Materials Chemistry and Physics 130 (2011) 1325 1328

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Materials Chemistry and Physics

j ourna l ho me pag e: www.elsev ier .com/ lo

Fast re SnOelectro era

Shulan W i Xa Department ob Institute for S lia

a r t i c l

Article history:Received 20 JaReceived in reAccepted 10 S

Keywords:CuO-doped SnH2S detectionSelectivityElectrodeposit

O-doous f the Cll casSnO2ntroluO

invesrespo

SnO2spon

1. Introduction

H2S, one of the combustion products of fuels, is a highly toxic andammable gbecome extbe the mostproperties oforms as thers and hethave been pmal synthes[15], therming [17,18],of the CuOdecreased t48 min [2,1doped SnO2

In the ptalline lmoxidizationnanosized porous, and

CorresponE-mail add

structure and its gas response of the CuO doped SnO2 lms wasfound to be fast to H2S gas at the low temperature.

0254-0584/$ doi:10.1016/j.as. The fast monitoring of such toxic gases has thereforeremely important. CuO doped SnO2 has been found to

sensitive material to H2S gas [1]. To improve the sensingf CuO doped SnO2, various CuOSnO2 materials in suchin/thick lms, bulk CuOSnO2 [25], CuSnO2 bilay-erostructures [68], and nano-CuO doped SnO2 [913]repared through different techniques, i.e., hydrother-is [1012], solgel synthesis [11,14], aerosol depositional evaporation [5], sputtering [16], electrostatic spray-

and screen printing [20]. Although the response time doped SnO2 to the H2S gas at 20200 ppm could beo less than 1 min, the recovery time was still long, about7,1921]. Therefore, it is very attractive to prepare CuOwith fast response and recovery properties to H2S gas.resent work, CuO doped-SnO2 porous and polycrys-s have been prepared by an electrodeposition and

method. It was grown different microstructures, likeCuO dotted island doped SnO2 and ultra-uniform,

thin CuO lm coated SnO2. It has been made a sensor

ding author. Tel.: +61 2 42215727; fax: +61 2 42215731.ress: dongqi@uow.edu.au (D. Shi).

2. Experimental

The CuO doped SnO2 lms were prepared by an electrodeposition and oxidationmethod. 1.75 g SnCl2, 6.25 g Na3C6H5O7, and balanced distilled water were com-bined in a 250 mL ask, labeled as solution a. Solution b was prepared by the samemethod as solution a, except that the SnCl2 was replaced by 0.1 g CuCl2.

A piece of indium tin oxide (ITO) glass (10 mm 20 mm) was dipped in 50 mLof solution a, and a 1 mA current was passed through the ITO glass for 3600 s usingan EG&G M273 potentiostat, a platinum counter electrode (1 cm2 in area), and asaturated camel reference electrode, with the electrodes placed near the ITO glass.The same ITO glass was also dipped in 50 mL of solution b, and a 0.7 mA current waspassed through it for 600 s using the same method. Tin and copper were nominallydeposited on the ITO glass in the atomic ratio of 8.6:1, which was estimated fromthe electric charge passed.

After the electrodeposition, the ITO glass pieces were red in air for 810 hat 500 C and 600 C and the copper and tin on the ITO glass were oxidized dur-ing the ring. X-ray diffraction (XRD) patterns of the oxidized lms were collectedusing a Philips PW3040/60 diffractometer at a scanning rate of 0.03 min1 for2 C in the range of 1080 . Scanning electron microscope (SEM) images of the as-electrodeposited lm and the oxidized lms were captured using a scanning electronmicroscope (SSX-550) operated at an acceleration voltage of 30 kV.

