Novel covalent organic nanosheets for the construction of ultrafine and well-dispersed metal nanoparticles

Abstract

The development of supported and well-dispersed ultrafine metal nanoparticles (U-MNPs) with high metal content is a research priority, yet remains a significant challenge. Herein, we propose an effective strategy involving functional covalent organic nanosheets (CONs) to construct well-dispersed U-MNPs. To construct the corresponding CON–DAI–TFP, 4,7-diamino-1H-indazole (DAI) and 1,3,5-triformylphloroglucinol (TFP) are strategically chosen as precursors. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM) clearly confirm the nanosheet structure of CON–DAI–TFP. CON–DAI–TFP is used as a substrate to immobilize Pd nanoparticles (Pd-NPs). The supported Pd-NPs are ultrafine, highly dispersed, and possess high metal content (average size, 1.74 nm; metal content, 20.47 wt%), which is superior to many of the reported supported Pd-NPs. Moreover, the supported Pd-NPs show excellent catalytic activity and recyclability in a p-nitrophenol reduction reaction. In addition to Pd-NPs, this strategy can be applied to produce other U-MNPs with similar features, including Ir-NPs and Pt-NPs (1.99 nm and 17.18 wt% for Ir-NPs, 2.25 nm and 29.46 wt% for Pt-NPs), suggesting that this strategy is universal. For comparison, a bulk COF (COF–DAI–TFB), the analogue of CON–DAI–TFP, is designed and synthesized. In contrast, many large Pd-NPs with an average size of 17.86 nm, which is more than 10 times the size of Pd-NPs on CON–DAI–TFP, are observed on the surface of the COF–DAI–TFB. This result further confirms the significance of CONs in the preparation of well-dispersed and high-loading U-MNPs.