More Graphene Surprises

Material Science: Researchers are shocked to find that the thin carbon sheet can decompose and can conduct protons

Mitch Jacoby

Ultrathin films of carbon known as graphene have generated intense interest because of the potential applications enabled by the material’s outstanding physical and chemical properties. One of those properties, chemical stability, was called into question this year by an investigation showing that the material can decompose when used as a supporting layer in catalysis and in electronic devices. For those applications, researchers typically conduct studies using a solution-phase form of graphene called reduced graphene oxide, or RGO. But RGO may not be as stable as assumed. Prashant V. Kamat of the University of Notre Dame and colleagues demonstrated that aqueous suspensions of RGO-supported TiO2 nanoparticles unexpectedly decompose upon exposure to ultraviolet light (Chem. Mater. 2014, DOI: 10.1021/cm5026552). The team found that surfaces of the photocatalytic nanoparticles generate hydroxyl radicals, which oxidatively attack RGO. The process causes RGO sheets to fragment, forming polyaromatic hydrocarbon compounds. The group reported that continued exposure to UV light eventually decomposes the organic compounds completely, leaving behind CO2 and water. And graphene surprised researchers in another way this year. Andre K. Geim of the University of Manchester, in England, and coworkers demonstrated that pristine single layers of graphene—thought to be impermeable—can conduct protons unexpectedly well (Nature 2014, DOI: 10.1038/nature14015). This finding could make the material attractive for use in fuel cells, which require a thin proton-conducting membrane.

The thinner electron clouds between atoms in 2-D boron nitride and graphene membranes facilitate proton transport better than the denser clouds of monolayer MoS2.The thinner electron clouds between atoms in 2-D boron nitride and graphene membranes facilitate proton transport better than the denser clouds of monolayer MoS2. Credit: Nature

The thinner electron clouds between atoms in 2-D boron nitride and graphene membranes facilitate proton transport better than the denser clouds of monolayer MoS2.The thinner electron clouds between atoms in 2-D boron nitride and graphene membranes facilitate proton transport better than the denser clouds of monolayer MoS2. Credit: Nature

UV light initiates an oxidation process that decomposes a water-dispersible form of graphene, as depicted in this cartoon that illustrates fragmentation (not actual bonding) and indicated by the gradual lightening of the solutions. Credit: James G. Radich/Auburn U

UV light initiates an oxidation process that decomposes a water-dispersible form of graphene, as depicted in this cartoon that illustrates fragmentation (not actual bonding) and indicated by the gradual lightening of the solutions. Credit: James G. Radich/Auburn U

comments ( 2 )

  • Interesting, graphenes may degrade into PAHs.

  • Generally it is known that extended conjugation/delocalization is not as effective compared to localized ones. For example, if we compare benzene, naphthalene and pentacene, the stability gradually decreases to the point of being air-sensitive. So, this is an unexpectedly high stability for graphene. But it should be noted that this was only a “kinetic stability” not a “thermodynamic stability” towards air/oxidation. Catalytic oxidation should be expected and does not affect the stability claim in anyway. Kinetic stability does not preclude any catalytic reactions (even in H-H or C-H bonds). This finding reminds us that basic fact and interesting in that way.

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