In the field of nanofluidics, it has been an ultimate but seemingly distant goal to controllably fabricate capillaries with dimensions approaching the size of small ions and water molecules. We report ion transport through ultimately narrow slits that are fabricated by effectively removing a single atomic plane from a bulk crystal. The atomically flat angstrom-scale slits exhibit little surface charge, allowing elucidation of the role of steric effects. We find that ions with hydrated diameters larger than the slit size can still permeate through, albeit with reduced mobility. The confinement also leads to a notable asymmetry between anions and cations of the same diameter. Our results provide a platform for studying the effects of angstrom-scale confinement, which is important for the development of nanofluidics, molecular separation, and other nanoscale technologies.

Bioactivity of Escherichia coli bacteria (as a simple model for microorganisms) and interaction of them with the environment were controlled by their capturing within aggregated graphene nanosheets. The oxygen-containing functional groups of chemically exfoliated single-layer graphene oxide nanosheets were reduced by melatonin as a biocompatible antioxidant. While each one of the graphene (oxide) suspension and melatonin solution did not separately show any considerable inactivation effects on the bacteria, aggregation of the sheets in the melatonin-bacterial suspension resulted in trapping the bacteria within the aggregated sheets, i.e., a kind of inactivation. The bacteria trapped within the aggregated sheets were biologically disconnected from their environment, because they could not proliferate in a culture medium and consume the glucose of their environment. However, after removing the sheets from the surface of the microorganisms by using sonication, they could again interact with their environment. The reactivated bacteria consumed glucose and could be proliferated; i.e., they were alive within the aggregated graphene sheets (here, at least for 24 h). The trapped alive bacteria could be photothermally inactivated forever by near-infrared irradiation at 808 nm. These results suggest that graphene nanosheets may potentially serve as an encapsulating material for delivery of such microorganisms and as an effective photothermal agent for inactivation of the graphene-wrapped microorganisms.

TiO2 nanoparticles were physically attached to chemically synthesized single-layer graphene oxide nanosheets deposited between Au electrodes in order to investigate the electrical, chemical, and structural properties of the TiO2/graphene oxide composition exposed to UV irradiation. X-ray photoelectron spectroscopy showed that after effective photocatalytic reduction of the graphene oxide sheets by the TiO2 nanoparticles in ethanol, the carbon content of the reduced graphene oxides gradually decreased by increasing the irradiation time, while no considerable variation was detected in the reduction level of the reduced sheets. Raman spectroscopy indicated that, at first, the photocatalytic reduction resulted in a significant increase in the graphitized sp2 structure over the disorders in the graphene oxides. After that, as the carbon content decreased by UV irradiation, further disorders appeared in the reduced graphene oxide sheets, confirming degradation of the reduced sheets after the photocatalytic reduction. Based on the current−voltage characteristic, the optimum time for the photocatalytic reduction resulted in a sharp decrease in the electrical resistivity of the reduced graphene oxide. However, longer photocatalytic processes caused a high increase in the resistivity, due to dominating the photodegradation process over the nearly completed photocatalytic reduction.

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