An efficient and recyclable enzyme catalytic system constructed through the synergy between biomimetic mineralization and polyamine–salt aggregate assembly†
In the present study, an efficient and easily recyclable enzyme catalytic system based on nanoparticle-assembled microcapsules (NAMCs) is constructed by using both biomimetic mineralization and polyamine–salt aggregate assembly. Specifically, enzyme-encapsulated silica nanoparticles (NPs) are prepared by polyethyleneimine (PEI, a typical cationic polymer)-induced silicification in the presence of enzymes. The as-acquired NPs are then spontaneously adsorbed and assembled onto the surfaces of poly (allylamine hydrochloride) (PAH)–citrate microaggregates, which are synthesized through citrate-induced PAH aggregation. After continuous stirring, the internal parts of the PAH–citrate microaggregates are disassembled, and the NAMCs-based enzyme catalytic system is finally acquired. During the continuous stirring process, the PAH moieties on the surfaces of PAH–citrate microaggregates play two crucial roles: (1) adsorbing NPs onto the surfaces of PAH–citrate microaggregates by electrostatic interactions; and (2) catalyzing the subsequent condensation of the Si–OH groups on the surfaces of two adjacent NPs to form Si–O–Si networks, thus generating an intact capsule wall. In this process, the citrate moieties in the internal parts of PAH–citrate microaggregates are released into the bulk aqueous solution, and this release causes the disassembly of PAH–citrate microaggregates, thus generating the capsule lumen. The resultant enzyme catalytic system exhibits high activity and stability, and particularly, easy recyclability for converting formaldehyde into methanol using NADH as the cofactor. More specifically, this system displays an NADH conversion of ∼92.7%, and can be nearly completely recycled using low-speed centrifugation (<3000 rpm), which ensures that the NADH conversion is maintained almost unaltered after reusing the system 10 times. This study will be useful for the facile construction of diverse catalytic systems with high efficiency and excellent recyclability.