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: films
First-principles study of strain-induced modulation of energy gaps of graphene/BN and BN bilayers
First-principles calculations based on density functional theory are performed on graphene/BN and BN bilayers to investigate the effect of the strain on their energy gaps. For the graphene/BN bilayer, the bands have characteristic graphenelike features with a small band gap at K. Application of strain modulates the band gap, whose magnitude depends on the strength of interaction between constituent monolayers. For the BN bilayer, on the other hand, a large band gap is predicted, which remains nearly the same for small strains. The increased inhomogeneity in charge density of different carbon sublattices due to a stronger interplanar interaction is the cause of the predicted variation in the band gap with strains applied along the perpendicular direction in the graphene/BN bilayer.
Stability of field emission current from various types of carbon nanotube films
A series of emission current measurements were taken from various types of multiwalled carbon nanotube (MWCNT) films in order to examine their stability for electron field emission. We found that the MWCNTs films grown by the catalytic thermal chemical vapor deposition (CVD) method exhibited much improved emission stability as compared to MWCNT films grown by the plasma-enhanced CVD (PECVD) method. We explain this difference of performance by referring to the graphitic order of these MWCNTs as detected by transmission electron microscopy and Raman spectroscopy. Results indicate that MWCNTs with high-order tubular structures demonstrate stable electron field emission. The best performing sample exhibits a constant current degradation of ̈3% per hour at an emission current density of ̈1 mJ/cm2.
Stable Electron Field Emission from PMMACNT Matrices
We have created PMMACNT matrices by embedding opened-tip vertically aligned multiwalled
carbon nanotubes (VA-MWCNTs) with poly(methyl methacrylate) (PMMA). These PMMACNT matrices are
excellent electron field emitters with an emission threshold field of 1.675 V/m, more than 2-fold lower that
that of the as-grown sample. In addition, the emission site density from these matrices is high, merely filling up
the entire sample surface. Emission stability test at 1.35 mA/cm2 was performed continuously for 40 h with no
significant degradation. On the basis of our theoretical simulation and hypothetical modeling, we attribute these
performances to the reduced screening effect and fewer Joule heatings due to the shorter effective transport
distance of the electrons in MWCNTs.
Functionalization, Dispersion, and Cutting of Boron Nitride Nanotubes in Water
High-quality boron nitride nanotubes (BNNTs) were functionalized for the first time with water-soluble and biocompatible PEGylated phospholipid [methoxy-poly(ethylene glycol)-1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N conjugates (mPEG-DSPE)]. We found that BNNTs can be suspended in water for more than 3 months without precipitation. By comparing the dispersion stability of mPEG-DSPE/BNNTs in various solvents and the related Hansen solubility parameters, we found that polarized and hydrogen bonds between water and the hydrophilic mPEG play important roles in maintaining stable dispersion of BNNTs and preventing aggregation of mPEG-DSPE/BNNTs in the solutions. This has led to the formation of composite films with well-dispersed BNNTs and the coating of self-assembled monolayer (SAM) BNNTs. Furthermore, the lengths of these functionalized BNNTs can be shorterned, for the first time, from >10 μm to ∼500 nm by ultrasonication. Experiments suggest that effective dispersion of BNNT in solution is necessary for such cutting, where effective energy transfer from the sonicator to nanotubes is achieved. Our results will form the basis for stable functionalization, dispersion, and effective cutting of BNNTs with water-soluble and biocompatible PEGylated phospholipid, which are important for biomedical and composite applications.
Growth of adhesive cubic phase boron nitride films without argon ion bombardment
Previously, in situ bombardment of massive ions (Ar+, Kr+, etc.) was considered to be necessary for the formation of c-BN films. Because of
the accumulated stress, bombardment of massive ions has led to the formation of c-BN films with poor adhesion. Here we show that c-BN films
can be grown without involving bombardment of massive ions. This is achieved by using plasma-assisted pulsed-laser deposition (PLD) in pure
N2 RF plasma. Furthermore, we show that c-BN films can be grown in a vacuum ( ̈105 mbar during growth) by PLD without auxiliary ion
source. We show that these are possible at a reduced deposition rate. Energetic growth species initiated by PLD and the pure N2 plasma is
sufficient to form adhesive c-BN films at moderate deposition rate as long as the energy transfer rate per growth species is sufficient.
D 2005 Elsevier B.V. All rights reserved.