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Rapid detection of ozone in the parts per billion range using a novel Ni–Al layered double hydroxide
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Rapid detection of ozone in the parts per billion range using a novel Ni–Al layered double hydroxide Guiying Kang a , Zhen Zhu b , Bing-Hong Tang c , Chun-Han Wu c , Ren-Jang Wu c,∗ a b c
Department of Applied Chemistry, College of Petrochemical Engineering, Lanzhou University of Technology, Lanzhou 730050, PR China School of Environmental Science and Safety Engineering, Tianjin University of Technology, Tianjin 300384, PR China Department of Applied Chemistry, Providence University, Shalu, Taichung 43301, Taiwan, ROC
a r t i c l e
i n f o
Article history: Received 3 May 2016 Received in revised form 29 September 2016 Accepted 4 October 2016 Available online xxx Keywords: Ni–Al layered double hydroxide Ozone Gas sensor
a b s t r a c t A novel ozone sensor based on Ni–Al layered double hydroxide (NiAl–LDH) that operates at room temperature (25 ◦ C) was developed. The NiAl–LDH was successfully synthesized using a hydrothermal method and characterized using X-ray diffraction, Scanning electron microscopy, and Fourier transform infrared spectroscopy. Selective detection of ozone was readily achieved with the NiAl–LDH sensor even in the presence of other gases such as H2 , NO2 , and C2 H5 OH. The NiAl–LDH sensor exhibited a sensor response of 1.22–15 ppb ozone, and the response and recovery times of the sensor were both measured as 4 s. In addition, the NiAl–LDH sensor revealed good reproducibility and reversibility, and the response displayed no obvious changes after 19 days of testing. Furthermore, the sensor presented excellent selectivity and stability for ozone, and the response value of the NiAl–LDH sensor to 700 ppb ozone was 1.84. Moreover, a possible ozone sensing mechanism of the NiAl–LDH sensor is presented. The NiAl–LDH sensor is a promising candidate for the detection of ozone in parts per billion levels at room temperature (25 ◦ C). © 2016 Elsevier B.V. All rights reserved.
1. Introduction Ozone (O3 ) is a useful oxidation agent with numerous practical applications, including operations in the pharmaceutical, textile, and chemical industries; food processing and storage; water treatment; and purification of gases [1]. Furthermore, because of its bactericidal and virus inactivating activity, it has provided a satisfactory replacement for various ecologically damaging and physiologically noxious compounds. In contrast to some other oxidants, the ozone oxidation process does not produce toxic waste (only oxygen) [2]. However, when ozone exceeds a certain threshold level, exposure becomes hazardous to human health, causing headache, burning eyes, respiratory irritation, and lung damage [3]. In many developed countries, the maximum allowed safe concentration of ozone is 50 ppb for continuous exposure and 100 ppb for short-term exposure [4]. Accidental leakage and emission of ozone into the atmosphere can easily occur from certain processes. For example, the processes of UV irradiation and electric arc welding are generally accompanied by ozone generation [5]. Additionally, ozone is produced in office environments by photocopiers and laser printers [6]. Moreover, ozone in the atmosphere at low concentra-
∗ Corresponding author. E-mail addresses: [email protected], [email protected] (R.-J. Wu).
