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) by using magnetic actuation. The nanowires are a single-entity, robust, magnetic-catalyst with a huge catalytically-active surface area.We show that apart from conventional parameters, like the size and morphology of the nanowires, other 2 factors can be optimized to enhance their catalytic activity. In particular, given the magnetic character of the nanowires, rotating magnetic fields are a very powerful approach to boost the performance of the catalyst. In particular, the magnetic field induces them to act 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 as little as 0.1 mg mL -1 of 25 nm wide CoPt mesoporous nanowires (with 3 nm pore size) as catalysts, kinetic normalized constants knor as high as 20667 and 21750 s -1 g -1 for 4-nitrophenol and methylene blue reduction, respectively, are obtained. In addition, 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. Graphical AbstractHighlights  Magnetic actuation of purely magnetic mesoporous nanowires (NWs) is revealed as a novel and efficient catalysis procedure in reactions of heterogeneous catalysis in environmental and energy fields. Mesoporous CoPt NWs are simultaneously effective catalysts itself and the stirring device, using magnetic fields, to catalyse reactions in solution. The procedure allows ultra-fast degradation of different types of pollutants. 3 The NWs show very high effectivity for hydrogen generation (25.0 L H2 g -1 min -1 ) by catalysing the hydrolysis of sodium borohydride using magnetic actuation.

Role of Nanomaterials in the Treatment of Wastewater: A Review

“…The most intensively studied state is heterogeneous nanophotocatalysis in modern era, due to its wide scope in water decontamination and environmental related applications. In case of heterogeneous photocatalysis, it implies the prior development of an interface between fluid (both reactants and products of reaction) and solid photocatalyst (such as metal or semiconductor) [59,60]. Generally, the word "heterogeneous photocatalysis" is mostly employed where a light-based semiconductor photocatalysts are used, which is in interaction with gaseous or liquid phase [61].…”

Microemulsion-Based One-Step Electrochemical Fabrication of Mesoporous Catalysts

“…The combination of soft-and hard-templating approaches, also known as multiple-templating strategy, is a powerful tool for the creation of complex and hierarchical porous materials, with different properties and enhanced capability and competitiveness for several applications, being particularly useful in heterogeneous catalysis [1,5,[21][22][23]41,42]. The multi-templating approach can be adopted for two different reasons: (i) for the generation of multiple porosity, i.e., to obtain porous materials with various well-defined porous shapes or sizes; or (ii) for the fabrication of porous materials with a desired shape (e.g., mesoporous nanowires or nanorods synthesized using a hard-template as a shape director and a soft-template as a porogen agent).…”

“…The multi-templating approach can be adopted for two different reasons: (i) for the generation of multiple porosity, i.e., to obtain porous materials with various well-defined porous shapes or sizes; or (ii) for the fabrication of porous materials with a desired shape (e.g., mesoporous nanowires or nanorods synthesized using a hard-template as a shape director and a soft-template as a porogen agent). Therefore, the main advantage is the possibility to obtain complex or hierarchical porous materials, but this approach also has limitations: for example, it requires multiple templates, and the multistep procedures is time consuming [1,5,[21][22][23]41,42].…”

“…However, from an electrochemical point of view, classical microemulsions are not realistic or competitive electrochemical media due to their high ohmic resistance, which is introduced by the oil and surfactant components. In this regard, the substitution of oil dielectric component with an ionic liquid allows the main limitation of this approach to be overcome for the shape-controlled electrodeposition of nanostructured materials and for the electrosynthesis of well-defined porous nanostructures (Figure 7) [21][22][23]68,69].…”

“…For instance, highly mesoporous Co 3 O 4 nanoflakes synthesized applying a microwave-assisted hydrothermal and low-temperature conversion method produced excellent electrochemical performance as an anode in lithium batteries and as an electrocatalyst in the oxygen evolution reaction (OER) [19]. Mesoporous Rh nanoparticles (NPs) fabricated by conducting chemical reduction on polymeric micelles resulted in an improved catalytic performance for the electro-oxidation of methanol [20], and mesoporous Pt-based nanowires (NWs), which were prepared by means of electrodeposition with enhanced catalytic performance for water decontamination [21][22][23] demonstrate the potential of mesoporous materials. Nanostructured materials, especially inorganic, are expected to, therefore, play an important role in fabricating competitive mesoporous catalysts.…”