-
1
Investigation of In2O3-based Oxide Films by Direct
Imprinting
for TFT Application
Doctoral Degree Tokumitsu Laboratory
Student number: 1620011 Student name: Puneet Jain
1. Research content
1.1 Introduction
Indium oxide (In2O3) and indium tin oxide (ITO) are very mature
metal-oxides, which have been in research from many years due to
the advantages that they show n-type semiconducting behaviour with
high transparency in visible light. Due to these properties, ITO is
used as a transparent electrode in thin-film-transistor
liquid-crystal display (TFT-LCD), organic solar-cells,
electrochromic devices, window coatings, gas sensors, and touch
screens. To fabricate In2O3 and ITO films, various methods have
been used such as sputtering, pulsed laser deposition (PLD), spray
pyrolysis, vacuum evaporation, and solution process, etc. Among
them, the solution process has advantages over other techniques,
such as low-cost (as it does not require costly vacuum system),
less time requirement (as no need for vacuum formation). Also,
solution process is compatible with printing techniques, ease to
coat on substrates with different geometries, simple processing,
feasibility of direct patterning, with good source consumption
efficiency.
Printed electronics have recently gained attention due to their
low environmental impact, fewer fabrication steps, large area
fabrication, ease of patterning on organic and inorganic substrates
and low cost. Among various printed electronics techniques, inkjet
printing is a popular method, but is not appropriate for the
miniaturization of advanced electronic devices as the required
resolution is sub-micrometers or less, which cannot be realized by
inkjet printing. Furthermore, it is hard to achieve precise shape
control of the film via inkjet printing. A novel printing technique
known as nano-rheology printing (n-RP), based on direct imprinting
of precursor gel films, can fabricate patterns as small as 100 nm
with good shape control. n-RP is a resist-free, direct printing
method which utilizes the rheological properties of a metal-oxide
precursor gel to form patterns in the precursor gel.1)
In this work, at first electrical and patterning properties of
In2O3 and ITO were studied by n-RP process. Also, the electrical
properties of imprinted In2O3 and ITO films were also studied and
compared with that of non-imprinted films. Finally, bottom gate
thin film transistor (TFT) using n-RP, has been fabricated with
solution process derived In2O3 as a channel and source/drain; while
solution process derived HfO2 as a gate insulator. Platinum (Pt) is
used as gate electrode.
2. Research Purpose
The objective of this research is to study the electrical
properties of In2O3 and ITO film prepared by the n-RP process and
to fabricate TFT using n-RP process with chemical solution
processed In2O3 as channel and solution processed HfO2 as a high-k
gate insulator.
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2
2.1 Results and Discussion
At first In2O3 thin films were prepared by solution process
using indium acetyacetonate (In(acac)3) as a precursor in propionic
acid (PrA). The electrical properties of In2O3 were studied by
varying annealing time and annealing temperature. An optimum
condition was obtained at which high mobility and carrier
concentration were obtained. It is found that high mobility of
around 42.7 cm2 /Vs with a carrier concentration of 9.47 x 1018
cm-3 is obtained when In2O3 precursor gel film was annealed in O2
at 600 oC annealing for 1h. Then ITO thin films were prepared using
two different precursors of tin (Sn), keeping In(acac)3 in PrA,
same. One precursor was tin acetylacetonate (Sn(acac)2) and another
was tin chloride (SnCl2). ITO films were also annealed in O2 for 1
h at 600 oC. ITO concentration was varied from 1 to 10 wt.%. It is
found that as the Sn concentration increases, mobility decreases
due to the reason that Sn acts as impurity in In2O3 cubic bixbyite
structure. Therefore, more the Sn content, more impurity
scattering, hence less mobility. The resistivity as low as 2.6 x
10-3 Ωcm for our ITO films was obtained for 1 wt.% ITO via
Sn(acac)2 with a mobility of 24 cm2/Vs and carrier concentration of
1.0 x 1020 cm-3, when ITO film was annealed in O2 for 1 h at 600
oC. Figure 1 shows resistivity of ITO films prepared by SnCl2 and
Sn(acac)2. Resistivity of In2O3 films is also shown in Fig. 1, for
reference.
0 15 30 45 60 75 90 1050
10
20
30
40
50
Hal
l Mob
ility
(cm
2 /Vs )
Annealing time (min)
Annealed in O2 at 600 oC
0 2 4 6 8 10 1210-3
10-2
10-1Annealed for 1 h in O2 at 600
oC
Sn wt.%
Resis
tivity
(Ω.cm
)
In2O3 ITO via Sn(acac)2 ITO via SnCl2
Fig. 1: (a) Hall mobility of In2O3 and (b) resistivity of ITO
with respect to Sn wt.%.
Figure 2 shows the patterns of In2O3 and ITO formed by using
n-RP, while Fig. 3 shows the electrical properties of imprinted and
non-imprinted In2O3 and ITO films. Figure 2 shows that with the
addition of tin (Sn) to In2O3 (i.e. ITO) degrades the n-RP
properties because the tan δ value of ITO is smaller than that of
In2O3 (tan δ is a measure of viscoelasticity of a material. It is 1
for viscoelastic material, less than1 for solids and greater than 1
for liquids). From Fig. 3, it is seen that, the electrical
properties of imprinted ITO films are not altered as much as
compared to non-imprinted ITO films, but are greatly affected in
the case of imprinted In2O3 compared to the non-imprinted In2O3
films. The Hall mobility of imprinted In2O3 decreases due to the
trapped carbon, as confirmed by SIMS measurements, which showed
that even after annealing at 600 oC for 1 hour, there was more
carbon in the imprinted In2O3 than non-imprinted In2O3. An increase
in the carrier concentration in imprinted films is due to the
increase in oxygen vacancies in In2O3 after imprinting, as
confirmed by XPS studies.
Fig. 2: Patterns of In2O3 and ITO.
In2O3 ITO via Sn(acac)2 ITO via SnCl2
In2O3 ITO
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3
0
4
8
12
16
20
Car
rier c
once
ntra
tion
(cm
-3)
Imprinted
In2O3
Hal
l mob
ility
(cm
2 /V.s)
Non-imprinted
1017
1018
1019
1020
0
1
2
3
4ITO via SnCl2ITO via Sn(acac)2
1017
1018
1019
1020
1021
Imprinted Non-imprinted
Car
rier c
once
ntra
tion
(cm
-3)
Hal
l mob
ility
(cm
2 /V.s)
Fig. 3: Electrical properties of imprinted and non-imprinted
In2O3 and ITO.
Since the high-k gate insulator is required to fabricate TFTs
using In2O3 with relatively high carrier concentration, HfO2 films
were fabricated by the solution process. Polarization-electric
field (P-E) and capacitance-voltage (C-V) of the solution processed
HfO2, fabricated using hafnium acetylacetonate (Hf(acac)4) in PrA
and annealed in O2 at 700 oC for 15 min is shown in Fig 4. It is
seen from Fig. 4 that pure HfO2, is linear in nature and shows
paraelectricity. The extracted relative dielectric constant (εr)
from the P-E slope and C-V is 17, while the leakage current density
at 1 MV/cm is 1.0 x 10-6 A/cm2 with breakdown field of 5.8
MV/cm.
-6 -4 -2 0 2 4 6-12
-8
-4
0
4
8
12
Electric field (MV/cm)
Pola
rizat
ion
(µC/
cm2 )
Annealing temp.: 700 oC, 15 minITO/HfO2(45nm)/Pt
-20 -10 0 10 20
05
10152025303540
Voltage (V)
Capa
citan
ce (p
F)
Annealing temp.: 700 oC, 15 minITO/HfO2(45nm)/Pt
Fig. 4: Electrical properties of HfO2 thin films annealed at 700
oC for 15 min in O2.
Figure 5 shows the schematic structure of TFT fabricated by n-RP
process. It can be seen that using n-RP, the fabricated TFT has
source/drain and channel, all are fabricated by the same material
in just one press, simultaneously.
Fig. 5: Schematic of TFT fabricated by n-RP process.
Normal n-channel transistor operation was observed. The
calculated TFT parameters are, on/off ratio is in the order of
~105, SS: 2.3 V/dec, mobility: 0.13 cm2/Vs, and threshold voltage:
1.9 V.
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4
References: 1. T. Kaneda et al., J. Mater. Chem. C 2 40
(2014).
Research Accomplishments
Journal Publications 1. “Electrical Properties of In2O3 and ITO
Thin Films Formed by Solution Process using
In(acac)3 Precursors”, Puneet Jain, Yuji Nakabayashi, Ken-ichi
Haga, and Eisuke Tokumitsu (submitted in Japanese Journal of
Applied Physics).
2. “Electrical and Patterning Properties of Indium Oxide (In2O3)
and Indium Tin Oxide (ITO) by Direct Nanoimprinting Technique”,
Puneet Jain, Chang Su, Ken-ichi Haga and Eisuke Tokumitsu, Jpn. J.
Appl. Phys., 58 SDDJ051-SDDJ058 (2019).
International conferences 1. “Hall Mobility and Carrier
Concentration of In(acac)3 Precursor Derived Solution
Processed In2O3 and ITO Thin Films”, Puneet Jain, Ken-ichi Haga,
and Eisuke Tokumitsu, The 7th International Symposium on Organic
and Inorganic Electronic Materials and Related Nanotechnologies
(EM-Nano’ 19), June 19-22, 2019, Shinshu University, Nagano, Japan
(poster).
2. “Electrical Properties of In2O3 and In-Sn-O Films Prepared by
Direct Nanoimprinting”, Puneet Jain, Ken-ichi Haga, and Eisuke
Tokumitsu, The 31st International Microprocessor and Nanotechnology
Conference (MNC’ 18), November 13-16, 2018, Sapporo Park Hotel,
Sapporo, Japan (poster).
Domestic conferences 1. “Electrical Properties of In2O3 and ITO
Thin Films Prepared by Solution Process using
In(acac)3 Precursor”, Puneet Jain, Ken-ichi Haga, and Eisuke
Tokumitsu, Japan Society of Applied Physics (JSAP 66th Spring
Meeting’ 19), March 9-12, 2019, Tokyo, Japan (poster).