tions is colorless and odorless. It is therefore necessary to monitor the concentration of ozone in the atmosphere for reliable concentration control. Various technological methods, including gas sensing, electrochemical, impedance spectroscopic, amperometric, optical, resistive, work functional, and UV light photoreduction methods [7–14], have been employed to determine concentrations of ozone. Among these methods, gas sensing (based on solid-state sensors)—because of its many advantages over traditional chemical analysis techniques such as high sensitivity, short response times, low cost, low weight, simple design, online operation, low working temperature (25 ◦ C), ease of use, and low energy consumption [15–17]—has been widely used for the detection of trace amounts of ozone in the atmosphere. Recently, sensors based on metal oxide semiconductors, including ZnO, WO3 , SnO2 , In2 O3 , NiO, CuO, and SrTi0.85 Fe0.15 O3 [18–24], have been developed and extensively used for ozone detection. However, no experimental data regarding interference by other gases and stability tests of the sensors have been reported [18–23]. The SrTi0.85 Fe0.15 O3 sensor was used for 800 ppb ozone sensing at 250 ◦ C [24], the sensor response was 9.0, and the response and recovery times were determined as 28 s and 161 s, respectively. However, strong interference of NO2 gas was revealed, and no short or long term stability tests of the sensor were carried out [24]. Layered double hydroxides are a family of anionic
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Please cite this article in press as: G. Kang, et al., Rapid detection of ozone in the parts per billion range using a novel Ni–Al layered double hydroxide, Sens. Actuators B: Chem. (2016), http://dx.doi.org/10.1016/j.snb.2016.10.012
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clay materials, represented by the general formula [M2+ 1−x M3+ x (OH)2 ]x+ (An− ) x/n ·mH2 O, where M2+ is a divalent metal ion, such as Mg2+ , Ca2+ , or Zn2+ ; M3+ is a trivalent metal ion, such as Al3+ , Cr3+ , Fe3+ , or Co3+; and An− is an anion, such as Cl− , CO3 2− , or NO3 − [25]. Layered double hydroxides have attracted considerable attention because of their high surface area, excellent electrical conductivity, low toxicity, inexpensiveness, ease of preparation, high ionic exchange capacity, environmental friendliness, and good thermal stability [26–28]. However, there are only a few studies about their gas sensing properties [29,30] and no reports about their ability to sense ozone. To fill this gap, the aim of this study was to develop an easy and cost-effective route for synthesizing a fast-response, highly sensitive, and selective ozone sensor based on Ni–Al layered double hydroxide (NiAl–LDH). The structural and microstructural properties of NiAl–LDH samples were characterized through X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) spectroscopy. We also investigated the ozone sensing properties of the gas sensor based on NiAl–LDH at atmospheric room temperature (25 ◦ C).
2. Experimental 2.1. Fabrication of NiAl–LDH The NiAl–LDH was fabricated using a hydrothermal process. NiSO4 ·6H2 O (0.26 g), Al2 (SO4 )3 (0.17 g), and urea (0.21 g) were dissolved in deionized water (20 mL) to form a clear solution that was then transferred into a 100 mL Teflon-lined stainless steel autoclave. Hydrothermal treatment was performed for a period of at least 24 h at a temperature of at least 100 ◦ C. Subsequently, the obtained product was separated using a centrifuge, washed thoroughly with deionized water several times, and dried in an oven at 80 ◦ C for 12 h. 2.2. Characterization of NiAl–LDH The morphology and structure of the NiAl–LDH were investigated through TEM (JEM-2100F), energy dispersive spectrometry (EDX; JEM-2100F), and SEM (Nova TM NanoSEM 230). The crystal structures of the NiAl–LDH were characterized using an XRD-6000 Shimadzu X-ray diffractometer with Cu K␣ radiation at 40 kV and 30 mA between 10◦ and 70◦ (2), with the scanning rate being 2◦ /min. The infrared spectrum of NiAl–LDH was measured on a Nicolet Nexus 870 FTIR spectroscope in the frequency range
