Enhanced catalytic performance of Cu/Cu2O nanoparticles via introduction of graphene as support for reduction of nitrophenols and ring opening of epoxides with amines established by experimental and theoretical investigations

doi:10.1016/j.jcat.2019.11.012

Journal of Catalysis

Volume 381, January 2020, Pages 329-346

https://doi.org/10.1016/j.jcat.2019.11.012 Get rights and content

Highlights

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Constructive modification of Cu/Cu₂O by introducing graphene as solid support.
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Proficient catalysts for reduction of nitrophenols and ring opening of epoxides.
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Enhanced surface area and interfacial charge transfer resulted in high efficacy.
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Increase in the graphene content significantly augmented reaction rate.
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Validation of experimental findings by computational studies.

Abstract

A comprehensive investigation was performed to enhance the catalytic performance of Cu/Cu₂O nanoparticles via introduction of graphene as a beneficial support for two organic transformations viz. reduction of nitrophenols to aminophenols and ring opening of epoxides with amines. Cu/Cu₂O@Graphene nanostructures bestowed significant catalytic features owing to the increased accessibility of catalytically active surface sites and the augmented efficacy with increase in graphene content was validated by enhanced specific surface area. The reaction routes were traced by performing computations within DFT formalism. Cu/Cu₂O nanocatalyst guided the reactions through a barrierless transition state and the enhanced efficacy of nanoparticles supported on graphene was demonstrated by their favorable adsorption on nanosurface with interfacial charge transfer between the two. Interestingly, the catalytic reactions provide significant contribution to environmental sustainability with the view of conversion of recalcitrant pollutants to useful compounds. The present study outlines the versatile potential of graphene based nanostructures in catalytic reactions.

Graphical abstract

Introduction

Metal based nanoparticles including metals, metal oxides and metal/metal oxide have carved a niche as important functional nanomaterials in modern material science owing to their wide range of potential in various fields including catalysis [1], medicine [2], sensing [3], energy conversion and storage applications [4]. The diverse applicability of these materials is because of their natural abundance, ease of synthesis, low cost and excellent stability [5]. The metal based nanoparticles have been extensively employed as catalysts due to availability of active metal centers, large surface area and high reactivity. The employment of metal based nanoparticles as catalysts in organic transformations has emerged as vital region of research [6], [7], [8], [9], [10], [11].

Metal based nanoparticles offer innumerable advantages which make them proficient and high performance catalysts in organic transformations. However, their low stability owing to high surface energy and tendency to aggregate result in the decrease in the exposure of active sites, thereby diminishing the catalytic behavior [12]. One of the effective methodologies for preventing the aggregation is the immobilization of metal based nanoparticles on solid supports exhibiting large surface area, high mechanical strength and astonishing electrical conductivity. The supported metal based nanoparticles acquire uniform dispersion and stability and also achieve enhanced physicochemical properties. Amongst various solid supports available, the use of carbonaceous materials such as graphene and derivatives [13], [14], [15], [16], carbon nanotubes (CNT’s) [17], [18], [19], [20] and cellulose [21], [22], [23], [24] have attracted considerable attention for augmenting the catalytic performance of metal based nanoparticles in various organic transformations.

Graphene and its derivatives as supports for anchoring metal based nanoparticles have become the limelight of research because of excellent properties like high surface area, stability, extraordinary electrical conductivity, tunable surface properties, inertness and low cost of manufacturing [25]. Furthermore, there exists a great possibility of significant synergistic interactions between metal based nanoparticles and graphene which can greatly enhance the catalytic activity of metal based nanoparticles in organic reactions. Huang et al. [13] explored the catalytic performance of Mn₃O₄/RGO composites for the reduction of nitrophenols. The significant enhancement in the catalytic behavior of Mn₃O₄ by the introduction of RGO was observed owing to the synergistic bonding between Mn₃O₄ and RGO. The anchoring of Mn₃O₄ on RGO prevented the agglomeration of Mn₃O₄ nanoparticles and increased the accessibility of active sites. Adyani and Soleimani [14] fabricated Ag/Fe₃O₄/RGO nanocomposites and employed them as proficient catalysts for the reduction of organic pollutants (4-nitrophenol, methylene blue, methyl green, methyl orange) in the presence of NaBH₄. The catalytic outcomes unveiled astonishing efficacy of the nanocomposites attributed to the synergistic effect and high surface area.

