論文内容要口

チョウハイリン
氏
名
与
授
学位
張市森
博士(学術)
学位記番号
学術(環)博第 140 号
学位授与年月日
平成 2 3 年 3 月 2 5 日
学位授与の根拠法規
学位規則j 第 4 条第 1 項
研究科，専攻の名称
東北大学大学院環境科学研究科(博士課程)環境科学専攻
学位論文題目
Synthesis and Environmental Purification Property of
Visible-light Responsive Photocatalyst Based on Nitrogen
Doped Titanium Dioxide (窒素ドープ二酸化チタン基可視光応答
性光触媒の合成と環境浄化機能)
指導教
員東北大学教授佐藤次雄
論文審査委員主査東北大学教授佐藤次雄
東北大学教授本間
格
東北大学教授垣花異人
(多元物質科学研究所)
論文内容要
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1
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Chapter 2 Influence of synthesis method on the property of Ti0 2 _,N y
In this section, the influence of synthesis methods on the properties and photocatalytic activities of nitrogen
doped Ti0 2 was studied. Two high heating-efficient methods, "microwave-assisted solvothermal synthesis", and
"rapid solvothermal synthesis", were employed for the solvothermal synthesis of Ti0 2_xN y with titanium
trichloride and hexamethylenetetramine (HMT) as raw materials, where the HMT played an important role as both
the precipitant and the nitrogen source. The results revealed that by altering the adding amount of HMT or the
reaction solvent, the hydrolysis and precipitation rate could be controlled, and thus the Ti0 2_xN y with the
crystalline phases of brookite, rutile, anatase or mixed phases could be selectively formed .
By
the
solvothermal
microwave-assisted
method,
particles with nano size less than 30
nm, or with spherical morphology
could be synthesized in H 20
and
ethanol, respectively, as shown in Fig.
1. Both of them showed excellent
photocatalytic
activities
for
the
SOOnm
oxidative decomposition of NO gas
under both visible light and UV light
irradiation.
Figure 1. TEM images of the samples prepared at 190°C for 30 min in (a) H20
with 3 g HMT and (b) in EtOH with 2.5 g HMT
On the other hand, by the rapid solvothermal synthesis,
35
owning to the high heating efficiency and thermal conductivity of
30
the reaction system, Ti0 2_xN y could be synthesized in an
extremely short reaction time as 10 min. This reaction condition
not only reduced the operation time and energy consumption but
also led to the formation of Ti0 2_xN y nanoparticles with mixed
crystalline phases, high crystallinity and uniform rod-like
;,R
o
25
-0---
~ 20
(;
:.c
ro
O X 15
performance photocatalyst was determined as the reaction in H 20
zQ)
o 10
-<r--
under the irradiation of the visible light with a long wavelength of
300°
O°C
5
o~~--~----~----~----~
627(R)
for 10 min at 300°C, as shown in Fig. 2. The synergy effect led to
the extra- ordinarily high photocatalytic activity of Ti0 2_xN y , even
190°C
200°C
--<?- 250°C
------b-
_
morphology. The optimum reaction condition to obtain high-
P25 Ti0 2
530(G)
Wavelength I nm
445(8)
Figure 2. Photocatalytic activities of Ti02_xNy
prepared by rapid solvothermal method
627 nm.
Chapter 3. Influence of metal ion co-doping on the property of Ti0 2_xNy
This section investigated the influence of metal ion co-doping on the property and photocatalytic activity of
-
101 -
Ti0 2_xN y. By a facile hydrothermal method, nanopartic1es of Ti0 2_xN y co-doped with Ta, Nb, and Fe were
synthesized using TiCh, TaCI 5 , NbCI 5 , FeCh and hexamethylenetetramine as raw materials. The existences ofTa,
Nb, Fe, and N in the final products were confirmed by the EDX and XPS analysis. The obtained samples showed
extremely small crystallite sizes around 20 nm, and no change in crystalline phases, regardless of the co-doped
metal ions. Co-doping with Nb or Ta caused no change in the light absorption property, but slight decrease in
specific surface areas. Co-doping with Fe could enhance the visible light absorption, but showed no influence on
specific surface areas. However, for the photocatalytic activities in the decomposition of NO, the co-doping ofNb
and Ta showed a positive effect in enhancing the activity, while the Fe co-doping caused the decrease in activity.