400–4000 cm−1 . The sample was pulverized and dispersed in KBr pellets before recording the spectrum. 2.3. Fabrication of the NiAl–LDH sensor A sensing material was fabricated by mixing the prepared sample and a binder of 90 wt% ethyl alcohol. The sensing film was fabricated by dip-coating it on a pair of comb-like gold electrodes existing on an alumina substrate with dimensions of 10 mm × 5 mm. The sensing film was placed in a room temperature (25 ◦ C) environment for 24 h to wait for the ethyl alcohol to volatilize. 2.4. Gas sensing properties of the NiAl–LDH sensor The ozone response measurement was conducted in a dynamic flow system, in which the sensors were housed in a glass cover chamber (gas sensing chamber), shown in Fig. 1. The diameter of the glass cover was 12.3 cm. The ozone gas was produced by an ozone generator (TCA 158, Tsun Cheng Co., Taiwan), was diluted with air to 15–3580 ppb by adjusting two mass flow controllers, and was monitored with a commercial ozone sensor (MIL-RAM 01-2313). The commercial ozone sensor was calibrated according to the standard concentration by the Center for Measurement Standards/Industrial Technology Research Institute (CMS/ITRI) in Taiwan. The NOx concentration was measured by the CMS/ITRI as less than 420 ppb. The total flow rate of the testing gas (ozone/air) was fixed at 400 cm3 /min during measurements and the temperature of the sensor device was controlled at 25 ± 2 ◦ C, with relative humidity (RH) maintained at 50 ± 5%. The RH varied among 12%, 20%, 30%, 40%, 50%, 60%, 70%, 80% and 90% ± 5% by divided flow system. The sensor response (S) was defined as S = Rair /Rozone , where Rozone is the electrical resistance of the sensor in ozone gas, and Rair is its electrical resistance in air. The response time (t90 ) was defined as the time taken for the saturation value to increase from 10% to 90%, whereas the recovery time (tr90 ) was the reverse of the response time. Other gas inference tests were performed under the same conditions. Interference gases of CH3 OH (700 ppb), C2 H5 OH (700 ppb), NO2 (700 ppb), CH3 COCH3 (700 ppb), and H2 (700 ppb) were employed for the sensing system. The sensor response (S) of reducing gas and oxidizing gas was defined as S1 = Rg /Rair and S = Rair /Rg , respectively, where Rg is the resistance in an environment containing gas. The sensor process in the interference tests was the same as that in the ozone gas condition. The gas sensing resistance measurements were performed using a Jiehan 5000 data acquisition system, a simple voltage circuit was used to measure the sensor resistance with an input DC voltage of 2 V, and a
Fig. 1. Ozone detection system. (a) Ozone generator, (b) air pump, (c) mass flow controller and power box, (d) drying tube, (e) pipe tee, (f) UV ozone detector, (g) gas control valve, (h) glass cover and ozone sensor device, (i) power supply, (j) circuits, (k) data acquisition system, and (l) computer.
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Fig. 2. XRD patterns of NiAl–LDH.
Fig. 3. FTIR spectra of NiAl–LDH.
computer was used to perform data acquisition and processing. An inductance–capacitance–resistance meter (HIOKI 3532-50) was used to measure the complex impedance (Z) of the sensors in a test chamber (frequency = 1 kHz, applied voltage = 1 V) under various humidity conditions (RH = 12–90%). 3. Results and discussion 3.1. Structure characterization In Fig. 2, the peaks corresponding to the (003), (006), (012), (015), and (018) planes, respectively, are attributed to the characteristic reflections of the NiAl–LDH structure [31], and no other crystalline phase is evident. Moreover, the typical doublet of the d (110)–d (113) planes of NiAl–LDH can be clearly observed in the zone around 2 = 60–62◦ . The XRD pattern for NiAl–LDH is similar to those reported in the literature [31], indicating that NiAl–LDH of high purity was successfully prepared. IR spectra of NiAl–LDH between 400 and 4000 cm−1 are shown in Fig. 3. NiAl–LDH has a broad band centered at 3363 cm−1 , which is attributed to the stretching mode of the OH group with hydrogen bonding and that of interlayer water molecules. The peak at 1646 cm−1 can be attributed to the bending mode of water molecules. The peaks at 1140 cm−1 and 1072 cm−1 can be assigned to the 1 (SO4 )2− symmetric and 3 (SO4 )2− antisymmetric stretching modes, respectively. In addition, the bands recorded at the low
Fig. 4. (a) SEM image of NiAl–LDH, (b) TEM image of NiAl–LDH, (c) EDS spectrum of NiAl–LDH.
frequency region (below 700 cm−1 ) are ascribed to M O vibrations and M O H bending (M = Ni, Al). The morphology of the NiAl–LDH was characterized through SEM and TEM. The SEM image of the NiAl–LDH is shown in Fig. 4a, indicating that the NiAl–LDH consists of platelets stacked upon each other and forming solid agglomerates with a flower-like structure. Furthermore, the NiAl–LDH exhibits a flake-like morphology with a larger lateral dimension than the longitudinal one, which is the typical feature of layered materials, as illustrated in Fig. 4b. Moreover, the EDX spectrum of the NiAl–LDH can be observed in Fig. 4c.
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Table 1 Sensing properties of various kinds of sensing materials to 700 ppb ozone at room temperature. Various kinds of sensing materials
S
t90 /s
tr90 /s
RH (%)
Ni(OH)2 Al(OH)3 NiAl-LDH
1.56 1.10 1.84
8 36 8
244 22 74
50 50 50
Fig. 6. (a) Resistance and (b) sensor response of NiAl–LDH upon exposure to three cycle tests at ozone concentrations of 45, 350, 610, and 2000 ppb at room temperature.
