Immobilized lipase in bio-based metal-organic frameworks constructed by biomimetic mineralization: A sustainable biocatalyst for biodiesel synthesis

Herein, thermophilic lipase QLM from Alcaligenes sp. has been successfully immobilized in bio-based metalorganic frameworks (MOFs) through biomimetic mineralization, using zinc acetate and adenine as metal ion and organic ligand, respectively. The morphology and structure of lipase@Bio-MOF was systematically characterized by scanning electron microcopy (SEM), transmission electron microcopy (TEM), powder X-ray diffraction (PXRD) and Fourier transform infrared spectra (FT-IR). The enzyme loading in immobilized enzyme was measured to be 15.9 % by thermogravimetric analysis (TGA). Further, it was demonstrated to possess favorable catalytic activity and stability under high temperature and alkaline conditions and in the presence of metal ions, using the hydrolysis of p-nitrophenyl caprylate as a model. Finally, the immobilized enzyme was successfully applied in the preparation of biodiesel through the trans-esterification of sunflower oil with methanol, obtaining a conversion of > 60 % at a high oil/methanol ratio of 8:1. Meanwhile, it showed excellent recyclability during the biodiesel production, and no changes of morphology and crystal structure were observed after being used for 3 cycles. Overall, the immobilized lipase in bio-based MOFs provided an economically and environmentally viable biocatalyst for the synthesis of biodiesel.