2. “Direct Imprinting and Electrical Properties of ITO Precursor
gel”, Puneet Jain, Ken-ichi Haga, and Eisuke Tokumitsu, Japan
Society of Applied Physics (JSAP 65th Spring Meeting’ 18), March
17-20, 2018, Tokyo, Japan (oral).
3. “Study of Electrical and Imprinting Properties of ITO
Precursor Gel using Direct Imprinting”, Puneet Jain, Chang Su,
Ken-ichi Haga, and Eisuke Tokumitsu, Japan Advanced Institute of
Science and Technology (JAIST) Japan-India Symposium, March 5-6,
2018, JAIST, Japan (poster).
Keywords: solution process, imprinting, oxide-semiconductors,
high-k dielectric, thin film transistors
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1
Studies on Low-voltage Dual-gate Organic Transistor based
Pressure-sensing
Devices
OGUNLEYE, Olamikunle Osinimu (s1620402)
Doctoral Course, Materials Science
Murata Laboratory
Part 1: Research Content
Background
Organic materials are good candidates to meet the demand of
transistor switches for sensing applications
because they require solution-processing methods to fabricate
these devices known today as organic field-
effect transistors (OFETs) at temperatures less or equal to 100
ͦC on a wide range of substrates. Some of the
advantages of using OFETs as readout elements for pressure
sensing applications include monitoring of
environmental pressure, electronic skin, human-machine
interaction, monitoring of the footprints of the
elderly in care homes [1-4]. Typical organic pressure sensors
operate in high voltages usually above 10 V.
There is a need to develop organic pressure sensors that can be
powered by portable battery cells. The
operation voltage of the sensor is strongly dependent on the
drive voltage of the OFET. Recently, our group
demonstrated a pressure-sensing device using a piezoelectric
copolymer film of Polyvinylidene Fluoride-
Trifluoroethylene (P(VDF-TrFE)) as the sensing layer and a
low-voltage OFET as the readout element [5].
We achieved high sensitivity with the device operating at a low
voltage of 5 V. The device configuration is
such that pressure exerted on the sensing layer is assumed to
induce the generation of charges from the
piezoelectric layer, which transduces as threshold voltage and
drain current changes observed in the
electrical output of the OFET. However, the reason for the
change in threshold voltage and drain current
when pressure is applied to the sensing layer has not been
quantitatively proved yet.
Objective
The objective of this research is to study the operation
mechanism of a low-voltage dual-gate organic
pressure sensor device by quantitative analysis. The results
obtained from the dual-gate organic pressure
sensor and a dual-gate OFET were used to estimate the
piezoelectric constant of the sensing layer used for
the pressure sensing device. To verify the estimated value,
direct measurement of d33 was carried using
quasistatic (belincourt) method. Comparing the measured d33 to
the estimated d33 led to the conclusion that
the operation mechanism of the device was due to the
piezoelectric behavior of the sensing layer.
Summary of results
In chapter 2, a low-voltage OFET was developed using poly (vinyl
cinnamate) (PVCN) as the dielectric
layer. The most important step for the dielectric layer to be
suitable for a low voltage OFET is the
photochemical crosslinking process of PVCN. This makes the
dielectric chemically resistant to
chlorobenzene solvent. It also leads to a low trap state at the
interface between the dielectric layer and
semiconducting layer, therefore, causing the device to operate
at low voltage. In addition, the gate leakage
current of the device is reduced. Figure 1 (a) shows the effect
of crosslinking the PVCN layer: the current
density at -5 V was about 10-11A/cm2 and 10-7 A/cm2 for the
crosslinked and pristine PVCN layer
respectively. Figure 1(b) shows a typical p-type transfer
characteristic of the OFET device with a low gate
leakage current of 10-11A, thus, confirming that the PVCN
crosslinking process was effective. The device
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2
has a field-effect mobility of 0.18 cm2/V.s, high
on/off ratio of 106, subthreshold swing of 125
mV/decade and threshold voltage of -0.15 V.
The low-voltage OFET was then used as the readout
element for the dual-gate organic pressure sensing
device in chapter 3. A polarized P(VDF-TrFE) layer
coupled with the low-voltage OFET formed the
organic pressure sensor with the sensing layer placed
on the active layer of the OFET. Figure 2a shows the
device configuration of the organic pressure sensor.
The piezoelectric layer generated charges when
pressure load was exerted on it leading to a shift in
transfer characteristics similar to that of the
conventional dual-gate OFET. However, for the latter
device, the top-gate voltage controls the shift in
transfer characteristics. Figure 3(a) confirms that the
sensing layer was polarized; Fig. 3b shows the shift
in transfer characteristics with respect to the pressure
load while Fig. 3c shows a linear relation of the
pressure load to the threshold voltage (Vth); thus,
confirming the operation of the dual-gate organic
pressure sensor device [5]. To explain the device
mechanism by quantitative analysis, the charge
generated from the sensing layer was estimated using
results from a conventional dual- gate OFET with the
same bottom-gate OFET as the organic pressure
sensor.
In chapter 4, a low-voltage dual-gate OFET with
controllable Vth shift was developed [6]. Figure 4 (a)
shows the shift in transfer characteristics. This shift is
consistent with that obtained by the dual-gate organic
pressure sensor. In addition, the linear relation between the
top-gate voltage and Vth was achieved (see Fig.
4b). From these results, the amount of charges generated by the
piezoelectric P(VDF-TrFE) layer was
estimated from the slope of Fig. 4c. Furthermore, by a
quantitative analysis of results obtained from both
the dual-gate pressure sensor developed in chapter 3 and a
conventional dual-gate OFET developed in
chapter 4, d33 of the sensing layer was estimated. In chapter 5,
the quantitative analysis is summarized as
Fig. 1. (a) UV crosslinking of PVCN dielectric
layer (b) Transfer characteristics of OFET
device.
Fig. 3. (a) Threshold shift when polarized P(VDF-TrFE) was
placed on the active layer (b) transfer curve
shifts corresponding to pressure load (c) linear relationship
between pressure and threshold voltage.
Fig. 2. Device structure of (a) low-voltage
dual-gate organic pressure sensor (b) dual-
gate OFET
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3
follows:
The amount of charges per unit area, Q depleted by the top-gate
bias voltage, Vtop is calculated from equation
(1) given below [6].
Q = Ctop Vtop ………. (1)
Where Ctop (2.065 nF/cm2) is the capacitance of the top gate
dielectric. In order to determine the
piezoelectric constant, d33, equation (2) which states that the
quantity of charges, Q, developed by the
piezoelectric sensing layer is proportional to force applied, F,
with the piezoelectric constant, d33, as the
proportionality constant was used [7].
Q = d33 F ………. (2)
Deducing F from the pressure applied on the 0.87 cm2 sensing
area (A), equation (1) can be modified to
this:
Q V = d33 F/A V ………. (3)
Both sides of equation (3) were extracted from the slope of Fig.
3b and Fig. 4c which are values c.a. 11.2
× 105 Pa/V and 8.1 nC/cm2V, respectively. The absolute value of
the piezoelectric constant d33 was
calculated to be 72 pC/N. d33 of the piezoelectric layer was
measured directly with a piezoelectric
measurement system to be an average of 53 pC/N. These results
conclude that the operation mechanism of
the dual-gate pressure sensor was due to the piezoelectric
behavior of the P(VDF-TrFE) layer used in the
device. In Chapter 6, the surface charges on the polarized
PVDF-TrFE layer required to cause the initial
Vth shift, with respect to the magnitude of electric field used
to polarize the P(VDF-TrFE) layer was
quantified using results of a conventional dual-gate OFET.
Chapter 7 summarizes the results achieved in
the previous chapters, future research as well as prospective
applications of this work.
Part 2: Research Purpose
In this research, the sensing mechanism of a dual-gate organic
pressure sensor was investigated by
quantitative analysis. The main results in the dissertation
describe in details the analysis using results from
a dual-gate OFET and the dual-gate organic pressure sensor. d33
of the sensing layer was estimated from
the results for both the dual-gate organic pressure senor and a
dual-gate OFET. The estimated value of d33 was found to be 72 pC/N.
The estimated d33 was reasonably consistent with that of directly
measured d33 (53 pC/N) of the sensing layer. In conclusion, the
operation mechanism of the device was due to the
piezoelectric behavior of the sensing layer. This research could
lead to further research areas into organic
pressure sensors using the dual-gate device configuration as
well as reducing the operation voltage of these
sensors.
Fig. 4. (a) Threshold shift of the OFET corresponding to
top-gate voltage (b) graph of top-gate
voltage against threshold voltage (c) graph of charge per unit
area against threshold voltage.
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4
REFERENCES
1. G. Schwartz, et al., Nat. Commun. 4 (2013) 1-8. 2. S. Lai, et
al., IEEE Trans. Electron Device Lett. 34 (2013) 801-803.
3. Y. Zang et al., Nat. Commun. 6 (2015) 1-9.
4. J. B. Andrews et al. IEEE Sensors Journal. 18 (2018)
7875-7880.
5. Y. Tsuji., et al., APEX. 10 (2017) 021601.
6. M.J. Spijkman., et al., Adv Mater. 23 (2011) 3231-3242
7. ANSI/IEEE, IEEE standard on piezoelectricity. IEEE Standard
176-1987 (1987)
Part 3: Research Accomplishments
Publications
1. Ogunleye Olamikunle Osinimu, Heisuke Sakai, Yuya Ishii,
Hideyuki Murata. “Investigation of the sensing
mechanism of dual-gate low-voltage organic transistor based
pressure sensor,” Organic Electronics (under
review)
2. Ogunleye Olamikunle Osinimu, et al. A degradable
biosynthesized polyamide as the gate dielectric for
low-operating voltage solution-processable organic field-effect
transistors. (manuscript in preparation)
Conferences
1. Ogunleye Olamikunle Osinimu, Yohei Yoshinaka, Heisuke Sakai,
Tatsuo Kaneko, and Hideyuki Murata.
“A Biodegradable Biopolymer as Dielectric for Low-Voltage
Solution-Processed Organic Field-Effect Transistors”,
International Symposium on Organic Electronic
Molecular Electronics, Saga, Japan. May 31st – June 2nd,
2018.