Two platinum wires (0.5 mm in diameter) at a distance of 10 mm were xed onthe ITO glass. The platinum wires were xed onto the ITO glass by a clamp to make agood electric connection. This assembly was then put in the bottom of a one endedand air-tight quartz tube (60 mm in inner diameter, 65 mm in outdiameter, 600 mmin height) and the quartz tube was heated in a vertical furnace. The H2S gas wasdiluted in a container. According to the designed detection concentration, a certainamount of the diluted H2S gas was taken and injected into the quartz tube. Theresistance of the oxidized lms was recorded by a multimeter (Aglient A34401) anda computer. The sensor response of the oxidized lms to the H2S gas at 50300 ppm

see front matter 2011 Published by Elsevier B.V.matchemphys.2011.09.023sponse detection of H2S by CuO-doped deposition and oxidization at low temp

anga, Yang Xiaoa, Dongqi Shib,, Hua Kun Liub, Shf Chemistry, School of Sciences, Northeastern University, Shenyang 110004, Chinauperconducting and Electronic Materials, University of Wollongong, NSW 2522, Austra

e i n f o

nuary 2011vised form 30 July 2011eptember 2011

O2

ion

a b s t r a c t

Fast response detection of H2S by Cuprocess: electrodeposition from aquephase constitution and morphology oand scanning electron microscopy. In athe CuO deposited on the individual microstructures were obtained via coand ultra-uniform, porous, and thin Clms to H2S gas at 50300 ppm wasthe CuO-doped SnO2 lms show fast uniform, porous, and thin CuO coatedrecovery time was about 1/3 of the recate /matchemphys

2 lms prepared byture

ue Doub

ped SnO2 lms prepared was prepared by a simple two-stepsolutions of SnCl2 and CuCl2, and oxidization at 600 C. TheuO-doped SnO2 lms were characterized by X-ray diffractiones, a polycrystalline porous lm of SnO2 was the product, withparticles. Two types of CuO-doped SnO2 lms with different

of oxidation time: nanosized CuO dotted island doped SnO2lm coated SnO2. The sensor response of the CuO doped SnO2tigated within the temperature range of 25125 C. Both ofnse and recovery properties. The response time of the ultra-to H2S gas at 50 ppm was 34 s at 100 C, and its correspondingse time.

2011 Published by Elsevier B.V.

1326 S. Wang et al. / Materials Chemistry and Physics 130 (2011) 1325 1328

20

(d)

(c)

(b)

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+ SnO2

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nsity

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Fig. 1. XRD paglass substrate600 C for 8 h,

was tested. Wture, air was l25, 50, 75, 100temperature c

3. Results

The phaX-ray diffraFig. 1. The number 038 h ring atSnO2 lms windexed to 077-0447). red at 500of Sn3O4 (JCture (from phase increSn3O4 phasred at 600card numbe

ScanninelectrodepoAs can be ssisted of unpresenting and the ave3 mm. How8 h at 600

destroyed aislands on texisted betwgrowth of onanosized Cporous, andparticles (F

Sensors separately sors in air w50300 ppmstants and to the H2S 7060504030

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tterns of the ITO glass substrate and the oxidized lms: (a) the ITO, (b) tin oxide lm red at 500 C for 8 h, (c) tin oxide lm red atand (d) CuO doped SnO2 lm red at 600 C for 8 h.

hen the response remained constant at a xed operating tempera-et in immediately. The temperature of the furnace was controlled at

and 120 C, respectively, by a type N thermocouple and a DTC-2Bontroller.

and discussion

se and purity of the oxidized lms were determined byction (XRD), and the diffraction patterns are shown indiffraction patterns of the ITO glass (In2O3 JCPDS card-065-3170) were also collected for comparison. After

500 C and 600 C in air, tin oxide lms and CuO dopedere obtained. All the patterns of SnO2 could be readily

the tetragonal phase of SnO2 (JCPDS card number 01-However, the X-ray diffraction patterns of tin oxide lmC also show peaks corresponding to the triclinic phasePDS card number 16-0737). With increasing tempera-Fig. 1(b) and (c)) the intensity of the tetragonal SnO2ases signicantly, while the intensity of the triclinice is reduced. In the patterns of CuO doped SnO2 lmC for 8 h, the diffraction peaks of CuO emerge (JCPDSr 03-065-2309) (Fig. 1(d)).g electron microscope (SEM) images of the as-sited lm and the oxidized lms are shown in Fig. 2.

