It is about my master thesis, ıts including gas sensor best conditions for work

1. Ugur Acar
Master Student of Material Science
and
Engineering

2. Acetone gas sensors
based on graphene-
ZnFe2O4 composite
prepared by
solvothermal method
Feng Liu, Xiangfeng Chu∗, Yongping Dong, Wangbing Zhang, Wenqi Sun, Liming Shen School of
Chemistry and Chemical Engineering, Anhui University of Technology, Maanshan 243002, Anhui,
PR China
Article history: Received 28 December 2012 Received in revised form 18 May 2013 Accepted 20
June 2013 Available online 4 July 2013

4. A b s t r a c t
In order to study the gas-sensing properties of graphene-ZnFe2O4 composite,
graphene-mixed ZnFe2O4 with different mixing ratios are prepared via
solvothermal method and characterized by X-ray diffraction using CuK.

5. Introduction
In this paper, graphene mixed ZnFe2O4was prepared viasolvothermal method
and the effects of graphene mixing andsolvothermal temperature on the gas-
sensing responses of the sen-sors to acetone vapor were investigated. The
responses to acetonevapor, ethanol vapor, formaldehyde vapor, ammonia,
acetaldehydevapor, toluene vapor and acetic acid vapor were also studied. It
wasfound that graphene mixing and solvothermal temperature havegreat
influence on the gas response, especially, the sensor basedon 0.125 wt%
graphene mixed ZnFe2O4(0.125%G-ZnFe2O4) showedbest gas-sensing
performance to acetone vapor.

6. Experimental
ZnFe2O4compositeThe preparation method of graphene is similar to that
reportedin literature . Graphene oxide (GO) was synthesized fromgraphite
powder by Hummers method. Then, GO was reduced byhydrazine hydrate at
90◦C for 2 h to obtain graphene. The graphene was identified by FT-IR
spectrometer and Raman spectrometer.

7. Measurement of gas sensing
performance
A paste was prepared from a mixture of the sample with ter-pineol, and then
the paste was coated with a small brush onto anAl2O3tube on which two gold
leads had been installed at each end.The Al2O3tube was about 8 mm in length, 2
mm in external diame-ter and 1.6 mm in internal diameter. The Al2O3tube was
heated in air at 100◦C for 10 h to remove terpineol. A heater of Ni–Cr wire
Was inserted into the Al2O3tube to supply the operating temperature that could
be controlled in a range of 80–350◦C.The response is defined as the ratio of the
electrical resistance of the sensor in air (Ra) to that in the mixture of the
detected gas and air (Rg) when the resistance of the sensor reaches a stable
value.

8. The sensor was placed in the air bottle at least 5 min after the electrical
resistance of the sensor was stable, then the sensor was taken out from the air
bottle and placed in a closed bottle filled with the mixture of the detected gas
and air. If the resistance of the sensor could not recover from the previous
exposure, the operating temperature was adjusted to 80–350◦Cand kept for about
10 min to let the detected gas desorb out side the air bottle. The resistance
change of the sensor was recorded by a computer.

9. Results and Discussion
1. Characterization of Graphene
Fig. 1a shows the Raman spectrum of the graphene. It shows the D
and G band of graphene at 1324 cm−1and 1586 cm−1, respec-tively.
Fig. 1b shows the FT-IR spectra of graphene in the range4000–1000
cm−1. The absorption peak of graphene appeared at3440 cm−1due
to the presence of OH groups. The peaks appearedat 1647, 1547,
1399, 1173 and 1072 cm−1are because of C Ostretching, C H
stretching, C OH stretching, C O C stretching and C O stretching
respectively. The results are similar to that reported in literature .

10. 2.Phase composition of Graphene and G ZnFe2O4composite
The typical XRD patterns of graphene, pure
ZnFe2O4(180◦C,10 h) and 0.125%G-
ZnFe2O4prepared under different
solvo thermal temperature (160◦C, 180◦C,
200◦C) are presented in Fig. 2. Thereis a
characteristic broad diffraction peak
centered at 2 = 23.95◦in the XRD pattern of
graphene.

