An improved Hummers method for eco-friendly synthesis of graphene oxide
TL;DR: In this paper, an improved Hummers method without using NaNO3 can produce graphene oxide nearly the same to that prepared by conventional Hummers methods, which does not decrease the yield of product and simplifies the disposal of waste water because of the inexistence of Na+ and NO3− ions.
About: This article is published in Carbon.The article was published on 2013-11-01. It has received 1683 citations till now.
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TL;DR: In this paper, the influence of different solvents on the structure and electrical properties of graphene oxide was studied by using modified hummers method in which different from conventional hummer's method.
886 citations
01 Apr 2019
TL;DR: The electrochemical reduction of nitrogen is being intensely investigated as the basis for future ammonia production from renewable energy sources as mentioned in this paper, and the issue of catalyst selectivity and the approaches to promote the electrochemical nitrogen reduction reaction (NRR) over H2 production are discussed.
Abstract: Ammonia is a widely produced chemical that is the basis of most fertilisers. However, it is currently derived from fossil fuels and there is an urgent need to develop sustainable approaches to its production. Ammonia is also being considered as a renewable energy carrier, allowing efficient storage and transportation of renewables. For these reasons, the electrochemical nitrogen reduction reaction (NRR) is currently being intensely investigated as the basis for future mass production of ammonia from renewables. This Perspective critiques current steps and miss-steps towards this important goal in terms of experimental methodology and catalyst selection, proposing a protocol for rigorous experimentation. We discuss the issue of catalyst selectivity and the approaches to promoting the NRR over H2 production. Finally, we translate these mechanistic discussions, and the key metrics being pursued in the field, into the bigger picture of ammonia production by other sustainable processes, discussing benchmarks by which NRR progress can be assessed. The electrochemical reduction of nitrogen is being intensely investigated as the basis for future ammonia production. This Perspective critiques current steps and missteps towards this goal in terms of experimental methodology and catalyst selection, proposing a protocol for rigorous experimentation.
843 citations
TL;DR: Through reviewing the significant advances on this topic, it may provide new opportunities for designing highly efficient 2D graphene-based photocatalysts for various applications in photocatalysis and other fields, such as solar cells, thermal catalysis, separation, and purification.
Abstract: In recent years, heterogeneous photocatalysis has received much research interest because of its powerful potential applications in tackling many important energy and environmental challenges at a global level in an economically sustainable manner. Due to their unique optical, electrical, and physicochemical properties, various 2D graphene nanosheets-supported semiconductor composite photocatalysts have been widely constructed and applied in different photocatalytic fields. In this review, fundamental mechanisms of heterogeneous photocatalysis, including thermodynamic and kinetics requirements, are first systematically summarized. Then, the photocatalysis-related properties of graphene and its derivatives, and design rules and synthesis methods of graphene-based composites are highlighted. Importantly, different design strategies, including doping and sensitization of semiconductors by graphene, improving electrical conductivity of graphene, increasing eloectrocatalytic active sites on graphene, strengthening interface coupling between semiconductors and graphene, fabricating micro/nano architectures, constructing multi-junction nanocomposites, enhancing photostability of semiconductors, and utilizing the synergistic effect of various modification strategies, are thoroughly summarized. The important applications including photocatalytic pollutant degradation, H2 production, and CO2 reduction are also addressed. Through reviewing the significant advances on this topic, it may provide new opportunities for designing highly efficient 2D graphene-based photocatalysts for various applications in photocatalysis and other fields, such as solar cells, thermal catalysis, separation, and purification.
766 citations
10 Jan 2017
TL;DR: In this article, a modified Hummers method was used to synthesize reduced graphite oxide (rGO), which was then used as a precursor for graphene synthesis by thermal reduction processes.
