Study of surface modifications of multiwalled carbon nanotubes by functionalized ionic liquid to immobilize Candida antarctic lipase B

Multiwalled carbon nanotubes modified on the surface by imidazole ionic liquids with different types of anions (Br⁻, BF₄, PF₆ or H₂PO₄) as a new-generation carrier were fabricated. Subsequently, Candida antarctic lipase B (CALB) was immobilized on the functionalized MWNTs via physical attachment, and its enzymology properties were tested. The morphology of the MWNTs before and after the modification was determined by transmission electron microscopy (TEM)， Raman spectroscopy, thermo gravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). These characterizations were used to study the influence of surface modification of materials on the enzymatic properties. The results revealed that CALB immobilized on MWNTs modified by ionic liquids not only had a higher specific activity as compared with that of CALB immobilized on pure MWNTs, but also better tolerance (high temperature, high pH), thermostability, and reusability. The different anions of ionic liquids, which were used to modify MWNTs, exert a remarkable effect on the properties of immobilized enzyme. The specific activity of MWNTs-IL (PF₆)-CALB were the highest and were five times higher than that of MWNTs-CALB with no modification. The analysis of kinetic parameters of immobilized enzymes showed that the modification of ionic liquids for carriers enhanced the affinity between the enzyme and the substrate, so as to increase the enzyme activity.