Ceylon Graphite Corp. ("Ceylon") (TSX-V: CYL) (OTC: CYLYF) (FSE:
CCY) is pleased to announce that Ceylon graphite achieved new
concentration and conductivity records when studied in the
manufacture of an adaptable sensing platform for chemical sensing.
The research, published in the Royal Society of Chemistry’s
“Nanoscale” Journal, was conducted by partners at the Molecular
Sciences Research Hub at Imperial College London and specifically
incorporated Ceylon’s vein graphite to produce a
low-surface-tension sprayable graphene ink that was key to the
sensor’s functionality.
A summary of the test results, completed in
January 20231 is highlighted below:
- Ceylon graphite was used to create
high concentration, graphene/polyvinylpyrrolidone inks, with
record-breaking concentrations as high 3.2 mg mL−1.
- Raman spectroscopy was used to show
high-quality graphene flakes produced via liquid phase
exfoliation.
- The Ceylon-based graphene device
was successfully used to detect for pH within the range of pH 3 –
11.
- These results demonstrate the
potential of high-quality graphite to empower the next generation
of nanomaterial-based diagnostics for biological and chemical
sensing.
“Our findings highlight the promising pH sensing
capabilities of the Ceylon graphene-based devices for pH sensing,
which can be deployed for a variety of medical and environmental
applications,” said Dr. Felice Torrisi, corresponding author of
this work and principal investigator. “In particular, the sprayed
“Electrolyte-gated Graphene Field-effect transistor” (EG-GFET)
fabricated using Ceylon graphite outperforms any other EG-GFET
prepared by any other technique, demonstrating the unique
characteristics of Ceylon graphite for high quality graphene inks
with electronic grade suitable for large area printed electronics,
integrated circuits and sensing. We see this as a breakthrough with
Ceylon vein graphite aiming to uncap the potential of graphene inks
for printed electronics by demonstrating high-performance devices
suitable for applications ranging from flexible and wearable
electronics to sensing and automotive.”
“We are thrilled that world-leading researchers
have discovered the advantages of our high-carbon vein graphite and
its potential applications in the worlds of graphene and
nano-technologies,” said Ceylon CEO, Sasha Jacob. “This is a key
area of our future development and one that provides high-margin
value-added products to our portfolio.”
Dr. Felice Torrisi is a Senior Lecturer in
Chemistry of 2D materials and Wearable Electronics in the
Department of Chemistry at Imperial College London and Fellow of
Trinity College, Cambridge. He previously held a University
Lectureship in Graphene Technology in the Department of Engineering
at the University of Cambridge, where he jointly managed the Centre
for Doctoral Training in Graphene Technology and the Cambridge
Graphene Centre.
Results in Summary:
Graphene ink formulation
Graphene inks have emerged as a new
revolutionary element for high-performance printed, flexible and
wearable electronics.2 Among the various methods available for
preparing graphene ink, sonication-assisted liquid-phase
exfoliation (LPE) has been chosen due to its simplicity and
compatibility with low-boiling solvents. This process involves
subjecting graphite (in powder or flakes) and low-boiling point
solvents, such as 2-propanol (IPA), along with small amounts (20
mg) of the polymer stabiliser, resulting in a graphene ink with
desired electronic propertied for printed electronics and
significantly enhanced shelf life of the ink. IPA was selected as
the solvent for the graphene ink as it has a boiling point of 82 °C
and impressively low surface tension of only 20.34 mN m−1,
satisfying the criteria for a scalable spray-coating as well as
inkjet printing of the optimised ink.3 The sonication process lasts
for 9 hours, ensuring thorough exfoliation of the graphite flakes.
Centrifugation at 2.000 – 13,000 g is then employed to further
refine the ink and effectively eliminate any remaining unexfoliated
flakes.
The optical absorption spectrum (OAS) of the
graphene ink, as depicted in Figure 1a, exhibits the characteristic
profile associated with graphene inks, a flat absorption pattern in
the visible spectrum and a distinctive peak in the UV region,
confirms the ink is mainly composed by high-quality graphene
flakes. The concentration of graphene flakes in the ink is
estimated to be ~ 1 mg mL-1 when centrifuged at 13,000 g and as
high as 3.2 mg mL−1 when centrifuged at 2,300 g (Figure 1b). This
concentration surpasses those reported in the literature for
graphene inks stabilised by polyvinylpyrrolidone (PVP) by an order
of magnitude, underscoring the exceptional quality and potential of
this formulation.
Please click here to view image
Figure 1: Ceylon inks show optimal graphene/PVP
ink concentrations. a) OAS data for Ceylon-based graphene/PVP ink.
b) Ceylon-based graphene/PVP ink can accommodate > × 3 the flake
concentration than previously reported inks when prepared under
similar conditions.
