Robust and Recyclable Two-Dimensional Nanobiocatalysts for Biphasic Reactions in Pickering Emulsions

Abstract

In this study, a facile, yet effective surface-engineering method was reported to confer graphene oxide (GO) nanosheets with amphiphilic feature and numerous binding sites toward enzymes for biphasic reactions in Pickering emulsions. Briefly, the surface of GO nanosheet is first modified and simultaneously reduced by polydopamine to endow with catechol groups. A portion of catechol groups is utilized to anchor zeolitic imidazolate framework 8 (ZIF-8) nanoparticles onto the polydopamine-modified graphene oxide (P-rGO) nanosheets through Zn<sup>2+</sup>–catechol coordination. The remaining uncoordinated catechol groups in P-rGO nanosheets are utilized to immobilize lipase onto the P-rGO nanosheets through chemical conjugation. The resulting two-dimensional P-rGO/ZIF-8/Lipase nanobiocatalysts with an enzyme loading percent values of 34.05–48.75% could be spontaneously assembled at the oil/water interface, which were then utilized to catalyze the hydrolysis of water-insoluble <i>p</i>-nitrophenyl palmitate (<i>p</i>-NPP) into water-soluble <i>p</i>-nitrophenol (<i>p</i>-NP). The Pickering emulsions, which were robustly stabilized by P-rGO/ZIF-8/Lipase, facilitated the diffusion of <i>p</i>-NP from the oil/water interface to aqueous phase, acquiring an enzymatic activity recovery of ∼60%. Moreover, P-rGO/ZIF-8/Lipase exhibited remarkably enhanced stabilities against multiple reuses and various harsh conditions compared with free lipase, GO/Lipase, and P-rGO/Lipase, showing great potential in practical applications

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