een from Fig. 2(a), the as-electrodeposited lm con-iformly distributed irregular crystals, some of them

rectangular section. Both the average size of the crystalsrage size of the spaces between the crystals are aboutever, after the as-electrodeposited lm was red forC in air, the as-electrodeposited irregular crystals wasnd instead consisted of porous, nanosized, CuO dottedhe SnO2 particles in the lm (Fig. 2(b)). The space thateen the crystals in Fig. 2(a) was largely occupied by thexide particles. After further ring for 2 h at 600 C, theuO particles were transformed into an ultra-uniform,

thin CuO lm coating on the top of the porous SnO2ig. 2(c)).were assembled by the CuO doped SnO2 lms connectedwith two platinum wires. The resistances of the sen-ere rst recorded in a few minutes and the H2S gas at

was ejected gradually after the resistances are con-the sensing properties of the CuO doped SnO2 lmsgas were measured within the temperature range of

Fig. 2. SEM imelectrodepositisland doped Slm coated Sn

25125 C. the resistan

Fig. 3 sholm as functemperaturejection of after the garoom tempincreasing ages of the as electrodeposited lm and the oxidized lms: (a) as-ed lm with rectangular-shaped crystals, (b) nanosized CuO dottednO2 red at 600 C for 8 h, and (c) ultra-uniform, porous, and thin CuOO2 red at 600 C for 10 h.

The sensitivity is dened as Ra/Rg, where Ra and Rg areces in air and in the detected atmosphere, respectively.ws the baseline and sensitivities of the CuO doped SnO2tions of the concentration of H2S gas and the operatinge. The sensor resistance is stable before and after the100 ppm H2S gas. The ratio of the resistance before ands ejection is around 3. The sensor response started aterature and reached maximum value at 100 C. Withoperating temperature, the response times of both the

S. Wang et al. / Materials Chemistry and Physics 130 (2011) 1325 1328 1327

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Fig. 3. Baselinto H2S gas: (a)H2S at 25 C; to 100 ppm H2ultra-uniform,operating tem

CuO dopeddecreased tCuO dotted100 s withinever, this rporous, and

ring at 600 C greatly decreased the response time of the CuOdoped SnO2 lms to the H2S gas. However, the response time wasincreased by increasing the concentration of H2S gas. At 100 C, the

se time of the CuO lm coated SnO2 to 50 ppm H2S gas wasnd thes thith a eratiion mtherrespon34 s, aindicatlm wlow opoxidat

Ano35030025020015010050

300 ppm200 ppm

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5004003002001000t, s

2252001751501251007550250Time(s)

25oC 50oC 75oC 100oC 125oC

e and sensitivity versus response time curve of CuO doped SnO2 lms the baseline of nanosized CuO dotted island doped SnO2 to 100 ppm(b) the sensitivity of the nanosized CuO dotted island doped SnO2S at operating temperatures of 25125 C; (c) the sensitivity of the

porous, and thin CuO lm coated SnO2 to H2S gas at 50300 ppm atperatures of 25100 C.

SnO2 lms decreased. At 125 C, the response valueso one (Fig. 3(a)). The response time of the nano-sized

island doped SnO2 to 100 ppm H2S ranged from 160 to the temperature range of 25100 C (Fig. 3(a)). How-

ange was decreased to 6646 s for the ultra-uniform, thin CuO lm coated SnO2 (Fig. 3(b)). A further 2 h

fast recoverery time o100 ppm H4030 s, andSnO2. The rabout 1/3 oshorter thaThe ultra-usensing areCuO dottedlm coatedbution of Cnanosized Clayer at theas well as tdoped SnO2coated SnOdoped SnO2sensitivity. temperatur

4. Conclus

We preplms prepaWe designeof the CuO-of the electwere prepaSnO2 and ndoped SnOroom tempuniform, poof responseted island dporous, and34 s at 100of the respo

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Fast response detection of H2S by CuO-doped SnO2 films prepared by electrodeposition and oxidization at low temperature1 Introduction2 Experimental3 Results and discussion4 ConclusionsReferences