Keeping in view the enhancement in the catalytic behavior of metal based nanoparticles via introduction of graphene support, the present study employed graphene supported Cu/Cu₂O nanoparticles as versatile catalysts in organic transformations. Cu/Cu₂O@Graphene nanostructures were fabricated via liquid phase dispersion method using graphene oxide (GO) as precursor for graphene support. To the best of our knowledge, it is for the first time that experimentally observed proficient catalytic performance of Cu/Cu₂O@Graphene nanostructures for reduction of nitrophenols to aminophenols has been fully corroborated by computational calculations. Furthermore, the substrate scope of Cu/Cu₂O@Graphene nanostructures has been explored experimentally and theoretically for the first time for the conversion of epoxides to β-aminoalcohols by ring opening with amines. The investigation has also been performed to evaluate the influence of varying amount of GO on the catalytic behavior of nanostructures. Reduction of nitrophenols is a significant organic transformation reaction as nitrophenols are the major water pollutants that are accumulated in water sources through industrial and agricultural wastes. Nitrophenols are highly toxic, carcinogenic and mutagenic in nature and are listed as priority pollutants by U.S. environmental protection agency [26]. Whereas, aminophenols produced are very less toxic and can be easily removed and mineralized in comparison with nitrophenols [27], [28]. Furthermore, aminophenols are important industrial compounds used as intermediates for the production of analgesic and antipyretic drugs [29]. Aminophenols are also employed as corrosion inhibitors in paints, anti-corrosion lubricating agents in fuels, photographic developers and dyeing agents. On the other hand, epoxides belong to one of the major classes of pollutants that adversely affect ecosystem and thus need to be removed from the environment [30]. Also, the ring opening of epoxides with amines is beneficial because the obtained product i.e. β-aminoalcohols have extensive applicability as chiral ligands in asymmetric synthesis and medicinal chemistry. The mechanistic pathways for both the reactions and the catalytic behavior of Cu/Cu₂O@Graphene nanostructures have been theoretically investigated by density functional theory (DFT) calculations.

Section snippets

Synthesis of Cu/Cu₂O@Graphene nanostructures

Firstly, GO was synthesized by modified Hummer’s method using graphite flakes [31]. Then, Cu/Cu₂O@Graphene nanostructures were fabricated by liquid phase dispersion method. The reaction procedure involved the dispersion of GO in distilled water ultrasonically followed by addition of 8 mmol NaOH solution. Further, 4 mmol CuSO₄·5H₂O was added and the mixture was ultrasonically treated for 5 min that resulted in the formation of Cu(OH)₂ precipitates. L-ascorbic acid (4 mmol) was then added and the

Powder X-ray diffraction (XRD) studies

The evaluation of the structural characteristics of the fabricated nanocatalysts was performed by powder XRD studies. The XRD patterns of GO, Cu/Cu₂O and Cu/Cu₂O@Graphene nanostructures are shown in Fig. 1(a). GO indicated characteristic diffraction peak at approximately 10° indicating complete oxidation of graphite flasks [38]. The XRD patterns of Cu/Cu₂O revealed all the characteristic peaks corresponding to cubic phased Cu₂O (JCPDS Card No. 34-1354) [39] and fcc metallic Cu (JCPDS Card No.

Conclusion

In the present work, Cu/Cu₂O@Graphene nanostructures were employed as versatile and high performance catalysts for organic transformations. The catalytic studies demonstrated enrichment in the efficacy of Cu/Cu₂O nanoparticles with the introduction of graphene as a beneficial support for the reduction of nitrophenols and ring opening of epoxides with amines. Furthermore, the catalytic activity was observed to increase with increase in amount of GO. The reduction of 4-nitrophenol was completed

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The authors express their deep gratitude to Council of Scientific & Industrial Research (CSIR), India (grant numbers 01(02833)/15/EMR-II, 09/135(0721)/2015-EMR-I) and Department of Science & Technology (DST), India (Technology Missions Division), (grant number TPN 24831 for financial support. The authors are also thankful to SAIF, Panjab University for the instrumentation facilities required for characterization.

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Enhanced catalytic performance of Cu/Cu2O nanoparticles via introduction of graphene as support for reduction of nitrophenols and ring opening of epoxides with amines established by experimental and theoretical investigations

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Synthesis of Cu/Cu2O@Graphene nanostructures

Powder X-ray diffraction (XRD) studies

Conclusion

Declaration of Competing Interest

Acknowledgements

Adv. Powder Technol.

Electrochim. Acta.

Prog. Org. Coat.

Tetrahedron Lett.

Compos. Part B

Catal. Commun.

Appl. Surf. Sci.

J. Taiwan Inst. Chem. Eng.

Int. J. Hydr. Energy

Mater. Chem. Phys.

Org. Lett.

J. Environ. Chem. Eng.

Catal. Commun.

Int. J. Hydrog. Energy.

Appl. Catal., B.

J. Colloid Interface Sci.

Appl. Catal., A.

J. Ind. Eng. Chem.

J. Ind. Eng. Chem.

Ultrason. Sonochem.

Mater. Lett.

Appl. Catal. A

Appl. Catal. A

Electrochim. Acta

Chem. Eng. J.

Mater. Chem. Phys.

Silver nanoparticles: synthesis methods, bio-applications and properties

Crit. Rev. Microbiol.

Recent advances in metal oxide-based electrode architecture design for electrochemical energy storage

Adv. Mater.

Enhanced catalytic performance of Cu/Cu₂O nanoparticles via introduction of graphene as support for reduction of nitrophenols and ring opening of epoxides with amines established by experimental and theoretical investigations

Synthesis of Cu/Cu₂O@Graphene nanostructures