2. Ogunleye Olamikunle Osinimu, Heisuke Sakai, Yuya Ishii,
Hideyuki Murata. “Investigation of the
Sensing Mechanism of the Dual-gate Low-voltage Organic
Transistor based Pressure Sensor”, International
thin-film transistor conference, Okinawa, Japan. Feb. 28th –
Mar. 2nd, 2019.
3. Ogunleye Olamikunle Osinimu, Heisuke Sakai, Yuya Ishii,
Hideyuki Murata. “Investigation of the
Sensing Mechanism of the Dual-gate Low-voltage Organic
Transistor for Pressure Sensing by Quantitative
Analysis,” JSAP spring meeting, Tokyo, Japan. Mar. 9th –
Mar.12th, 2019.
Keywords: Dual-gate pressure sensor; Dual-gate organic
field-effect transistor; threshold voltage; P(VDF-
TrFE); Piezoelectric constant.
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First Principles and Experimental Study of the
Valleytronics Properties of Two Dimensional
Materials
Materials Science,Graduate School of Advanced Science and
Technology
Mizuta-Manoharan Laboratory
Kareekunnan Afsal (s1620404)
1 Research Content
1.1 Background
Charge carriers have different degrees of freedom. They can have
positive and negativecharges which constitute the field of
electronics. They also have up and down spin degrees offreedom,
which constitute spintronics. In recent years scientists have come
up with yet anotherdegree of freedom for electrons, known as the
valley degree of freedom. As per this degree offreedom, the charge
carriers residing in the valleys of the band structure of certain
materials behaveopposite to each other. This gave rise to a new
branch of physics, namely, valleytronics. To controland manipulate
any degree of freedom, there should be a physical quantity which
behaves contrarilylike charge and spin in electronics and
spintronics respectively. In valleytronics, such a physicalquantity
is the Berry curvature. The symmetry arguments of the Berry
curvature require either thetime-reversal symmetry or the spatial
inversion symmetry to be broken for the emergence of
Berrycurvature. While systems which preserve both these symmetries
show no Berry curvature and hencecannot be used as a valleytronic
material, systems with broken inversion symmetry show
oppositevalues of Berry curvature at the two in-equivalent valleys
of the band structure (Fig. 1(a)). Hence,the Berry curvature, which
can be understood as a pseudo-magnetic field in the reciprocal
spacedrives the carriers in the two in-equivalent valleys to the
opposite edges of the sample in the presenceof an in-plane electric
field. This phenomenon is called the valley Hall effect (Fig.
1(b)).
Figure 1: a Schematic diagram showing opposite Berry curvature
at K and K′ valleys in systemswhere inversion symmetry is broken. b
Schematic representation of valley Hall effect.
1
-
1.2 Aim
From a theoretical perspective, this study aims to look into the
emergence of Berry curva-ture in systems with broken inversion
symmetry such as bilayer graphene and bilayer
graphene/hexagonalboron nitride heterostructure. It also explores
the control and manipulation of the magnitude as wellthe polarity
of the Berry curvature using external perturbation such as an
out-of-plane electric field.Experimentally, the study aims to
investigate the effect of spontaneous charge transfer, doping,
andsubstrate in inducing Berry curvature and hence valley Hall
effect in ungated bilayer graphene.
1.3 Results
Although bilayer graphene (BLG) is widely considered to be
symmetric, there havebeen several theoretical studies and
experimental observations arguing about an inherent
asymmetrypersistent in ungated bilayer graphene. Thus we performed
Berry curvature calculations in ungatedbilayer graphene and
observed a non-zero Berry curvature with opposite values at K and
K′ valleys,validating the argumentation of the asymmetry persistent
in ungated bilayer graphene (Fig. 2(a)).The asymmetry comes from
the spontaneous charge transfer to one of the layers as a result
oflong-range Coulomb interaction between the electrons (Fig. 2(b)).
This charge imbalance resultsin a layer asymmetry in the system.
Application of an out-of-plane electric field (of the order
ofµV/nm) reduces the magnitude of the Berry curvature and dies out
at a threshold electric field(Fig. 2(c)). When the magnitude of the
electric field is increased beyond the threshold value, the
Figure 2: a Berry curvature calculated at different electric
fields for bilayer graphene. b Schematicrepresentation of the
charge asymmetry in bilayer graphene. c Magnitude of the Berry
curvaturecalculated at both K and K′ valleys for different
out-of-plane electric fields.
Berry curvature reappears but with a change in the polarity at K
and K′ valleys. This indicatesthat the polarity of the layer
asymmetry also switches beyond the threshold electric field.
However,application of higher electric fields (of the order of
V/nm) shows a reduction in the magnitude ofthe Berry curvature with
the increase in field strength. As for AA-stacked bilayer graphene,
eitherungated system or system under out-of-plane electric field
did not show any Berry curvature owingto the symmetry present in
the system.
Nonetheless, observation of valley current in ungated bilayer
graphene is experimen-tally challenging as it requires ultra-clean
sample which is isolated from external perturbation. Thuswe studied
theoretically the possibility of breaking the symmetry in bilayer
graphene with the useof hexagonal Boron Nitride (hBN) as a
substrate or as an encapsulation layer. Although the roleof hBN in
breaking the layer symmetry in bilayer graphene and sublattice
symmetry in single-layergraphene is well known, the effect of the
alignment and orientation of hBN layer on the emergenceof Berry
curvature in these systems is not studied in detail yet. Thus we
carried out Berry curvaturecalculations in hBN/BLG heterostructure
with various configurations. In the case of hBN/BLG
2
-
heterostructure with the hBN layer beneath the BLG (Fig. 3(a)
inset), a large Berry curvaturewith opposite values at K and K′
valleys are observed (Fig. 3(a)). This is attributed to the
layer
Figure 3: a-c Berry curvature calculated for different
configurations of hBN/BLG heterostructure.d-f Difference in charge
density between the layers of BLG for the configurations in a-c
respectively.
asymmetry introduced by the hBN layer in bilayer graphene. This
was confirmed by calculatingthe difference in charge density
between the top and bottom layers in BLG (Fig. 3(d)).
However,encapsulation of BLG with an hBN layer (in this
configuration, the top and bottom hBN layersare aligned opposite to
each other (Fig. 3(b) inset)) reduces the asymmetry and hence the
Berrycurvature (Fig. 3(b)). This is also reflected in the charge
density difference between the layers (Fig.3(e)). Interestingly,
reversing the direction of the top hBN layer (Fig. 3(c) inset))
induces asymme-try (Fig. 3(f)) as well as Berry curvature in the
system (Fig. 3(c)). Application of an out-of-planeelectric field
could manipulate the magnitude as well as the polarity of the Berry
curvature in thesesystems. On the other hand, single-layer graphene
hBN systems are found to be rather insensitive tothe configuration
of the hBN layer. Although the magnitude of the Berry curvature
depends on thealignment of the hBN layer, the orientation of the
hBN layer or application of out-of-plane electricfield does not
impact the polarity of the Berry curvature.
We have also conducted experimental studies to observe Berry
curvature induced val-
Figure 4: a The local and non-local resistance measurement for
ungated bilayer graphene. b Thecalculated Ohmic contribution to the
non-local resistance.
3
-
ley Hall effect in ungated bilayer graphene exfoliated on
Si/SiO2 substrate. The non-local resistancemeasurement method is
employed to detect the valley Hall effect. A non-zero non-local
resistancewhich is an indication of valley Hall effect was observed
in ungated bilayer graphene (Fig. 4(a)).To validate the observed
non-local resistance, the Ohmic contribution to the non-local
resistancewas calculated (Fig. 4(b)). The negligible Ohmic
contribution implies that the non-local resistanceis indeed from
the valley Hall effect. As for the asymmetry induced in the system,
apart from thespontaneous charge transfer discussed earlier, the
substrate induces different potentials on the bot-tom and top layer
due to proximity effect. This also enhances the asymmetry in the
system. Fromthe temperature-dependent measurements, it was
confirmed that the bilayer graphene is gapped andthe bandgap is
calculated to be around 60 meV. The bandgap opening also
substantiates that thesystem is asymmetric. On the other hand,
measurements conducted on single-layer graphene didnot show any
valley current, implying the symmetry persistent in the system.
2 Research Purpose
The distinct behavior of electrons in the two equivalent valleys
intrinsically as well as towardsexternal perturbation makes them
promising to be used to store binary information. However,finding
suitable material for practical applications is a challenging task.
In this work, we studied thevalley related phenomena such as Berry
curvature in BLG and hBN/BLG heterostructure. Both thesystems were
found to possess a non-zero Berry curvature owing to the asymmetry
in the system. Themagnitude, as well as the polarity of the Berry
curvature, could be controlled with the applicationof an
out-of-plane electric field, which makes these systems promising
candidates for valleytronicsapplications.
3 Research Accomplishment
Journal Publications
1. Afsal Kareekunnan, Manoharan Muruganathan, and Hiroshi
Mizuta, Electrically ControlledValley States in Bilayer Graphene,
Nanoscale (2019) (Accepted) (Peer reviewed).
2. Afsal Kareekunnan, Manoharan Muruganathan, and Hiroshi
Mizuta, Manipulating Berry Cur-vature in hBN-Bilayer Graphene
Heterostructure (In preparation).
3. Afsal Kareekunnan, Manoharan Muruganathan, and Hiroshi
Mizuta, Substrate Induced ValleyHall Effect in Ungated Bilayer
Graphene (In preparation).
Conferences
1. K. Afsal, M. Manoharan and H. Mizuta, Evolution of pz Orbital
with out-of-plane ElectricField in Bilayer Graphene, The 65th JSAP
Spring Meeting, March 17-20, 2018, Tokyo, Japan.
2. K. Afsal, M. Manoharan and H. Mizuta, First-Principle Study
of Bilayer Graphene ValleyStates, The 79th JSAP Autumn Meeting,
September 18-21, 2018, Nagoya, Japan.
3. K. Afsal, M. Manoharan and H. Mizuta, Berry Curvature Study
of hBN-Bilayer GrapheneHeterostructure, The 66th JSAP Spring
Meeting, March 09-12, 2019, Tokyo, Japan.
4. K. Afsal, M. Manoharan and H. Mizuta, Experimental Study of
the Valley States in BilayerGraphene, International Workshop
Spintronics and Valleytronics of Two-dimensional Materi-als, May
20-24, 2019, PCS IBS, Daejeon, South Korea.
