photocatalytic properties of hierarchical zno flowers synthesized by a

Applied

Surface

Science

259 (2012) 557–

561
Contents

lists

available

at

SciVerse

ScienceDirect
Applied

Surface

Science
j

our

nal

ho

me

p

age:

www.elsevier.com/loc

ate/apsusc
Photocatalytic

properties

of

hierarchical

ZnO

flowers

synthesized

by

a
sucrose-assisted

hydrothermal

method
Wei

Lv
a
,

Bo

Wei
b
,

Lingling

Xu
a,b,∗
,

Yan

Zhao
c,∗∗
,

Hong

Gao

a
,

Jia

Liu
a
a
Key

Laboratory

of

Photonic

and

Electric

Bandgap

Materials,

Ministry

of

Education,

School

of

Physics

and

Electronic

Engineering,

Harbin

Normal

University,

Harbin

150025,

PR

China
b
Center

for

Condensed

Matter

Science

and

Technology,

Department

of

Physics,

Harbin

Institute

of

Technology,

Harbin

150080,

PR

China
c
Department

of

Physics,

Northeast

Forestry

University,

Harbin

150040,

PR

China
a

r

t

i

c

l

e

i

n

f

o
Article

history:
Received

6

November

2011
Received

in

revised

form

4

April

2012
Accepted

5

April

2012
Available online 24 July 2012
Keywords:
ZnO

flowers
Photocatalytic

properties
Hydrothermal

method
Sucrose
a

b

s

t

r

a

c

t
In

this

work,

hierarchical

ZnO

flowers

were

synthesized

via

a

sucrose-assisted

urea

hydrother-
mal

method.

The

thermogravimetric

analysis/differential

thermal

analysis

(TGA–DTA)

and

Fourier
transform

infrared

spectra

(FTIR)

showed

that

sucrose

acted

as

a

complexing

agent

in

the

synthe-
sis

process

and

assisted

combustion

during

annealing.

Photocatalytic

activity

was

evaluated

using
the

degradation

of

organic

dye

methyl

orange.

The

sucrose

added

ZnO

flowers

showed

improved
activity,

which

was

mainly

attributed

to

the

better

crystallinity

as

confirmed

by

X-ray

photoelec-
tron

spectroscopy

(XPS)

analysis.

The

effect

of

sucrose

amount

on

photocatalytic

activity

was

also
studied.
© 2012 Elsevier B.V. All rights reserved.
1.

Introduction
In

the

last

decade,

zinc

oxide

(ZnO)

nanostructures

have

aroused

tremendous

attention

due

to

its

distinguished

performance

in
piezoelectric

systems,

optoelectronics,

photovoltaic

energy

con-
version,

photocatalytic

decomposition

of

organic

pollutants

and

as
chemical

sensing

elements.

Also,

it

has

been

found

that

those

prop-
erties

can

be

improved

with

special

morphologies,

shapes,

sizes
and

crystallinity

of

ZnO

nanostructures

[1–6].

Thus,

the

designed
and

controllable

fabrications

of

ZnO

with

specific

morphologies

and
structures

have

been

explored

to

gain

superior

properties

in

recent
years

[7–10].
Three-dimensional

hierarchical

ZnO

exhibited

excellent

optical
and

catalytic

properties.

Primary

routes

for

three-dimensional

hier-
archical

ZnO

synthesis

include

vapor–liquid–solid

(VLS)

growth

at
relatively

high

temperature,

electrochemical

and

solution-based
methods

for

self-assembly

of

hierarchical

ZnO

[11,12].

Among

these
synthesis

methods,

the

hydrothermal

method

is

a

simple,

facile

and
∗
Corresponding

author

at:

Key

Laboratory

of

Semiconducter

Nanocomposite
Materials,

Ministry

of

Education

Department

of

Physics,

School

of

Physics

and

Elec-
tronic

Engineering,

Harbin

Normal

University,

Harbin

150025,

PR

China.
Tel.:

+86

451

88060526;

fax:

+86

451

88060629.
∗∗
Corresponding

author.