Abstract: Over the span of years, improvements over various synthesis methods of graphene are constantly pursued to provide safer and more effective alternatives. Though the extraction of graphene through Hummers method is one of the oldest techniques yet it is one of the most suitable methods for the formation of bulk graphene. Graphene can be obtained in the form of reduced Graphite oxide, sometimes also referred as Graphene oxide. The effectiveness of this oxidation process can be evaluated by the magnitude of carbon/oxygen ratio of the obtained graphene. Here, graphene oxide (GO) was prepared by oxidizing the purified natural flake graphite (NFG) by a modified Hummers method. The attempts have been made to synthesize GO having few layers by using a modified Hummers method where the amount of NaNO3 has been decreased, and the amount of KMnO4 is increased. The reaction has been performed in a 9:1 (by volume) mixture of H2SO4/H3PO4. This modification is successful in increasing the reaction yield and reducing the toxic gas evolution while using a varied proportion of KMnO4 and H2SO4 as those required by Hummers method. A new component of K2S2O8 has been introduced to the reaction system to maintain the pH value. Reduced graphene oxide (rGO) was thereafter extracted by thermal modification of GO. Here, GO has been used as a precursor for graphene synthesis by thermal reduction processes. The results of FTIR and Raman spectroscopy analysis show that the NFG when oxidized by strong oxidants like KMnO4 and NaNO3, introduced oxygen atoms into the graphite layers and formed bonds like C=O, C-H, COOH and C-O-C with the carbon atoms in the graphite layers. The structure and morphology of both GO and rGO were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy, Raman spectroscopy, Brunauer-Emmett-Teller (BET) surface area analysis and differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).
665 citations
Cites background from "An improved Hummers method for eco-..."
...95 ̊ disappeared indicate the efficient exfoliation of the multiple layers during the thermal reduction of GO [22] [23] [24]....
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TL;DR: An improved NaNO3-free Hummers method is reported by partly replacing KMnO4 with K2FeO4 and controlling the amount of concentrated sulfuric acid, which greatly reduces the reactant consumption while keeps a high yield.
Abstract: As an important precursor and derivate of graphene, graphene oxide (GO) has received wide attention in recent years. However, the synthesis of GO in an economical and efficient way remains a great challenge. Here we reported an improved NaNO3-free Hummers method by partly replacing KMnO4 with K2FeO4 and controlling the amount of concentrated sulfuric acid. As compared to the existing NaNO3-free Hummers methods, this improved routine greatly reduces the reactant consumption while keeps a high yield. The obtained GO was characterized by various techniques, and its derived graphene aerogel was demonstrated as high-performance supercapacitor electrodes. This improved synthesis shows good prospects for scalable production and applications of GO and its derivatives.
510 citations
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26,456 citations
TL;DR: This review will be of value to synthetic chemists interested in this emerging field of materials science, as well as those investigating applications of graphene who would find a more thorough treatment of the chemistry of graphene oxide useful in understanding the scope and limitations of current approaches which utilize this material.
Abstract: The chemistry of graphene oxide is discussed in this critical review Particular emphasis is directed toward the synthesis of graphene oxide, as well as its structure Graphene oxide as a substrate for a variety of chemical transformations, including its reduction to graphene-like materials, is also discussed This review will be of value to synthetic chemists interested in this emerging field of materials science, as well as those investigating applications of graphene who would find a more thorough treatment of the chemistry of graphene oxide useful in understanding the scope and limitations of current approaches which utilize this material (91 references)
10,126 citations
"An improved Hummers method for eco-..." refers background in this paper
...On the other hand, KMnO4 is one of the strongest oxidants, especially in acidic media [22]....
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...[22] Dreyer DR, Park S, Bielawski CW, Ruoff RS....
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TL;DR: An improved method for the preparation of graphene oxide (GO) is described, finding that excluding the NaNO(3), increasing the amount of KMnO(4), and performing the reaction in a 9:1 mixture of H(2)SO(4)/H(3)PO(4) improves the efficiency of the oxidation process.
