hydrothermal synthesis and humidity sensing property of zno nanostructures

Their morphology, structure, chemical composition and growth mechanism are discussed; furthermore, we would like to point out the effect of nanocomposite formation and morphology on the

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Hydrothermal synthesis and humidity sensing property of ZnO nanostructures

Edit Pála,⇑, Viktória Hornokb, Robert Kuna, Albert Oszkóc, Torben Seemannd, Imre Dékányb,

Matthias Bussea,d

a

University of Bremen, Faculty of Production Engineering, FB 04, Near Net Shape Technologies, Wiener Str 12, 28359 Bremen, Germany

b Supramolecular and Nanostructured Materials Research Group of the Hungarian Academy of Sciences, Aradi vt 1, 6720 Szeged, Hungary

c

Department of Physical Chemistry and Material Science, University of Szeged, Aradi vt 1, 6720 Szeged, Hungary

d

Fraunhofer Institute for Manufacturing Technology and Advanced Materials Research (IFAM), Wiener Str 12, 28359 Bremen, Germany

a r t i c l e i n f o

Article history:

Received 27 February 2012

Accepted 18 April 2012

Available online 26 April 2012

Keywords:

ZnO nanoparticles

Indium hydroxide

Hydrothermal method

Nanocomposites

Photoluminescence

Water vapor sensor

a b s t r a c t

Prism- and raspberry-like ZnO nanoparticles and ZnOAIn(OH)3nanocomposites were prepared by tem-plate free hydrothermal method XRD investigations and microscopic studies showed that pill-like In(OH)3particles with body-centered cubic crystal structure formed on the surface of ZnO nanoparticles resulting in increased specific surface area TEM–EDX mapping images demonstrated that not only nano-composite formation took place in the course of the synthesis, but zinc ions were also built into the crys-tal lattice of the In(OH)3 However, only undoped In(OH)3was found on the surface of the pill-like particle aggregates by XPS analyses The raspberry- and prism-like ZnO particles exhibit strong visible emission with a maximum at 585 and 595 nm, respectively, whose intensity significantly increase due to nano-composite formation Photoelectric investigations revealed that photocurrent intensity decreased with increasing indium ion concentration during UV light excitation, which was explained by increase in vis-ible fluorescence emission QCM measurements showed that morphology of ZnO and concentration of In(OH)3had an influence on the water vapor sensing properties

1 Introduction

Sensing the relative humidity of our environment is a very

important issue in various ﬁelds like medical, automotive, food

processing and semiconductor industries, in agriculture and for

material allow better sensing properties than their bulk phase

materials owing to their huge surface-to-volume ratio In the last

years, many metal oxide nanostructures including In2O3, WO3,

SnO2, ZrO2, TiO2, ZnO, etc have been studied[2,3] ZnO is an n-type

semiconductor oxide with a wide band gap energy (3.37 eV) and a

large excitation binding energy (60 meV) Due to its favorable

structural, optical and catalytic properties, it is often used as

photocatalyst[4–6], UV nanolaser[7]in UV light emitting diode

well

ZnO nanoparticles have been synthesized by various physical

evaporation[15,16], chemical vapor deposition[17], chemical bath

deposition[18], spray pyrolysis[19,20], sol–gel technique[21,22],

precipitation reaction[23], hydrolysis[24,25], microwave assisted

method is a relatively simple preparation technique of hierarchical ZnO nano- and micro-structures such as ZnO prisms, ﬂowers, rods and spheres In the course of the hydrothermal reaction, water-soluble capping or chelating agent like polymers[29,30],

forma-tion of the hierarchical structures during the self-assembly reac-tion Not only the capping or chelating agent can inﬂuence the growth pattern of the structure, but also the concentration of reac-tants, the temperature and time of hydrothermal process, and pH value[36,37]

ZnOApolyelec-trolyte) provide the possibility for enhanced functionality, such as optical property[38], photocatalytic activity[39], UV photosensi-tivity[40] or humidity sensitivity [41] In(OH)3 is an important semiconductor having potential application in solar energy and electronics[42] Its band gap is 5.15 eV[43] Recently, only several papers deal with the investigation of In(OH)3nanoparticles These

different morphologies, like cubes, ﬂowers, rods, spheres by wet

⇑Corresponding author Fax: +49 421 2246300.