11. The six broad peaks, centered at 2Teta = 29.96◦, 35.19◦, 42.69◦, 53.36◦, and
56.69◦and 62.26◦, respectively, match well with the ZnFe2O4crystal faces [2 2 0],
[3 1 1],[4 0 0] , [4 2 2], [5 1 1] and [4 4 0], respectively. The main diffraction peaks
in the pattern of pure ZnFe2O4can be indexed to spinel type structure
ZnFe2O4(JCPDS card No. 82-1049), there is no peaks of impurity in the pure
ZnFe2O4sample. However, graphene peaks could not be found in the XRD patterns
of 0.125%G-ZnFe2O4 under different solvo thermal temperature.

12. 3. Responses of Sensors Based on Pure ZnFe2O4 and G-ZnFe2O4 Toward
1000 ppm of Acetone Vapor
The responses to acetone vapor (1000 ppm) of sensors based on G-ZnFe2O4with
different mixing ratio are shown in Fig. 3. The response of metal-oxide semiconductor
sensors is mainly determined by the interaction of a target vapor and the surface of
metal-oxide material. The following reactions may occur in the surface reaction.
When acetone vapor (CH3COCH3) reacts with oxygen species(O−) on the surface of
metal-oxide material, it is oxidized to carbondioxide and water, and releases free
electrons (e−), thus the resistance of the sensor decreases. The surface reaction
occurs only if the thermal energy of the vapor molecules is high enough to overcome
the activation energy barrier of the surface reaction.

13. Thus, the occurrence of the surface reaction at a low operating temperature
can be attributed to that the activation energy of the surface reaction is lowered
by mixing graphene. Moreover, due to the high specific surface area (2600 m2/g )
of graphene, mixing graphene can facilitate molecular absorption.
e− (ZnFe2O4 or G − ZnFe2O4) + O2 → O−2 (1)
e− (ZnFe2O4 or G − ZnFe2O4) + O−2 → 2O− (2)
CH3COCH3 + 8O− → 3CO2 + 3H2O + 8e− (3)

14. 4. Effect of Solvo Thermal Temperature
on Gas Response
The size of ZnFe2O4particles has a great influence on the response. High
solvo thermal temperature may result in the aggregation of ZnFe2O4particles,
while low solvo thermal temperature can hinder crystal growth of ZnFe2O4.
Thus, the effect of solvo thermal temperature on the gas-sensing property should
be investigated. As shown in Fig. 4, the responses of G-ZnFe2O4com-posite
prepared under different solvo thermal temperature have a similar changing
trend. The sensors based on 0.125%G-ZnFe2O4(180◦C, 10 h) show the highest
response to acetone vapor at 275◦C.

16. 5.Gas-Sensing Selectivity and
Reproducibility
The responses of the sensors based on 0.125%G-ZnFe2O4(180◦C,10 h) to
seven kinds of vapor (1000 ppm) are shown in Fig. 5. Obviously,the gas-sensing
selectivity of sensor based on 0.125%G-ZnFe2O4(180◦C, 10 h) in high
concentration (1000 ppm) is not ideal. The probably reason is that graphene can
adsorb different vapors easily due to its high specific surface area. And the
selectivity of this sensor toward acetone is still highly disturbed by acetic acid in
high concentration (1000 ppm). It was supposed that this is due to the similarity
of these organic compounds. Both acetone and acetic acid have C=O group.

17. 6. Response Acetone Vapor in Different Concentrations
Response-recovery characteristics are very important parameters of the gas
sensor. In general, the response time and recovery time are defined as the times
for a sensor to reach 90% of the final signal. The response transients of the
sensors based on 0.125%G-ZnFe2O4(180◦C, 10 h) to acetone vapor (1, 10, 100,
200, 500and 1000 ppm) at 275◦C are shown in Fig. 7
The response time and recovery time for acetone gas in different concentrations
are listed in Table 1. From Table 1, we can see that the response time decreases
with the concentration of acetone gas increasing, while the recovery time
increases with the concentration of acetone gas increasing.

20. 4. Conclusions
In summary, we found that the operating temperature of thesensors based
on ZnFe2O4to acetone vapor can be lowered by mixing graphene. The sensor
based on 0.125%G-ZnFe2O4(180◦C,10 h) exhibits good selectivity and
reproducibility to 10 ppm ace-tone vapor at 275◦C, and the response time of the
sensor decreases with the concentration of acetone gas increasing, while the
recovery time increases with the concentration of acetone gas increasing.This
sensor may be applied to detect diabetes mellitus via measuring the acetone
vapor at low temperature if the selectivity and response are improved further
and the amount relation of sensing response versus concentration of acetone is
found.

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24. Thank You for Listening