Visible-Light-Induced Selective Oxidation of Amines into Imines over UiO-66-NH₂@Au@COF Core–Shell Photocatalysts

Abstract

Efficient and stable photocatalysts for selective oxidative coupling of amines to imines are crucial to the conversion of sustainable solar energy to value-added chemical energy. In this work, UiO-66-NH 2 @ Au@COF core−shell nanocomposites with intercalated Au nanoparticles between the UiO-66-NH 2 core and the covalent-organic framework (COF) shell have been demonstrated to exhibit enhanced activity and stability for visible-light-driven aerobic selective oxidation of amines to imines. With optimized Au and two-dimensional π-conjugated COF content, the obtained UiO-66-NH 2 @Au 0.5 @COF1 photocatalyst exhibited the highest conversion of benzylamine with an imine yield of 66.9% for at least five cycles. It is revealed that the introduction of appropriate Au and COF could not only broaden the visible-light absorption band but also promote the separation of photoinduced charge carriers and enhance the photocatalytic performance. Furthermore, a rational mechanism was explored to elucidate the process of photocatalytic reaction. The intercalated Au nanoparticles with the localized surface plasmon resonance (LSPR) effect act as generators of hot electrons and also transfer channels for the photo-generated electrons from the COF shell to the UiO-66-NH 2 core. Importantly, the MOF@metal@COF photocatalysts might provide a promising strategy to construct photocatalysts with desirable activity and stability under visible-light illumination.

Highly hydrophilic covalent organic frameworks as efficient and reusable photocatalysts for oxidative coupling of amines in aqueous solution

“…Based on our results and literature observations, 47–49 a proposed mechanism for the photocatalytic oxidative coupling of benzylamines is shown in Fig. 5.…”

Extended phenothiazines: synthesis, photophysical and redox properties, and efficient photocatalytic oxidative coupling of amines

“…, LED light). 48,54–56 In comparison, phenothiazine 3 as a photocatalyst for oxidative coupling of amines demonstrated several merits such as low catalyst loadings, short reaction times and mild conditions (Fig. S26†).…”

“…54 Generally, most of the reported photocatalytic oxidative couplings of amines to imines required high catalyst loading or extremely long reaction times, and were usually carried out under an articial light source (e.g., LED light). 48,[54][55][56] In comparison, phenothiazine 3 as a photocatalyst for oxidative coupling of amines demonstrated several merits such as low catalyst loadings, short reaction times and mild conditions (Fig. S26 †).…”

Efficient Near-Infrared-Activated Photocatalytic Hydrogen Evolution from Ammonia Borane with Core-Shell Upconversion-Semiconductor Hybrid Nanostructures

“…The photo-generated electrons are excited from the valence band (VB) to the conduction band (CB) of Cu 2 O, while positively charged holes are left in the VB to react with H 2 O molecules to form hydroxyl radicals. The intermediate of hydroxyl radicals is crucial in the investigation of the mechanism for the photocatalysis, and various methods were reported for the detection [92][93][94][95]. The formation of hydroxyl radicals was confirmed by the addition of 2-propanol acting as the hydroxyl radical scavenger during the photcatalytic H 2 evolution under 980 nm NIR laser irradiation.…”