E-mail address: edit.pal@uni-bremen.de (E Pál).

Journal of Colloid and Interface Science 378 (2012) 100–109

Contents lists available atSciVerse ScienceDirect

Journal of Colloid and Interface Science

w w w e l s e v i e r c o m / l o c a t e / j c i s

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precipitation [45], solvothermal [46] and hydrothermal method

has not been reported yet

Fig 1 SEM image of prism-like ZnO (a), and ZnOAIn(OH) 3 nanocomposites at 1 at.% (b), 5 at.% (c), and 10 at.% (d) In(III) concentration.

Fig 2 SEM image of raspberry-like ZnO (a), and ZnOAIn(OH) 3 nanocomposites at 1 at.% (b), 5 at.% (c), and 10 at.% (d) In(III) ion concentration.

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In this study, prism-like and raspberry-like ZnO particles and

were prepared by template free hydrothermal method at 80 °C

Their morphology, structure, chemical composition and growth

mechanism are discussed; furthermore, we would like to point

out the effect of nanocomposite formation and morphology on

the optical, and humidity sensing properties of the samples

2 Experimental

2.1 Materials

Zinc nitrate hexahydrate (Zn(NO3)26H2O Fluka,P99 %), sodium

hydroxide (NaOH, Fluka,P99 %), indium chloride tetrahydrate

(In-Cl34H2O, Sigma–Aldrich, 97 %) and distilled water were used as

re-ceived to prepare zinc oxide nanoparticles

2.2 Preparation of ZnO nanoparticles with different morphology

0.744 g zinc nitrate was dissolved in 37.5 ml distilled water and

heated in a 100 ml autoclave at 80 °C, then 12.5 ml sodium

hydrox-ide solution (c = 0.4 mol/dm3) was added into the solution under

vigorous stirring By the preparation of raspberry-like ZnO

parti-cles, the sodium hydroxide solution was added dropwise that

re-sults in the formation of a white suspension immediately In case

of the prism-like ZnO particles, sodium hydroxide solution was

added simultaneously; thus, ﬁrst a colorless solution then a white

suspension was formed In the course of the preparation of

nano-composite samples, the zinc nitrate and indium chloride at

ade-quate atomic ratio (1, 5, 10 at.% In(III)) were dissolved together in

distilled water After 3 h heat treatment, the autoclave was cooled

naturally and the white precipitate was collected by centrifugation

at 9000 rpm/10 min, washed with distilled water and dried in air at

50 °C

2.3 Methods Morphology of ZnO nanoparticles was studied by a FEI Helios Nanolab™ 600 Dualbeam™ scanning electron microscope (FIB– SEM)

X-ray diffraction (XRD) measurements were taken on a Siemens D5000 (Cu Karadiation, 40 kV, 30 mA) diffractometer at ambient temperature in 20–80° 2H range Speciﬁc surface areas (as,BET) were determined using a Quantachrome gas adsorption analyzer

at 196 °C in liquid nitrogen Prior to the measurements, samples were preheated at 50 °C in vacuum (0.01 Torr) for 48 h The adsorption isotherms were analyzed by the means of BET equation The chemical composition of alloy nanoparticle surfaces was analyzed by X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX) X-ray photoelectron spec-troscopy (XPS) measurements were taken on a Specs, PHoibos

150 MCD9 X-ray photoelectron spectrometer The excitation

(15 kV, 15 mA) The pressure in the analyzing chamber was less

binding energy of adventitious carbon was used as energy refer-ence: it was taken at 285.1 eV EDX spectra and EDX mapping images were taken by a Tecnai F20 S-Twin transmission electron microscope (TEM) equipped with an EDAX r-TEM energy-dispersive X-ray detector (EDX) using gold/silicon TEM grids Thermogravimetric (TG) and differential scanning calorimetric (DSC) measurements were taken on a Netzsch STA 409 thermoan-alytical instrument The samples (m = 40 mg) were heated in Al2O3

Table 1

Primary particle size of In(OH) 3 nanoparticles determined from SEM images.