Fig. 5. (a) Resistance and (b) sensor response of NiAl–LDH to 540 ppb ozone at room temperature.
According to the EDX data, Ni, Al, O, and S elements are the major components. In addition, the Ni/Al molar ratio is calculated to be 1, which is close to the designated ratio. This result implies that the interlayer anions of NiAl–LDH are possibly sulphate ions. 3.2. Ozone-response properties of NiAl–LDH The sensing properties of Ni(OH)2 , Al(OH)3 , and NiAl–LDH sensors were studied at room temperature (25 ◦ C) under exposure to 700 ppb ozone, and the sensing properties are listed in Table 1. The sensor response of NiAl–LDH, 1.84, is higher than those of the other sensing materials. Table 1 also reveals that the response times of NiAl–LDH and Ni(OH)2 are both 8 s, shorter than that of Al(OH)3 . According to Fig. 5 (a), the sensor resistance is decreasing of introducing ozone gas and sensor resistance increasing by removing ozone gas. This NiAl-LDH sensor is a p-type semiconductor gas sensor. As illustrated in Fig. 5 (b), the response of the NiAl–LDH sensor was increased by the introduction of 540 ppb ozone and reduced by opening an air inlet. Additionally, the sensor response (S) of the NiAl–LDH sensor to 540 ppb ozone was calculated as 1.74. Moreover, the NiAl–LDH sensor clearly exhibited total reversibility and good stability of the baseline after 15 cycle tests, and the response and recovery were fairly reproducible and quick. To further investigate the stability of the NiAl–LDH sensor, the sensor response was tested under various ozone concentration levels, as shown in Fig. 6 (a) and (b). The NiAl–LDH sensor retained the original response with no significant change after three cycle tests
Fig. 7. Stability test of the ozone sensor based on NiAl–LDH to 540 ppb ozone at room temperature.
at ozone concentrations of 45, 350, 610 and 2000 ppb, demonstrating its suitability for measuring different ozone concentrations. Furthermore, the short term stability of the NiAl–LDH sensor was measured at 700 ppb ozone for 19 days, as shown in Fig. 7. Notably, the sensor exhibited almost constant sensor signals during the test, with responses of 1.75, 1.73, 1.72, 1.78, and 1.76 on days 0, 1, 7, 13, and 19, respectively, indicating that the NiAl–LDH sensor has excellent short term stability. Selectivity is a crucial parameter for evaluating the performance of the NiAl–LDH sensor. To investigate the selectivity of the NiAl–LDH sensor, a series of interference tests was conducted. The responses of the NiAl–LDH sensor to 700 ppb hydrogen gas (H2 ), acetone (CH3 COCH3 ), methanol (CH3 OH), ethanol (C2 H5 OH), and nitrogen dioxide (NO2 ) are presented in Table 2. The response value of the NiAl–LDH sensor to ozone is 1.84, which is considerably higher than those to other gases at the same concentrations. Therefore, the NiAl–LDH sensor exhibits excellent selectivity to ozone at room temperature (25 ◦ C). Table 3 reveals that the sensor response increased from 1.41 to 1.97 as the RH increased from 10% to 90% to 400 ppb ozone. This variation of sensor response is due to water vapor, and the
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Table 2 Sensor response of various gases at room temperature. Various kinds of reducing gases
Concentration (ppb)
S1
t90 /s
tr90 /s
RH (%)
Hydrogen (H2 ) Acetone (CH3 COCH3 ) Methanol (CH3 OH) Ethanol (C2 H5 OH)
700 700 700 700
1.00 1.02 1.21 1.02
— 2 210 2
— 2 80 2
50
Various kinds of oxidizing gases
Concentration (ppb)
S
t90 /s
tr90 /s
RH (%)
Nitrogen dioxide (NO2 ) Ozone (O3 )
700 700
1.00 1.84
— 8
— 74
50 50
50 50
Table 3 Sensor response of 400 ppb ozone concentrations under various humidity condition at room working temperature. RH (%)
S
t90 /s
tr90 /s
10% 30% 50% 70% 90%
1.41 1.50 1.69 1.86 1.97
20 18 8 6 5
25 30 30 30 35
Table 4 Sensor impedance under various humidity condition at room working temperature on NiAl-LDH. RH (%)
Sensor impedance (M)
12% 20% 30% 40% 50% 60% 70% 80% 90%
14.94 15.06 15.08 15.42 15.68 15.42 15.17 14.87 14.85
Fig. 8. Sensor response versus various ozone concentrations from 15 to 3580 ppb on NiAl–LDH at room temperature.