5. K. Afsal, M. Manoharan and H. Mizuta, Valley Hall Effect in
Unbiased Bilayer Graphene, The21st International Conference on
Electron Dynamics in Semiconductors, Optoelectronics
andNanostructures, July 14-19, 2019, Nara, Japan.
4
-
Fine-tuning of solid-state thermoresponsive behaviour of various
LCST
showing organic-inorganic hybrid systems
Matsumi Laboratory, s1620410, Surabhi Gupta
Background
Stimuli responsive properties of smart polymers have gained much
attention in the recent past. Over
the top, thermosensitive materials have already rendered much
applications in the field of biomedical
and chemistry with highly importance projected in the future
than it has ever been in the past.
Nowadays, environmentally benign “green” solvents ionic liquids
with their enormous database of
distinguished cationic and anionic counterparts have enabled the
researchers over the globe to invest
more time into their future applications. There have been
reports about ionic liquids showing
thermoresponsive properties as well, in addition to polymers.
Considering the vitality of these smart
materials, the present research will be addressing synthesis and
study of thermoresponsive properties
of various polymer-based/ ionic liquid based/ and their
copolymer based materials and their tunability
over critical solution temperatures.
Aim
The primary aim of this thesis work is to focus on the
thermosensitivity and tunability of various
polymer and ionic liquid system. In the present thesis,
thermoresponsive property is examined on
three kinds of states:
(1) Solid-supported LCST showing materials,
(2) LCST showing hydrogels and
(3) LCST in liquid-liquid equilibria-Phase transitions of
imidazolium based ionic liquids in water.
Successful completion of this research would open several
strategies and aspects to prepare
innovative thermoresponsive smart materials with enhanced
properties. It will also provide with the
ability to tune phase transitions of these materials for the
fabrication of smart and intelligent thermal
devices.
Results and Discussion
In Chapter 2, the research is directed towards improving the
tuning of LCST behaviour of
oxazoline based thermoresponsive copolymer and creating a
solid-supported hybrid materials. In this
context, a copolymer of 2-ethyl-2-oxazoline and
2-isopropyl-2-oxazoline was synthesized by ring
opening polymerization which showed LCST at 77 oC as detected by
DSC. Further, TMOS was
chosen as the inorganic precursor to form organic-inorganic
hybrids. Samples with varied ratio of
copolymer and silicate moiety were prepared and their LCST and
tunability were analysed. The LCST
of the synthesized hybrid materials could be tuned over a
temperature range from 42-58 oC. A typical
-
concave-up type phase diagram was obtained suggesting the
dependence of LCST on the copolymer
concentration in the hybrid system. (Graphical abstract Fig.
1).
Chapter 3 describes a yet another method to form solid-supported
LCST showing materials utilizing
silicon wafers and polyoxazoline as the thermoresponsive
material. In this work, silicon wafers were
exposed to extreme acidic conditions to covalently bind with the
thermosensitive polymer of 2-ethyl-
2-oxazoline. The polymer was terminated with triethoxysilyl
group to enhance the surface bonding
abilities. The formation of self-assembled monolayers of the
thermoresponsive polymer was
confirmed using FT-IR and XPS analysis. The coated surface
become hydrophobic as seen by the
contact angle measurements. DSC showed that the LCST of the
modified polymer was 75 oC. The
system was observed to work as a solid-supported phase gradient
(Graphical abstract Fig. 2.).
Fig 2. Graphical illustration showing solid-supported
thermoresponsive polymer modified silicon
wafer for thermal devices
Chapter 4 includes the synthesis of novel plasmonic
nanoparticles (like Au and Ag) embedded
thermally sensitive PNIPAM-based hydrogels. In this chapter,
imidazolium-based polymerizable
ionic liquids solvents as copolymers were used. Synthesis of
gold and silver nanoparticles was done
using trisodium citrate as the primary reducing and stabilizing
agent, and the size was varied from 10
Fig. 1. Graphical illustration of fine-tuning of LCST of
polyoxazoline based copolymer using
inorganic silicate material
-
- 45 nm. The hydrogels
formed were studied for
their factors like size of
NPs and effect of ionic
liquid structure on its
LCST. The results were
consistent for both types
of nanoparticles. The
hydrogels possessed the
swelling and shrinking
abilities below and above
LCST, respectively. The
work made the LCST
tuning for these
hydrogels matrixes over a
wide temperature range of
23 – 67 oC. (Graphical
abstract Fig. 3.).
Lastly, focus was made to study liquid-liquid
phase systems. It has been known that some
imidazolium-based ionic liquids show LCST in water.
However, it became difficult to detect CST in room-
temperature low molecular weight imidazolium-based
ionic liquids. Therefore, Chapter 5 deals with the
study as to why previous techniques fail in the
detection and finding of a diagnostic tool to evaluate
LCST and UCST of ionic liquids. A more advance,
superior and informative technique which is
electrochemical impedance spectroscopy was used as
the diagnostic tool to evaluate the phase transition
temperature as clear visualization of the separation
which cannot be observed optically. Major factors
affecting the CST in these ionic liquids were also
detected by Kamlet-Taft parameter studies. Moreover,
a structure-activity relationship table was also
constructed based on factors like Gibbs free energy
change, hydrogen-bond energy change and van der
Waals energy change as scrutinized by COSMO-RS
simulations. It helped to foresee the type of the phase
transition phenomenon showed by the ionic liquid (Graphical
abstract Fig. 4).
Hence, this thesis work present various strategies to fine-tune
the phase transitions of various
thermoresponsive organic-inorganic hybrid systems.
Fig 4. Graphical illustration showing
factors affecting phase transitions in
imidazolium-based ionic liquids.
Fig 3. Graphical abstract representing the role of nanoparticle
size
in the nanoparticles embedded PNIPAM based hydrogels using
polymerized ionic liquids.
-
Table of Contents:
Chapter Chapter Title Page
1 Introduction to thermoresponsive property 1
2 Fine-tuning of LCST behavior of oxazoline copolymer based
organic-
inorganic hybrids as solid-supported sol-gel materials
72
3 Silicon wafer modification with thermoresponsive oxazoline
based
copolymer as solid-supported phase gradients
95
4 Controlled phase behaviour of thermally sensitive poly(n-
isopropylacrylamide/ionic liquid) hydrogels with embedded Au and
Ag
nanoparticles
116
5 Can we predict the critical solution temperature (CST) for
imidazolium-
based ionic liquids?
153
6 Conclusions 198
A) Publication (Peer Reviewed):
1. Surabhi Gupta, Tomoharu Kataoka, Masao Watanabe, Mamoru
Ishikiriyama and
Noriyoshi Matsumi, “Fine-Tuning of LCST behavior of oxazoline
copolymer based
organic-inorganic hybrids as solid-supported sol-gel materials”,
J. Appl. Polym.
Sci. 2019, 136, 48163.
B) Submitted:
[1] Surabhi Gupta, Ankit Singh and Noriyoshi Matsumi,
“Controlled phase behaviour of
thermally sensitive poly(N-isopropylacrylamide/ionic liquid)
with embedded Au
nanoparticles”, submitted.
[2] Surabhi Gupta, Kamiya Jain, Raman Vedarajan, Masaki
Watanabe, Mamoru
Ishikiriyama and Noriyoshi Matsumi* “Evaluation of phase
transitions in imidazolium-
based ionic liquid/water system using Impedance Spectroscopy and
Kamlet-Taft
parameter studies”, submitted.
-
Nanostructured Thermoelectric Materials Fabricated using
Chemically-synthesized Cu-Sn-S Based Nanoparticles as Building
Blocks
Materials Science
Maenosono Laboratory 1620415
Zhou Wei Research Content:
Owing to the dramatic growth demand of energy in the world,
thermoelectric (TE) devices have attracted much attention. TE
conversion efficiency is defined by the dimensionless figure of
merit ZT = σS2T/κ, where σ, S, κ and T are the electrical
conductivity, seebeck coefficient, thermal conductivity and
absolute temperature, respectively. The energy and environmental
issue drive people to look for sustainable TE materials with high
efficiency for TE applications. Even though, many approaches have
been introduced to improve the TE efficiencies of Te based, Se
based materials; the toxicity and low abundance in nature still
limit them for commercial use. Cu-Sn-S system1 is thought as
alternative TE material, which consist of green and abundant
elements and exhibits modest TE properties at relatively low
temperature range (< 200°C). Many research works have been done
to investigate the bulk copper tin sulfide (CTS) as TE materials.
However, almost no reports about the studied in nanostructed CTS as
TE material before. My research is focused on the study of the
nanostructured CTS based materials as TE materials. Bottom-up and
hot injection chemical approaches have been used to fabricate
Cu-Sn-S nanoparticles (NPs). These synthetic approaches enable us
to direct control over shape, size and crystal phase of NPs.
Chapter 1 gave a basic introduction of thermoelectricity and
background about CTS material and its potential and challenges for
being chosen as TE materials. A brief review of the chosen
strategies to enhance the TE efficiency and current research work
on CTS based TE materials have been given.
Chapter 2 demonstrated the chemically synthesized uniform
hole-doped Cu2Sn1–xZnxS3 (x=0-0.2) NPs and fabricated TE materials
by sintering the NPs into dense bulk materials using pulse electric
current sintering (PECS) technique after ligand exchange. Then, the
structure and composition-property relationships in the
Cu2Sn1–xZnxS3 TE materials were analyzed (Figure 1). By introducing
Zn doping effect and nanostructuring, the highest ZT value of 0.37
at 670 K was achieved in both Cu2Sn0.95Zn0.05S3 and
Cu2Sn0.85Zn0.15S3 nanostructured materials, which
-
was comparable to the ZT value at the same temperature of the
Cu2Sn0.9Zn0.1S3 non-nanostructured material.