The determining factor was attributed to the amount of anion vacancy in the samples with different
co-doping metal ions. In the N doped Ti0 2, since 0 2- was substituted by N 3-, anion vacancy would be formed for
charge compensation. Vacancy is usually considered as the recombination center of photo-induced electrons and
holes and would cause the decrease in photocatalytic activity. By co-doping a higher valence metal ion (Ta, Nb)
into Ti02_xN y, the amount of anion vacancy can be reduced; therefore, the photocatalytic activity can be enhanced.
In contrast, co-doping with a lower valence metal (Fe) ion would cause the increase in anion vacancy and result in
the decrease in photocatalytic activity, as shown in Fig. 3
35
«(
/I.=390nm
~ 30 .. *.
o
~
·e·····s.:;···············
OX 25
z
Q)
o
60
50 ....f::, ... ~.
50 ....f::, ...............•....•...•
o
o
:.0
n:s
60
o
v
f::,
A=445nm
v·····
···········t7················
/,=530nm
'·9· ........................................ .
~ 40
~
OX
....0 ... 0 ....... 0 ...................................... .
o
30 ... -O"'(j
o
A>400nm
[)
~ 20
o
20 ~
o
/,>510nm
10
Nb & Nco-doped Ti0 2
/,>290nm
<f? 40
~
2
4 6 8 10 12 14 16
Nb content / mol. %
~
0
... .o ...?
~ 30 ....
OX
~ 20
o
E] . •
~
),>400nm
...... ::?................................... o ... .
•..•.•.. 0 .......
[J ......................... .
Ic>510nm
10
Fe and Nco-doped Ti02
O~~~~~I~~~~~~~
o
........•.•.•..•.•.•..........
o
2
4
6
8
Fe content / mol. %
10
o
2
4
6
8
Fe content / mol. %
10
Figure 3. Photocatalytic activities of Ti02 co-doped with Nb & N, and Fe & N, and the composite of Ti02-xNy/Fe203
On the other hand, by simply altering the synthesis sequence, instead of Fe co-doped Ti02_xN y,
Ti02_xNylFe203 composite was also prepared. The coupling of these two compounds with different band gap
structure could effectively depress the recombination of electrons and holes by heterogeneous electron transfer,
and result in a high photocatalytic activity. The results also indicated that the status of Fein the samples would
greatly affect the performance of the samples in photocatalytic reaction.
Chapter 4. Enhancement of photocatalytic activity by structure control
This section represented the enhancements in photocatalytic activity by constructing two kinds of
heterostructured photocatalysts, KO.81 Ti1.73Lio.2704/Ti02-xNy, and attapulgite/Ti02_xN y'
By the coupling of Ti02_xN y nanopartic1es with plate-like
-102-
KO.81 Tiu3Lio.2704
without visible light
responsiveness, a sandwich-like structure
o
cf?
co 120
~
co
~
~ 80
::J
en
u
1+=
.~ 40
a.
was
30
which
processes
high
specific surface area and porosity due to
the bridging structure. The photocatalytic
activity in decomposing NO gas was also
greatly enhanced by coupling, especially
en
o
o0
formed,
o
20 40 60 80 100
Ti02 _X Ny / mass%
A>510nm
A>400nm
under
visible
light
irradiation.
optimum Ti0 2_xN y content was 70-90
20 40 60 80 100
Ti0 2 _X Ny / mass%
mass%,
and
the
composite
Figure 4. Specific surface areas and photocatalytic activities of the
KO.81 Tk73Lio.2704+ Ti02- xNy composites
The
with different Ti02- xNy contents
showed excellent activity similar or even
higher than unsupported Ti0 2 _xN y • Such enhancement in photocatalytic activity should be due to the bridging
structure and interaction between two semiconductors. Furthermore, the durability in photocatalytic reaction could
also be enhanced by forming this sandwich-like structure.
On the other hand, attapulgite/Ti0 2_xN y composites were
prepared by three different methods, including mixing by
CJ P 25 Ti0 2
70
hydrothermal reaction, impregnation in H 2 0 or soft grinding.