Tel.:

+86

451

88060526;

fax:

+86

451

88060629.
E-mail

addresses:

xulingling



(L.

Xu),


(Y.

Zhao).

controllable

way

to

obtain

large

yields

with

unique

morphology.
ZnO

can

be

used

as

a

kind

of

photocatalyst,

which

decomposes
organic

pollutants

with

ultra-violet

light

excitation

[2,4,13].

The
hierarchical

structures

increased

the

efficiency

of

optical

absorp-
tion

and

enhanced

the

photocatalytic

activity.

To

synthesize

the
hierarchical

mesoporous

ZnO,

the

multi-layered

basic

zinc

car-
bonate

(LBZC)

was

reported

to

be

used

as

a

precursor

in

the
urea

precipitation

or

hydrothermal

method

[14,19].

Several

reports
about

the

fabrication

of

LBZC

have

concerned

about

the

effects

of
surfactants.
In

the

past

decade,

kinds

of

morphologies

of

ZnO

can
be

synthesized

with

different

surfactant,

like

cetyltricetyl-
trimethylammonium

bromide

(CTAB),

sodium

dodecyl

sulfate
(SDS),

polyethylene

glycol

(PEG)

and

so

on

[21,4,22,23].

Usu-
ally,

the

environmentally-friendly,

low-cost

and

easily-obtainable
sucrose

is

used

as

fuel

in

the

combustion

synthesis

procedure

for
ceramic

material

fabrication

[5,6,15–17].

Also,

it

is

reported

that
sucrose

can

play

the

role

of

chealting

agent

after

the

hydroly-
sation

in

acid

solution.

In

this

work,

sucrose

was

introduced

in
the

urea

hydrothermal

procedure

to

fabricate

hierarchical

ZnO
flowers

as

a

chelating

agent

and

fuel.

The

annealing

process
of

sucrose

added

precursor

was

performed

and

more

heat

and
gases

were

released,

resulting

in

the

good

crystallization

and
large

reaction

areas

in

ZnO

flowers.

The

photocatalytic

proper-
ties

of

ZnO

flowers

dependent

on

the

sucrose

content

were

also
discussed.

0169-4332/$

–

see

front

matter ©

2012 Elsevier B.V. All rights reserved.
/>558 W.

Lv

et

al.

/

Applied

Surface

Science

259 (2012) 557–

561

2.

Experimental
2.1.

Preparation

of

ZnO

flowers
All

the

chemicals

were

analytical

grade

reagents

and

were

used
without

further

purification.

Firstly,

0.002

M

zinc

nitrate

solution
was

prepared

by

dissolving

proper

Zn(NO
3

)
2
in

deionized

water.

In
a

typical

procedure,

0.006

mol

urea

powder

was

added

into

20

mL
0.002

M

Zn(NO
3
)
2
solution

with

variable

quantity

of

sucrose.

After
a

continuous

stirring

for

15

min,

the

mixed

solution

was

transferred
into

a

50

mL

Teflon

bottle

held

in

a

stainless

steel

autoclave,

which
was

kept

at

90
◦
C

for

2

h.

The

white

precursor

was

washed

for

sev-
eral

times

with

deionized

water

followed

by

drying

in

air

at

75
◦
C

for
12

h.

Further

heat-treated

was

carried

out

to

obtain

the

final

ZnO

at

300
◦
C

for

2

h.

The

samples

with

0.08

g

and

0

g

sucrose

added

were
labeled

as

P
0
and

S
0
.

In

order

to

assess

the

relationship

between
the

amount

of

sucrose

and

the

photocatalytic

activity

of

ZnO,

vari-
able

amount

of

sucrose

added

samples

were

prepared

through

the
similar

process,

labeled

as

P
−2
,

P
−1
,

P
1
and

P
2
for

0.04

g,

0.06

g,

0.1

g
and

0.25

g,

respectively.
2.2.

