4 research outputs found
Versatile in Situ Gas Analysis Apparatus for Nanomaterials Reactors
We
report a newly developed technique for the in situ real-time
gas analysis of reactors commonly used for the production of nanomaterials,
by showing case-study results obtained using a dedicated apparatus
for measuring the gas composition in reactors operating at high temperature
(<1000 °C). The in situ gas-cooled sampling probe mapped the
chemistry inside the high-temperature reactor, while suppressing the
thermal decomposition of the analytes. It thus allows a more accurate
study of the mechanism of progressive thermocatalytic cracking of
precursors compared to previously reported conventional residual gas
analyses of the reactor exhaust gas and hence paves the way for the
controlled production of novel nanomaterials with tailored properties.
Our studies demonstrate that the composition of the precursors dynamically
changes as they travel inside of the reactor, causing a nonuniform
growth of nanomaterials. Moreover, mapping of the nanomaterials reactor
using quantitative gas analysis revealed the actual contribution of
thermocatalytic cracking and a quantification of individual precursor
fragments. This information is particularly important for quality
control of the produced nanomaterials and for the recycling of exhaust
residues, ultimately leading toward a more cost-effective continuous
production of nanomaterials in large quantities. Our case study of
multiwall carbon nanotube synthesis was conducted using the probe
in conjunction with chemical vapor deposition (CVD) techniques. Given
the similarities of this particular CVD setup to other CVD reactors
and high-temperature setups generally used for nanomaterials synthesis,
the concept and methodology of in situ gas analysis presented here
does also apply to other systems, making it a versatile and widely
applicable method across a wide range of materials/manufacturing methods,
catalysis, as well as reactor design and engineering
Probing the Bonding in Nitrogen-Doped Graphene Using Electron Energy Loss Spectroscopy
Precise control of graphene properties is an essential step toward the realization of future graphene devices. Defects, such as individual nitrogen atoms, can strongly influence the electronic structure of graphene. Therefore, state-of-the-art characterization techniques, in conjunction with modern modeling tools, are necessary to identify these defects and fully understand the synthesized material. We have directly visualized individual substitutional nitrogen dopant atoms in graphene using scanning transmission electron microscopy and conducted complementary electron energy loss spectroscopy experiments and modeling which demonstrates the influence of the nitrogen atom on the carbon K-edge
Direct Evidence of the Exfoliation Efficiency and Graphene Dispersibility of Green Solvents toward Sustainable Graphene Production
Achieving a sustainable
production of pristine high-quality graphene
and other layered materials at a low cost is one of the bottlenecks
that needs to be overcome for reaching 2D material applications at
a large scale. Liquid phase exfoliation in conjunction with N-methyl-2-pyrrolidone (NMP) is recognized as the most efficient
method for both the exfoliation and dispersion of graphene. Unfortunately,
NMP is neither sustainable nor suitable for up-scaling production
due to its adverse impact on the environment. Here, we show the real
potential of green solvents by revealing the independent contributions
of their exfoliation efficiency and graphene dispersibility to the
graphene yield. By experimentally separating these two factors, we
demonstrate that the exfoliation efficiency of a given solvent is
independent of its dispersibility. Our studies revealed that isopropanol
can be used to exfoliate graphite as efficiently as NMP. Our finding
is corroborated by the matching ratio between the polar and dispersive
energies of graphite and that of the solvent surface tension. This
direct evidence of exfoliation efficiency and dispersibility of solvents
paves the way to developing a deeper understanding of the real potential
of sustainable graphene manufacturing at a large scale
Controlling the Orientation, Edge Geometry, and Thickness of Chemical Vapor Deposition Graphene
We report that the shape, orientation, edge geometry, and thickness of chemical vapor deposition graphene domains can be controlled by the crystallographic orientations of Cu substrates. Under low-pressure conditions, single-layer graphene domains align with zigzag edges parallel to a single ⟨101⟩ direction on Cu(111) and Cu(101), while bilayer domains align to two directions on Cu(001). Under atmospheric pressure conditions, hexagonal domains also preferentially align. This discovery can be exploited to generate high-quality, tailored graphene with controlled domain thickness, orientations, edge geometries, and grain boundaries