Abstract
Cellulase from Aspergillus niger was immobilized onto β-cyclodextrin-conjugated magnetic particles by silanization and reductive amidation. The immobilized cellulase gained supermagnetism due to the magnetic nanoparticles. Ninety percent of cellulase was immobilized, but the activity of immobilized cellulase decreased by 10%. In this study, ionic liquid (1-butyl-3-methylimidazolium chloride) was introduced into the hydrolytic process because the original reaction was a solid-solid reaction. The activity of immobilized cellulase was improved from 54.87 to 59.11 U g immobilized cellulase−1 at an ionic liquid concentration of 200 mM. Using immobilized cellulase and ionic liquid in the hydrolysis of rice straw, the initial reaction rate was increased from 1.629 to 2.739 g h−1 L−1. One of the advantages of immobilized cellulase is high reusability—it was usable for a total of 16 times in this study. Compared with free cellulase, magnetized cellulase can be recycled by magnetic field and the activity of immobilized cellulase was shown to remain at 85% of free cellulase without denaturation under a high concentration of glucose (15 g L−1). Therefore, immobilized cellulase can hydrolyze rice straw continuously compared with free cellulase. The amount of harvested glucose can be up to twentyfold higher than that from the hydrolysis by free cellulase.
Highlights
Magnetic nanoparticles (MNPs) have been applied to enzyme immobilization because the high surface areas of such particles at the nanometer scale are beneficial to enzyme loading
Immobilization of cellulase on magnetic nanoparticles (MNPs) allows for the recycling of the most costly ingredient of the rice straw hydrolysis process
As the βcyclodextrin concentration increased, the size of the obtained Fe3O4 crystallite decreased. These results showed that βcyclodextrin can be used to effectively limit the particle size of magnetite
Summary
Magnetic nanoparticles (MNPs) have been applied to enzyme immobilization because the high surface areas of such particles at the nanometer scale are beneficial to enzyme loading. The most common method for producing synthetic MNPs is the coprecipitation of ferrous and ferric ions at a molar ratio of 1 : 2 by alkali solutions. The reaction is indicated as follows: Fe2+ + 2Fe3+ + 8OH− → Fe3O4(s) + 4H2O (1). This method of preparing MNPs is well known, the phase and size of MNPs are difficult to control. (2) initial pH [2, 5], (3) stirring velocity [6], (4) different iron salt solutions with varying ratios of ferrous and ferric ions [3, 7], (5) types and concentrations of alkali [3, 8], (6) surfactants [5], and (7) ionic strength of the solution [4]. A functional silane compound, such as 3-aminopropyltriethoxysilane (APTES), can self-assemble onto the surface of a magnetite and form
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