Efficient and Selective Visible-Light-Driven Oxidative Coupling of Amines to Imines in Air over CdS@Zr-MOFs

Construction of porous photoactive MOF-based composite systems is regarded as one of the most effective strategies to improve light harvesting, increase the surface area, provide plenty of exposed active sites, and promote the reduction and oxidation abilities of some organic photocatalytic reactions. Herein, we synthesized porous CdS@Zr-MOF photocatalysts based on the representative photocatalyst CdS and crystalline Zr-MOFs, such as MOF-808, NU-1000, and PCN-222, to illustrate their excellent photocatalytic performance for the synthesis of imines in air. The morphology and composition of these photocatalysts were investigated by X-ray powder diffraction (XRD), inductively coupled plasma-atomic emission spectrometry (ICP-AES), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), indicating their crystallinity, high porosity, and interfacial interaction between constituents. Compared with individual components, these porous CdS@Zr-MOF composites could remarkably promote photocatalytic activity for the oxidative coupling of amines under air and visible-light conditions. The photocatalytic reaction showed broad substrate suitability. More importantly, the conversion yield reached up to 95% for the inactive aliphatic amines, and imines were formed as the single product. The improvement of the photocatalytic performance of CdS@Zr-MOF composites can be mainly ascribed to their high surface areas, more exposed active sites, excellent dispersion of CdS, and special porous photocatalytic systems, which tune the band gap, broaden the light response range, and facilitate the carrier separation.