Characterization
The

thermal

decomposition

process

of

the

precursors

was

inves-
tigated

by

thermogravimetric

analysis/differential

thermal

analysis
(TGA–DTA)

using

a

TA

SDT

2960

instrument.

It

was

performed

in

air
from

40

to

1000
◦
C

with

a

heating

rate

and

flow

rate

of

10
◦
C

min
−1
and

100

mL

min
−1
,

respectively.

Powder

X-ray

diffraction

(XRD)
analysis

was

carried

out

by

a

Rigaku

D/Max-2550/pc

diffractome-
ter

using

Cu-K␣

radiation.

The

IR

spectra

of

sucrose

and

samples
before/after

heat

treatment

were

determined

by

Fourier

trans-
form

infrared

spectroscopy

(FTIR,

Bruker

IFS

66

v/s)

using

KBr

disc
method.

The

ratio

of

KBr

to

samples

was

about

300:1

in

weight.
The

morphologies

of

ZnO

flowers

obtained

with

various

sucrose
amounts

were

revealed

by

a

scanning

electron

microscope

(SEM,
Hitachi

S-4800).

X-ray

photoelectron

spectroscopy

(XPS)

experi-
ments

were

measured

with

a

K-Alpha

(Thermofisher

Scienticfic
Company)

X-ray

photoelectron

spectrometer

using

Al

K␣

radiation
(12

kV,

6

mA).

The

binding

energies

of

elements

were

calibrated

by
taking

carbon

C1s

(285.06

eV)

as

reference.
2.3.

Photocatalytic

activities

tests
In

this

work,

the

photocatalytic

activities

of

hierarchical

struc-
tures

ZnO

were

tested

by

using

methyl

orange

(MO)

as

the

model
pollutant.

0.02

g

sample

was

added

into

50

mL,

1.2

×

10
−5
M

MO
solution

and

mechanically

stirred

in

dark

for

20

min

to

achieve

the
adsorption

equilibrium

of

MO

with

ZnO

before

the

UV

irradiation.
In

a

cool

water

bath,

the

mixture

was

irradiated

by

two

UV

lamps
(Philips,

8

W)

with

continuous

stirring.

The

samples

were

taken

out
from

the

mixed

suspension

at

every

20

min

to

check

the

changes

of
MO

concentration.

To

remove

the

catalysts

of

ZnO,

centrifugation
was

carried

out

at

10,000

rpm

for

10

min.

The

UV–vis

absorption
spectra

of

the

centrifuged

solutions

were

measured

on

the

HITACHI
UV/vis

spectrometer

(U-3010).
3.

Results

and

discussion
To

investigate

the

appropriate

calcinations

temperature

for

the
transformation

of

the

precursor

to

ZnO,

the

thermal

analysis

in

air
atmosphere

was

conducted.

Typical

TGA/DTA

plots

for

the

pre-
cursor

of

sample

P
0
is

shown

in

Fig.

1.

At

the

beginning,

a

small
endothermic

peak

with

5.4%

weight

loss

can

be

observed,

which

is

mainly

attributed

to

the

evaporation

of

water

in

the

precursors.
In

the

temperature

range

of

100–400
◦
C,

an

obvious

endothermic
Fig.

1.

TGA–DTA

curves

of

the

precursor

of

P
0
.
Fig.

2.

XRD

patterns

of

the

samples:

(a)

the

precursor

of

P
0
,

(b)

P
0
.

peaks

centered

at

259.3
◦
C

can

be

found

in

DTA

curve.

Simultane-
ously,

a

faster

weight

loss

stage,

claimed

as

25.8%

can

be

observed

in
TGA

curve.

The

thermal

decomposition

processes

can

be

ascribed

to
the

decomposition

and

oxidation

of

the

precursor

by

the

releasing
of

water

and

carbon

dioxide.

Therefore,

the

annealing

temperature
was

chosen

at

300
◦
C

to

obtain

the

final

products.
The

purity

and

crystalline

phase

of

P
0
and

the

precursor

of

P
0
were

determined

by

XRD.