Attapulgite
E22ZI Atta+1 0% Ti0 2 _ Ny
60 E:3 Atta+25% Ti0 2_ Ny
X
The unique structure of attapulgite made it easy to be well
dispersed with Ti0 2_xN y nanoparticles regardless of the
coupling methods. The results revealed that even less than 10
wt.% addition of Ti0 2 _xN y , the attapulgite/Ti0 2 _xN y composite
showed excellent visible light responsive photocatalytic
activity, and by increasing the Ti02 _xN y content to more than
~
o
50
~
~
X
~
Atta+50% Ti0 2 _X Ny
~
Atta+ 70% TiO Ny
~ 40
OX
zQ)
30
Cl
20
10
25 wt. %, the activity of the composite even exceeded that of
unsupported
Ti0 2 _xN y •
The
excellent
> 510nm
photocatalytic
performance of the composites may be attributed to the high
absorptive ability of attapulgite for polar molecules.
> 400nm
> 290nm
Wavelength I nm
Figure
5.
Photocatalytic
activities
of
attapulgite, Ti02- xNy and the composites
Chapter 5. Summary and conclusions
In the present thesis, enhancements in the photocatalytic activity of Ti0 2_xN y were accomplished based on a
panoscopic assembling concept, in which the properties of Ti0 2-xN y were modified via a step by step control from
atomic to composite's level. The results suggested the importance of elements status, crystalline phases and
crystallinity in determining the photocatalytic activity of Ti0 2_xN y , which could be optimized by controlling the
synthesis methods. In order to fabricate a low-cost and high-performance visible light photocatalyst, supporting
Ti02_xN y on attapulgite clays was proven to be an easy and effective approach.
-103-
論文審査結果の要旨
クリーンで無尽蔵な太陽エネルギーを利用するう間的某反応は、持続可能な社会システムの構築に貢献する非
化石エネルギーフ。ロセスとして注目されており、セルフクリーニング、脱臭、抗菌、防曇等の分野で既に実用
化され、さらに環境浄化への利用が期待されている。しかし、現在利用されている酸化チタンう鵠帥某は約 3 e
V
の比較的大きなバンドギャップエネルギーを有し、紫外線しカ呼Ij用できないため、太陽光や室内灯の主成分で
ある可視光を利用可能な可視光応答性環境浄化う団故葉の開発が求められている。
本研究は、可視光吸収能を付与した窒素ドープ酸化チタンの高結晶化度ナノ粒子をソルボ、サーマル即臼こよ
り合成する手法を開発し、環境浄化湖故剥朝生 l こっし、て系統的に調べた研究であり、全編 5 章よりなる。
第 1 章は緒論であり、湖帥某反昆#輪、湖帥某の高活性化法、可視光応答性湖蝦などに関する過去の研究
を網羅し、その鞘教を述べ、また、重要ながら未解明な事項を列挙し、その上で、本研究の目指す方向とその
概要を述べている。
第 2 章では、水やアルコール水樹夜を用し、るソルボ、サーマル回芯により、窒素ドーフ酸化チタンナノ粒子を
合成し、う胡虫媒活性に及ぼす合成反応条件の影響について詳細に検討し、マイクロウェーブ加熱ソルボサーマ
ル即芯や急速昇温ソルボサーマル即剖こより、高活性可視光応答性窒素ドーフc酸化チタン淵蝶の合成が可能
であることを明らかにした。
第 3 章では、窒素ドーフ酸化チタンのうt鰍駒性に及ぼす糊日物の効果につして詳細に検討し、 Ti 4+ より高電
荷を有するNb5+や Ta5+ と窒素とのコドーヒ。ングによるアニオン欠陥形成の抑制、およひ鞍イ七鉄との複合化による
窒素ドーブ酸化チタンから酸化鉄への電子移動を利用した電子一正孔再結合の判制により、 7t角蚊尉舌性が向上
することを見出している。
第 4 章では、窒素ドープ酸化チタンのう間故知舌性に及ぼす複合化の効果について詳細に検討し、レピドクロ
サイト型層状チタン酸リチウムカリウムの層間剥離を利用して合成したサンドイツチ型複合体や、優れたガス
吸着特性を有するアタパルジャイト(粘土鉱物)ナノファイノ〈ーとの複合体を合成し、優れた環境浄化湖蝶
活性を有することを明らかにした。
第 5 章は結論であり、各章の結言を要約している。
以上、要するに本論文は、クリーンで無尽蔵な太陽エネルギーを利用する環境浄イ防団蚊葉の開発を目的とし
て、種々の可視光厄答性窒素ドーフ酸化チタンの合成法を開発するとともに、う団蛾鞘舌性に及ぼす諸国子の影
響について系統的に調べた研究で、あり、環境科学、物質科学の分野の発展に寄与するところ少なくない。
よって，材命文同専士(学術の学位論文として合格と認める。
-104-

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