Prism-like Raspberry-like ZnOAIn(OH) 3 1 at.% In(III) 78.7 ± 6.0 35.6 ± 9.2

ZnOAIn(OH) 3 5 at.% In(III) 14.6 ± 4.8 21.0 ± 4.7

ZnOAIn(OH) 3 10 at.% In(III) 9.2 ± 4.6 11.2 ± 3.3

2Θ (°)

ZnO-In(OH) 3 10 at % In(III)

ZnO ZnO-In(OH) 3 1 at % In(III) ZnO-In(OH) 3 5 at % In(III)

ZnO

200 cps

In(OH) 3

In(OH)3

In(OH) 3

Fig 3 XRD patterns of the raspberry-like ZnO and ZnOAIn(OH) nanocomposites.

Table 2 Average crystallite size of ZnO and In(OH) 3 determined from the XRD patterns.

d (101)ZnO

(nm)

d ð200ÞInðOHÞ 3

(nm)

d (101)ZnO

(nm)

d ð200ÞInðOHÞ 3

(nm)

ZnOAIn(OH) 3 1 at.%

In(III)

ZnOAIn(OH) 3 5 at.%

In(III)

ZnOAIn(OH) 3

10 at.% In(III)

102 E Pál et al / Journal of Colloid and Interface Science 378 (2012) 100–109

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sample holder in the temperature range of 25–1000 °C with

10 °C/min heating rate in air

Absorbance spectrum of powder samples was measured by a

Micropack Nanocalc spectrophotometer equipped with a

Micro-pack HPX-2000 xenon light source (P = 50 W) using an integration

sphere Fluorescence emission properties of the powder samples

were determined by a Horiba Jobin Yvone Fluoromax-4

spectroﬂu-orometer at 350 nm excitation wavelength Photoelectric

measure-ments were taken by a Keithley Model 2001 Series Multimeter

using an EA-PSI8160-04 DT power supply The applied light source

was a Dymax Blue Wave 200 mercury lamp (P = 200 W) During

measurements, the applied voltage was 3 V and the distance

be-tween the electrode and the light source was 5 cm The baseline

was recorded in dark, followed by the irradiation of the ZnO and

irradiation, a current signal could be detected The concentration

of samples on the electrode surface was 10 ± 0.05 mg/cm2.Water

vapor sensor tests were carried out by quartz crystal microbalance

(SRS QCM 200) at room temperature in a self constructed

measur-ing cell Thin layers of powder samples (m = 100lg) were

depos-ited by dropping of their isopropanolic suspension onto the

surface of 5 MHz chrome/gold crystals, and the frequency and

resistivity decrease were detected over saturated solution of LiCl,

resistivity change in ZnO covered quartz crystal as follows: Response ð%Þ ¼R 0 R RH

R 0 100, where R0is the resistivity of the ZnO layer dried in desiccator and RRHis the resistivity measured at gi-ven relative humidity The mass change upon water vapor adsorp-tion was calculated from the following equaadsorp-tion:Dm ¼ D f

Cf, where

Dm is the mass change (g/cm2),Df is the change in frequency (Hz) and Cfsensitivity factor of the crystal (56.6 Hz cm2/g)

3 Results and discussion 3.1 Morphological, structural properties and chemical composition of ZnO and In(OH)3nanocomposite samples

The morphology of the samples was studied by scanning elec-tron microscopy It was found that prism-like ZnO particles with

ZnOAIn(OH)3 nanocomposites illustrate, pill-like particle aggre-gates were formed on the surface of ZnO prisms whose amount in-creases with the indium ion concentration (Fig 1b–d)

nanocomposites are presented According to the acquired images, the raspberry-like ZnO nanoparticles have a diameter of 200 nm Fig 4a TEM–EDX analysis of prism-like ZnOAIn(OH) 3 nanocomposites at 1 at.% In(III) concentration.

