第27回無機材料に関する最近の研究成果発表会

東海大学校友会館, Jan. 25, 2010

ソフト溶液反応による酸化亜鉛粒子膜の精密構造制御と高次機能性

殷 澍Shu YIN
E-mail: shuyin@tagen.tohoku.ac.jp
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University
2-1-1 Katahira, Aoba-ku, Sendai 980-8577, JAPAN

溶液プロセスによる機能性無機材料のナノ構造制御--研究のコンセプト
e-光触媒材料

e- + O2 → ・O2h+ + OH- → ・OH

UV遮蔽材料hυ → e- + h+

発光材料

e- + h+ → hυ

hυ
Eb
光誘起機能

TiO2

h+NOｘ、SOｘ

細菌

大気浄化

抗菌

タバコ臭CeO2ZnO

脱臭

オゾン層

光触媒
有機塩素化合物

砂、埃浄水

Re2O3UV

防汚Absorption
皮膚超撥水性超親水性

窒素ドープ酸化チタン

可視光応答型光触媒

紫外線遮蔽材料

高輝度発光材料

表面機能材料

微細構造、形態制御によるセラミックス材料の環境刺激応答機能性制御
１．微粒子; ２．薄膜の微細構造と形態・組成制御
ソフト溶液反応は有効、且つ環境にやさしい材料合成手段

Introduction
処理プロセスとエネルギー消費 - 溶液プロセス ---- 環境に優しいプロセス
14VaporPlasmaFree energy (G)

△G v

Glass
△G m

Supercooledmelt△G aq.s ol

Aqe oussolution

Ceramic
mater ials(solid)

Solid

Log pressure (Pascal)

12

Ultra highPressure

Environmentally stressedHigh pressure108
Hydrothermal

6Solution
Flux
Solid state r eaction

Melt

4

Environmentallystressed

Plasma2Vapor deposition

Melt0

Ultra hightemper atureEnvironmentally stressed

01000

2000

Temperature (ÞC)
Temperature (T)Fig. Schematic energy diagram (G-T) in a single component system[*].

Fig. Schematic P-T diagram for preparative techniques[*].

*M.Yoshimura etc. Solid State Ionics, 98, 197-208, 1997

Hydrothermal Process
It has become a promising method for material synthesis
because of the possibility of producing nanosize crystals
with soft agglomeration, and controlling the phasecomposition or morphology by optimizing reaction
conditions, shows advantages in novel material synthesis.

Why Hydrothermal /Solvothermal ?

Table Advanced Oxide Powder Process Comparison [*, **]CostComposition Control
Morphology Control
Powder reactivity
Purity(%)
Homogeneity
Agglomeration
Calcination stepMilling step

Conventional

Sol-GelLow-moderate
Poor
Poor
Poor
< 99.5Poor
Moderate
Yes
Yes

High
Excellent
Moderate
Good> 99.5
Very goodModerate
Yes
Yes

Coprecipitation

Moderate
Good
Moderate
Good> 99.5
GoodHigh
Yes
Yes

Hydrothermal /Solvothermal
Moderate
Excellent
GoodGood> 99.5
Very goodLow
NoNo

Instead of water, some organic solvents can be used as reaction media Æ Solvothermal Process
Ref.* Dawson, W. J., 1988, Am. Ceram. Soc. Bull., 67, 1673-1678.
**Cousin, P., and Ross, R. A., 1990, Mater. Sci. Eng., A130, 119-125.

Introduction

溶液反応に用いられる溶媒の性質

Table Physical properties of various solvents[＊]
Solventb.p.

Water
EtOH
Propanol
Butanol
Ethylene glycol
Glycerol
1,2-Propanediol
1,3-Propanediol
1,3-Butanediol
1,4-Butanediol
1,5-Pantanediol
1,6-Hexanediol

/ oC
100
78.2
97.2
117.7
197.8
290
187.6
214.4
207.5
230
238
208

Viscosity(25oC)/ mPas
0.890
1.074
0.321
2.544
16.1
934
40.4-DielectricConstant(20oC)
80.1
25.3
20.8
17.84
41.4
45.7
27.5
35.1
28.8
31.9
26.2
25.86

Thermalconductivity(25oC)/ Wm-1K-1
0.607
0.169
0.154
0.154
0.256
0.292
0.200
-＊D.Lide and H.Frederikse (ed.) CRC Handbook of Chemistry and Physics, 76th Edn., CRC Press, Inc.,
NeYork, 1995-1996.