Application: A graphene field-effect transistor
as a scalable and low-cost high-performance biosensor
The EG-GFET channel is formed using an automatic
spray-coating process, ensuring consistent and scalable deposition
of the graphene ink onto the PCB test strip. The graphene ink
exhibits excellent wetting properties that contribute to film
uniformity. As the individual ink droplets merge into a thin film
before evaporating, this wetting behaviour plays a vital role in
achieving uniformity.
While the addition of PVP stabilizer enhances
the concentration and stability of the ink, it is important to note
that PVP is known to adversely affect the electrical conductivity
of nanostructured graphene thin films due to its insulating
properties. However, a solution has been found by utilizing a xenon
intense pulsed light (IPL) source, which effectively degrades the
PVP polymer without subjecting the PCB substrate to temperatures
exceeding its decomposition threshold. This method proves to be the
most suitable for this specific application. The spray coated
graphene ink achieved an approximate channel resistivity of 100 Ω
after IPL annealing suitable for flexible and plastic electronics
and currently used in industry.
Please click here to view image
Figure 2: Photonic annealing of Ceylon-based
graphene improves electrical properties. a) Raman spectroscopy data
indicating the absence of noticeable modification upon photonic
annealing. b) IPL annealing causes a decrease in resistance of the
graphene film.
The quality of the graphene flakes is assessed
using Raman spectroscopy. Figure 2a displays typical Raman spectra
of the graphene ink deposited on Si/SiO2, before and after photonic
annealing (black and red curves, respectively), to monitor any
potential effects on the SLG/FLG flakes. The red and black curves
in Figure 2a exhibit the characteristic D peaks at approximately
1346 cm−1, 2D peaks at approximately 2690 cm−1, and G peaks at
approximately 1581 cm−1 (red) and 1580 cm−1 (black). The D peak
displays a full-width at half maximum (FWHM) of 37.9 cm−1 (red) and
38.9 cm−1 (black). These values align with those reported for LPE
graphene inks indicating the high quality of the SLG and FLG flakes
in the graphene ink and the absence of noticeable modifications
upon photonic annealing.
To assess the impact of photonic annealing on
the electrical resistance of the EG-GFET channel, the PCB test
strip is exposed to three different intensities of xenon IPL (IPL)
energy. The exposure at 2.5 J cm−2, 3.75 J cm−2, and 5.0 J cm−2
results in a similar decrease in resistance from 310 Ω (not
annealed, red curve) to 112 Ω, 108 Ω, and 115 Ω, respectively.
Consequently, the lowest IPL energy (2.5 J cm−2) is employed for
all subsequent experiments, ensuring an enhanced channel resistance
while minimising the risk of PCB damage.
The response of the EG-GFETs to variations in pH
was investigated by conducting experiments that involved altering
the pH of the solution using a strong base or acid, while
monitoring the corresponding response. The obtained results reveal
valuable insights into the pH sensitivity of the EG-GFETs. Figure
3a illustrates the relationship between the drain current (ID) and
the gate-source voltage (VGS) for the EG-GFETs exposed to pH values
ranging from 3 to 11. Notably, the plot exhibits a discernible
shift of the Dirac point from 60 mV to 270 mV, indicating the
sensitivity of the devices to changes in pH. It is important to
highlight that this pH sensitivity is attributed to the type and
density of unintentional defects introduced during the LPE
process.
Please click here to view image
Figure 3: pH response of Ceylon-based graphene
chemical sensor. a) Shift in characteristic electrical transfer
curves of EG-GFETs to changing solution pH. b) Transient pH change
within the range of 7.2 – 7.5 pH units.
The corresponding pH-dependent shift in the
Dirac point is depicted in Figure 3a, showcasing a maximum Dirac
point of 270 mV at pH 11. A linear fit analysis of the Dirac point
values (red dashed line) reveals a sensitivity of 25.8 ± 0.5 mV per
pH within the linear pH range of 11 to 3. While this sensitivity
falls below the theoretical maximum predicted by the Nernst
equation (59.16 mV per pH), it outperforms graphene pH sensors
prepared using alternative graphene fabrication techniques, such as
chemical vapor deposition (CVD)-grown graphene on SiO2 (21–22 mV
per pH), suspended graphene (17 mV per pH), epitaxial graphene on
silicon carbide (19 mV per pH), and mechanically exfoliated
graphene on SiO2 (20 mV per pH). Moreover, transient pH changes
observed in Figure 3b, show how the graphene devices respond to pH
changes in < 10s, with a resolution as small as 0.04 pH units.
These findings highlight the promising pH sensing capabilities of
the Ceylon graphene-based devices for pH sensing, which can be
deployed for a variety of medical and environmental
applications.
Concluding remarks:
Ceylon has the correct characteristics to become
a key player in graphene ink preparation, and achieved the highest
concentrations of graphene flakes in the inks, as estimated using
OAS. This high concentration of graphene flakes offers several
advantages during the spray coating process. Firstly, it promotes
improved uniformity in the deposition of the graphene ink.
