Magnetically-actuated mesoporous nanowires for enhanced heterogeneous catalysis

Abstract

We study the optimization of the catalytic properties of entirely magnetic CoPt compact and mesoporous nanowires of different diameters (25 - 200 nm). The nanowires are a single-entity magnetic-catalyst with a huge catalytically-active surface area, making them robust and easy to fabricate. We show that apart from the size and morphology of the nanowires, other factors can be optimized to enhance the catalytic activity of the nanowires. In particular, given the magnetic character of the nanowires, rotating magnetic fields are a very powerful approach to improve the performance of the catalyst by acting as nano-stirrers, improving the local flow of material towards the active sites of the catalyst. We demonstrate the versatility of the procedure by optimizing (i) the degradation of different types of pollutants (4-nitrophenol and methylene blue) and (ii) hydrogen production. For example, by using 25 nm wide CoPt mesoporous nanowires as catalysts, kinetic normalized constants knor as high as 20667 and 21750 s-1g-1 for 4-nitrophenol and methylene blue reduction, respectively, are obtained, and activity values for hydrogen production from borohydride are as high as 25.0 L H2 g-1 min-1, even at room temperature. These values outperform any current state-of-the-art proposed catalysis strategies for water remediation reactions by at least 10-times and are superior to most advanced approaches to generate hydrogen from borohydride. The recyclability of the nanowires together with the simplicity of the synthetic method makes this approach (using not only CoPt but also other mesoporous magnetic catalysts) very appealing for very diverse types of catalytic applications.