ZnO:古くて新しい素材
幅広い応用

工業原料

ゴム添加剤

陶器
ウルツ鉱結晶構造: 六方晶、c-axis: 極性顔料

近年：
半導体としての新しい性質が注目されている：

医薬品

圧電性(中心対称を持たないため)酸化亜鉛透明導電膜(In代替材 )食品添加剤

色素増感太陽電池
青色発光LED(ＧａＮ代替材 )など

電子材料

Photographs: http://www.ruilaibao.com/html/index.html

化粧品

Introduction

ZnO のユニークな形態を応用する研究例
Nanogenerators

Zhonglin Wang, et Piezoelectric Nanogenerators
Based on Zinc Oxide Nanowire Arrays
Science, 312,2006,242

Introduction

ZnO のユニークな形態を応用する研究例
Nanogenerators

Zhonglin Wang, etPiezoelectric Nanogenerators Based on ZincOxide Nanowire Arrays
Science, 312,2006,242

微細構造の制御された酸化亜鉛はバルク材料にないスマートな特性が期待される
Introduction
ZnO has wide applications in short-wavelength ultraviolet lasers, blue light emitting
diodes (LEDs), photocatalytic reaction, solar cell, sensor, pigments, UV shieldingmaterial, etc. It is expected that the physical-chemical properties greatly change withthe morphology of the zinc oxide crystals. It is important to synthesize ZnO withhigh specific surface area and controllable morphology.

ZnO is a very old material, recently, very new functions were discovered.
Solid-State Thermal Sublimation Process:Z.L. Wang, et al Piezoelectric Nanogenerators Based on Zinc Oxide
Nanowire Arrays, Science, 312,2006,242
Z.L. Wang, Self-assembled nanoarchitectures of polar nanobelts/nanowires,
J.Mater.Chem, 15,2005, 1021

In the present talk:溶液プロセスによる酸化亜鉛の形態制御

realize the morphological control by a low-temperature heating processusing various organic solvents;
clarify the crystalline growth mechanism of ZnO with nano structures.
Effect of zinc concentration, reaction time, reaction media, kinds of precipitates
Precursor:[Zn2+]: Zn(NO3)2 ・6H2O : ZnCl2; Zn(AC)2・2H2O; ZnSO4

Precipitates:

Hexamethylenetetramine (HMT, C6H12N4) ; Urea(N2H4CO)[Zn2+ ] : [HMT] or [urea]= 1:1

Reaction Media/Additives:

Aqueous solution
Organic solvent-aqueous solutions mixture(e.g. Alcohols, Hexane, Ethylene Glycol ) et al.

Reaction Conditions:

95oC, 3-192 h, together with a glass substrate

C6H12N4 + 6H2O Æ 6HCHO + 4NH3(Hydrolysis)(1)

N2H4CO + H2O ÆCO2 + 2NH3

(Hydrolysis)(2)

Zn2++ 4NH3 + 4H2OÆ Zn(OH)2 +4NH4+ + 2OHÆ [Zn(NH3)4]2+ +4H2OÆ ZnO + 2OH- + 4NH4+ +H2O (Precipitation & Crystallization) (3)キーワード：精密構造制御と高次機能性
特性評価例：
発光特性
光触媒活性
ＵＶ遮蔽特性
親水性、撥水性センサー特性Effect of Zn2+ concentration ---- Aqueous reaction system 核生成速度制御

1M [Zn2+]

0.1M [Zn2+]

0.01M [Zn2+]0.001M [Zn2+]
Homogeneous ZnO film on substrate
withwell -dispersed fine hexagonal particles
0.001M [Zn2+]

0.0001M [Zn2+]

Fig. SEM photographs of ZnO powders prepared by heating various concentration of Zn2+-HMT aqueous solution at 95oC for 3 h.

ZnO nano-rod can not be produced at high zinc concentration [Zn2+] > 1 M- Low concentration/precipitation rate prefer to form perfect crystalline structure
The crystalline size & aspect ratio of nano-rod decreased with [Zn2+] concentration

Morphological Control ---- in Aqueous reaction system

95oC, 3h

Zn/HMT = 1:1

95oC, 76h

SEM images of (a)hexagonal and (b)screw-like ZnO nano rod prepared byheating Zn2+-HMT aqueous solution at 95oC for 3 and 76 h, respectively.

Microstructure of ZnO also changed with treatment timeFormation mechanism of the nanoscrews from nanorods
During the “Dissolution - Reprecipitation” process:The existence of complex and molecules may affectthe precipitation position
NH4+ adsorption site : Dissolution Site[Zn(NH3)4]2+ complex site : Precipitation Site
Selective precipitation on different direction /surface

In most case, because of the repulsion force among the disks, [Zn(NH3)4]2+ complex preferred
to be adsorbed on the edge of the disks and crystallized to form large (001) area and lead tothe “Formation of Parallel Disks”.

