We demonstrate a universal approach to extract one- and two-dimensional nanomaterials from contaminated water, which is based on a microscopic oil−water interface trapping mechanism. Results indicate that carbon nanotubes, graphene, boron nitride nanotubes, boron nitride nanosheets, and zinc oxide nanowires can be successfully extracted from contaminated water at a successful rate of nearly 100%. The effects of surfactants, particle shape, and type of organic extraction fluids are evaluated. The proposed extraction mechanism is also supported by in situ monitoring of the extraction process. We believe that this extraction approach will prove important for the purification of water contaminated by nanoparticles and will support the widespread adoption of nanomaterial applications.
Category: 2015
MoS2 Quantum Dot: Effects of Passivation, Additional Layer, and h‐BN Substrate on Its Stability and Electronic Properties
The inherent problem of a zero-band gap in graphene has provided motivation to search for the next-generation electronic materials including transition metal dichalcogenides, such as MoS2. In this study, a triangular MoS2 quantum dot (QD) is investigated to see the effects of passivation, additional layer, and the h-BN substrate on its geometry, energetics, and electronic properties. The results of density functional theory calculations show that the monolayer QD is metallic in nature, mainly due to the coordinatively unsaturated Mo atoms at the edges. This is reaffirmed by the passivation of the S edge atoms, which does not significantly modify its metallic character. Analysis of the chemical topology finds that the Mo−S bonds associated with the edge atoms are predominantly covalent despite the presence of metallic states. A bilayer QD is more stable than its monolayer counterpart, mainly due to stabilization of the dangling bonds of the edge atoms. The degree of the metallic character is also considerably reduced as demonstrated by the I−V characteristics of a bilayer QD. The binding strength of a monolayer QD to the h-BN substrate is predicted to be weak. The substrate-induced modifications in the electronic structure of the quantum dot are therefore not discernible. We find that the metallic character of the QD deposited on the insulating substrate can therefore be exploited to extend the functionality of MoS2-based nanostructures in catalysis and electronics applications at the nanoscale level.
Ice nucleation at the contact line triggered by transient electrowetting fields
Supercooled water is found to have a significantly enhanced freezing temperature during transientelectrowetting with electric fields of order 1 V/lm. High speed imaging reveals that the nucleationoccurs randomly at the three-phase contact line (droplet perimeter) and can occur at multiple points during one freezing event. Possible nucleation mechanisms are explored by testing various substrate geometries and materials. Results demonstrate that electric field alone has no detectable effect on ice nucleation, but the moving boundary of the droplet on the substrate due to electrowetting is associated with the triggering of nucleation at a much higher temperature. VC 2015 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4938749]
Switching Behaviors of Graphene- Boron Nitride Nanotube Heterojunctions
High electron mobility of graphene has enabled their application in high-frequency analogue devices but their gapless nature has hindered their use in digital switches. In contrast, the structural analogous, h-BN sheets and BN nanotubes (BNNTs) are wide band gap insulators. Here we show that the growth of electrically insulating BNNTs on graphene can enable the use of graphene as effective digital switches. These graphene-BNNT heterojunctions were characterized at room temperature by four-probe scanning tunneling microscopy (4-probe STM) under real-time monitoring of scanning electron microscopy (SEM). A switching ratio as high as 105 at a turn-on voltage as low as 0.5V were recorded. Simulation by density functional theory (DFT) suggests that mismatch of the density of states (DOS) is responsible for these novel switching behaviors.