Direct Z-Scheme Polymer/Polymer Double-Shell Hollow Nanostructures for Efficient NADH Regeneration and Biocatalytic Artificial Photosynthesis under Visible Light

The design of a highly efficient polymer photocatalyst is an essential prerequisite for photo-biocatalysis in a polymer–enzyme coupled system, which offers an important platform for the synthesis of pharmaceuticals and fine chemicals. However, current polymers still suffer drawbacks of poor water wettability, low visible light absorption, and high recombination rate of photoinduced electron/hole pairs, which severely limit their application in photo-biocatalysis. Herein, we demonstrate a polymer/polymer double-shell hollow nanostructure (PCN@PDBTS-HN) via a facile two-step polymerization with polymeric carbon nitride (PCN) and poly-dibenzothiophene sulfone (PDBTS) as internal and external shells, respectively. The covalent connection of those two polymer layers ensures the spontaneous electron transfer from PDBTS to PCN, as reflected in X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and fluorescence spectra, which could effectively accelerate the charge separation and migration. Thanks to its improved light-harvesting, increased hydrophilicity, and enhanced redox capacity, the obtained PCN@PDBTS-HN demonstrates an excellent catalytic efficiency in visible-light-promoted NADH regeneration with a conversion of 85.4% being achieved in 40 min (turnover frequency of 0.859 mmol g–1 h–1). This value is 1.4 and 2.6 times higher than that of pristine PCN and PDBTS, respectively, indicating an essential role of Z-scheme heterojunction in improving the catalytic efficiency. In addition, PCN@PDBTS-HN also displays excellent photocatalytic selectivity for 1,4-NADH regeneration, remarkable photostability, and good biocompatibility. A total amount of 2.12 mM methanol and 8.39 mM l-glutamate was accumulated in the polymer/alcohol dehydrogenase (YADH) and polymer/glutamate dehydrogenase (GDH) coupled system, respectively, implying high flexibility of fine chemical production via the photo-biocatalytic approach.