Z (10%): Sensor impedance under relative humidity 10%. Z (10%) = 14.94 M. Z (50%): Sensor impedance under relative humidity 50%. Z (50%) = 15.68 M. Z (90%): Sensor impedance under relative humidity 90%. Z (90%) = 14.85 M.
Table 5 Sensor response of ozone concentrations from 15 to 3580 ppb on NiAl-LDH at room working temperature. Ozone (ppb)
S
t90 /s
tr90 /s
RH (%)
15 35 70 140 240 340 540 740 1740 3580
1.22 1.35 1.53 1.56 1.65 1.67 1.75 1.86 2.02 2.20
4 6 8 8 8 8 8 8 8 8
4 6 8 8 8 16 36 124 168 212
50 50 50 50 50 50 50 50 50 50
response time is faster on higher relative humidity condition in Table 3. Specifically, water and ozone molecules were adsorbed at the sites of NiAl–LDH (higher RH) and took part in the sensing reaction. We obtained the change in sensor impedance to relative humidity from 12% to 90% at 25 ◦ C in Table 4, in order to evaluate the interference from water vapor under no ozone gas condition. As the standard humidity condition of the ozone gas sensing system is RH = 50%. We calculated the low humidity interference by ratio of Z(50%)/Z(10%) = 1.05, and also estimated the high humidity interference by ratio of Z(50%)/Z(90%) = 1.06 from Table 4. Therefore, it is no significant interference of low and high humidity conditions. The relationship between sensor response and concentration of ozone is shown in Fig. 8 and Table 5. The sensor response increased
from 1.22 to 2.20 when the ozone concentration increased from 15 to 3580 ppb. Fig. 8 illustrates that the slope of the response curve is higher for a low ozone concentration than for a high ozone concentration. This shows that the sensor possesses the ability to sense a low ozone concentration. The sensor exhibited a sensor response of 1.22 to 15 ppb ozone, and the response and recovery times of the sensor were measured as 4 s and 4 s (Table 5), respectively. In addition, for all concentrations, the response time was not greater than 8 s. 3.3. Probable gas sensing mechanism Fig. 9a reveals that the NiAl–LDH sensing materials possess NiAl–LDH, and low concentration ozone gas is easily attracted to the surface. Because ozone is an oxidative molecule, it quickly captures an electron from Ni2+ on the NiAl–LDH structure as shown in Fig. 9b, and Ni3+ and adsorbed O3 − are then formed according to equation (1) [22]. The adsorbed O3 − is decomposed to oxygen gas and adsorbed O− (Eq. (2)). Eq. (3) shows that an adsorbed O− can easily react with Ni3+ to form Ni2+ and an adsorbed oxygen atom for attracting positive Ni3+ and a negative oxygen ion. Surfaceadsorbed oxygen atoms carry on combination reactions to yield oxygen gas according to Eq. (4). O3 + Ni2+ → Ni3+ + O3 − (ad) O3
−
(ad)
→ O
−
(ad)
+ O2
(1) (2)
O− (ad) + Ni3+ → O(ad) + Ni2+
(3)
2O(ad) → O2
(4)
The short response and recovery times (Table 4) arise from the high charge transfer speed between Ni2+ and Ni3+ in the NiAl–LDH structure (Eqs. (1) and (3)) [28]. Ozone can easily penetrate the NiAl–LDH structure (Fig. 9a and 9b) to approach Ni2+ ; thus, the reversible cycle between Ni2+ and Ni3+ in the NiAl–LDH sensor is
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Fig. 9. (a) Simple representation of ozone gas on NiAl–LDH structure. (b) Scheme of the simple sensing mechanism.
