Enhanced Organic Photocatalysis in Confined Flow through a Carbon Nitride Nanotube Membrane with Conversions in the Millisecond Regime.

Yajun Zou,Jian-Wen Shi,Yevheniia Markushyna,Tobias Heil,Aleksandr Savateev,Kai Xiao,Qing Qin,Lei Jiang,Markus Antonietti

doi:10.1021/acsnano.0c09661

Abstract

Bioinspired nanoconfined catalysis has developed to become an important tool for improving the performance of a wide range of chemical reactions. However, photocatalysis in a nanoconfined environment remains largely unexplored. Here, we report the application of a free-standing and flow-through carbon nitride nanotube (CNN) membrane with pore diameters of 40 nm for confined photocatalytic reactions where reactants are in contact with the catalyst for <65 ms, as calculated from the flow. Due to the well-defined tubular structure of the membrane, we are able to assess quantitatively the photocatalytic performance in each of the parallelized single carbon nitride nanotubes, which act as spatially isolated nanoreactors. In oxidation of benzylamine, the confined reaction shows an improved performance when compared to the corresponding bulk reaction, reaching a turnover frequency of (9.63 ± 1.87) × 105 s–1. Such high rates are otherwise only known for special enzymes and are clearly attributed to the confinement of the studied reactions within the one-dimensional nanochannels of the CNN membrane. Namely, a concave surface maintains the internal electric field induced by the polar surface of the carbon nitride inside the nanotube, which is essential for polarization of reagent molecules and extension of the lifetime of the photogenerated charge carriers. The enhanced flow rate upon confinement provides crucial insight on catalysis in such an environment from a physical chemistry perspective. This confinement strategy is envisioned not only to realize highly efficient reactions but also to gain a fundamental understanding of complex chemical processes.

Highlights

Bioinspired nanoconfined catalysis has developed to become an important tool for improving the performance of a wide range of chemical reactions
We demonstrated that the flow-through carbon nitride nanotube (CNN) membrane with 1D nanochannels can be employed as a photocatalytically active nanoreactor for confined organic conversions
The membrane displayed an excellent performance in methylene blue (MB) degradation with a rate of 2308 ± 145 molecules s−1 in a single carbon nitride nanotube

Summary

Introduction

Bioinspired nanoconfined catalysis has developed to become an important tool for improving the performance of a wide range of chemical reactions. Nanoconfined catalysis has emerged as a viable strategy for achieving challenging chemical transformations.[1] It offers means to isolate both catalytic sites and reactant molecules in nanosized cavities, where catalytic reactions behave significantly different from those observed in bulk systems.[2] Previous studies reveal that a confined environment induces a change in energetics and kinetics of catalytic reactions by imposing specific orientations and conformations on reactant molecules.[3] Confinement effects give rise to higher activity, improved selectivity, catalyst stabilization, and better catalyst recovery and recyclability.[4] These advantages are envisioned to be applicable to all types of catalytic transformations, with the final goal of overcoming some of the drawbacks in conventional catalytic systems. Despite tremendous advances in semiconductor photocatalysis related to synthesis of valueadded organic compounds,[22−27] a major challenge in this area is to develop catalytic tools that are recovered and reused so as to be compatible with setups for larger scale production

Methods

Discussion

Conclusion