSiO2(410), the enzyme reaction was expedited up to 24 and 30.8 times of the system without particles due to an enhanced CO2 uptake, as a collaborative result of mesoporous structure and amino-functionalization. Following that, PDA/PEI-mSiO2(410) was used as the carrier for the co-immobilization of formate dehydrogenase and carbonic anhydrase, which could retain 86.7% activity after use for 10 times and 55.2% activity after 21 days at 4 °C, while 29.6% for free enzymes.