Fig.

2(a)

showed

the

XRD

patterns

of
the

precursor.

As

a

comparison,

the

XRD

pattern

of

ZnO

product
(P
0
)

after

calcination

was

also

presented

(Fig.

2(b)).

The

diffraction
peaks

in

Fig.

2(a)

can

be

identified

as

the

Zn
4
(CO
3
)(OH)
6
H
2
O,

which
was

consistent

with

JCPDS

Card

No.11-0287.

While,

the

diffraction
peaks

of

P
0
can

be

identified

as

pure

hexagonal

ZnO

(JCPDS

Card
No.

36-1451).

The

XRD

patterns

of

P
0
and

the

precursor

are

con-
sistent

with

our

previous

results

with

no

sucrose

added

synthesis
procedure

[19].

It

shows

that

the

sucrose

as

complexing

agent

will
not

influence

the

formation

of

the

precursor

(Zn
4
(CO
3
)(OH)

6
H
2
O)
and

the

final

product

ZnO.
In

the

synthesis

process,

sucrose

was

introduced

into

the

urea
hydrothermal

procedure.

To

clarify

the

role

of

sucrose

acting

in
the

crystal

growth,

FTIR

spectra

were

measured

to

verify

the

possi-
ble

intermediate

by-products

and

the

results

were

shown

in

Fig.

3.
We

found

that

sucrose

played

the

roles

of

complexing

agent

and
fuel

in

the

synthesis

process.

In

acidic

solution,

the

sucrose

firstly
hydrolyzes

into

glucose

and

fructose,

which

can

be

further

oxidized
into

saccharic

acid,

glycolic

acid

and

trihydroxy-butyric

acid

with

a
large

number

of–COOH

and–OH

groups.

Furthermore,

the

COOH
groups

can

easily

combine

with

metal

ions

in

the

solution,

which
is

quite

similar

to

the

citric

acid

complexing

mechanisms.
W.

Lv

et

al.

/

Applied

Surface

Science

259 (2012) 557–

561 559
Fig.

3.

FTIR

spectra

of

samples

(a)

sucrose

(b)

the

precursor

of

P

0
(c)

calcined

at
300
◦
C

(P
0
).
Fig.

3(a)

shows

the

FTIR

spectrum

of

sucrose

and

its

typical
absorptions

are

in

agreement

with

the

spectrum

in

database

[18].
It

is

worth

noticing

that

no

obvious

absorption

is

present

between
1500

cm
−1
and

2500

cm
−1
.

While,

the

spectrum

for

the

precursor
of

P
0
shown

in

Fig.

3(b)

clearly

shows

the

coordinated

COO
−
sym-

metric

stretching

with

broad

absorption

around

1618

cm
−1
,

which
comes

from

the

products

of

the

sucrose

hydrolyzation

[20].

Consid-
ering

the

complexing

ability

mentioned

above,

it

can

be

identified
that

the

metal

ions

are

well

complexed

by

the

COOH

groups,

form-
ing

stable

COOZn
2+
.

And

in

fact,

no

precipitation

was

observed
during

the

stirring.

Moreover,

the

broad

absorption

band

centered
at

3400

cm
−1
can

be

observed

due

to

the

OH

stretching

vibration,
which

can

be

attributed

to

the

existence

of

crystallization

water
in

the

precursor.

The

absorption

band

around

1385

cm
−1
is

typ-
ical

asymmetric

stretching

vibration

of

NO
3
−
,

which

comes

from
the

raw

material

Zn(NO
3
)

2
.

After

calcination

at

300
◦
C

(Fig.

3c),

the
chelating

complexes

decomposed

and

a

mass

of

gases

are

gener-
ated,

which

are

favored

for

the

formation

of

porous

product.

As
curve

(b)

showed,

in

infrared

absorption

spectra

of

the

precursor,
the

absorption

peak

at

1048

cm
−1
,

830

cm
−1
,

711

cm
−1
are

ascribed
to

CO
3
2−
lattice

vibration

induced

infrared

absorption.