Abstract: An improved method for the preparation of graphene oxide (GO) is described. Currently, Hummers’ method (KMnO4, NaNO3, H2SO4) is the most common method used for preparing graphene oxide. We have found that excluding the NaNO3, increasing the amount of KMnO4, and performing the reaction in a 9:1 mixture of H2SO4/H3PO4 improves the efficiency of the oxidation process. This improved method provides a greater amount of hydrophilic oxidized graphene material as compared to Hummers’ method or Hummers’ method with additional KMnO4. Moreover, even though the GO produced by our method is more oxidized than that prepared by Hummers’ method, when both are reduced in the same chamber with hydrazine, chemically converted graphene (CCG) produced from this new method is equivalent in its electrical conductivity. In contrast to Hummers’ method, the new method does not generate toxic gas and the temperature is easily controlled. This improved synthesis of GO may be important for large-scale production of GO as well as the ...
9,812 citations
"An improved Hummers method for eco-..." refers background or methods or result in this paper
...Either GO1 or GO2 has a medium oxidation degree compared with those of less [15] and highly oxidized counterparts [20]....
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...2e and S2e) show the following characteristic functional groups of GO [20,28]: C O C ( 1000 cm ), C O (1230 cm ), C@C ( 1620 cm ) and C@O (1740–1720 cm ) bonds....
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...Tour and co-workers improved the Hummers method by excluding NaNO3, increasing the amount of KMnO4, and performing the reaction in a 9:1 (by volume) mixture of H2SO4/H3PO4 [20]....
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...It should be noted here that the oxidation degrees of GO products vary with their synthesis conditions [11,15,20]....
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...[20] Marcano DC, Kosynkin DV, Berlin JM, Sinitskii A, Sun Z, Slesarev A, et al....
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TL;DR: An overview of the synthesis, properties, and applications of graphene and related materials (primarily, graphite oxide and its colloidal suspensions and materials made from them), from a materials science perspective.
Abstract: There is intense interest in graphene in fields such as physics, chemistry, and materials science, among others. Interest in graphene's exceptional physical properties, chemical tunability, and potential for applications has generated thousands of publications and an accelerating pace of research, making review of such research timely. Here is an overview of the synthesis, properties, and applications of graphene and related materials (primarily, graphite oxide and its colloidal suspensions and materials made from them), from a materials science perspective.
8,919 citations
"An improved Hummers method for eco-..." refers background in this paper
...[10] Zhu Y, Murali S, Cai W, Li X, Suk JW, Potts JR, et al....
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...GO is the precursor of rGO; thus, it plays a crucial role in controlling the structure, property and the application potential of rGO [10 16]....
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TL;DR: It is reported that chemically converted graphene sheets obtained from graphite can readily form stable aqueous colloids through electrostatic stabilization, making it possible to process graphene materials using low-cost solution processing techniques, opening up enormous opportunities to use this unique carbon nanostructure for many technological applications.
Abstract: Graphene sheets offer extraordinary electronic, thermal and mechanical properties and are expected to find a variety of applications. A prerequisite for exploiting most proposed applications for graphene is the availability of processable graphene sheets in large quantities. The direct dispersion of hydrophobic graphite or graphene sheets in water without the assistance of dispersing agents has generally been considered to be an insurmountable challenge. Here we report that chemically converted graphene sheets obtained from graphite can readily form stable aqueous colloids through electrostatic stabilization. This discovery has enabled us to develop a facile approach to large-scale production of aqueous graphene dispersions without the need for polymeric or surfactant stabilizers. Our findings make it possible to process graphene materials using low-cost solution processing techniques, opening up enormous opportunities to use this unique carbon nanostructure for many technological applications.
8,534 citations
"An improved Hummers method for eco-..." refers background in this paper
...Although GO1 has a slightly higher zeta potential than that of GO2, its value is still lower than 30 mV, providing it with a good dispersibility in aqueous media [25]....
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...[25] Li D, Mueller MB, Gilje S, Kaner RB, Wallace GG....
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