Noble metals supported on substrates have been proven as highly efficient catalysts for the reduction of nitrocompounds. However, their large-scale applications are still limited by the problems of fouling and transport during the mass production process. Herein, we first fabricated a spherical montmorillonite (Mt) substrate via spray drying technique, followed by the deposition of Au NPs through polydopamine chemistry to synthesize spherical Au nanoparticles supported Mt (Au@Mt) microspheres. The Au loading is 14.5 wt%, whereas the specific surface area of the Au@Mt microspheres is 47.3 m 2 g −1 , endowing the prepared Au@Mt microspheres with excellent catalytic activity to the reduction of 4-nitrophenol (4-NP) in the presence of NaBH 4 with the optimized apparent reduction rate constant higher than 1.05 min −1. Furthermore, the microspheres can be easily recycled with self-sedimentation without any devices involved and showed excellent stability and recyclability for at least 20 cycles without almost unchanged spherical morphology and catalytic performance. Our straightforward strategy to solve the issue of the mass production process through granulation of amorphous nanomaterial substrate facilitates the practical application of these catalysts in the reduction of nitro-compounds.

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The weak conductivity of covalent organic frameworks (COFs) limits their wide application in electrochemical sensors. Here, a novel electrochemical sensor (AuNFs/COF-SH/CNTs/GCE) was designed and constructed by a one-step electrochemical deposition of Au nanoflowers (AuNFs) on a hybrid nanocomposite of sulfhydryl-functional covalent organic framework/carbon nanotubes (COF-SH/CNTs) for the determination of Cu(II) in seawater. AuNFs/COF-SH/CNTs/GCE was prepared in a three-step method including in situ synthesis, post-synthesis, and one-step electrochemical deposition. The adsorption and catalytic performances of the modified electrode were improved based on the mechanism of “adsorption-catalysis stripping determination”. By combining the excellent catalytic properties of the AuNFs with the good adsorption capacity of COF-SH toward Cu(II), as well as the good conductivity of CNTs, the AuNFs/COF-SH/CNTs/GCE exhibited excellent performance for the determination of Cu(II). Through optimization of the experimental conditions, a low detection limit of 0.47 nM and a wide linear range of 1.6 nM-4.7 μM were obtained. Moreover, the sensor possessed good stability with a relative standard deviation of less than 5% after 20 repeated measurements. The results are consistent with certified values when used for the determination of certified reference materials. In summary, the AuNFs/COF-SH/CNTs/GCE, with high stability and sensitivity, has been successfully applied for the determination of Cu(II) in seawater samples with satisfactory results.