Fig 4b TEM–EDX mapping images of prism-like ZnOAIn(OH) 3 nanocomposites at 5 at.% In(III) concentration.

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and pill-like aggregates form besides the raspberry-like particles in

the presence of indium ions

in-dium ion concentration that can be explained as follows: at low

resulting in larger primary crystallite size and smaller aggregates

At higher precursor concentrations, the numerous nuclei formed

hinder each other’s growth resulting in smaller crystallite size,

and due to the attractive interactions they form larger aggregates

The phase structure of the samples was characterized using

rasp-berry-like ZnO nanoparticles and nanocomposite samples It can

be established that the ZnO sample has hexagonal wurtzite type

crystal structure, and no other or impurity phase appears in the

patterns (36-1451 JCPDS card) In the XRD pattern of the nanocom-posite samples, new peaks can be observed, which are

(76-1463 JCPDS card) It can also be seen that the intensity of ZnO peaks diminishes and their width slightly broadens, while the intensity of In(OH)3peaks increases and their width broadens

as a consequence of rising indium ion concentration indicating that the average primary particle size of ZnO and In(OH)3reduces The crystallite sizes determined from the d(101)and d(200)diffraction peaks of ZnO and In(OH)3are listed inTable 2 The crystallite sizes

of In(OH)3determined from the XRD patterns are in a good agree-ment with the SEM studies

EDX and XPS measurement were carried out in order to deter-mine the chemical composition of the nanocomposite samples

nanocomposite sample at 1 at.% In(III) concentration The EDX spectrum taken from a prism-like crystal (area 1) shows the pres-ence of zinc and the abspres-ence of indium in this area The second analysis was taken from the pill-like particles (area 2), where not only indium but also zinc peaks could be detected

TEM–EDX mapping images of the nanocomposite sample at

5 at.% In represent similar results, namely the prism-like particles are build up from ZnO, while the pill-like In(OH)3particles contain zinc ions (Fig 4b) The EDX analysis of prism-like nanocomposite sample at 10 at.% In(III) and raspberry-like nanocomposite series provided similar results

The chemical composition of particle surfaces was investigated

by XPS.Fig 5shows the Zn 2p3/2, O 1s and In 3d XPS spectra of the

2p3/2peak of all samples located at 1021.7 eV is characteristic of the wurtzite type ZnO[31] The high resolution O 1s XPS spectrum

of the ZnO sample can be ﬁtted into three peaks The peak found at 530.4 eV belongs to the ZnAO bonding in ZnO[49], while the peaks

adsorbed water and CO2molecules, respectively The O 1s spectra

of the nanocomposite samples are similar, but the peak at ca 531.9 eV can be assigned not only to the ZnAOH bonding, but also the InAOH bonding[50] The indium 3d peaks appear at 444.7 eV

Fig 5 Zn 2p, O 1s and In 3d XPS spectra of prism-like ZnO and ZnOAIn(OH) 3 nanocomposites.

80

82

84

86

88

90

92

94

96

98

100

T (°C)

0 0.2 0.4 0.6 0.8 1

ZnO

Exo

Fig 6 TG and DSC curves of raspberry-like ZnO and ZnOAIn(OH) 3 nanocomposites.

