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.

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

3

0

4

8

12

16

20

Car

rier c

once

ntra

tion

(cm

-3)

Imprinted

In2O3

Hal

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(cm

2 /V.s)

Non-imprinted

1017

1018

1019

1020

0

1

2

3

4ITO via SnCl2ITO via Sn(acac)2

1017

1018

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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.

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

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

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

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.

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.

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