A facile bottom-up method for the synthesis of highly fluorescent nitrogen-doped graphene quantum dots (N-GQDs) has been developed via a one-step pyrolysis of citric acid and tris(hydroxymethyl)aminomethane. The obtained N-GQDs emitted strong blue fluorescence under 365 nm UV light excitation with a high quantum yield of 59.2%. They displayed excitation-independent behavior, high resistance to photobleaching and high ionic strength. In addition to the good linear relationship between the fluorescence intensity of the N-GQDs and pH in the range 2-7, the fluorescence intensity of the N-GQDs could be greatly quenched by the addition of a small amount of 2,4,6-trinitrophenol (TNP). A sensitive approach has been developed for the detection of TNP with a detection limit of 0.30 μM, and a linearity ranging from 1 to 60 μM TNP could be obtained. The approach was highly selective and suitable for TNP analysis in natural water samples.

An effective and facile fluorescence sensing approach for the determination of 2,4,6-trinitrophenol (TNP) using the chemically oxidized and liquid exfoliated graphitic carbon nitride (g-C3N4) nanosheets was developed. The strong inner filter effect and molecular interactions (electrostatic, π-π, and hydrogen bonding interactions) between TNP and the g-C3N4 nanosheets led to the fluorescence quenching of the g-C3N4 nanosheets with efficient selectivity and sensitivity. Under optimal conditions, the limit of detection for TNP was found to be 8.2 nM. The proposed approach has potential application for visual detection of TNP in natural water samples for public safety and security.

High quality AFM force curves are presented with detailed potential dependent layering behaviors of the ionic liquid molecules, from which charged interior and neutral exterior layers are distinguished. The electric double layer is confined within the interior layers of one to two molecular size within the potential range of up to 1 V negative of the PZC.

Electrochemical techniques and atomic force microscopy based force curve measurements under potential control are combined to investigate the effect of small amounts of water on the structure of the electric double layer of an Au(111)/1‐butyl‐1‐methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA) interface. Three to five layering structures, including two charged layers, are observed at the Au(111)/BMPTFSA interface at potentials more negative than the point of zero charge. With an increase in the water concentration, the stiffness values for both the first and second layers decrease, which demonstrates that more water molecules adsorb on the Au(111) surface or interact with the ionic liquid, and thus weaken the interactions between cations, anions, and the electrode surface and lower the stability of the layering structures. The thicknesses of the charged interior layers (the first and second layers in this system) increase with an increase in the water concentration and the thicknesses of neutral exterior layers (the next one to three layers in this system) remain almost unchanged. The structure of the first layer of the interface varies dramatically with the change in the water concentration.

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