Shielding of Enzymes on the Surface of Graphene-Based Composite Cellular Foams Through Bioinspired Mineralization

Immobilization of enzyme on the surface of graphene-based composite cellular foams (GCCFs) is commonly prone to acquire stable and ultrahigh loading of enzymes and fast transport of substrates during the catalytic process. In this chapter, we reported a method of preparing GCCFs through combination of redox assembly and biomimetic mineralization with in situ enzyme immobilization. Briefly, GCCFs were first prepared through redox assembly of graphene oxide (GO) nanosheets enabled by polyethyleneimine (PEI). The cationic PEI in the resultant reduced GO/PEI (rGO/PEI) cellular foams acted as the mineralization-inducing agent could catalyze the condensation of silicate to form silica (biomimetic silicification) on the reduced graphene oxide (rGO) surface, where enzyme (with penicillin G acylase as model enzyme) is in situ entrapped and shielded within the silica network. Enzymes could be stably resided on the surface of GCCFs without any leaching against a broad range of pH values (3.5-10.0). GCCFs show a three-dimensional (3D) porous structure, which facilitates the fast transfer of substrate and, thereby, leads to desirable catalytic activity. Combined with the monolithic feature, GCCFs exhibit ease of recyclability and superior thermal/recycling stabilities during the catalytic synthesis of 6-aminopenicillanic acid (6-APA, an important pharmaceutical intermediate) compared to free enzyme and enzyme adsorbed on rGO/PEI cellular foams.