Therefore,

the

FTIR

shows

the

precursor

is

the

Zn
4
(CO
3
)(OH)
6
H
2
O,

which
is

consistent

with

the

XRD

results.

After

annealing

at

300
◦
C,

the
infrared

absorption

spectra

(Fig.

3(c))

shows

that

a

new

absorption
peak

centered

at

474

cm
−1
appears,

indicating

the

formation

of

ZnO
and

the

complete

decomposition

of

the

precursors.
Fig.

4(a)

shows

the

typical

SEM

images

of

the

products

after
annealing

at

300
◦
C.

Obviously,

the

hierarchical

structure

was

con-
structed

by

large

quantities

of

fluffy

nanosheetes

with

a

uniform
size

distribution

of

micro-flowers.

The

enlarge

view

of

the

P
0

in
Fig.

4(b)

shows

that

the

diameter

of

ZnO

flowers

is

about

10

␮m.
The

nanosheets

petals

are

narrow

in

width

and

ended

with

a
sharp

tip.

The

abundance

of

petals

will

greatly

increase

the

con-
tact

area

between

the

catalysts

and

organic

dyes.

Moreover,

the

gap
formed

by

the

adjacent

nanosheets

would

enhance

the

absorption
of

exciting

light

and

promote

the

photocatalytic

activities

of

ZnO.
The

optical

absorption

efficiency

increased

by

the

diffuse

reflec-
tion

happens

among

the

petals,

as

shown

in

the

inserted

figure

of
Fig.

4(b).

On

the

other

hand,

the

microstructure

of

the

nanosheets
petals

also

shows

differences

between

sucrose

adding

sample

P
0
and

no

sucrose

adding

one

S
0
.

The

high

magnification

SEM

images
of

petals

from

S
0
and

P
0
were

shown

in

Fig.

4(c,

d).

Apparently,

the
pores

on

the

nanosheets

are

quite

distinguished

from

each

other.
The

microstructure

of

S
0
presents

that

the

pores

are

embedded
in

the

petals,

like

large

number

of

holes

on

a

flat

surface.

While,
for

the

sucrose

added

sample

P
0
,

the

pores

were

formed

by

the
Fig.

4.

SEM

images.

(a)

Flower-like

ZnO

of

P
0

.

(b)

An

enlarge

view

of

P
0
.

The

inserted

shows

the

abridged

general

view

of

the

possible

light

absorption

in

the

sample

P
0
.

(c)
The

microstructure

of

S
0
(d)

the

microstructure

of

P
0
.
560 W.

Lv

et

al.

/

Applied

Surface

Science

259 (2012) 557–

561
Fig.

5.

Photodegradation

of

MO

in

the

solution

with

S
0
and

P
0
ZnO

flowers.
connection

of

a

great

quantities

of

ZnO

nanoparticles

presenting
larger

surface

areas

compared

with

S
0
.

In

fact,

there

is

no

obvi-
ous

difference

in

the

flowerlike

status

between

the

precursors

of
P
0
and

S
0
,

indicating

that

the

sucrose

effects

on

the

morphology
of

LBZC

(Zn
4
(CO
3
)(OH)
6

H
2
O)

is

not

obvious.

However,

to

gain

the
final

ZnO

hierarchical

structures,

annealing

process

was

carried

out
and

the

role

of

sucrose

was

activated

during

the

decomposition

of
LBZC.

In

the

process

of

synthesis,

the

sucrose

hydrolyzes

into

two
kinds

of

monosaccharides,

glucose

and

fructose

that

is

homodis-
perse

in

the

Zn
4
(CO
3
)(OH)
6
H
2
O

and

assist

combustion

during

the
annealing.