easily obtained. The unique characteristic of selective ozone sensing is that ozone has a strong oxidative property and can perform the M2+ and M3+ cycle reversibly in a NiAl–LDH sensor (Fig. 9b). 5. Conclusion In this study, we successfully synthesized NiAl–LDH for use as a sensor for ozone. The obtained NiAl–LDH sensor exhibits high sensitivity to ozone at parts per billion levels, total reversibility, good reproducibility, and good stability, indicating that it is a promising sensing material for the detection of ozone. References [1] R.J. Wu, Y.C. Chiu, C.H. Wu, Y.J. Su, Application of Au/TiO2 –WO3 material in visible light photoreductive ozone sensors, Thin Solid Films 574 (2015) 156–161. [2] G. Korotcenkov, B.K. Cho, Ozone measuring: what can limit application of SnO2 -based conductometric gas sensors, Sens. Actuators B: Chem. 161 (2012) 28–44. [3] L.S.R. Rocha, C.R. Foschini, C.C. Silva, E. Longo, A.Z. Simões, Novel ozone gas sensor based on ZnO nanostructures grown by the microwave-assisted hydrothermal route, Ceram. Int. 42 (2016) 4539–4545. [4] L. Berry, J. Brunet, Oxygen influence on the interaction mechanisms of ozone on SnO2 sensors, Sens. Actuators B: Chem. 129 (2008) 450–458. [5] Z.-M. Qi, H.-S. Zhou, I. Honma, K. Itoh, H. Yanangi, A disposable ozone sensor based on a grating-coupled glass waveguide coated with a tapered film of copper tetra-t-butylphtalocyanine, Sens. Actuators B: Chem. 106 (2005) 278–283. [6] Y. Hosoya, Y. Itagaki, H. Aono, Y. Sadaoka, Ozone detection in air using SmFeO3 gas sensor, Sens. Actuators B: Chem. 108 (2005) 198–201. [7] T.C.E. Marcus, M.H. Ibrahim, N.H. Ngajikin, A.I. Azmi, Optical path length and absorption cross section optimization for high sensitivity ozone concentration measurement, Sens. Actuators B: Chem. 221 (2015) 570–575.
[8] D. Ebeling, V. Patel, M. Findlay, J. Stetter, Electrochemical ozone sensor and instrument with characterization of the electrode and gas flow effects, Sens. Actuators B: Chem. 137 (2009) 129–133. [9] A. Labidi, C. Jacolin, M. Bendahan, A. Abdelghani, J. Guérin, K. Aguir, M. Maaref, Impedance spectroscopy on WO3 gas sensor, Sems. Actuators B: Chem. 106 (2005) 713–718. [10] M. Zimmer, M. Burgmair, K. Scharnagl, A. Karthigeyan, T. Doll, I. Eisele, Goldand platinum as ozone sensitive layer in work-function gas sensors, Sens. Actuators B: Chem. 80 (2001) 174–178. [11] A. Gaddari, F. Berger, M. Amjoud, J.B. Sanchez, M. Lahcini, B. Rhouta, D. Mezzane, C. Mavon, E. Beche, V. Flaud, A novel way for the synthesis of tin dioxide sol–gel derived thin films: application to O3 detection at ambient temperature, Sens. Actuators B: Chem. 176 (2013) 811–817. [12] S. Christoulakis, M. Suchea, E. Koudoumas, M. Katharakis, N. Katsarakis, G. Kiriakidis, Fast-response ozone sensor with ZnO nanorods grown by chemical vapor deposition, Appl. Surf. Sci. 252 (2006) 5351–5354. [13] Z. Zhu, J.L. Chang, R.J. Wu, Fast ozone detection by using a core-shell Au@TiO2 sensor at room temperature, Sens. Actuators B: Chem. 214 (2015) 56–62. [14] S. Addanki, J. Jayachandiran, K. Pandian, D. Nedumaran, Development of optical sensors for the quantitative detection of ozone using gold and silver thin film nanoislands, Sens. Actuators B: Chem. 210 (2015) 17–27. [15] S. Vallejos, V. Khatko, K. Aguir, K.A. Ngo, J. Calderer, I. Gràcia, C. Cané, E. Llobet, X. Correig, Ozone monitoring by micro-machined sensors with WO3 sensing films, Sens. Actuators B: Chem. 126 (2007) 573–578. [16] F.S.S. Chien, C.R. Wang, Y.L. Chan, H.L. Lin, M.H. Chen, R.J. Wu, Fast- response