Additionally, the increase in graphene to PVP ratio leads to
enhanced flake conductivity, as excessive PVP deposition can hinder
conductivity. Raman spectroscopy analysis of the functionalized
graphene ink demonstrated results consistent with those observed in
LPE graphene, indicating a low defect area. This characteristic
further enhances the overall quality and performance of the
graphene ink.
The combination of these unique properties
enabled the successful detection of pH using a Lab-on-PCB
architecture for the first time. The graphene-based sensor
exhibited a pH sensitivity of 25 mV per pH unit, showcasing its
ability to precisely measure pH variations. Furthermore, the
response times of the sensor were found to be less than 10 seconds,
highlighting its rapid and efficient performance. This breakthrough
in pH sensing utilizing the Lab-on-PCB platform demonstrates the
potential of Ceylon-derived graphene in enabling advanced sensing
technologies
About Ceylon Graphite Corp.
Ceylon is a public company listed on the TSX
Venture Exchange, that is in the business of mining for graphite,
and developing and commercializing innovative graphene and graphite
applications and products. Graphite mined in Sri Lanka is known to
be some of the highest grade in the world and has been confirmed to
be suitable to be easily upgradable for a range of applications
including the high-growth electric vehicle and battery storage
markets as well as construction, healthcare and paints and coatings
sectors. The Government of Sri Lanka has granted the Ceylon’s
wholly owned subsidiary Sarcon Development (Pvt) Ltd. an IML
Category A license for its K1 mine and exploration rights in a land
package of over 120km². These exploration grids (each one square
kilometer in area) cover areas of historic graphite production from
the early twentieth century and represent a majority of the known
graphite occurrences in Sri Lanka.
Further information regarding Ceylon is
available at www.ceylongraphite.com
Sasha Jacob, Chief Executive Officer and Rita Thiel, Chair of
the Board of Directors
info@ceylongraphite.com
Corporate Communications
+1(604) 924-8695
Neither TSX Venture Exchange nor its Regulation
Services Provider (as that term is defined in policies of the TSX
Venture Exchange) accepts responsibility for the adequacy or
accuracy of this release
FORWARD LOOKING STATEMENTS:
This news release contains forward-looking
information as such term is defined in applicable securities laws,
which relate to future events or future performance and reflect
management's current expectations and assumptions. The
forward-looking information includes statements about the potential
value of graphene inks produced with Ceylon graphite, applications
for future graphene ink technologies, Ceylon’s role as a potential
market leader in graphene ink technology preparation, expectations
related to development of Ceylon’s properties, strategic
partnerships, potential customers and sales, plans for Ceylon’s
subsidiaries and Ceylon’s mining operations. Such forward-looking
statements reflect management's current beliefs and are based on
assumptions made by and information currently available to Ceylon
e, including the assumption that, there are no material adverse
changes effecting development and production at the M1 mine or on
other properties, testing related to the performance of Ceylon’s
vein graphite material are accurate, there will be no material
adverse change in graphite and metal prices, there will be
continued demand for graphite powered batteries, all necessary
consents, licenses, permits and approvals will be obtained,
including various Local Government Licenses. Investors are
cautioned that these forward-looking statements are neither
promises nor guarantees and are subject to risks and uncertainties
that may cause future results to differ materially from those
expected. Risk factors that could cause actual results to differ
materially from the results expressed or implied by the
forward-looking information include, among other things, the
results of Ceylon’s graphite testing being inaccurate or
incomplete, the market for graphene ink related technologies not
developing as expected, failure to obtain or maintain patents and
proprietary technology, loss or failure to acquire available high
quality graphite, any failures to obtain or delays in obtaining
required regulatory licenses, permits, approvals and consents, an
inability to access financing as needed, a general economic
downturn, a volatile stock price, labour strikes, political unrest,
changes in the mining regulatory regime governing Ceylon, a failure
to comply with environmental regulations and a weakening of market
and industry reliance on high quality graphite. Ceylon cautions the
reader that the above list of risk factors is not exhaustive.
1 Fenech-Salerno, B., Holicky, M., Yao, C., Cass, A. E. G. &
Torrisi, F. A Sprayed Graphene Transistor Platform for Rapid and
Low-Cost Chemical Sensing. Nanoscale 15,
3243-3254. (2023).
2 Torrisi, F. & Carey, T. Graphene, related
two-dimensional crystals and hybrid systems for printed and
wearable electronics. Nano Today 23, 73–96
(2018).
3 Lefebvre, A. H. & Mcdonell, V. G. General
Considerations. in Atomization and Sprays (eds. Brenn, G., Hung, D.
L. S., Herrmann, M. & Chigier, N.) 1–16 (Taylor & Francis
Group, 2017).
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