Considering

the

sucrose

can

be

used

as

fuel

in

the

fab-
rication

of

oxides,

the

high

temperature

decomposition

process

of
LBZC

with

sucrose

adding

can

be

treated

as

a

more

intensive

and
rapid

combustion,

leading

to

the

precursor

burning

much

more
sufficiently

and

the

crystallinity

of

ZnO

particles

improved.

Good
crystalline

quality

can

be

reflected

from

the

micro

structure

of

sam-
ples.

Spherical

nanoparticles

constituting

the

resultant

nanosheets
were

formed

by

the

additional

heating

from

the

added

sucrose,
which

would

be

beneficial

to

the

photocatalytic

activity.To

evaluate
the

sucrose

effects

on

the

photocatalytic

activity,

the

performances
of

S
0
and

P
0
were

investigated

by

the

degradation

of

MO

dye

under
UV

irradiation.

Fig.

5

compares

the

photodegradation

of

MO

as

a
function

of

irradiation

time

for

the

P
0
and

S
0
samples.

As

clearly
shown,

after

irradiation

for

100

min,

the

photocatalytic

degradation
of

MO

on

S
0
is

80%.

In

fact,

we

have

discussed

the

superior

photocat-
alytic

properties

of

the

multi-layered

mesoporous

ZnO

structures
(S
0
)

decomposing

the

MO,

which

showed

the

superior

photocat-
alytic

activity

to

the

commercial

ZnO
19
.

Surprisingly,

in

comparison
with

the

S
0
,

a

small

amount

of

sucrose

adding

sample

P
0
displayed
much

higher

decomposition

efficiency

with

a

degradation

rate

of

nealy

100%

after

irradiation

for

80

min.

Considering

the

differences
in

the

synthesized

procedure,

sucrose

adding

plays

an

important
role

in

improving

the

photocatalytic

properties.
The

surface

sensitive

diagnostic

test

XPS

was

conducted

to

elu-
cidate

the

oxidation

states

of

S
0
and

P
0
.

Fig.

6

demonstrates

the
high-resolution

XPS

spectra

of

O1s

states

of

sample

S
0
and

P
0
.

Obvi-
ously,

the

XPS

spectra

of

O1s

peaks

is

asymmetric

and

broadening,
which

can

be

resolved

into

two

peaks

by

a

Gaussian

distribution
fitting

centered

at

530.1

±

0.2

eV

and

531.7

±

0.2

eV,

respectively.
The

fitting

indicates

that

at

least

two

oxygen

species

are

present

in
the

near-surface

region.
O
A
signal

peaks

are

centered

at

530.1

±

0.2

eV

is

due

to

oxygen

in

the

wurtzite

structure

of

ZnO

(lattice

oxygen),

and

the

intensity

of
this

peak

is

a

measure

of

fully

oxidized

oxygen

atoms

[24].

O
B
signal
526

528

530 53

2

534
(a)
S
0
Intensity (a.u.)
Bindin

g Energ

y (e

V)
O1s Scan

B
O1s Scan

A
526 52

8

530

532

534
(b)
P
0
Intensity (a.u.)
Binding En

ergy (eV)
O1s Scan A
O1s Sc

an B
Fig.

6.

The

high-resolution

XPS

spectra

of

O1s

states

of

sample

S
0
(a)

and

P
0
(b).
peaks

at

531.7

±

0.2

eV

corresponds

to

the

adsorbed

oxygen,

which
is

ascribed

to

the

presence

of

adsorbed

oxygen,

including

hydroxyl
and

carbonate

groups

adsorbed

on

the

material

surface.[25–28]

The
integrated

intensity

of

peak

O
A
can

be

compared

with

that

of

peak
O
B
using

the

O
A
to

O
B
integrated

intensity

ratio

“X,”

which

was
approximately

2.0

and

1.7

for

P
0

and

S
0
,

respectively.

Apparently,
the

lattice

oxygen

in

the

sucrose

added

sample

P
0
is

higher

than
that

of

sample

S
0
.

This

result

also

indicates

that

the

crystallinity

of
P
0
is

superior

to

S
0
due

to

the

added

sucrose

providing

with

more
energy

during

annealing.

