Carbonic anhydrase immobilized on encapsulated magnetic nanoparticles for CO2 sequestration.

Bovine carbonic anhydrase (BCA) was covalently immobilized onto OAPS (octa(aminophenyl)silsesquioxane)-functionalized Fe(3)O(4)/SiO(2) nanoparticles by using glutaraldehyde as a spacer. The Fe(3)O(4) nanoparticles were coated with SiO(2), onto which was grafted OAPS, and the product was characterized using SEM, TEM, XRD, IR, X-ray photoelectron spectroscopy (XPS), and magnetometer analysis. The enzymatic activities of the free and Fe(3)O(4)/SiO(2)/OAPS-conjugated BCA (Fe-CA) were investigated by hydrolyzing p-nitrophenylacetate (p-NPA), and hydration and sequestration of CO(2) to CaCO(3). The CO(2) conversion efficiency and reusability of the Fe-CA were studied before and after washing the recovered Fe-CA by applying a magnetic field and quantifying the unreacted Ca(2+) ions by using ion chromatography. After 30 cycles, the Fe-CA displayed strong activity, and the CO(2) capture efficiency was 26-fold higher than that of the free enzyme. Storage stability studies suggested that Fe-CA retained nearly 82 % of its activity after 30 days. Nucleation of the precipitated CaCO(3) was monitored by using polarized light microscopy, which revealed the formation of two phases, calcite and valerite, at pH 10 upon addition of serine. The magnetic nanobiocatalyst was shown to be an excellent reusable catalyst for the sequestration of CO(2).