8 research outputs found
An Experimental study of Graphene Quantum Dots as a Potential Fluorescent, Anti-Bacterial Additive for Water Based Paint
An experimental study of Graphene quantum dots was conducted as a potential fluorescent, anti-bacterial additive for water-based paints using GQDs synthesized from L Glutamine. The L-Glutamine was polymerized to form light blue GQDs of low fluorescence intensity, which lost all fluorescence once added to the paint. The GQDs were tested for antibacterial properties against the growth of E.coli but failed to inhibit any growth. Raman and UV/vis spectroscopy were also conducted to determine functional groups as well as to determine peak light absorbance trends. While it was concluded that this method of GQD synthesis did not result in a promising additive for water-based paints, future research could continue the antibacterial testing by adding low concentrations of hydrogen peroxide as well as testing other facile methods of synthesis
Phonon Polaritons in Monolayers of Hexagonal Boron Nitride.
Phonon polaritons in van der Waals materials reveal significant confinement accompanied with long propagation length: important virtues for tasks pertaining to the control of light and energy flow at the nanoscale. While previous studies of phonon polaritons have relied on relatively thick samples, here reported is the first observation of surface phonon polaritons in single atomic layers and bilayers of hexagonal boron nitride (hBN). Using antenna-based near-field microscopy, propagating surface phonon polaritons in mono- and bilayer hBN microcrystals are imaged. Phonon polaritons in monolayer hBN are confined in a volume about one million times smaller than the free-space photons. Both the polariton dispersion and their wavelength-thickness scaling law are altered compared to those of hBN bulk counterparts. These changes are attributed to phonon hardening in monolayer-thick crystals. The data reported here have bearing on applications of polaritons in metasurfaces and ultrathin optical elements
Graphene Oxide Membranes: Controlled Laser Reduction for Sensing Applications
Reduced graphene oxide (rGO) has attracted attention as an active electrode material for flexible electrochemical devices due to its high electric conductivity and large surface area. Compared to other reduction processes, laser reduction is a precise, low-cost, and chemical-free process that is directly applied to graphene oxide (GO) membranes. This study aims to develop rGO through laser irradiation for application as electrodes in thin flexible electrochemical sensors. Laser irradiation parameters will be optimized to achieve reduction of a low oxygen to carbon (O/C) ratio and surface impedance. The influence of humidity on the impedance of rGO electrodes will be studied. The observed instability of the rGO electrode is related to incomplete reduction and oxygenated defects involved in reduction. Partially removed oxygenated functional groups not only influence the impedance of the electrode but make it sensitive to the humidity of the working environment. The result provides references for GO’s laser reduction optimization, demonstrates the potential of applying rGO as an electrode in sensing applications, but also reveals the limitation of applying the laser reduced rGO electrode in a non-constant humidity environment
Al3+ Modification of Graphene Oxide Membranes: Effect of Al Source
Graphene oxide (GO) membranes are promising materials for water filtration applications due to abundant nanochannels in the membrane structure. Because GO membranes are unstable in water, metal cations such as Al3+ are often introduced to the membrane structure to promote cross-linking between individual GO sheets. Here, we describe a simple yet versatile method to incorporate Al3+ into GO membranes formed via a slow self-assembly process. Specifically, we directly added aluminum to acidic GO sheet solutions from a variety of sources: Al2O3, AlCl3 and Al foil. Each species reacts differently with water, which can affect the GO solution pH and thus the density of carboxylate groups on the sheet edges available for cross-linking to the Al3+ cations. We demonstrate through characterization of the GO sheet solutions as well as the as-formed membranes’ morphologies, hydrophobicities, and structures that the extent to which the Al3+ cross-links to the GO sheet edges vs. the GO sheet basal planes is dependent on the Al source. Our results indicate that greatest enhancements in the membrane stability occur when electrostatic and coordination interactions between Al3+ and the carboxylate groups on the GO sheet edges are more extensive than Al3+–π interactions between basal planes
Using Al3+ to Tailor Graphene Oxide Nanochannels: Impact on Membrane Stability and Permeability
Graphene oxide (GO) membranes, which form from the lamination of GO sheets, attract much attention due to their unique nanochannels. There is much interest in controlling the nanochannel structures and improving the aqueous stability of GO membranes so they can be effectively used in separation and filtration applications. This study employed a simple yet effective method of introducing trivalent aluminum cations to a GO sheet solution through the oxidation of aluminum foil, which modifies the nanochannels in the self-assembled GO membrane by increasing the inter-sheet distance while decreasing intra-sheet spacing. The Al3+ modification resulted in an increase in membrane stability in water, methanol, ethanol, and propanol, yet decreased membrane permeability to water and propanol. These changes were attributed to strong interactions between Al3+ and the membrane oxygenated functional groups, which resulted in an increase in membrane hydrophobicity and a decrease in the intra-sheet spacing as supported by surface tension, contact angle, atomic force microscopy, and X-ray photoelectron spectroscopy measurements. Our approach for forming Al3+ modified GO membranes provides a method for improving the aqueous stability and tailoring the permeation selectivity of GO membranes, which have the potential to be implemented in vapor separation and fuel purification applications
Anisotropic Etching of Hexagonal Boron Nitride and Graphene: Question of Edge Terminations
Chemical
vapor deposition (CVD) has been established as the most
effective way to grow large area two-dimensional materials. Direct
study of the etching process can reveal subtleties of this competing
with the growth reaction and thus provide the necessary details of
the overall growth mechanism. Here we investigate hydrogen-induced
etching of hBN and graphene and compare the results with the classical
kinetic Wulff construction model. Formation of the anisotropically
etched holes in the center of hBN and graphene single crystals was
observed along with the changes in the crystals’ circumference.
We show that the edges of triangular holes in hBN crystals formed
at regular etching conditions are parallel to B-terminated zigzags,
opposite to the N-terminated zigzag edges of hBN triangular crystals.
The morphology of the etched hBN holes is affected by a disbalance
of the B/N ratio upon etching and can be shifted toward the anticipated
from the Wulff model N-terminated zigzag by etching in a nitrogen
buffer gas instead of a typical argon. For graphene, etched hexagonal
holes are terminated by zigzag, while the crystal circumference is
gradually changing from a pure zigzag to a slanted angle resulting
in dodecagons
Synthesis of Hexagonal Boron Nitride Monolayer: Control of Nucleation and Crystal Morphology
Monolayer
hexagonal boron nitride (hBN) attracts significant attention due to
the potential to be used as a complementary two-dimensional dielectric
in fabrication of functional 2D heterostructures. Here we investigate
the growth stages of the hBN single crystals and show that hBN crystals
change their shape from triangular to truncated triangular and further
to hexagonal depending on copper substrate distance from the precursor.
We suggest that the observed hBN crystal shape variation is affected
by the ratio of boron to nitrogen active species concentrations on
the copper surface inside the CVD reactor. Strong temperature dependence
reveals the activation energies for the hBN nucleation process of ∼5
eV and crystal growth of ∼3.5 eV. We also show that the resulting
h-BN film morphology is strongly affected by the heating method of
borazane precursor and the buffer gas. Elucidation of these details
facilitated synthesis of high quality large area monolayer hexagonal
boron nitride by atmospheric pressure chemical vapor deposition on
copper using borazane as a precursor