ABSTRACT
With its exceptional charge mobility, graphene holds great promise for applications in next-generation electronics. In an effort to tailor its properties and interfacial characteristics, the chemical functionalization of graphene is being actively pursued. The oxidation of graphene via the Hummers method is most widely used in current studies, although the chemical inhomogeneity and irreversibility of the resulting graphene oxide compromises its use in high-performance devices. Here, we present an alternative approach for oxidizing epitaxial graphene using atomic oxygen in ultrahigh vacuum. Atomic-resolution characterization with scanning tunnelling microscopy is quantitatively compared to density functional theory, showing that ultrahigh-vacuum oxidization results in uniform epoxy functionalization. Furthermore, this oxidation is shown to be fully reversible at temperatures as low as 260 °C using scanning tunnelling microscopy and spectroscopic techniques. In this manner, ultrahigh-vacuum oxidation overcomes the limitations of Hummers-method graphene oxide, thus creating new opportunities for the study and application of chemically functionalized graphene.
Subject(s)
Graphite/chemistry , Catalysis , Microscopy, Scanning Tunneling , Oxidation-Reduction , Oxygen/chemistry , Temperature , VacuumABSTRACT
Due to their unique optoelectronic structure and large specific surface area, carbon nanomaterials have been integrated with titania to enhance photocatalysis. In particular, recent work has shown that nanocomposite photocatalytic performance can be improved by minimizing the covalent defect density of the carbon component. Herein, carbon nanotube-titania nanosheet and graphene-titania nanosheet composites with low carbon defect densities are compared to investigate the role of carbon nanomaterial dimensionality on photocatalytic response. The resulting 2D-2D graphene-titania nanosheet composites yield superior electronic coupling compared to 1D-2D carbon nanotube-titania nanosheet composites, leading to greater enhancement factors for CO2 photoreduction under ultraviolet irradiation. On the other hand, 1D carbon nanotubes are shown to be more effective titania photosensitizers, leading to greater photoactivity enhancement factors under visible illumination. Overall, this work suggests that carbon nanomaterial dimensionality is a key factor in determining the spectral response and reaction specificity of carbon-titania nanosheet composite photocatalysts.
ABSTRACT
To facilitate the proposed use of graphene and its derivative graphene oxide (GO) in widespread applications, we explored strategies that improve the biocompatibility of graphene nanomaterials in the lung. In particular, solutions of aggregated graphene, Pluronic dispersed graphene, and GO were administered directly into the lungs of mice. The introduction of GO resulted in severe and persistent lung injury. Furthermore, in cells GO increased the rate of mitochondrial respiration and the generation of reactive oxygen species, activating inflammatory and apoptotic pathways. In contrast, this toxicity was significantly reduced in the case of pristine graphene after liquid phase exfoliation and was further minimized when the unoxidized graphene was well-dispersed with the block copolymer Pluronic. Our results demonstrate that the covalent oxidation of graphene is a major contributor to its pulmonary toxicity and suggest that dispersion of pristine graphene in Pluronic provides a pathway for the safe handling and potential biomedical application of two-dimensional carbon nanomaterials.
Subject(s)
Biocompatible Materials/metabolism , Graphite/metabolism , Lung/metabolism , Lung/pathology , Poloxamer/metabolism , Animals , Biocompatible Materials/administration & dosage , Biocompatible Materials/chemistry , Biocompatible Materials/toxicity , Graphite/administration & dosage , Graphite/chemistry , Graphite/toxicity , Male , Mice , Mice, Inbred C57BL , Oxidation-Reduction , Poloxamer/administration & dosage , Poloxamer/chemistry , Poloxamer/toxicity , Reactive Oxygen Species/metabolismABSTRACT
With its unique electronic and optical properties, graphene is proposed to functionalize and tailor titania photocatalysts for improved reactivity. The two major solution-based pathways for producing graphene, oxidation-reduction and solvent exfoliation, result in nanoplatelets with different defect densities. Herein, we show that nanocomposites based on the less defective solvent-exfoliated graphene exhibit a significantly larger enhancement in CO(2) photoreduction, especially under visible light. This counterintuitive result is attributed to their superior electrical mobility, which facilitates the diffusion of photoexcited electrons to reactive sites.
Subject(s)
Carbon Dioxide/chemistry , Graphite/chemistry , Nanocomposites/chemistry , Solar Energy , Titanium/chemistry , Catalysis , Nanotechnology , Oxidation-Reduction , Particle Size , Photochemistry , Surface PropertiesABSTRACT
Efficient graphene exfoliation in a nontraditional solvent, ethanol, is achieved through the addition of a stabilizing polymer, ethyl cellulose. Iterative solvent exchange is further demonstrated as a rapid, room-temperature, ultracentrifugation-free approach to concentrate the graphene solution to a level exceeding 1 mg/mL. The outstanding processability and electrical properties of these graphene inks are verified through the realization of aligned graphene-polymer nanocomposites and transparent conductive graphene thin films.