Figure 1. TEM images of Cu2SnS3 (CTS) and Cu2Sn1-xZnxS3 (x= 0,
0.05, 0.1, 0.15, 0.2) NPs: (a) CTS (ZB), (b) CTS (WZ), (c) x=0.05,
(d) x=0.1, (e) x = 0.15, and (f) x = 0.2. XRD patterns of
nanoparticles (g) and pellets (h) of Cu2Sn1-xZnxS3 (x= 0, 0.05,
0.1, 0.15, 0.2). Electrical conductivity σ (i), Seebeck coefficient
S (j), Thermal conductivity κ (k), and ZT of Pellets Cu2Sn1-xZnxS3
(x= 0, 0, 0.05, 0.1, 0.15, 0.2). Filled black circles, filled black
triangle, filled pink circles, filled blue circles, filled brown
circles, and filled gray circles represent Pellet CTS (WZ), CTS
(ZB) and Pellets Cu2Sn1-xZnxS3 (x=0.05, 0.1, 0.15, 0.2),
respectively. The open circle represents the data of undoped
non-nanostructured monoclinic CTS taken from Ref. 4.
Chapter 3 described the one pot chemical method and hot
injection method synthesized Cu-Sn-S materials with controllable
size, shape and structure. The resulting particles after ligand
exchange were pelletized by using PECS technique for further TE
measurements. CTS pellets with three identical grain sizes (28.6
nm, 39.3 nm, 47.2 nm) have been fabricated under controllable
conditions. The grain size effect and composition-property
relationships in the CTS TE materials have been analyzed (Figure
2). It was found that the lattice thermal conductivities decreased
with grain sizes and could be strongly suppressed when the grain
size of pellet decreased to around 30nm. In addition, the ratio of
Sn/Cu in CTS materials has been found to have huge effect on the
carrier concertation.
-
Figure 2. TEM images of CTS particles with (a) small, (b) middle
and (c) ultra large size. XRD patterns of particles (d) and pellets
(e) of CTS. Lattice thermal conductivity κlat of pellets, filled
purple circles, filled orange circles and filled dark blue circles
represent Pellet S, Pellet M and Pellet UL, respectively. The open
circle represents the data of undoped non-nanostructured monoclinic
CTS taken from Ref. 4.
Chapter 4 studied the enhanced TE properties of blended
Cu2Sn1–xZnxS3 nanobulk materials, which fabricated by sintering a
mixture of chemically synthesized Cu2Sn0.85Zn0.15S3 (high σ and
high κ) and Cu2Sn0.9Zn0.1S3 (low σ and low κ) NPs with different
weight ratios into dense bulk materials by PECS technique (Figure
3). Cu2Sn0.85Zn0.15S3 (Zn15-CTS) has been used as a host material
and Cu2Sn0.9Zn0.1S3 (Zn10-CTS) used as nanoinclusions. By using
different chemical mixing methods, these two heterogeneous (but
nearly identical) NPs were blended in a weight fraction of 9:1 for
making a nanobulk material, the pellet showed ZT = 0.64 at 670 K,
which is 1.7 and 1.9 times higher than the ZT values of the
pristine Cu2Sn0.85Zn0.15S3 and Cu2Sn0.9Zn0.1S3 nanobulk materials,
respectively.
Figure 3. Schematic illustration of (a) fabrication of nanobulk
material, (b) the possible mechanism of carrier and phonon
transport in Pellets, (c) five different nanobulk materials in this
study including fabrication methods (“L.E.” and “PECS” denote
ligand exchange and pulse electric current sintering,
respectively).
-
Chapter 5 gave the general conclusions, and future prospects of
the overall research work. (1) Shen, Y.; Li, C.; Huang, R.; Tian,
R.; Ye, Y.; Pan, L.; Koumoto, K.; Zhang, R.; Wan, C.;
Wang, Y. Sci. Rep. 2016, 6, 32501. (2) Biswas, K.; He, J.; Blum,
I. D.; Wu, C.-I.; Hogan, T. P.; Seidman, D. N.; Dravid, V. P.;
Kanatzidis, M. G. Nature 2012, 489, 414−418. (3) Zhao, L.-D.;
Lo, S.-H.; He, J.; Li, H.; Biswas, K.; Androulakis, J.; Wu, C.-I.;
Hogan, T. P.;
Chung, D.-Y.; Dravid, V. P.; Kanatzidis, M. G. J. Am. Chem. Soc.
2011, 133, 20476−20487. (4) Liang, Q. Eur. J. Inorg. Chem. 2016,
2016, 3634.
Research Purpose:
The objective of this research is to investigate the sustainable
TE materials with high efficiency, copper tin sulfide, which
emerged as promising TE material and has been widely studied for
solar cells, was chosen as the target material because it contains
environmentally friendly, earth abundance and low cost elements.
Moreover, the nanostucturing2, all-scale hierarchical
architectureing3 and Zn doping1 strategies were employed in my
research work to investigate their effect on the final TE
efficiencies of CTS materials for designing the sustainable TE
materials.
(i) We are the first who using chemical methods to fabricate
Cu2SnS3 nanoparticles as building block to introduce mesoscale
defects into pellets, which helps to reduce the lattice thermal
conductivity. (ii) We are the first to study the grain size
effects on the thermal properties of this material. (iii) We are
the first to introduce nanoinclusions using chemical methods.
Importantly, we mixed the material with the same elements but
different compositions. Based on this, the ZT value of such blended
materials has been enhanced drastically, while similar reports have
not been presented so far.
Research Accomplishments: (1) W. Zhou, P. Dwivedi, C. Shijimaya,
M. Ito, K. Higashimine, T. Nakada, M. Takahashi, D.
Mott, M. Miyata, M. Ohta, H. Miwa, T. Akatsuka, and S.
Maenosono. “Enhancement of theThermoelectric Figure of Merit in
Blended Cu2Sn1-xZnxS3 Nanobulk Materials”. ACS Appl. Nano Mater. 1,
4819-4827, 2018.
(2) W. Zhou, C. Shijimaya, M. Takahashi, M. Miyata, D. Mott, M.
Koyano, M. Ohta, T. Akatsuka, H. Ono, and S. Maenosono.
“Sustainable Thermoelectric Materials Fabricated by using
Cu2Sn1-xZnxS3 Nanoparticles as Building Blocks”. Appl. Phys. Lett.
111, 263105, 2017.
-
Synthesis and Application of Nano-Sized Metal-Organic Frameworks
for Nanofiltration Membranes
Shangkum, Yildun Goji, (s1620414) Doctoral Course, Materials
Science
Taniike Laboratory
Part 1: Research Content
Background
Clean water scarcity is one of the serious global challenges
because of exponential population growth, drastic climate change,
and rapid industrialization. Water purification technologies such
as membrane-based filtration plays a vital role in accessing
superior water quality with an integrated sustainability in terms
of no chemical additives, low energy consumption, minimal land
usage, and ease of operation. Polymeric membranes are predominantly
used in membrane-based filtration because of the stated advantages.
Despite these advantages of membranes-based filtration, it is
limited in application due to challenges like tradeoff between
permeability-selectivity as well as fouling. Metal-organic
frameworks (MOFs) have emerged as a new class of hybrid materials
with potential for a broad range of applications. Design of
nanosized MOFs composite membranes would show remarkable
permeability and selectivity because of presence of nanochannel in
their MOFs structure.
Therefore, to address permeability-selectivity tradeoff and
fouling problems, hybridization of nanosized MOFs with polymeric
membranes is a novel technique to solve the problems. Several
methods have been employed to integrate MOFs into flexible
polymeric membranes for nanofiltration, but the major challenge
faced is how to form a MOF-based selective layer on a heterogeneous
support without defects. The nucleation and growth of MOFs require
harsh thermal treatment, which severely limits the combination
between MOFs and a polymeric support to form a uniform selective
layer without deteriorating the support. Therefore, facile and
scalable process to access a performant and flexible composite
membrane having selective layer of a metal organic framework UiO-66
is by deposition of preformed nanoparticles onto a regenerated
cellulose porous polymer support via a suction filtration, which
would offer both flexibility and stability of the composite
membrane.
Objective
The objective of this study is therefore to address
selectively-permeability tradeoff and fouling through systematic
investigation on the design principle for MOF-deposited composite
membranes for nanofiltration. Strategically, it was achieved
through synthetic control of nanoparticle size using water as
modulator, evaluation of particle size effects on nanofiltration
performance, development of bimodal membrane as well as
manipulation of pore surfaces by modified ligands and application
in nanofiltration and chemical selectivity.
-
Summary of Results
From aforementioned novel technique, Chapter 2 of this
dissertation describes the design of semi-continuous selective
layer based on UiO-66 nanoparticle-deposited composite membrane
that was successfully developed and applied for nanofiltration, in
which series of UiO-66 nanoparticles having different particle
sizes were varied by using water as modulator. The impacts of these
particle sizes and its distribution as the constituent of the
selective layer were examined on the membrane performance for the
methylene blue rejection. It was found that deposition of the
UiO-66 nanoparticle greatly improved the filtration performance of
the membrane irrespective of particle size as displayed in Figure
1a. Notwithstanding, it was also found that the size of the UiO-66
nanoparticles had great influences on the performance of the
composite membranes. The deposition of smaller nanoparticles
afforded a selective layer having a greater external surface area
and narrower interparticle voids. These features made the
deposition of smaller nanoparticles more advantageous in terms of
the flux and rejection, i.e. an excellent flux of 773 L/m2 h at
100% rejection could be achieved. The deposition of greater
nanoparticles afforded a selective layer more tolerant to the
membrane fouling. The advantages of the individual nanoparticles
was successfully combined by depositing mixed smaller and greater
UiO-66 nanoparticles to prepare bimodal membranes, thus
demonstrating promising aspects of the new type of MOF-based
composite membranes for nanofiltration as illustrated in Figure 1b.
Excellent performance was obtained because of facile production and
easy optimization through the size distribution of MOF
nanoparticles, that can be ex-situ prepared.
Figure 1. Filtration performance of composite membranes: a)
methylene blue rejection and permeate volume for the UiO-66
deposited membranes having different particle sizes and b)
permeability compared by the flux values at the first 5 min and at
the timing of the 99% rejection for the bimodal composite
membranes.