-- Low concentration prefers to form thin and large circle structure ?

Formation mechanism of ZnO nano screw
3.0 h001

76 h001

192 h001

001
001

- 010
110 100

Microstructure:Related to the Dissolution - Reprecipitation process
Dissolution: lead to decrease of diameter of HEXAGON
Reprecipitation [at very low Zn2+ concentration]:
J.Mater.Chem., 15, 4584-4587, 2005.
Lead to increase of diameter of SCREW & surface area

ZnO Nano Screw --- Oriented growth of Zinc Oxide
001
001[0001]

SEM, TEM, and electronic diffraction pattern of the screw-like ZnO nanoparticles prepared by heating Zn2+-HMT aqueous solution at 95oC for 192h.

Effect factors on the microstructure of ZnO particles:

Solvent effect:different

dielectric constantviscosity
shows
different diffusion coefficientdifferent solubility of ZnO
lead todifferent nuclear formation rate
different morphology
during the dissolution-reprecipitation process.
Surfactant / Additive:
affect the adsorption of ions on different crystal planes
Zinc complex formation:affect the nuclear growth during the reprecipitation
Zinc ion:easy to form 4-coordinated tetrahedron structure
6-coordinated octahedron structure
Structure of zinc complex: affected by the existence ofammonia, HCHO, CO2 and solvent (e.g. EG)

Lotus Leaf: Microstructure Hydrophobic Mechanism

http://www.snpc.org.cn/train/view.asp?ID=1061

Water-repellent legs of water striders

Photocatalyst: Light Induced Hydrophilic Mechanism

L.Jiang, Nature,432, 36, 2004

A.Fujishima, Nature,388, 431 1997

Application:

Self CleaningHydrophilicity of ZnO film with various morphologies

超溌水

光照射なし！光触媒と異なる超親水化メカニズム！

Superhydrophobic surface

超親水Superhydrophilic surface

同一材料にもかかわらず、形態の異なるものは正反対的な性質を示す

Superhydrophobic surface

Superhydrophilic surface

Physical-Chemical Properties

Active oxygen species

Water contact angle

8000160

SuperhydrophilicSurface

SuperhydrophobicSurface

Contact Angle (degree)

Chemical Luminous Intensity (cps)

10000

6000

4000

2000

Nano rod superstructures

12080

Nano-screw superstructures

40000204060

80

Reaction time (h)

100

120

1400255075
100 125 150
Reaction time (h)175Fig. The chemical luminous intensity and the contact angle of water drops on
the surface of ZnO films of ZnO films prepared by heating Zn2+-HMTaqueous solution at 95oC for various reaction times.

200

Effect of EG Additive & Reaction Time(a)-12h(a)-24h(a)-120h( b)-12h( b)-24h( b)-120h

SEM images of ZnO crystal prepared in (a) aqueous solution(b) 50%EG solution for 12h; 24h; and 120h.

Effect of EG additive on themorphologies of ZnO

アスペクト比の制御6(b)5aspect ratio

(a)

432
103040506070

EG vol.%(c)(d)SEM images of ZnO crystals prepared in EG Solution with different
concentrations (a) 30% (b)50% (c)70% (d)80%

Selective synthesis of ZnO nanorods with various aspect ratios

80Effect of Precursors: 50% EG-50%aqueous solution system

前躯体の影響ZnO:

ZnO:

Monodispersed
nano rodL ≒ 1.35 µ;D≒0.19 µ ;Aspect ≒ 7,in ZnNO3

Porous Rod

Zn5(OH)8Cl2・H2O:

in ZnNO3ZnO Nut:

Simonkoleite

in ZnCl2

InZn(CH3COO)2

SEM photographs of ZnO particles prepared from (a)0.001M Zn(NO3)2, (b)0.05M Zn(NO3)2, (c)0.05M ZnCl2, (d)0.05M (Zn(CH3COO)2 solutions with 50% EG additive at 95oC for 3h.

