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

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: [email protected]

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

Institute of Multidisciplinary Research for Advanced Materials, Tohoku University

2-1-1 Katahira, Aoba-ku, Sendai 980-8577, JAPAN

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

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

h⁺ e^-

hυ

E_b ^{UV遮蔽材料}

光触媒材料

発光材料 e^- + h⁺→hυ hυ→ e^- + h⁺ e^- + O₂→ ・O₂^- h⁺ + OH^- → ・OH

光誘起機能

超撥水性 超親水性

Absorption

オゾン層

皮膚

UV

窒素ドープ酸化チタン 光触媒

大気浄 化

脱臭

防汚 浄水

抗菌

NOｘ、SO_ｘ

タバコ臭

有機塩素 化合物

細菌

砂、埃

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

TiO ₂ CeO ₂ Re ₂ O ₃ ZnO

Temperature (T)

Free energy (G)

Va por P la sma

S uperc ooled melt

Aqe ous solution

S olid C era m ic

m ater ials (solid)

Melt Glass

△G_v

△G_m

△G_{a q.s ol}

Ultra high

P ressure Environmenta lly str essed High pr essure

Hydr othe rmal S olution

F lux

S olid sta te r ea ction Melt Environm enta lly stresse d

Va por de position

Environmenta lly str essed

P la sma

Ultra high tem per ature

0      1000       2000

Temperature (ÞC)

10 12 14

0 8 6 4

Log pressure (Pascal) 2

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

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

Introduction

Table Advanced Oxide Powder Process Comparison [*, **]

Conventional Sol-Gel Coprecipitation Hydrothermal / Solvothermal

Cost Low-moderate High Moderate Moderate

Composition Control Poor Excellent Good Excellent

Morphology Control Poor Moderate Moderate Good

Powder reactivity Poor Good Good Good

Purity(%) < 99.5 > 99.5 > 99.5 > 99.5

Homogeneity Poor Very good Good Very good

Agglomeration Moderate Moderate High Low

Calcination step Yes Yes Yes No

Milling step Yes Yes Yes No

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.

Why Hydrothermal / Solvothermal ?

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 phase

composition or morphology by optimizing reaction

conditions, shows advantages in novel material synthesis.

Instead of water, some organic solvents can be used as reaction media Æ Solvothermal Process

Table Physical properties of various solvents^[＊]

Solvent b.p. Viscosity Dielectric Thermal (25^oC) Constant conductivity / ^oC / mPas (20^oC) (25^oC)/ Wm^-1K^-1

Water 100 0.890 80.1 0.607

EtOH 78.2 1.074 25.3 0.169

Propanol 97.2 0.321 20.8 0.154

Butanol 117.7 2.544 17.84 0.154

Ethylene glycol 197.8 16.1 41.4 0.256

Glycerol 290 934 45.7 0.292

1,2-Propanediol 187.6 40.4 27.5 0.200

1,3-Propanediol 214.4 - 35.1 -

1,3-Butanediol 207.5 - 28.8 -

1,4-Butanediol 230 - 31.9 -

1,5-Pantanediol 238 - 26.2 -

1,6-Hexanediol 208 - 25.86 -

＊D.Lide and H.Frederikse (ed.) CRC Handbook of Chemistry and Physics, 76th Edn., CRC Press, Inc., NeYork, 1995-1996.

溶液反応に用いられる溶媒の性質

Introduction

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

ZnO:

幅広い応用

ウルツ鉱結晶構造: 六方晶、c-axis: 極性 近年：

半導体としての新しい性質が注目されて いる：

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 ) 色素増感太陽電池

青色発光LED(ＧａＮ代替材 ) など

顔料

化粧品 医薬品

食品添加剤

電子材料 工業原料

ゴム添加剤

陶器

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, et

Piezoelectric Nanogenerators Based on Zinc Oxide Nanowire Arrays

Science, 312,2006,242

Introduction

Nanogenerators

Z.L. Wang, et alPiezoelectric 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

Introduction

ZnO has wide applications in short-wavelength ultraviolet lasers, blue light emitting diodes (LEDs), photocatalytic reaction, solar cell, sensor, pigments, UV shielding material, etc. It is expected that the physical-chemical properties greatly change with the morphology of the zinc oxide crystals. It is important to synthesize ZnO with

high specific surface area and controllable morphology.

ZnO is a very old material, recently, very new functions were discovered.

Solid-State Thermal Sublimation Process:

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

In the present talk:

realize the morphological control by a low-temperature heating process using various organic solvents;

clarify the crystalline growth mechanism of ZnO with nano structures.