-
In Chapter 3, tuning of chemical and physical nature of MOF
through pore engineering by manipulation of pore surfaces of
modified ligands and application for nanofiltration and chemical
selectivity was examined. This was achieved by engineering the
UiO-66 nanoparticle through linker design to obtained modified
UiO-66 nanoparticles, UiO-66-CH3 and UiO-66-NH2. The tolerance
ability for leakage of unmodified and modified particles, for
solute leakage was estimated as shown in Figure 2a. Results
indicated that irrespective of the UiO type, tolerance to leakage
was greater for smaller particles/crystallites, however the
modified UiO was found to be superior for leakage tolerance
probably because of variation in particle morphology by the ligand
modification through denser packing of the selective layer in
membrane as compared to unmodified MOF based membranes. The results
therefore suggested that chemical environment and pore engineering
have significant effects on the filtration process. Furthermore,
the permeability test results for solvents with varied viscosities:
methanol, water and acetone is as shown in Figure 2b. Though the
particle size of UiO1-NH2 and UiO1-CH3 was much bigger than that of
UiO1, the flux was found to be comparable or greater. This implies
that nanopore environment significantly contributed to the permeate
flux differential behaviour. The hydrophilicity/hydrophobicity of
UiO-66-NH2/UiO-66-CH3 nanoparticles presented different chemical
environment, which would specifically account for high/low flux of
water to other solvents because of chemical environment around the
nanopores.
Figure 2. Filtration performance: a) cumulative rejection of
composite membrane for ligand effect on leakage tolerance and b)
permeability test of three different composite membranes for
different solvents.
Chapter 4 highlighted remarkable performances of these membranes
designed by deposition method. The filtration results obtained from
these composite membranes demonstrated the novelty of the technique
for membranes preparation, which could be applied for large-scale
nanofiltration.
Part 2: Research Purpose
The highlighted experimental results in this dissertation
provide an understanding of designing novel composite membrane by
the deposition technique to address permeability-selectivity
tradeoff and fouling in polymeric membranes for nanofiltration. The
particle size
-
effects on nanofiltration performance, manipulation of pore
surfaces by ligands modification are considered as a promising
approach not only to tailor the membrane performance, but also to
have breakthrough of the bottleneck in the currently used polymeric
membranes as well as to study the structure-performance
relationship for basic understanding, “how nanochannels contribute
to the performance. Thus, pore engineering was found to be
effective to improve the membrane performance as well as its design
for chemoselectivity applications.
References
(i) Trinh, D. X.; Tran, T. P. N.; Taniike, T. Fabrication of New
Composite Membrane Filled with UiO-66 Nanoparticles and Its
Application to Nanofiltration. Sep. Purif. Technol. 2017, 177,
249–256.
(ii) Goji. S. Y.; Trinh X. Dai.; Patchanee, C.; Taniike, T.
Design of Semi-Continuous Selective Layer Based on UiO-66
Nanoparticles for Nanofiltration. Membranes 2018, 8, 129, 1–14.
Part 3: Research Accomplishments
Publications
(i) S. Y. Goji., Trinh X. Dai., Patchanee Chammingkwan., and
Toshiaki Taniike. Design of Semi-Continuous Selective Layer Based
on Deposition of UiO-66 Nanoparticles for Nanofiltration.
Membranes, 2018,129, 1–14. (Peer-reviewed)
(ii) S. Y. Goji., Trinh X. Dai., Patchanee Chammingkwan., and
Toshiaki Taniike. Pore Engineering of UiO-66 Nanoparticles and
Applications to Nanofiltration (In preparation)
Conferences
(i) S. Y. Goji., Trinh X. Dai., Patchanee Chammingkwan.,
Toshiaki Taniike. Design of Semi-Continuous Selective Layer Based
on Deposition of UiO-66 Nanoparticles for Nanofiltration. Poster
presentation at The 12th SPSJ International Polymer Conference (IPC
2018), Dec 4–7, 2018, Hiroshima, Japan. (Without Peer-review) (ii)
S. Y. Goji., Trinh X. Dai., Patchanee Chammingkwan., and Toshiaki
Taniike. Design of Semi-continuous Selective Layer Based on UiO-66
Nanoparticles Deposition Composite Membrane. Poster Presentation at
JAIST World Conference, Feb 26–28, 2018, Japan. (Without
Peer-review)
Keywords: Metal-Organic Framework, UiO-66, pore engineering,
composite membrane,
chemical environment.
-
Synthesis and Application of Covalent Organic
Frameworks (COFs) and COF Derived Carbons
Chao Yang
S1620435
Supervisor: Shinya Maenosono
Graduate School of Advanced Science and
Technology
Japan Advanced Institute of Science and
Technology
(Materials Science)
-
Research Content
As an emerging class of ordered conjugated organic polymer
materials, covalent organic frameworks
(COFs) possess many unique properties such as predictability,
inherent porosity, structural periodicity,
large surface area, and high stability. The design and synthesis
of COFs are based on the reticular
chemistry and geometry of building blocks, which play a very
significant role on the formation, topology
and porosity of COF. Due to simultaneous polymerization and
crystallization, it is key to keep the balance
between dynamic error correction and non-covalent interlayer
interaction. In this regard, the linkers in 2D
COFs via [3 + 2], [3 + 3], [4 + 2] or [6 + 2] pathways should be
small molecules in order to tune the free
movement of monomers as well as thermodynamic and kinetic of
system. However, forming 2D COFs via
[4 + 4] pathway in the solution phase remains a big challenge
when both of building units are
tetrafunctional so that they can not twist or bend in a large
range like bi- or tri-functional building blocks.
On the other hand, stable and porous 1D COFs have not been
reported due to the lack of relevant
knowledges of controlling the covalent interaction and
non-covalent interaction. However, it is an important
and fundamental issue that tune the dimension because 1D
nanostructures always exhibit a distinct
property with their 2D or 3D counterparts. In addition, owing to
the thermal stability and designable
heteroatoms, COFs also might be ideal precursors for metal-free
carbon nanomaterials as electrocatalysts.
In this thesis, 2D [4 + 4] COFs are successfully synthesized in
solvothermal method. Due to the good
matching between building blocks, trade off between interlayer
interaction and crystallization, and special
connection patyway, high porosity (BET surface areas: 650~1100
m2 g-1) and micropores (~1 nm) can be
achieved. In addition, methyl groups can be decorated to modify
the pore surface of 2D [4 + 4] COFs.
Moreover, 1D COFs are first reported. By designing a series of
bifunctional V-type linkers to combine with
tetragonal knots, the covalent extension is limited in only one
direction. These microporous 1D COFs are
very designable since they can be modified by various
heteroatoms and functional groups and tuned by
the angle of building blocks. Due to the high microporosity, 1D
COF exhibits a good performance for CO2
separation.
2D [4 + 4] COFs also exhibit good performances for CO2 capture.
Methyl group decorated COFs
achieve an enhanced capture (100 mg g-1) and separation (w/w,
26/1, CO2 over N2) of CO2 at 1 atm and
273 K due to the increased microporosity and the strong
affiliation between COFs and CO2 induced by
methyl groups.
Porous and metal-free N,P co-doped carbon via carbonizing and
phosphorizing 2D [4 + 4] COFs and
TAPB-DMTA COF exhibit remarkable performances as ORR/HER
electrocatalysts with the half-wave
potential of 0.81 V vs. RHE in alkaline medium and overpotential
of 260 mV at 10 mA cm-2 in acid medium
comparable to those of commercial Pt/C.
Various 2D and 1D COFs are designed and successfully synthesized
under solvothermal conditions
mainly considering the geometry, angle, functional group and
symmetry of building blocks. The topology,
dimension and pore surface can be tuned controllably.
Especially, the finding of 1D COFs will overturn
the traditional view that COFs are 2D and 3D rather than 1D.
This will much enrich the diversity of COFs
and promote the development of chemistry of COFs. Moreover,
microporous 2D [4 + 4] COFs with methyl
groups and 1D COFs show a good performance for CO2 capture and
separation, suggesting the promising
prospect of these COFs and the effect of methyl groups for CO2
application. On the other hand, the
remarkable electrochemical performance of N,P co-doped carbons
derived from 2D COFs will open a new
way to synthesize high-performance metal-free electrocatalysts
and broaden the application of emerging
COF-derived carbons.
-
Research Purpose
With the increasing population and demand of energy, the
environmental issues caused by the
utilization of fossil fuels have been paid more and more
attention. Moreover, the development and
commercial application of new clean energy is still at the
primary stage. The demand of high-performance
materials with specific properties becomes more and more urgent.
Among these, advanced porous
materials such as COFs and their derived composites are playing
important roles.
Although the research field of COF emerged as recently as 2005,
the enormous possible design
space available with COF structures is reflected in the
significant number of structures that have been
realized to date. The size, symmetry and connectivity of the
linkers predefine the geometry of the resulting
framework. However, considering rare reported successful
examples of 2D [4 + 4] COFs, forming 2D
COFs via [4 + 4] pathway compared with other pathways. Here, a
series of 2D [4 + 4] COFs are
successfully synthesized employing Schiff base condensation.
Especially, well-defined micropores with
large surface areas can be achieved because via [4 + 4] pathway
the number of building blocks consisting
of each pore are decreased by at most two-third of those via
other pathways, leading to smaller pore sizes,
which are crucial to achieve a high gas uptake density for gas
like carbon dioxide. Moreover, methyl
groups are demonstrated to be effective to enhance the
performance of CO2 capture due to the interaction
with CO2.
Unlike 2D and 3D COFs, however, stable and porous 1D COFs have
not been reported due to the
lack of relevant knowledges of controlling the covalent
interaction and non-covalent interaction. For
example, the crystallinity, surface area and stability of woven
COF-505 and demetalated COF-505 are
much poor. On the other hand, 1D nanostructures always exhibit a
distinct property with their 2D or 3D
counterparts. Therefore, synthesis of 1D COFs with high
crystallinity, surface area and stability is very
important to figure out fundamental issues such as the
connectivity, topology and property of COFs. To
our best knowledge, here a series of microporous true 1D COFs
with high crystallinity and surface area
are achieved for the first time. In this way, heteroatoms,
planar conjugated groups or short alkyl chain can
be introduced into 1D COFs to realize their functionalization
and applications for CO2 separation at the
same time.
On the other hand, owing to the novel properties such as large
surface area, thermal stability, and
designable heteroatoms, COFs also might be ideal precursors for
metal-free carbon nanomaterials as
electrocatalysts. A series of metal-free, porous, and N,P
co-doped carbon catalysts are facilely prepared
by direct carbonization and phosphorization from high
crystalline 2D COFs such as TAPB-DMTA COF.