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(In 3d5/2) and at 452.1 eV (In 3d3/2), which are characteristic of

the XPS spectra of the samples, no peak shift of Zn 2p, O 1s and

In 3d peaks could be observed, it can be asserted that only pure

(undoped) ZnO and pure In(OH)3are on the surface of the particles

demonstrate similar XPS characteristics

Based on the above discussed results, the formation mechanism

of the ZnO and ZnOAIn(OH)3nanocomposite structures are proba-bly as follows In case of the preparation of prism-like particles, adding rate of the NaOH solution is rapid; thus, the concentration

formation of a colorless reaction system containing [Zn(OH)4]2

ZnO nuclei form[51], which start to grow into the direction of c-axis due to repeating nucleation occurred on the c-face area of the crystals [37] By the preparation of raspberry-like particles, the adding rate of the room temperature NaOH solution is moder-ated, thus the concentration of OHions slowly increases So thus, only Zn(OH)2precipitate is forming, which can immediately trans-form to ZnO nuclei Since during the addition of NaOH solution, the generation of Zn(OH)2particles is continually and their conversion

to ZnO nuclei is continuous as well, we assume that the ZnO nuclei can grow together developing the raspberry-like form If indium ions are also present in the reaction system ZnO particles generate ﬁrst followed by the hydrolysis of indium precursor and condensa-tion of In(OH)3nuclei on the ZnO particle surfaces resulting pill-like In(OH)3 particles on the ZnO crystals Since the growth of the ZnO particles and the generation and condensation of In(OH)3 nuclei happen simultaneously, zinc complex species still presented

in the system can be capped in course of the formation of In(OH)3 particles At the end of the formation process of In(OH)3particles, there is no zinc complex species to be capped eventuate in the presence of undoped In(OH)3on the In(OH)3particle surfaces Thermal characteristics of ZnO and nanocomposite samples were also investigated The TG and DSC curves of raspberry-like series are presented inFig 6 The decomposition of raspberry-like ZnO sample takes place in two steps At lower temperature ranges (ca 25–150 °C), the physisorbed, while at higher temperature ranges (up to 260 °C), the chemisorbed, water molecules are re-leased in two endothermic steps The mass stability was reached

at 260 °C In case of the nanocomposite samples, two endothermic steps can be observed as well, but in the second step, the decom-position process of In(OH)3to In2O3 appears as well making the

nanocom-posite samples raises, the weight losses and DSC peak areas in-crease in the decomposition steps, the temperature of mass stability shift toward the higher temperature values The charac-teristic decomposition temperature ranges, the weight losses, DSC peak maxima and total enthalpy values are listed inTable 3

show similar thermoanalytic characteristics, but as the summa-rized data inTable 3show, the corresponding decomposition tem-perature ranges are developing at even lower temtem-peratures

Table 3

Thermoanalytic properties of ZnO and ZnO nanocomposite samples.

TG temperature range (°C)

Weight loss (%)

DSC peak maximum (°C)

DH (J/

g)

TG temperature range (°C)

Weight loss (%)

DSC peak maximum (°C)

DH (J/ g)

ZnOAIn(OH) 3 1 at.%

In(III)

ZnOAIn(OH) 3 5 at.%

In(III)

ZnOAIn(OH) 3 10 at.%

In(III)

Table 4

Speciﬁc surface area of the ZnO and ZnO nanocomposite samples.

Prism-like Raspberry-like

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

λ (nm)

ZnO

ZnO-In(OH)3 1 at % In(III)

Fig 7 Absorbance spectra of raspberry-like ZnO and ZnOAIn(OH) 3

nanocomposites.

Table 5

Optical properties of ZnO and ZnO nanocomposite samples.

Prism-like Raspberry-like

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To deﬁne the effect of nanocomposite formation on the speciﬁc

surface area, the samples were subjected to low temperature

nitro-gen adsorption measurements The adsorption isotherm of ZnO

revealing that the samples are not porous However, the speciﬁc

surface area values determined by BET method increase

signiﬁ-cantly with the concentration of indium ions owing to the

forma-tion of rising amount of In(OH)3nanoparticles (Table 4)

