Lipases are widely used in organic synthesis to prepare drugs and fine chemicals due to their high catalytic activity, wide range of sources, good enantioselectivity, and wide substrate applicability [1,2]. The separation of enzymes from the reaction system is difficult, and their reuse is problematic, also due to the significant decrease in enzyme activity. As a consequence, enzyme immobilization plays a crucial role in the industrial commercialization of enzyme catalysis technology [3,4]. In enzyme immobilization, free enzymes are combined with corresponding carriers through certain physical or chemical methods to enhance enzyme stability, facilitate preservation and transportation, and separate free enzymes from substrates, achieving the goal of reuse and cost reduction.

In enzyme immobilization technology, the selection of carrier materials has a direct impact on the activity of immobilized enzymes [5]. Reactive groups such as hydroxyl, amino, carboxyl, and aldehyde groups on the surface of the carrier can promote the binding between carrier and enzyme for better immobilization. Carriers with smaller sizes and higher specific surface areas have less steric hindrance when binding to the substrate, making it easier for them to crosslink with the enzyme. Therefore, using such carriers to immobilize enzymes is more efficient [6,7]. Metal-organic frameworks (MOFs) have an ultra-high volume ratio, structural diversity, controllability, adjustability, and good stability. They are formed by the coordination of metal nodes and organic ligands, and due to their good crystallinity, high porosity, open active sites, diverse synthesis conditions, and adjustable structure, the use of MOFs as support has greatly expanded the methods of enzyme immobilization and is expected to become a new platform for studying the interaction between enzymes and carrier materials [[8], [9], [10]]. The catalytic performance of enzyme–MOF biocomposites may be improved by weak interactions (such as van der Waals forces, hydrophilicity, and electrostatic interactions) or by coupling functional groups on the MOF ligand (such as carboxyl, aldehyde, amino, and hydroxyl groups) with groups on the enzyme surface [11,12]. However, several problems may arise during the separation and recovery of MOFs. For example, when MOFs are used in solid-phase catalysts for recovery, the catalysts are usually separated or filtered through high-speed centrifugation. However, high-speed centrifugation can damage the structure of enzymes and reduce their activity [13,14].

Magnetic Fe3O4 nanoparticles not only have the properties of nanomaterials, but also magnetic properties, including magnetic responsiveness and superparamagnetism. Rapid separation from solution can be easily achieved, and this material is one of the choices in drug delivery and macromolecule immobilization [15]. However, due to the high surface energy, magnetic nanoparticles are prone to agglomeration, resulting in uneven sizes, and the exposed Fe3O4 is susceptible to oxidation, resulting in a decrease in magnetic properties. Encapsulating inorganic materials, organic functional groups, and biological macromolecules on the surface of magnetic nanoparticles through chemical or physical interactions can reduce the surface Gibbs free energy and increase their stability [16].

Magnetic MOFs are magnetic nanoparticles, typically with strong application targeting, and are formed by encapsulating inorganic magnetic materials in MOFs. The specifically designed magnetic MOFs possess the common characteristics of magnetic nanoparticles and MOFs [17]. For different targets, magnetic MOFs with the required characteristics can be prepared by changing the conditions for synthesizing magnetic MOFs. The application of magnetic MOFs is convenient and fast. For example, during detection processes, it is difficult to separate the target analyte in complex samples by MOF enrichment, while magnetic MOFs can be separated from the sample using an external magnetic field after enriching the target analyte. Magnetic MOFs can be reused, and after separation, the used magnetic MOFs can be recycled after treatment [[18], [19], [20]].

Ionic liquids can be applied in enzyme-catalyzed reactions in various ways, e.g., as solvents or co-solvents, as modifiers of enzyme structures, or in the analysis of biological toxicity and evaluation of cell toxicity. As reaction media, ionic liquids can provide a suitable environment for enzyme catalysis or alter the secondary structure of enzymes to improve enzyme activity and stability [21,22]. Galai et al. [23] reported that 13 ionic liquids used as solvents could increase the activity of laccase by up to 451 %, which was achieved in choline dihydrogen phosphate [Chol][H2PO4]. Macedo et al. [24] compared water-soluble ionic liquids and found that the inactivation rate of laccase increased with the increase in alkyl chain length. Therefore, some scholars have modified carriers with ionic liquids to provide a suitable microenvironment for enzymes or increase their adsorption capacity, thereby further enhancing the performance of immobilized enzymes [25,26].

For lipase, there is helix lid covered its active center. When lipase is bound to hydrophobic interfaces, the lid opens and the catalytic activity of lipase increases [27,28]. Therefore, using highly hydrophobic immobilized carriers is beneficial for opening the lid of lipase and is an effective method for improving the activity of immobilized enzymes. In this work, amino-acid-based ionic liquids were used to modify magnetic nanoparticles/MOFs-compliant carriers with core-shell structures, improving the interfacial interaction between enzyme molecules and carriers. The anions and cations of ionic liquids have strong hydrogen bonding and charge interactions with enzyme molecules, which can improve the immobilization efficiency of enzymes through multiple interactions. Hexafluorophosphate, PF6−, was selected as the anion to enhance the hydrophobicity of the carrier surface and activate the immobilized lipase (Scheme 1).