Green synthesis of ultrathin 2D nanoplatelets, hematene and magnetene, from mineral ores in water, with strong optical limiting performance

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Abstract

Hematene and magnetene nanoplatelets have been produced by liquid phase exfoliation of natural mineral ores, in a water solution of melamine under mild sonication.

Abstract

Following the long-standing use of the liquid exfoliation of graphite for the production of graphene, a number of analogous van der Waals 2D nanomaterials have been also produced and studied extensively for several applications. Recently, liquid exfoliation has also been applied to isolate non-van der Waals 2D nanostructures. Here, we describe a green procedure for the liquid exfoliation of natural hematite and magnetite – natural iron ores – obtained from the Greek territory. Natural iron ores were exfoliated in a solution of melamine in water under mild sonication. The ultrathin exfoliated nanoplatelets, hematene and magnetene, respectively, form stable dispersions in pure water and have been extensively characterized by spectroscopic and microscopic techniques. Optical limiting experiments reveal the efficiency of the present non-van der Waals 2D nanomaterials, rendering them highly attractive for several applications in opto-electronics and photonics.

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High-yield production of graphene by liquid-phase exfoliation of graphite.

Yenny Hernandez, Valeria Nicolosi, Mustafa Lotya … (2008)

Fully exploiting the properties of graphene will require a method for the mass production of this remarkable material. Two main routes are possible: large-scale growth or large-scale exfoliation. Here, we demonstrate graphene dispersions with concentrations up to approximately 0.01 mg ml(-1), produced by dispersion and exfoliation of graphite in organic solvents such as N-methyl-pyrrolidone. This is possible because the energy required to exfoliate graphene is balanced by the solvent-graphene interaction for solvents whose surface energies match that of graphene. We confirm the presence of individual graphene sheets by Raman spectroscopy, transmission electron microscopy and electron diffraction. Our method results in a monolayer yield of approximately 1 wt%, which could potentially be improved to 7-12 wt% with further processing. The absence of defects or oxides is confirmed by X-ray photoelectron, infrared and Raman spectroscopies. We are able to produce semi-transparent conducting films and conducting composites. Solution processing of graphene opens up a range of potential large-area applications, from device and sensor fabrication to liquid-phase chemistry.

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Graphene via sonication assisted liquid-phase exfoliation.

Artur Ciesielski, Paolo Samorì (2014)

Graphene, the 2D form of carbon based material existing as a single layer of atoms arranged in a honeycomb lattice, has set the science and technology sectors alight with interest in the last decade in view of its astounding electrical and thermal properties, combined with its mechanical stiffness, strength and elasticity. Two distinct strategies have been undertaken for graphene production, i.e. the bottom-up and the top-down. The former relies on the generation of graphene from suitably designed molecular building blocks undergoing chemical reaction to form covalently linked 2D networks. The latter occurs via exfoliation of graphite into graphene. Bottom-up techniques, based on the organic syntheses starting from small molecular modules, when performed in liquid media, are both size limited, because macromolecules become more and more insoluble with increasing size, and suffer from the occurrence of side reactions with increasing molecular weight. Because of these reasons such a synthesis has been performed more and more on a solid (ideally catalytically active) surface. Substrate-based growth of single layers can be done also by chemical vapor deposition (CVD) or via reduction of silicon carbide, which unfortunately relies on the ability to follow a narrow thermodynamic path. Top-down approaches can be accomplished under different environmental conditions. Alongside the mechanical cleavage based on the scotch tape approach, liquid-phase exfoliation (LPE) methods are becoming more and more interesting because they are extremely versatile, potentially up-scalable, and can be used to deposit graphene in a variety of environments and on different substrates not available using mechanical cleavage or growth methods. Interestingly, LPE can be applied to produce different layered systems exhibiting different compositions such as BN, MoS2, WS2, NbSe2, and TaS2, thereby enabling the tuning of numerous physico-chemical properties of the material. Furthermore, LPE can be employed to produce graphene-based composites or films, which are key components for many applications, such as thin-film transistors, conductive transparent electrodes for indium tin oxide replacement, e.g. in light-emitting diodes, or photovoltaics. In this review, we highlight the recent progress that has led to successful production of high quality graphene by means of LPE of graphite. In particular, we discuss the mechanisms of exfoliation and methods that are employed for graphene characterization. We then describe a variety of successful liquid-phase exfoliation methods by categorizing them into two major classes, i.e. surfactant-free and surfactant-assisted LPE. Furthermore, exfoliation in aqueous and organic solutions is presented and discussed separately.