Effect of zinc concentration, reaction time, reaction media, kinds of precipitates

C₆H₁₂N₄+ 6H₂O Æ6HCHO + 4NH₃ (Hydrolysis) (1)

N₂H₄CO + H₂O ÆCO₂+ 2NH₃ (Hydrolysis) (2)

Zn²⁺+ 4NH₃ + 4H₂OÆZn(OH)₂+4NH₄⁺+ 2OH^-

Æ [Zn(NH₃)₄]²⁺ +4H₂OÆ ZnO + 2OH^- + 4NH₄⁺+H₂O (Precipitation & Crystallization) (3)

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: 95^oC, 3-192 h,

together with a glass substrate

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

キーワード：精密構造制御と高次機能性

Effect of Zn

concentration ---- Aqueous reaction system

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

1M [Zn²⁺] 0.01M [Zn²⁺]

0.0001M [Zn²⁺] 0.001M [Zn²⁺]

0.1M [Zn²⁺]

0.001M [Zn²⁺]

Homogeneous ZnO film on substrate with

well -dispersed fine hexagonal particles

ZnO nano-rod can not be produced at high zinc concentration [Zn

] > 1 M

- Low concentration/precipitation rate prefer to form perfect crystalline structure

The crystalline size & aspect ratio of nano-rod decreased with [Zn

] concentration

Morphological Control ---- in Aqueous reaction system

SEM images of (a)hexagonal and (b)screw-like ZnO nano rod prepared by heating Zn

-HMT aqueous solution at 95

C for 3 and 76 h, respectively.

95

C, 3h 95

C, 76h

Microstructure of ZnO also changed with treatment time

Zn/HMT = 1:1

Formation mechanism of the nanoscrews from nanorods

During the “Dissolution - Reprecipitation” process:

The existence of complex and molecules may affect the 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 to the “Formation of Parallel Disks”.

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

Formation mechanism of ZnO nano screw

192 h 76 h

3.0 h

Microstructure:Related to the Dissolution - Reprecipitation process Dissolution: lead to decrease of diameter of

Reprecipitation [at very low Zn

concentration]:

Lead to increase of diameter of

&

001 001

001 001 001

110 100- 010

J.Mater.Chem., 15, 4584-4587, 2005.

[0001]

SEM, TEM, and electronic diffraction pattern of the screw-like ZnO nano particles prepared by heating Zn

-HMT aqueous solution at 95

C for 192h.

ZnO Nano Screw --- Oriented growth of Zinc Oxide

001 001

Solvent effect:

different dielectric constant viscosity

shows different diffusion coefficient different solubility of ZnO

lead to different 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 of

ammonia, HCHO, CO

and solvent (e.g. EG)

Effect factors on the microstructure of ZnO particles:

Photocatalyst: Light Induced Hydrophilic Mechanism A.Fujishima, Nature,388, 431 1997

Lotus Leaf: Microstructure Hydrophobic Mechanism http://www.snpc.org.cn/train/view.asp?ID=1061

Water-repellent legs of water striders

L.Jiang, Nature,432, 36, 2004

Application:

Self Cleaning

Hydrophilicity of ZnO film with various morphologies

Superhydrophobic surface

Superhydrophilic surface

光照射なし！光触媒と異なる超親水化メカニズム！

超溌水

超親水

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

Fig. The chemical luminous intensity and the contact angle of water drops on the surface of ZnO films of ZnO films prepared by heating Zn

-HMT

aqueous solution at 95

C for various reaction times.

Physical-Chemical Properties

0 40 80 120 160

0 25 50 75 100 125 150 175 200

Contact Angle (degree)

Reaction time (h)

Nano rod superstructures

Nano-screw superstructures

0 2000 4000 6000 8000 10000

0 20 40 60 80 100 120 140

Chemical Luminous Intensity (cps)

Reaction time (h) Superhydrophobic

Surface

Superhydrophilic Surface

Active oxygen species Water contact angle

Effect of EG Additive & Reaction Time

(a)-12h (a)-24h (a)-120h

( b)-120h

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

( b)-12h ( b)-24h

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

30 40 50 60 70 80 0

1 2 3 4 5 6

aspect ratio

EG vol.%

(a) (b)

(c) (d)

Effect of EG additive on the morphologies of ZnO

Selective synthesis of ZnO nanorods with various aspect ratios

アスペクト比の制御

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

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 95^oC for 3h.

ZnO:

Monodispersed nano rod

L ≒ 1.35 µ;

D≒0.19 µ ; Aspect ≒ 7, in ZnNO₃

Zn₅(OH)₈Cl₂・H₂O:

Simonkoleite

in ZnCl₂

ZnO Nut:

In

Zn(CH₃COO)₂

ZnO:

Porous Rod

in ZnNO₃ 前躯体の影響

[Zn

]: 0.01M 0.05M 0.1M

EG: 0%

EG: 50%

Fig. SEM photographs of the crystals prepared at 95^oC 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.

Effect of ZnCl₂ - HMT mixed solution concentration and EG additive on the morphology

Zn₅(OH)₈Cl₂.H₂O ZnO

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

板状酸化亜鉛の合成

Fig. XRD patterns and FTIR spectra of the products prepared at 95^oC 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 XRD & FTIR

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

Agreed with SEM results

4000 3600 3200 2800 2400 2000 1600 1200 800 400 ZnO

ZnO

Zn5(OH)8Cl2.H2O

1630

520

520520

720

720 3434 898

(d)

(c) (b)

Transmittance

Wavernumber/cm-1 (a)

3434 898

O-H

1630 Zn5(OH)8Cl2.H2O

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

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

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

板状酸化亜鉛の合成

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

ZnO

シモンコーレアイト Zn₅(OH)₈Cl₂･H₂O

(002)に配向した板状酸化亜鉛

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 (30^oC); 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: NO_x analyzer (Yanaco, ECL-88A)

DeNOx光触媒評価装置 Continuous Reaction System

H

NO_x

Yanaco

ELC-88A

G I

J F, λ>400nm

E, λ>510nm

165mm

K, NO gas L, Air

M

N

A B C

D

Q

O P

R

NO → HNO

and/or HNO

h ν

Fig. DRS spectra of samples prepared at 95^oC in ZnCl₂ - HMT mixed aqueous solution. (a) plate-like simonkolleite; (b) rod-like ZnO; (c) plate-like ZnO; (d) commercial ZnO nanoparticles.