3.2 Optical properties of nanocomposites

nano-composite samples were also examined Both prism- and

rasp-berry-like series show similar characteristics As illustrated, the

UV–V is absorbance spectra of raspberry-like ZnO and

spectra of nanocomposites shift toward the shorter wavelength,

indicating the rise of band gap energy (Eg) explained by decreasing crystallite size of ZnO particles The Egvalues determined from the adsorption edge are summarized inTable 5

excitation wavelength The ZnO prisms exhibit a weak UV-emis-sion peak at 385 nm can be attributed to the direct exciton recom-bination, and a wide visible emission band with a maximum at

o)

nanocompos-ite sample, the intensity of UV- and visible-emission peaks of ZnO increases, in addition two new blue emission bands with a maxi-mum at 421 nm and 440 nm can also be observed These new bands originate from the In(OH)3particles attributed to the radia-tive recombination of photoexcited holes and electrons occupying the oxygen vacancies in In(OH)3[54] Further intensity increase in visible-emission band of ZnO can be detected, but the new blue

0.0E+00 4.0E+05 8.0E+05 1.2E+06 1.6E+06 2.0E+06

λ (nm)

0.E+00 5.E+04 1.E+05 2.E+05 2.E+05 3.E+05 3.E+05

λ (nm)

ZnO

ZnO-In(OH) 3

1 at % In(III)

ZnO-In(OH) 3

5 at % In(III)

ZnO-In(OH) 3

10 at % In(III)

ZnO

1 at % In(III)

5 at % In(III)

10 at % In(III)

Fig 8b PL emission spectra of raspberry-like ZnO and ZnOAIn(OH) 3 nanocomposites ((k g = 350 nm).

0.E+00 1.E+05 2.E+05 3.E+05 4.E+05 5.E+05 6.E+05 7.E+05

λ (nm)

0.E+00 1.E+05 2.E+05 3.E+05 4.E+05 5.E+05 6.E+05 7.E+05

λ (nm)

ZnO-In(OH) 3

10 at % In(III)

ZnO

ZnO-In(OH) 3

1 at % In(III)

ZnO-In(OH) 3

5 at % In(III)

ZnO

1 at % In(III)

5 at % In(III)

10 at % In(III)

Fig 8a PL emission spectra of prism-like ZnO and ZnOAIn(OH)3 nanocomposites(k g = 350 nm).

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emission bands of In(OH)3are absent in the spectrum of the

nano-composite samples at 5 and 10 at.% In(III), meaning that the

con-centration of oxygen vacancies in the ZnO rises, but lowers in the

In(OH)3 The ZnO raspberries also represent a weak UV emission

at 384 nm and a broad intensive visible emission at 585 nm, whose

intensity signiﬁcantly rises upon nanocomposite formation due to

the increasing concentration of oxygen vacancies in the ZnO

in the spectrum of the nanocomposite samples, but their intensity

diminishes with the indium ion concentration owing to the

con-centration decrease of oxygen vacancies in In(OH)3

raspberry-like ZnO and nanocomposite can be seen The detected

current intensity of both series during UV irradiation found to be

decreased with the indium ion concentration In case of the

nano-composite samples at highest indium ion content, no current

intensity could be measured This phenomenon can be explained

by the presence of visible PL emission originated from the electron

trapping by surface states, which becomes more intensive at

high-er indium ion concentration (Figs 8a and 8b) resulting in

diminish-ing photocurrent intensity It is worth to mention that the current

intensity of raspberry-like samples measured upon their UV

irradi-ation is one order of magnitude smaller than that of the members

of prism-like series due to their more intensive visible emission

3.3 Humidity sensing property of nanocomposites The humidity sensing of ZnO and ZnO nanocomposite samples were determined using QCM sensor crystals From the frequency decrease at different relative humidity, the adsorbed mass of water vapor was calculated.Fig 10arepresents the mass changes in the

function of relative humidity, which shows almost saturation char-acteristic It can also be seen that the adsorption capacity of nano-composite samples becomes more signiﬁcant at higher indium ion concentrations That can be explained by the presence of more In(OH)3nanoparticles that can promote the adsorption process of water molecules through their larger speciﬁc surface area In the course of the adsorption process, the resistivity of the ZnO and nanocomposite covered QCM crystals lowers due to the formation

of one or several water layers, which accelerate the transfer of H+

or H3O+[55]

determined from the resistivity change heightens with the relative

0 2 4 6 8 10 12

RH (%)