Under

the

UV

excitation,

electron-hole
pairs

carried

out

redox

reaction

and

more

surface

defects

will

be
companied

with

higher

combination

probability

of

surface

states
and

hole.

However,

the

high

crystallinity

would

decrease

surface

defects

and

the

combination

probability

of

surface

states

and

holes
that

can

enhance

photocatalytic

activity.

[5,6]

Considering

the

pho-
tocatalytic

activity

of

P
0
and

S
0
,

the

sucrose

induced

crystallinity
improvement

is

an

effective

treatment

to

increase

the

photoactiv-
ity

of

ZnO

photocatalysts.In

order

to

find

the

relationship

between
the

amount

of

sucrose

and

the

photocatalytic

activity

of

ZnO,

vari-
able

amount

of

sucrose

added

samples

were

prepared

through

the
similar

process.

Fig.

7

shows

the

plot

of

the

decolorization

efficien-
cies

of

MO

by

the

ZnO

with

variable

sucrose

after

40

min

reaction
time.

It

can

be

seen

that

no

sucrose

added

ZnO

S
0
show

nearly
60%

decolorization

efficiency.

With

the

sucrose

added,

ZnO

samples
showed

much

better

photocatalytic

activity

and

the

decolorization
efficiencies

were

greatly

increased.

As

shown

in

Fig.

7,

P
0
shows

the
superior

photocatalytic

activity

and

decolorization

efficiency

was
achieved

95%.

While,

other

ZnO

sample

with

fewer

or

more

sucrose
W.

Lv

et

al.

/

Applied

Surface

Science

259 (2012) 557–

561 561
Fig.

7.

Photocatativity

comparison

of

ZnO

flowers

after

MO

degradation

for

40

min.
The

sucrose

contents

of

S
0
,

P
−2
,

P
−1
,

P
0
,

P
1
,

P
2
were

0

g,

0.04

g,

0.06

g

0.08

g

0.1

g

and

0.25

g,

respectively.
added

show

lower

decolorization

efficiencies

during

the

same

reac-
tion

time.

Since

the

small

amount

of

sucrose

added

can

result

in
negligible

effects

on

the

morphology,

the

crystallinity

and

agglom-
eration

of

photocatalysts

should

be

considered.

In

some

cases,

it
was

found

that

the

heat

generated

during

the

reaction

could

be
more

prominent

to

cause

sintering

or

agglomeration

of

particles,
resulting

in

grain

growth

and

low

photocatalytic

reaction

sites.
Therefore,

the

optimization

of

reaction

condition

was

established
for

0.08

g

sucrose

added

ZnO

flowers.
4.

Conclusion
In

this

study,

hierarchical

structures

ZnO

was

successfully

syn-
thesized

via

a

sucrose

added

urea

hydrothermal

method.

The
prepared

ZnO

flowers

were

characterized

by

TG-DTA,

FTIR,

XRD
and

SEM.

The

photocatalytic

activities

of

ZnO

flowers

were

evalu-
ated

by

the

degradation

of

MO

and

results

show

that

the

sucrose
added

sample

presents

superior

decolorization

efficiency.

The

XPS
analysis

reflected

that

the

adding

of

sucrose

can

improve

the
crystallization

of

ZnO.

The

ZnO

flowers

synthesized

via

variable
sucrose

amount

were

also

estimated

by

the

decolorization

effi-
ciency

of

MO

after

40

min

reaction

time.

It

was

found

that

higher
sucrose

added

would

induce

a

slightly

reduction

effect

on

the
photocatalytic

activities

and

the

optimized

reaction

condition

was
estimated.
Acknowledgments
This

work

was

partly

supported

by

the

National

Natural

Science
Foundation

of

China

(No.

51102069).

This

work

was

also

supported
by

Heilongjiang

Education

Department

(12511164)

and

Innovative
Talents

Fund

of

Harbin

(2010RFQXG034).
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