Lipases are widely used in industry. Free lipases are difficult to recover and have poor stability under operational conditions. Herein, lipases are immobilized onto the methyltrimethoxysilane (MTMS)-modified ceramic membranes (~ 5 nm) with reverse filtration method, and further cross-linking by glutaraldehyde (GA) is used to improve the lipase stability. FTIR and XPS analyses demonstrate the successful immobilization of lipase. The immobilized lipases are used to hydrolyze glycerol triacetate (GT) to fatty acids and glycerol. Under the optimal immobilization conditions (MTMS concentration 0.1 M, lipase immobilization time 80 min, lipase concentration 3 mg/mL, and GA concentration 2%), the loading of lipases reaches 0.24 mg/g. Under the optimal operational conditions (temperature 45 °C, pH 7, pressure 0.2 MPa, GT concentration 0.05 M), the immobilized lipases have the highest catalytic activity of 25 U/mg. Moreover, the thermal and pH stabilities of immobilized lipases are found to be higher than those of the free lipases. In the long-term runs, the immobilized lipases still have 64% of the initial activity after 7 cycles, indicating good reusability. This paper provides a simple process for immobilizing lipase on ceramic membranes. The immobilized lipases have better stability at high temperature and basic environments (pH 7–9), which would have broad applications in lipase-catalyzed reactions. Graphical Abstract
Cellulose-based porous materials are promising for various fields and preferred for sustainable development. However, the low mechanical properties and high hydrophilicity of cellulose-based xerogels had a direct influence on their application in oil absorption. To address the challenge, an environmentally friendly and economical method for synthesizing MTMS/C0.2-TOCN0.9 xerogels with high hydrophobicity and excellent mechanical strength was successfully established. In this work, shape-recoverable using nanocellulose (TOCN)-based xerogels with porous structure (porosity of 91.5–98.7 %), as well as excellent hydrophobic properties were prepared by TOCN-stabilized wet foams with physical crosslinking, ice crystal-induced phase separation and MTMS modification through simple air-drying instead of the traditional freeze-drying. At the optimized ingredients of TOCN and crosslinker (Ca 2+ ), the xerogel (MTMS/C0.2-TOCN0.9) exhibited superior compressive performance (approximately 35 KPa) and exceptional structural stability after 50 cycles at a compression deflection of 60 %, which was still maintained at 71.5 % of the original stress. Moreover, the MTMS/C0.2-TOCN0.9 xerogel achieved stable superhydrophobicity (128.3°) and excellent oil absorption capacity (59.6 g/g), rendering it a desirable adsorbent for oil spill cleaning. Compared to the pseudo-first-order model, the pseudo-secondary model had higher validity in oil absorption kinetic theories. The MTMS/C0.2-TOCN0.9 xerogel was recyclable and nontoxic, which has the potential to promote environmental applications.
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