2 )

prism-like ZnO ZnO-In(OH) 3 5 at % In(III) ZnO-In(OH) 3 10 at % In(III) ZnO-In(OH) 3 1 at % In(III)

Fig 10a Adsorbed mass of water vapor of prism-like ZnO and ZnOAIn(OH) 3

nanocomposites.

0 10 20 30 40 50 60

RH (%)

prism-like ZnO

ZnO-In(OH)3 5 at % In(III) ZnO-In(OH)3 10 at % In(III)

Fig 10b Response (b) of prism-like ZnO and ZnOAIn(OH) 3 nanocomposites to

0

5

10

15

20

t (a.u.)

2 )

raspberry-like ZnO

ZnO-In(OH) 3 1 at.% In(III)

f o V U n

V U

Fig 9b Photoelectric properties of raspberry-like (b) ZnO and ZnOAIn(OH) 3

0

10

20

30

40

50

60

70

80

90

100

t (a.u.)

I (μ

ZnO-In(OH) 3 1 at.% In(III) ZnO-In(OH) 3 10 at.% In(III) ZnO-In(OH) 3 5 at.% In(III)

Fig 9a Photoelectric properties of prism-like ZnO and ZnOAIn(OH) 3

nanocomposites.

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humidity, meaning that the presence of In(OH)3 improve the

humidity sensing of ZnO prisms

In case of raspberry-like series, the water vapor adsorption

shows saturation characteristic; however, the adsorbed mass

found to be decreased with the indium ion concentration

the relative humidity also increases, but it is lower than that of

the ZnO raspberries (Fig 11b)

The differing water vapor adsorption behavior of prism- and

raspberry-like nanocomposite series can be explained by their

dis-similar morphology The raspberry-like ZnO grains have more

sur-face sites (sursur-face defects, steps, edges, terraces, etc.) favorable for

adsorption and higher speciﬁc surface area that make their

adsorp-tion capacity approximately four times higher than that of ZnO

prisms The presence of In(OH)3nanoparticles raises the speciﬁc

surface area of nanocomposite samples, but the In(OH)3particles

can partially occupy the active surface sites of ZnO grains hereby

easing the adsorption capacity and worsening the humidity sens-ing of ZnO raspberries

4 Conclusion Hydrothermal method was used for the preparation of ZnO

and microscopic investigations showed that prism- and rasp-berry-like ZnO nanoparticles with hexagonal crystal structure were generated by changing the addition rate of hydrolyzing agent, and in the nanocomposite samples, pill-like In(OH)3nanoparticle aggregates with body-centered cubic crystalline structures were formed on the surface of the ZnO particles PL studies demon-strated that the visible intensity of ZnO signiﬁcantly increased; fur-thermore two new blue bands appeared in the emission spectra due to the nanocomposite formation Humidity sensing tests of ZnO and ZnOAIn(OH)3nanocomposites revealed that the water va-por adsorption of samples strongly depends on the morphology of ZnO and on the concentration of In(OH)3

Acknowledgments This work was supported by the State and University of Bremen

in the framework of the Integrated Solutions in Sensorial Structure Engineering (ISIS), Fund No 54 416 915

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Tiêu đề	Hydrothermal synthesis and humidity sensing property of ZnO nanostructures
Tác giả	Edit Pỏl, Viktúria Hornok, Robert Kun, Albert Oszkú, Torben Seemann, Imre Dộkỏny, Matthias Busse
Trường học	University of Bremen
Chuyên ngành	Production Engineering
Thể loại	Bài báo
Năm xuất bản	2012
Thành phố	Bremen

Định dạng
Số trang	10
Dung lượng	2,1 MB