Preparation of magnetically recyclable CuFe2O4/RGO for catalytic hydrolysis of sodium borohydride
Introduction
Recently, the excessive exploitation of fossil fuels and the ever growing demand for energy have greatly inspired the seeking for new clean energies [1], [2], [3]. Due to the ideal characteristics of combustion efficiency, high energy density, and non-toxic harmless, hydrogen gas has become one of the most attractive energy in many energy carriers [4], [5]. In addition, as we all known, hydrogen is usually stored in the form of inorganic hydride and hydrocarbon compounds in nature, so electrolyzing of water, ethanol steam, hydrolyzing of boron hydride to produce hydrogen gas and so on has become commonly used methods [6], [7], [8]. In all kinds of hydrogen storage materials, sodium borohydride (NaBH4) and ammonia borane are considered as ideal hydrogen storage materials due to their highly favorable hydrogen storage, extensive source and suitable hydrogen production rate at low temperature. Therefore, hydrolytic dehydrogenation of NaBH4 is considered to be the most convenient approach for H2 production. However, though the reaction of NaBH4 hydrolysis is spontaneous, the rate is quite slow, so choosing appropriate catalysts to speed up the reaction is considered crucial and attractive. In recent years, lots of potential catalysts have been reported in the literature, such as Pt, Ru, Co and metallic alloy nanoparticles [9], [10], [11], [12], [13].
Non-noble Cu nanoparticles are cheap and easy fabrication compared to traditional catalysts [14], [15]. They displayed high activity in catalytically synthesizing diaryl ethers, aryl and vinyl dithiocarbamates in a satisfactory yield via Ullmann-type coupling and condensation. The catalytic performance of Cu nanoparticles depends on their size and dispersion [16], [17], [18], so using supporter or integrating with other metals has been demonstrated to be effective ways to enhance their catalytic performance [19], [20], [21]. Cu nanoparticles supported on TiO2 nanofibers were an effective photocatalyst for hydrolytic dehydrogenation of ammonia borane under solar radiation [22]. The results reveal that high rate of hydrogen was released from ammonia borane as compared with undecorated TiO2 nanofibers and pristine Cu NPs. Cu@FeCo core–shell nanoparticles containing Cu cores and FeCo shells exerted composition-dependent activities towards the catalytic hydrolysis of ammonia borane [23].
Graphene has a monolayer structure that contains carbon atoms tightly packed into two-dimensional honeycomb lattices [24]. Since it was reported in 2004 [25], graphene has attracted a great deal of attention for it potential applications in catalyst supports, nanoelectronic devices, energy, composite materials, and biological detection devices [26], [27], [28], [29], [30]. Because it has large surface area and large amounts of oxygen-containing functional group, graphene oxide (GO, oxidized graphene) has become one of the most ideal substrates to grow metal and metal oxide nanoparticles and maintain the stability of these nanoparticles during their usage [31].
Nanoparticles have large surface area and high density of surface active sites, so they usually exhibit excellent catalytic performance as catalysts. However, they also have some shortcomings, such as easy agglomeration and difficulty in removing them from the solution, which restricts their practical applications. In order to solve the problems, some approaches have been developed. Using supporter is an effective way to prevent agglomeration while magnetic modification can realize magnetically separating. Magnetically recyclable Fe3O4@C@Ag, Ag-coated Fe3O4@TiO2 and PtRu/Fe3O4/C for photocatalytic and chemical reactions have been developed [32], [33], [34]. Fe3O4@Ag nanocomposites showed outstanding catalytic activity, convenient magnetic separability, and long-term stability for the degradation of Rhodamine B and neutral red [35], [36].
In this paper, CuFe2O4/RGO nanostructures with various RGO contents were synthesized by using the hydrothermal process, and the factors that affect the shape and size of the attached CuFe2O4 nanoparticles were studied. The graphene acts as a supporter to prohibit agglomeration of CuFe2O4 nanoparticles. CuFe2O4 nanoparticle itself is magnetic and responses to external magnetic field, so it is easy to collect them by applying an external magnetic field with a magnet. At the same time, CuFe2O4 nanoparticles contain Cu element that is expected to have catalytic ability for hydrolytic dehydrogenation of NaBH4. So CuFe2O4/RGO is both magnetically separable and catalytically active. The catalytic performance of CuFe2O4/RGO for hydrolytic dehydrogenation of NaBH4 for hydrogen evolution was investigated. The hydrogen generation rate reached 622 (mL min_1 g_1), and the yields remained almost 100% after six rounds of reaction. It demonstrates that CuFe2O4/rGO nanostructures are recyclable catalysts in practical applications.
Section snippets
Materials
Graphite came from Qingdao Graphite Factory. NaNO3, KMnO4, H2O2 (30%), CuCl2.6H2O, H2SO4, polyvinylpyrrolidone (PVP), FeCl3.6H2O, ethylene glycol (EG), CH3COONa etc reagents were purchased from Tianjin Chemical Reagent Co. All the above chemicals were used as received.
Preparation of CuFe2O4/RGO nanostructures
GO was prepared by a modified Hummers method from purified natural graphite [31]. The detail procedure for synthesizing CuFe2O4/RGO nanostructures by a hydrothermal method is as follow: GO (25 mg) was ultrasonicated in a 50 mL
Results and discussion
Hydrothermal synthesis is an available way to prepare nanoparticles because it can adjust particle size, shape and architecture by adding additives or changing reaction conditions. The formation mechanism for CuFe2O4/RGO by hydrothermal method is illustrated in Fig. 1. The GO sheets have functional groups that can attract the metal ions that produce CuFe2O4 nanoparticles during hydrothermal process, and GO itself is reduced at the same time.
In order to obtain the best reaction conditions for
Conclusion
A simple hydrothermal method was developed to fabricate CuFe2O4/RGO nanostructures. Changing reactant concentration, reaction temperature and reaction time could change the morphology of the CuFe2O4 nanoparticles on CuFe2O4/RGO. Especially, GO plays an important role in tailoring both the size and shape of the CuFe2O4 nanoparticles. The as-prepared CuFe2O4/RGO exhibited good catalytic performance toward catalytic hydrolysis of NaBH4. The hydrogen generation rate reached 622 (mL min−1 g−1) or
Acknowledgment
This work was financial supported by the National Science Foundation of China (51573126).
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2021, Separation and Purification TechnologyCitation Excerpt :Crystal phase composition of CuFe2O4/ACF cathode was characterized by XRD in the scanning range of 2θ = 10–80°. As shown in Fig. 1, these peaks at 2θ = 18.22°, 30.31°, 35.51°, 43.29°, 57.51° and 62.49° were contributed to (1 1 1), (2 2 0), (3 1 1), (4 0 0), (5 1 1), and (4 4 0) planes of spinel CuFe2O4, respectively (JCPDS No. 25-0283) [28,29]. Moreover, it was observed that the (4 0 0) peak of CuFe2O4 had a higher intensity ability, indicating the oriented generation of the CuFe2O4 along the (4 0 0) direction.