These COF derived N,P co-doped carbon catalysts exhibit
excellent tolerances towards methanol
crossover, as well as comparable oxygen reduction reaction (ORR)
and hydrogen evolution reaction (HER)
performances to commercial Pt/C.
In summary, design and synthesis of COFs, a new class of
crystalline porous materials, have
attracted much interest in recent years due to their novel
properties such as well-defined pores and
tunable performances for gas storage. New 2D and 1D COFs
composed of aromatic units are synthesized.
Besides high crystallinity and stability, well-defined
micropores smaller than 1 nm are achieved, which are
important for gas storage and hard to be obtained for COFs.
Moreover, relevant methodology and
mechanism of 2D [4 + 4] COFs and 1D COFs have been developed by
modifying the units, angles,
functional groups, and soon on. These COFs show good performance
of CO2 capture and separation
owing to the novel porosity and pore surface. Furthermore, COF
derived N,P co-doped carbon catalysts
show excellent performances as bifunctional catalyst candidates
to replace commercial Pt/C, suggesting
the promising potential of COFs as precursors of metal-free
carbons. However, many opportunities remain
to explore the properties of such materials especially 1D COFs
at the molecular level that will undoubtedly
promote the development of COFs and their applications as
high-performance adsorbents and in the field
of energy storage and conversion.
-
Research Accomplishment
[1]. Designing Covalent Organic Frameworks from Two Dimension to
One Dimension, Chao Yang,
Donglin Jiang*. 日本化学会北陸地区講演会と研究発表会. December 2017, Ishikawa,
Japan, Style
of Presentation: Poster. (without peer review)
[2]. Imine Bonded Covalent Frameworks Constructed by
One-Dimensional Chains, Chao Yang, Donglin
Jiang*. The 98th CSJ (The Chemical Society of Japan) Annual
Meeting. March 2018, Funabashi,
Japan, Style of Presentation: Oral. (without peer review)
[3]. COF derived N,P Co-Doped Carbon as a Metal-Free Catalyst
for Highly Efficient Oxygen Reduction
Reaction, Chao Yang, Shinya Maenosono, Jingui Duan*, Xiaobin
Zhang. ChemNanoMater, 2019,
5, 957-963.
[4]. N, P Co-Doped Carbons from 2D [4 + 4] Covalent Organic
Frameworks as Bifunctional
Electrocatalysts for Oxygen Reduction and Hydrogen Evolution
Reactions, Chao Yang, Shanshan
Tao, Ning Huang, Xiaobin Zhang, Jingui Duan,* Rie Makiura,* and
Shinya Maenosono*. (Ready to
submit)
[5]. Design and Fabrication of One-Dimensional Covalent Organic
Frameworks, Chao Yang, Shanshan
Tao, Lipeng Zhai, Xianzhu Zhong, Xiaobin Zhang, Yoshifumi
Oshima, Jingui Duan, Matthew A.
Addicoat, Shinya Maenosono*. (Ready to submit)
[6]. 2D MOF-Derived Co@C Hybridized with Graphene as
High-Performance Electrocatalysts for Zn-Air
Batteries, Chao Yang, Haofan Wang, Wei Hong, Shinya Maenosono,
Xiaobin Zhang, Qiang Xu*.
(Ready to submit)
[7]. Recent Advances in Two-Dimensional Materials for
Electrochemical Energy Storage and
Conversion, Chao Yang, Qiang Xu*. Flat Chem (Ready to
submit).
[8]. Co-N/C@MoS2 Electrocatalysts for Oxygen Reduction Reaction
and Zn-Air Batteries, Chao Yang,
Shinya Maenosono, Xiaobin Zhang, Qiang Xu*. (In
preparation).
-
Development of onsite and instrument-free recombinase
polymerase
amplification for smart molecular diagnosis at species level
Doctor of philosophy in Material Science
Yuzuru Takamura Laboratory, Bioscience and Biotechnology
1620436
Himankshi Rathore
Research Content: Nucleic acid identification tests based on
conventional polymerase chain reaction (PCR) are often
instrumental in choosing the correct treatment for the infection
due to the rapidity, sensitivity and
specificity of these tests and can be used for the detection of
asymptomatic infections1, early stage
diagnosis and disease relapse2. Very interestingly, recombinase
polymerase amplification (RPA)-based
molecular tools have attracted great interest since their
initial publication in 20063 and are continually
emerging as an elegant method of choice for performing
amplification without the need for complex
instrumentation. Additionally, sampling methods such as liquid
biopsy are a burden to both patients
and physicians, and the DNA extraction and purification steps
involved in sampling in DNA-based
methods increase the time to diagnosis. Direct sampling via an
FTA card reduces the risk of
contamination and facilitates the transport and long-term
storage of the sample at room temperature. In
this work, a way to discriminate true-positive results from
false-positive and/or negative results
generated during the RPA reaction is explored and an FTA card is
used for direct sampling of RPA
reactions to eliminate the concerns involved with sample
contamination as well as the sample
preparation steps and a method for species level analysis of RPA
products obtained for leishmaniasis
disease is also developed.
First, we devised an RPA protocol using Leishmania species,
belonging to the subgenus Leishmania
and Viannia to detect leishmaniasis infection. Next, we
demonstrated a near-to-patient diagnostic tool
utilizing an integrated approach of RPA, using Whatman FTA card
as a direct sampling tool and body
heat as the source of incubation temperature targeting a 360-bp
gene segment of the 18S rRNA gene,
and one-inch gel electrophoretic system. Next, Micro-Temperature
Gradient Gel Electrophoresis
(uTGGE)-type device is utilized, which has a power to
distinguish, even a single nucleotide difference
between two DNA molecules based on their thermal
stabilities.
The schematic of the near-to-patient diagnosis is highlighted in
Fig.1. First, the sample can be obtained
from the patient and is then spotted onto the FTA card and
dried. Next, a 2.0-mm-diameter disc is
punched from the FTA card, washed and then subjected to liquid
RPA reagents supplied with primers
targeted to amplify the target gene fragment. This tube is then
held in closed fist for 10 minutes to
provide the incubation temperature for RPA using body heat.
Although the process was simple, the
weak true-positive signals amplified in the presence of a low
template load (10 parasite copies) could
not be distinguished from a negative reaction (no parasite
copies) using fluorescent dye. Therefore, the
-
amplified products from RPA are subjected to rapid and portable
gel-based detection using one-inch
gel electrophoresis. The expected 360-bp band was clearly
obtained with 104 copies. However,
byproducts of smaller fragment sizes were also obtained in
reactions containing 10 or no copies of
template parasites, which could be clearly distinguished from
weak true-positive signals using our
handheld electrophoretic device. Next, 10 min- Micro-Temperature
Gradient Gel Electrophoresis
(uTGGE)-type device is utilized, which has a power to
distinguish, even a single nucleotide difference
between two DNA molecules based on their thermal stabilities and
uses the same type of 1-inch gel
electrophoretic system. The melting profiles are obtained and
species identification dots are assigned.
Pattern similarity scores are then obtained using computer-aided
normalization and used to plot a
dendrogram. The results can then be submitted to a public
database for treatment assessment
programmes in epidemic conditions.
Figure 1: Schematic of near-to-patient nucleic acid-based
molecular diagnostic tests.
Research Purpose:
Routine healthcare check-ups are important for early stage
diagnosis of the disease. This needs the
development of systems to monitor healthcare regularly. Thus,
the development of simple, affordable
and sensitive point of care testing has become the need of the
hour to bridge the gap between diagnostics
and treatment of deadly diseases prevailing in today’s world.
The unavailability of health care resources
mainly in the developing world leads to an ever increasing rate
of spreading infection from one person
to another. However, conventional diagnostic methods such as
microscopy, culture-based methods,
immunologic tests, non-nucleic acid-based methods and PCR cannot
be used in the manufacturing of
POCT devices.
In the last decade, a milestone in molecular biology research
has been the development of isothermal
amplification methods based on some new researches in the
molecular biology of DNA/RNA synthesis
and their interaction with some accessory proteins. One of the
most widely used isothermal
amplification methods is recombinase polymerase amplification
(RPA) which amplifies the target at
10 min
5 min
104Template (parasite copy)
10 0
(a)750
150
300500
Bypr
oduc
ts
1000
(b’)
104 10 0
← Product(360 bp)
Template (parasite copy)
M
Sample-to-Answer (outside the laboratory)
④
①
②
③
⑤
(b)
-
37˚C for the detection of infection in just 10-20 minutes. There
have been many publications in the last
decade, but these developments have a long way to be available
commercially mainly due to the lack
of suitable sampling and detection methods as well as generation
of non-specific amplification which
leads to false-positive results for point-of-care purposes.
Detection methods such as flocculation assay
detection, electrochemical detection, chemiluminescent
detection, silicon microring resonator based
photonic detection, surface enhanced Raman scattering detection,
etc. are either not suitable for point-
of-care and low resource settings or are not able to
differentiate between specific and non-specific
amplification. Gel electrophoresis is the gold standard for the
detection of DNA amplification products,
although the tedious steps, time consuming protocol as well as
the requirement of transilluminators to
visualize the DNA bands renders it unsuitable for POC purposes.
Moreover, considering the increasing
number of cases of Leishmaniasis (Kala azar) in low resource
countries, the current diagnostic methods
such as microscopic and culture based detection or Leishmanianin
skin test are time consuming and
require expensive equipment which are generally available at
community centres which are often
responsible for 119 villages in India, for instance. Therefore,
in this dissertation we engaged to develop
a rapid and cost-effective method for the detection of
leishmaniasis which can also be used for other
diseases just by changing few reagents.
