Immobilization and enhanced catalytic activity of lipase on modified MWCNT for oily wastewater treatment

In this article, we report results of experiments on covalent immobilization of Candidia rugosa lipase enzyme on modified multiwall carbon nanotubes (MW-CNTs) for oily wastewater treatment application. MWCNTs were produced using chemical vapor deposition (CVD) and surface-modified by nitric acid and organic cross-linkers. Successful attachment and high enzyme loading up to 30 wt % was confirmed via FTIR and TGA analysis. Enzymatic activity and loading, which are dependent on the oxidized MWCNT surfaces, cross-linker types and concentrations, resulted with high thermal and operational stability in the microenvironment conditions. This demonstrates the potential for improved resistance to the severe conditions in industrial applications. Furthermore, the CNTs-immobilized enzyme yielded a catalytic activity about 93 times higher than those immobilized on other reported support materials. Up to 98% biological activity retention was also achieved, marking a significant improvement over literature-reported activities (1–20%). Titrimetric analysis of hydrolyzed samples using MWCNT-Lipase (after 1 hr reaction time at 37°C) resulted in an enzymatic activity increase of about five times over those from lyophilized lipase.