ozone sensor with ZnO nanorods grown by chemical vapor deposition, Sens. Actuators B: Chem. 144 (2010) 120–125. [17] M. Acuautla, S. Bernardini, L. Gallais, T. Fiorido, L. Patout, M. Bendahan, Ozone flexible sensors fabricated by photolithography and laser ablation processes based on ZnO nanoparticles, Sens. Actuators B: Chem. 203 (2014) 602–611. [18] I. Kortidis, K. Moschovis, F.A. Mahmoud, G. Kiriakidis, Structural analysis of aerosol spray pyrolysis ZnO films exhibiting ultra low ozone detection limits at room temperature, Thin Solid Films 518 (2009) 1208–1213. [19] W. Belkacem, A. Labidi, J. Guérin, N. Mliki, K. Aguir, Cobalt nanograins effect on the ozone detection by WO3 sensors, Sens. Actuators B: Chem. 132 (2008) 196–201. [20] G. Korotcenkov, I. Blinov, M. Ivanov, J.R. Stetter, Ozone sensors on the base of SnO2 films deposited by spray pyrolysis, Sens. Actuators B: Chem. 120 (2007) 679–686. [21] D. Klaus, D. Klawinski, S. Amrehn, M. Tiemann, T. Wagner, Light-activated resistive ozone sensing at room temperature utilizing nanoporous In2 O3 particles: influence of particle size, Sens. Actuators B: Chem. 217 (2015) 181–185. [22] R. Kumar, C. Baratto, G. Faglia, G. Sberveglieri, E. Bontempi, L. Borgese, Tailoring the textured surface of porous nanostructured NiO thin films for the detection of pollutant gases, Thin Solid Films 583 (2015) 233–238. [23] A. Bejaoui, J. Guerin, J.A. Zapien, K. Aguir, Theoretical and experimental study of the response of CuO gas sensor under ozone, Sens. Actuators B: Chem. 190 (2014) 8–15. [24] L.F. da Silva, V.R. Mastelaro, A.C. Catto, C.A. Escanhoela Jr., S. Bernardini, S.C. Zílio, E. Longo, K. Aguir, Ozone and nitrogen dioxide gas sensor based on a nanostructured SrTi0.85 Fe0.15 O3 thin film, J. Alloys Compd. 638 (2015) 374–379. [25] S. Senapati, R. Thakur, S.P. Verma, S. Duggal, D.P. Mishra, P. Das, T. Shripathi, M. Kumar, D. Rana, P. Maiti, Layered double hydroxides as effective carrier for anticancer drugs and tailoring of release rate through interlayer anions, J. Control. Release 224 (2016) 186–198. [26] M.F. Shao, F.Y. Ning, Y.F. Zhao, J.W. Zhao, M. Wei, D.G. Evans, X. Duan, Core–shell layered double hydroxide microspheres with tunable interior architecture for supercapacitors, Chem. Mater. 24 (2012) 1192–1197. [27] J. Xu, S.L. Gai, F. He, N. Niu, P. Gao, Y.J. Chen, P.P. Yang, Reduced graphene oxide/Ni1-x Cox Al-layered double hydroxide composites: preparation and high supercapacitor performance, Dalton Trans. 43 (2014) 11667–11675. [28] J. Wang, Y.C. Song, Z.S. Li, Q. Liu, J.D. Zhou, X.Y. Jing, M.L. Zhang, Z.H. Jiang, In situ Ni/Al layered double hydroxide and its electrochemical capacitance performance, Energy Fuel 24 (2010) 6463–6467. [29] Y. Guo, Y.P. Xiao, L.M. Zhang, Y.F. Song, Fabrication of (calcein–ZnS)n ordered ultra thin films on the basis of layered double hydroxide and its ethanol sensing behavior, Ind. Eng. Chem. Res. 51 (2012) 8966–8973. [30] Y.L. Ge, K. Kan, Y. Yang, L. Zhou, L.Q. Jing, P.K. Shen, L. Li, K.Y. Shi, Highly mesoporous hierarchical nickel and cobalt double hydroxide composite: fabrication, characterization and ultrafast NOx gas sensors at room temperature, J. Mater. Chem. A 2 (2014) 4961–4969. [31] L. Qiao, Y.M. Guo, X. Sun, Y.C. Jiao, X.Y. Wang, Electrochemical immunosensor with NiAl-layered double hydroxide/graphene nanocomposites and hollow gold nanospheres double-assisted signal amplification, Bioprocess Biosyst. Eng. 38 (2015) 1455–1468.