板状酸化亜鉛の合成
Effect of ZnCl2 - HMT mixed solution concentration and EG additive on the morphology[Zn2+]:

0.01M

0.05M

0.1M

EG: 0%

EG: 50%Zn5(OH)8Cl2.H2O

ZnO

Fig. SEM photographs of the crystals prepared at 95oC for 12h in (a) 0.01M, (b) 0.05M, (c) 0.1M
and in (d) 0.01M, (e) 0.05M, (f) 0.1M ZnCl2 - HMT mixed 50vol.% EG aqueous solution.
S. YIN et al, Nanoscale Res. Lett., 4, 247-253 (2009)

XRD & FTIR
Plate-like
Rod-like
Zn5(OH)8Cl2.H2O ZnO

Agreed with SEM results

Transmittance

(d)
(c)

Zn5(OH)8Cl2.H2O

1630
3434

(b)

520
898
720

ZnO
Zn5(OH)8Cl2.H2O(a)

1630

ZnO

O-H3434

898
720
520
520

4000

3600

3200

2800

2400

2000

16001200800400

Wavernumber/cm-1

Fig. XRD patterns and FTIR spectra of the products prepared at 95oC for 12h in (a) 0.01M,(b) 0.05M, (c) 0.1M ZnCl2 - HMT mixed aqueous solution and in (d) 0.01M, (e) 0.05M, (f)0.1M ZnCl2 - HMT mixed 50vol.% EG solution. (b),(c), (f): simonkolleite:Zn5(OH)8Cl2.H2O; (a), (d), (e): wurtzite ZnO

S. YIN et al, Nanoscale Res. Lett., 4, 247-253 (2009)

板状酸化亜鉛の合成

Fig. SEM images of samples prepared in (a) 0.05M ZnCl2 - HMT mixed aqueous solution
followed by calcination at (b) 300oC, (c) 600oC, (d) 1200oC; and in (e) 0.1M ZnCl2 - HMT
mixed 50 vol.% EG aqueous solution followed by calcination at (f) 300oC, (g) 600oC, (h)1200oC.
S. YIN et al, Nanoscale Res. Lett., 4, 247-253 (2009)

(002)に配向した板状酸化亜鉛
ZnO

シモンコーレアイト
Zn5(OH)8Cl2･H2O

Fig. XRD patterns of samples prepared in (a) 0.05M ZnCl2 - HMT mixed aqueous solution
followed by calcination at (b) 300oC, (c) 600oC, (d) 1200oC; and in (e) 0.1M ZnCl2 - HMT
mixed 50 vol.% EG aqueous solution followed by calcination at (f) 300oC, (g) 600oC, (h)1200oC.

DeNOx光触媒評価装置

Continuous Reaction SystemHhν
NO → HNO2 and/or HNO3GI
F, λ>400nm

J165mmR
YanacoE, λ>510nm
K, NO gas
M
L, AirONDA

B C

ELC-88A

NOxP

Q

Fig. Experimental apparatus used for photocatalytic destruction of nitrogen monoxide. A:
Sealed opaque reactor (Plastic, 373cm3); B: Glass holder; C: Catalyst (20×16×0.5 mm); D:
Colorless and transparent plastic cover; E: 510 nm cut off filter (Fuji, triacetyl cellulose); F:400 nm cut off filter (Kenko, L41 Super Pro(W)), ; G: 450W high-pressure mercury lamp; H:Pyrex jacket (cut off the light λ < 290nm); I: Cooling water (30oC); J: Electric fun; K: 2ppm
standard NO gas (Flow rate: 100ml/min); L: Air (Flow rate: 100ml/min); M: Gas mixer;
N,O,P: Three-way cock; Q: Thermometer; R: NOx analyzer (Yanaco, ECL-88A)

板状酸化亜鉛のＵＶ吸収特性と光触媒活性100(d) Commercial ZnO

Reflectance / %8060(b) Rod-like ZnO(a) Plate-likesimonkolleite(c) Plate-like ZnO
40200200300

400500

Wavelength / nm

600700Fig. DRS spectra of samples prepared at95oC in ZnCl2 - HMT mixed aqueoussolution. (a) plate-like simonkolleite; (b)rod-like ZnO; (c) plate-like ZnO; (d)commercial ZnO nanoparticles.

球状粒子・3Dバラ状粒子の合成と特性

5000

Sphere-like ZnO500(a) as prepared(b) after modified

4500

388 nm(a) sphere-like(b) 3D flower-like

400

3500

Intensity(a.u.)

Intensive/a.u.

4000

3D flower-like ZnO

3000
2500
20001500200(b)1000

100 101002

500
0300(b)200468 nm(a)100102(a)110103 112
0-5001020304050

2 Theta(degree)

6070

80

400

500600

Wavelength(nm)Fig. XRD patterns (Left) and room-temperature photoluminescence spectra (Right) of theZnO thin films consisted of different superstructures. (a) sphere-like (b) 3D flower-like.

様々な形態を示す酸化亜鉛の発光特性

Fig. Photoluminescence spectrum of ZnO crystals with different morphologies.

