Immobilization of lipase within carbon nanotube–silica composites for non-aqueous reaction systems

The immobilization of lipases within sol–gel derived silica, using multi-walled carbon nanotubes (MWNTs) as additives in order to protect the inactivation of lipase during sol–gel process and to enhance the stability of lipase, was investigated. Three sol–gel immobilized lipases (Candida rugosa, Candida antarctica type B, Thermomyces lanuginosus) with 0.33% (w/w) MWNT showed much higher activities than lipase immobilized without MWNT. The influence of MWNT content and MWNT shortened by acid treatment in the sol–gel process on the activity and stability of immobilized C. rugosa lipase was also studied. In hydrolysis reaction, immobilized lipase containing 1.1% pristine MWNT showed 7 times higher activity than lipase immobilized without MWNT. The lipase coimmobilized with 2.7% shortened MWNT showed 10 times higher activity in esterification reaction, compared with lipase immobilized without MWNT. The lipase coimmobilized with 2.7% shortened MWNT retained 96% of initial activity after 5 times reuse, while the lipase immobilized without MWNT was fully inactivated under the same condition.