Pickering emulsion stabilized with charge separation and transfer modulated photocatalyst for enzyme-photo-coupled catalysis

Abstract

Biocatalytic reduction is extensively employed in chemical and pharmaceutical industries due to its notable advantages including high activity, selectivity and mild reaction conditions, however, the stoichiometric use of the expensive NADH (reduced form of nicotinamide adenine dinucleotide) hinders its widespread application. Despite the persisting challenges of low charge separation efficiency and limited solubility of organic substrates in aqueous phase, in situ photocatalytic NADH regeneration remains a promising solution. Herein, we report the construction of an enzyme-photo-coupled catalytic system in Pickering emulsion droplet, which was stabilized by a charge separation and transfer modulated photocatalyst. The photocatalyst integrated with visible light driven conjugated polymer, TiO2 and electron mediator greatly enhanced the cascade electron transfer from photocatalyst to NAD+. Consequently, NADH production rate over the integrated photocatalyst reaches as high as 2.4 mmol·g−1·h−1 under visible light irradiation, 12 folds higher than the corresponding physical mixture. Furthermore, the enzyme-photo-coupled catalytic system was constructed with alcohol dehydrogenase/NAD+ confined in the emulsion droplet and photocatalyst assembled at the oil-water interface. The photoactive emulsion continuously catalyzed the n-butyaldehyde reduction to accumulate 16.1 mmol·L−1 butanol, equivalent to 14 cycles for NADH regeneration under visible light irradiation. The primary result demonstrates the potential application prospect of Pickering emulsion in enzyme-photo-coupled catalysis due to the facilitated charge transfer from photocatalyst to NAD+ and fast mass diffusion attributed to the large interfacial area of water and oil.