Enhanced performance of Rhizopus oryzae lipase immobilized onto a hybrid-nanocomposite matrix and its application for biodiesel production under the assistance of ultrasonic technique

In this study, a hybrid nanocomposite composed of superparamagnetic multi-walled nanotubes and four-arm polyethylene glycol amine ([email protected]2) was synthesized and employed as a matrix for covalent immobilization Rhizopus oryzae lipase. The performance of immobilized lipase ([email protected]2) was greatly improved, with maximum activity recovery of 3073% and a 30.73-fold superior in specific activity than its free form under optimum conditions: glutaraldehyde concentration 7.5 wt%, pH 7.0, immobilization temperature 40 °C, and immobilization time 2.5 h. The thermostability of [email protected]2 was 57.33% of its initial activity at 70 °C, a 13-fold higher than its free counterpart. Most significantly, [email protected]2 was applied for waste cooking oil transesterification to prepare biodiesel with the assistance of ultrasonic technique. Under optimized conditions: methanol/oil molar ratio 4:1, co-solvent 20%wt., water content 10%wt. at 40 ± 1 °C and ultrasound-assisted condition of 40% power and 40 kHz frequency, the highest conversion yield reached 94.72% within150 min. This was due to the ultrasound-assisted process leading to efficient yield in a short processing time. The immobilized ROL could maintain 71.55% biodiesel yield after 10 reuse cycles, indicating efficient operational stability. Therefore, [email protected]2 is a promising nanobiocatalyst, and ultrasound-assisted enzymatic reaction is a fast and clean process; together, they have potential use in future industrial applications.