200 300 400 500 600 700

0 20 40 60 80 100

Reflectance / %

(b) Rod-like ZnO

Wavelength / nm (a) Plate-like

simonkolleite

(d) Commercial ZnO

(c) Plate-like ZnO

板状酸化亜鉛のＵＶ吸収特性と光触媒活性

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

球状粒子・

3D

400 500 600

0 100 200 300 400 500

(b)

Intensity(a.u.) (a)

Wavelength(nm)

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

468 nm

388 nm

10 20 30 40 50 60 70 80

-500 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

200

103112 102 110

100 002

(b)

Intensive/a.u.

2 Theta(degree)

(a) as prepared (b) after modified

(a) 101

Sphere-like ZnO 3D flower-like ZnO

Fig. Photoluminescence spectrum of ZnO crystals with different morphologies.

様々な形態を示す酸化亜鉛の発光特性

(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

Table DeNO

ability of the samples prepared at different conditions

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！

Synthesis and Photocatalytic Activity of TiO_2-xN_y / ZnO Nano-screw / TiO_2-xN_y composites

Concept:

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TiO_2-xN_yナノ粒子を利用：

S.Yin, etc., J.Mater.Chem., 2005,15, 674.

Rod-like and Spherical Morphologies: Prepared by using HMT as precipitation reagent

Fig. TEM photographs of nitrogen doped titania prepared under solvothermal conditions.

Brookite

Rutile Anatase

Share coeners & 3 edges With neibour octahedra

Share coeners & 4 edges With neibour octahedra

Share coeners & 2 edges With neibour octahedra

S.Yin, etc., J.Mater.Chem., 2005,15, 674.

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

Anatase TiO_2-xN_y-サンドイッチ複合構造に使用

(a) (b)

(a) (b) (c)

(c)

Scanning electron micrographs of (a)TiO

N

thin film, (b)ZnO screw film, and (c)TiO

N

/ZnO composite film. Upper: cross section; Lower: Top view.

SEM

95^oC Zn²⁺

Solution

Zn²⁺

Solution

TiO_2-xN_y

Glass substrate

TiO_2-xN_y

Glass substrate Spin-Coating

Spin-Coating

Sintering (400℃, 10 min）

TiO_2-xN_y-ZnO-TiO_2-xN_yサンドイッチ複合構造の作製

Diffuse reflectance spectra of (a)TiO

N

thin film, (b)ZnO screw film, and (c)TiO

N

– ZnO composite film.

DRS

0 20 40 60 80 100

200 300 400 500 600 700

Reflectance / %

Wavelength / nm (a)

(b) (c)

(a)TiO_2-xN_ythin film (c)TiO_2-xN_y– ZnO composite film

(b)ZnO screw film

TiO_2-xN_y-ZnO-TiO_2-xN_yサンドイッチ複合構造膜の光吸収特性

0 20 40 60 80 100

λ > 510 510 > λ > 400 400 > λ > 290

DeNOx ability / %

Wavelength / nm (a)

(a)

(a) (b) (b)

(b) (c) (c)

(c)

(B) ^Vis _>510 ^Vis >510-400 UV-Vis >400-290

0.00 0.02 0.04 0.06 0.08 0.10

Quantum Effiency / %

(a)

(a) (a)

(b) (b)

(b) (c) (c)

(c)

(C) Vis _>510 Vis >510-400 UV-Vis >400-290

Photocatalytic deNOx ability and Quantium effiency of the thin film of ( (b)ZnO screw film, and (c)TiO_2-xN_y – ZnO composite film. The data were treated against various wavelength ranges.

DeNO

& QE

複合化行うことによって、

光の利用効率が向上し、

光触媒活性と量子収率が向上した！

S.Yin, et al

Res. Chem. Intermed., 34, 393-402 ,2008.

Photocatalytic deNO_x ability

(a)TiO_2-xN_y thin film, (b)ZnO screw film,

(c)TiO_2-xN_y/ZnO/ TiO_2-xN_y composite film

Photocatalytic Quantium effciency

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-

溶液プロセスによるZnO以外の無機材料の形態制御例

CeO₂

Re₂O₃

TiO_2-xN_y

100nm

500nm 50nm

K_0.81Ti_1.73Li_0.27O₄ Ce₂(PO₄)₂HPO₄ . H₂O

Thank you for your attention !

謝辞：

本研究は平成

18

同助成会に心より感謝致します。