This is the first report of a rapid and portable miniaturized
system known as one-inch gel electrophoresis
based on the previously developed micro-electrophoretic design
to perform onsite polyacrylamide gel
electrophoresis in less than 10 minutes. Moreover, FTA card has
been used for the first time as a direct
sampling tool in RPA reaction to the best of our knowledge. We
have used the combination of RPA
and one-inch gel electrophoretic system for primary
identification of leishmaniasis infection. However,
further we have also engaged to develop a method for species
level differentiation of Leishmania which
is instrumental in diagnosing the different forms of
leishmaniasis. The advanced detection utilises the
formally developed micro-temperature gradient gel
electrophoresis4 and RPA using 3-4 target gene
sequences. In the future, the methods proposed in this research
will be evaluated for clinical samples
directly for near to patient diagnosis of leishmaniasis. Being a
general method and just the need to
change the primers for RPA are advantageous as this approach can
easily be used for other targets. Our
results demonstrate that the combination of robust RPA with FTA
card-based direct sampling tools and
portable electrophoretic devices can revolutionize nucleic
acid-based molecular diagnostics for people
in settings with poor healthcare infrastructure.
Research Accomplishment: 1. Himankshi Rathore, Radhika Biyani,
Hirotomo Kato, Yuzuru Takamura and Manish Biyani. Palm-size
and one-inch gel electrophoretic device for reliable and
field-applicable analysis of recombinase
polymerase amplification. Under review. Manuscript ID:
AY-ART-07-2019-001476
2. Himankshi Rathore, Hirotomo Kato, Yuzuru Takamura and Manish
Biyani. Rapid electrophoretic
typing of Leishmania species for field-applicable point-of-care
testing. In preparation.
-
3. Himankshi Rathore, Madhu Biyani, Hiromi Ushijima, Yuzuru
Takamura and Manish Biyani.
Development of an advanced protocol for Recombinase polymerase
amplification using DEPSOR. In
preparation.
Conferences:
1. Himankshi Rathore, M. Biyani, Y. Takamura. Development of
‘PCR-on-paper’ based diagnostics for
infectious diseases. 6th ISAJ symposium on Recent Advances in
Science and Technology (ISAJ 2015),
Tokyo, Japan, Dec 4, 2015 (Poster Presentation)
2. Himankshi Rathore, Yuzuru Takamura, Manish Biyani. ‘Smart pad
diagnostics’, An automated Paper-
based DNA test for Personal Health monitoring. 26th Anniversary
World Congress on Biosensors 2016,
Gothenburg, Sweden, May 25-27, 2016 (Poster Presentation)
3. Himankshi Rathore, Yuzuru Takamura, Manish Biyani.
Development of Smart Wearable 'PCR-on-
Paper' Device for Personal Health Monitoring. The 12th
Biorelated Chemistry Symposium (CSJ 2016),
Osaka, Japan, Sept 7, 2016 (Poster Presentation)
4. Himankshi Rathore, Yuzuru Takamura, Manish Biyani.
PCR-on-paper for Wearable DNA Sensing
Device using Recombinase Polymerase Amplification and Body Heat.
Symposium, University of
Toyama, Toyama, Japan, Sept 15, 2016 (Poster Presentation)
5. Himankshi Rathore, Yuzuru Takamura, Manish Biyani.
PCR-on-paper for Wearable DNA Sensing
Device using Recombinase Polymerase Amplification and Body Heat.
Symposium, University of
Toyama, Toyama, Japan, Sept 15, 2016 (Oral Presentation)
6. Himankshi Rathore, Yuzuru Takamura, Manish Biyani.
PCR-on-Paper for Affordable Personal Health
Monitoring using Recombinase Polymerase Amplification and Body
Heat. Biyani International
Conference 2016 (BICON 2016), Jaipur, India, Oct 20-22, 2016
(Poster Presentation)
7. Himankshi Rathore, Hirotomo Kato, Yuzuru Takamura, Manish
Biyani. Field-applicable biosensing of
cutaneous leishmaniasis species by rapid Recombinase Polymerase
Amplification and Temperature
Gradient Gel Electrophoresis. 9th International Conference on
Molecular Electronics and Bioelectroics
(M&BE9), Kanazawa, Japan, June 26-28, 2017 (Poster
Presentation)
8. H. Rathore, S. Maki, E. Tamiya, Y. Takamura, M. Biyani. Rapid
Detection of Leishmaniasis using Solid-
phase Recombinase Polymerase Amplification and DEPSOR. JAIST
Japan-India Symposium
(JISMS2018), Nomi-shi, Ishikawa, Japan, March 5-6, 2018 (Poster
Presentation)
9. Himankshi Rathore, Hirotomo Kato, Yuzuru Takamura, Manish
Biyani. Biosensing of Leishmaniasis
using FTA card as Direct Sampling Tool for Recombinase
Polymerase Amplification. Indian Scientist
Association in Japan, Symposium 2018 (ISAJ 2018), Tsukuba,
Japan, Dec 7, 2018 (Poster Presentation)
References: 1 J. Martín-Sánchez, J. A. Pineda, F.
Morillas-Márquez, J. A. García-García, C. Acedo and J. Macías,
Am.
J. Trop. Med. Hyg., 2004, 70, 545–8.
2 C. N., L. V., G. Valiakos, V. Spyrou, K. Manolakou and C.
Billinis, in Leishmaniasis - Trends in
Epidemiology, Diagnosis and Treatment, InTech, 2014.
3 O. Piepenburg, C. H. Williams, D. L. Stemple and N. A. Armes,
PLoS Biol., 2006, 4, 1115–1121.
4 M. Biyani and K. Nishigaki, Electrophoresis, 2001, 22,
23–28.
-
Designed Synthesis of Functional Hydrazone-Linked Covalent
Organic Frameworks
Doctoral Course
Materials Science
Zhongping LI 1620438 Nagao’s Lab
Research Content:
COFs are novel porous crystalline materials that are constructed
by organic building units
into regular structures with atomic precision through organic
chemical reactions. Various
reactions have been used to develop different types of COFs,
such as B-O, C-N, and C-C
linkages. The B-O based COFs were the first example of
crystalline frameworks in 2005.
Various structures and functions of these COFs were developed in
the last few years.
However, B-O based COFs are vulnerable in humid conditions,
which limited their
application in a wide field. To improve the stability of these
frameworks, C-C and C-N linkage
COFs including imine, azine, hydrazone, and phenazine, were
gradually developed. The C-
N based COFs usually show excellent chemical stability. Compared
to imine, azine, and
phenazine linkage, the hydrazone-linked COFs have the active N-H
units on the walls, which
can easily achieve functional applications. For example, the
active N-H units on the walls of
frameworks can enhance carbon dioxide absorption ability.
Moreover, the hydrazone linkage
can give non-planar linkages for frameworks, which can weaken
strong π-π interaction that
is derived from adjacent layers to afford light-emitting
materials. Therefore, the hydrazone-
linked COFs are very useful to design light-emitting and
molecule sensing material. This
research focused on the design and synthesis of functional
hydrazone-linked COFs. Various
novel hydrazone-linked COFs including hexagonal and tetragonal
structure are designed
and synthesized. All hydrazone-linked COFs were characterized
using elemental analysis,
Fourier transform infrared spectroscopy (FT IR), electronic
absorption spectroscopy, field
emission scanning electron microscopy (FE SEM), and powder X-ray
diffraction
measurements (PXRD).
-
Scheme 1. Structure of TMHzcB-TFB-COF and TMHzcB-TFP-COF for
carbon dioxide adsorption.
In chapter 2, the microporous hydrazone-linked COFs,
TMHzcB-TFB-COF and TMHzcB-
TFP-COF (Scheme 1), were synthesized through the condensation of
1,3,5-tris(3’-methoxy-
4’-hydrazinecarbonylphenyl)benzene (TMHzcB) and
1,3,5-triformylbenzene
(TFB)/triformylphloroglucinol (TFP) under solvothermal
conditions. These COFs showed
high crystallinity, permanent micropores, excellent thermal and
chemical stability, and
abundant heteroatom activated sites on the walls. Interestingly,
TMHzcB-TFP-COF showed
good carbon dioxide uptake of 14.4 wt% at 273 K and 1 bar.
Scheme 2. Structure of the light-emitting hydrazone-linked
COFs.
In chapter 3, a series of light-emitting hydrazone-linked COFs
was successfully
synthesized (Scheme 2). Designing the different symmetrical
linkers or knots can provide
the hydrazone-linked COFs with the wide pore size from micropore
(1.3 nm) to mesopore
(3.7nm). These COFs not only showed excellent porosity but also
displayed good stability
in organic solvents, water, acid and base conditions for 24 h at
the room temperature. The
light-emitting activity of COFs can be improved through
introducing flexible building units or
-
functional active groups including methoxy and methyl groups. As
a result, the luminescence
of COFs can be tuned over a broad range of colors from blue to
green. Notably, COF-
TMHzcB-2,5-DMeTA showed the highest fluorescence quantum yield
over 19.5 % at solid
state, which is higher than most reported azine, imine, and
hydrazone based COFs.
Scheme 3. Structure of TFPPy-DETHz-COF.
In chapter 4, the hydrazone-linked TFPPy-DETHz-COF (Scheme 3)
was successfully
constructed through the Schiff-base condensation reaction under
solvothermal conditions.
The N-H bond in linkage on the walls can be deprotonated by
fluoride anion via a pinpoint
surgery to form an anionic species, which can eliminate the
nitrogen-related fluorescence
quenching pathway. The addition of fluoride anion eliminates the
photoinduced electron
transfer pathway and directly improves the light-emitting
activity. Surprisingly, the emission
is switched on in the presence of fluoride anion and its
intensity is enhanced in a linear
proportion to the amount of fluoride anion. The absolute
fluorescence quantum yield
increases to 17%, which is 3.8-fold as high as that of
as-synthesized TFPPy-DETHz-COF.
In contrast, other halogen anions, including chloride, bromide,
and iodide, retain inactive.
The detection limit of fluoride anions can be down to a ppb
level.
Research Purpose:
Various novel hydrazone-linked COFs including hexagonal and
tetragonal structure with
high porosity, crystallinity, and stability, can be designed and
synthesized. The pore size of
COFs can be adjustable from micropores (1.6 nm) and mesopores
(3.7 nm), which also
-
enriches the diversity of the COFs’ structure. Moreover,
fluorescence COFs showed the
highest quantum yield than most reported COFs through changing
flexible units and auxiliary
chromophore. I also used the pinpoint surgery on the N−H unit of
the hydrazone-linked
COFs and the first example of COFs for anion sensing. The
investigated results displayed
in this thesis demonstrate functional hydrazone-linked COFs that
open a new phase for not
only high adsorptive media but also light-emitting material