Graphene oxide (GO) has drawn tremendous interest as a tunable precursor in numerous areas, due to its readily manipulable surface. However, its inhomogeneous and nonstoichiometric structure makes achieving chemical control a major challenge. Here, we present a room-temperature based, controlled method for the stepwise reduction of GO, with evidence of sequential removal of each organic moiety. By analyzing signature infrared absorption frequencies, we identify the carbonyl group as the first to be reduced, while the tertiary alcohol takes the longest to be completely removed from the GO surface. Controlled reduction allows for progressive tuning of the optical gap from 3.5 eV down to 1 eV, while XPS spectra show a concurrent increase in the C/O ratio. This study is the first step toward selectively enhancing the chemical homogeneity of GO, thus providing greater control over its structure, and elucidating the order of removal of functional groups and hydrazine-vapor reduction.
Strong in-plane bonding and weak van der Waals interplanar interactions characterize a large number of layered materials, as epitomized by graphite. The advent of graphene (G), individual layers from graphite, and atomic layers isolated from a few other van der Waals bonded layered compounds has enabled the ability to pick, place, and stack atomic layers of arbitrary compositions and build unique layered materials, which would be otherwise impossible to synthesize via other known techniques. Here we demonstrate this concept for solids consisting of randomly stacked layers of graphene and hexagonal boron nitride (h-BN). Dispersions of exfoliated h-BN layers and graphene have been prepared by liquid phase exfoliation methods and mixed, in various concentrations, to create artificially stacked h-BN/G solids. These van der Waals stacked hybrid solid materials show interesting electrical, mechanical, and optical properties distinctly different from their starting parent layers. From extensive first principle calculations we identify (i) a novel approach to control the dipole at the h-BN/G interface by properly sandwiching or sliding layers of h-BN and graphene, and (ii) a way to inject carriers in graphene upon UV excitations of the Frenkell-like excitons of the h-BN layer(s). Our combined approach could be used to create artificial materials, made predominantly from inter planar van der Waals stacking of robust bond saturated atomic layers of different solids with vastly different properties.
If the components of a battery, including electrodes, separator, electrolyte and the current collectors can be designed as paints and applied sequentially to build a complete battery, on any arbitrary surface, it would have significant impact on the design, implementation and integration of energy storage devices. Here, we establish a paradigm change in battery assembly by fabricating rechargeable Li-ion batteries solely by multi-step spray painting of its components on a variety of materials such as metals, glass, glazed ceramics and flexible polymer substrates. We also demonstrate the possibility of interconnected modular spray painted battery units to be coupled to energy conversion devices such as solar cells, with possibilities of building standalone energy capture-storage hybrid devices in different configurations.
The richly functionalized basal plane bonded to polar organic moieties makes graphene oxide (GO) innately hydrophilic. Here, a methodology to synthesize fluorinated graphene oxide by oxidizing the basal plane of fluorinated graphite, allowing for tunable hydrophobicity of GO, is reported. Fluorine exists as tertiary alkyl fluorides covalently bonded to graphitic carbons, and using magic‐angle spinning (MAS) 13C NMR as a primary tool chemical structures for the two types of synthesized fluorinated graphene oxides (FGOs) with significantly different fluorine contents are proposed. The low surface energy of the C–F bond drastically affects GO's wetting behavior, leading to amphiphobicity in its highly fluorinated form. Ease of solution processing enables the fabrication of inks that are spray‐painted on various porous/non‐porous substrates. These coatings maintain amphiphobicity for solvents with surface tensions down to 59 dyn/cm, thus bypassing existing lithographic means to create similar surfaces. The approach towards fluorinating GO and fabricating graphene‐based surfaces with tunable wettability opens the path towards unique, accessible, carbon‐based amphiphobic coatings.
Fluorination of carbon nanomaterials has many advantages due to the unique nature of the carbon–fluorine (C–F) bond. In this work, we report the optical power limiting properties of fluorinated graphene oxide (F–GO) using the optical z-scan technique. In addition, we used the photoacoustic technique to gain insight into the nonlinear processes involved in the optical limiting of samples. The photoacoustic technique enabled us to confirm that optical limiting observed in F–GO at low fluence arises from nonlinear absorption, while that at higher fluence is due to nonlinear scattering. Moreover, we found that F–GO has high nonlinear absorption and nonlinear scattering and its optical limiting threshold is about an order of magnitude better than that of graphene oxide (GO).
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