ユニークな形態を有する酸化亜鉛粒子

(A)

(B)

(C)

(D)

(F)

(H)

(E)

(G)

(I)

ユニークな形態を有する酸化亜鉛粒子の光触媒特性
表面構造が発達させることによって、光触媒活性が向上した！

Table DeNOx ability of the samples prepared at different conditions

Concept: 光閉じ込め効果による光触媒活性の向上：
窒素ドープ酸化チタン/酸化亜鉛ナノスクリュー/窒素ドープ酸化チタン サンドイッチ構造
ZnO

ソルボサーマル反応によるアナターゼTiO2-xNyナノ粒子を利用：
S.Yin, etc., J.Mater.Chem., 2005,15, 674.

Synthesis and Photocatalytic Activity of TiO2-xNy / ZnO Nano-screw / TiO2-xNy composites

Rod-like and Spherical Morphologies: Prepared by using HMT as precipitation reagent
ソルボサーマル反応による窒素ドープ酸化チタンの合成：異なる結晶相を選択的合成できる

Brookite

AnataseShare coeners & 3 edges
With neibour octahedraRutile

Share coeners & 4 edges
With neibour octahedra

Share coeners & 2 edges
With neibour octahedra

Anatase TiO2-xNy-サンドイッチ複合構造に使用

Fig. TEM photographs of nitrogen doped titania prepared under solvothermal conditions.
S.Yin, etc., J.Mater.Chem., 2005,15, 674.

TiO2-xNy-ZnO-TiO2-xNyサンドイッチ複合構造の作製

SEM
Zn2+Solution

Zn2+Solution

95oC
Spin-Coating

Spin-Coating

TiO2-xNy

TiO2-xNy

Glass substrate

Glass substrate

Sintering (400℃, 10 min）

(a)

(b)

(c)

(a)

(b)

(c)

Scanning electron micrographs of (a)TiO2-xNy thin film, (b)ZnO screw film,and (c)TiO2-xNy/ZnO composite film. Upper: cross section; Lower: Top view.

DRS

TiO2-xNy-ZnO-TiO2-xNyサンドイッチ複合構造膜の光吸収特性100(b)ZnO screw film(b)Reflectance / %80(c)TiO2-xNy – ZnO composite film

(c)

60(a)

(a)TiO2-xNy thin film

40200200

300

400500
Wavelength / nm

600700Diffuse reflectance spectra of (a)TiO2-xNy thin film, (b)ZnO screw film, and(c)TiO2-xNy – ZnO composite film.

0.10

DeNOx & QEQuantum Effiency / %(C)

Vis >510

Vis >510-400

UV-Vis >400-290

0.08

Photocatalytic deNOx ability
0.06
(c)
(a)

0.04

(b)
0.02

(c)

(b)

(c)

(a)
(b)

(a)
0.00
100(B)80
DeNOx ability / %S.Yin, et al
Res. Chem. Intermed., 34, 393-402 ,2008.

Vis >510

Vis >510-400(a)TiO2-xNy thin film,(b)ZnO screw film,(c)TiO2-xNy/ZnO/ TiO2-xNy
composite film

UV-Vis >400-290

Photocatalytic Quantium effciency

60
(a)
(b)

40(c)
(c)
(a) (b)0

光の利用効率が向上し、

(a)

20(c)

λ > 510

複合化行うことによって、(b)510 > λ > 400

光触媒活性と量子収率が向上した！
400 > λ > 290

Wavelength / nm

Photocatalytic deNOx ability and Quantium effiency of the thin film of ( (b)ZnO screw film, and(c)TiO2-xNy – ZnO composite film. The data were treated against various wavelength ranges.

今後の展開、将来の展望
本課題を通して様々な形態を有する酸化亜鉛粒子及び粒子膜の合成に成功し、UV-熱線遮蔽材料、導電性薄膜材料、ガスセンサー、体質顔料としての応用を展開しており、薄膜のみならず、粉体としての性能発揮も期待でき、ユニークな形態に起因するスマートな新機能性の検討を行うと共に、デバイスの構築など実用化へ向けた更なる研究を推進する予定である。

溶液プロセスによるZnO以外の無機材料の形態制御例

CeO2Re2O3
500nm

50nm

100nm

TiO2-xNy

Ce2(PO4)2HPO4 . H2O

K0.81Ti1.73Li0.27O4

Thank you for your attention !
謝辞：
本研究は平成18年度日本板硝子材料工学助成会の研究助成を受けて行ったものである。
同助成会に心より感謝致します。