Effect of Different TiO 2 Morphologies on the Activity of Immobilized Lipase for Biodiesel Production.

Lipase catalytic activity is greatly influenced by immobilization on nanoparticles. In this study, lipase from Aspergillus niger was immobilized on TiO 2 nanoparticles with different morphologies: microspheres, nanotubes, and nanosheets. All TiO 2 samples were prepared by a hydrothermal method. Lipase/TiO 2 nanocomposites were prepared by a physical adsorption method through hydrophobic interactions. The prepared composites were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM). The catalytic activity of free and immobilized lipases was tested using sunflower oil in the presence of methanol to produce biodiesel at 40 °C for 90 min. The lipase immobilized on TiO 2 microspheres showed the highest activity compared to the lipase immobilized on TiO 2 nanotubes and nanosheets. To optimize the lipase-to-microsphere ratio, lipase was immobilized on TiO 2 microspheres in different microspheres/lipase, w/w, (S/L) ratios of 1:1, 1:0.75, 1:0.5, and 1:0.25. It was noticed that the hydrolytic activity follows the order 1:0.25 > 1:0.5 > 1:75 > 1:1. The immobilization yield activities were found to be 113, 123, 125, and 130% for the microspheres/lipase (S/L) ratios of 1:1, 1:0.75, 1:0.5, and 1:0.25, respectively.