Biographies Guiying Kang received a B.Sc. from the Department of Applied Chemistry, College of Petrochemical Engineering, Lanzhou University of Technology in 2013. She is now entering a master’s program in the Department of Applied Chemistry, College of
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Petrochemical Engineering, Lanzhou University of Technology. Her current scientific interests are Li battery and chemical sensor technology. Zhen Zhu received a B.Sc. and an M.E. from Tianjin Polytechnic University, China, and a Ph.D. in physical chemistry from Nankai University in 2014. He is now working in the School of Environmental Science and Safety Engineering at Tianjin University of Technology, Tianjin. His current scientific interests are photocatalysis, nanoscience, recourse recycling technology, and chemical sensor technology. Bing-Hong Tang received a B.Sc. from the Department of Applied Chemistry at Providence University, Taiwan in 2015. He is now entering a master’s program in the Department of Applied Chemistry at Providence University, Taiwan. His current scientific interests are dye-sensitized solar cell and chemical sensor technology.
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Chun-Han Wu received an M.S. degree from the Department of Applied Chemistry at Providence University, Taiwan in 2013. He is now enrolled in a Ph.D. program in the Department of Applied Chemistry at Providence University, Taiwan. His current scientific interests are dye-sensitized solar cells and chemical sensor technology. Ren-Jang Wu received a B.Sc. in Chemistry from National Tsinghua University in 1986, an M.S. in Chemistry from National Taiwan University in 1988, and a Ph.D. in Chemistry from National Tsinghua University in 1995. He is now a full professor in the Department of Applied Chemistry at Providence University, Taiwan. Ren-Jang is interested in chemical sensors, photocatalysis, nanoscience, and chemical standards technology.
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Contents lists available at ScienceDirect
Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb
Rapid detection of ozone in the parts per billion range using a novel Ni–Al layered double hydroxide Guiying Kang a , Zhen Zhu b , Bing-Hong Tang c , Chun-Han Wu c , Ren-Jang Wu c,∗ a b c
Department of Applied Chemistry, College of Petrochemical Engineering, Lanzhou University of Technology, Lanzhou 730050, PR China School of Environmental Science and Safety Engineering, Tianjin University of Technology, Tianjin 300384, PR China Department of Applied Chemistry, Providence University, Shalu, Taichung 43301, Taiwan, ROC
a r t i c l e
i n f o
Article history: Received 3 May 2016 Received in revised form 29 September 2016 Accepted 4 October 2016 Available online xxx Keywords: Ni–Al layered double hydroxide Ozone Gas sensor
a b s t r a c t A novel ozone sensor based on Ni–Al layered double hydroxide (NiAl–LDH) that operates at room temperature (25 ◦ C) was developed. The NiAl–LDH was successfully synthesized using a hydrothermal method and characterized using X-ray diffraction, Scanning electron microscopy, and Fourier transform infrared spectroscopy. Selective detection of ozone was readily achieved with the NiAl–LDH sensor even in the presence of other gases such as H2 , NO2 , and C2 H5 OH. The NiAl–LDH sensor exhibited a sensor response of 1.22–15 ppb ozone, and the response and recovery times of the sensor were both measured as 4 s. In addition, the NiAl–LDH sensor revealed good reproducibility and reversibility, and the response displayed no obvious changes after 19 days of testing. Furthermore, the sensor presented excellent selectivity and stability for ozone, and the response value of the NiAl–LDH sensor to 700 ppb ozone was 1.84. Moreover, a possible ozone sensing mechanism of the NiAl–LDH sensor is presented. The NiAl–LDH sensor is a promising candidate for the detection of ozone in parts per billion levels at room temperature (25 ◦ C). © 2016 Elsevier B.V. All rights reserved.
1. Introduction Ozone (O3 ) is a useful oxidation agent with numerous practical applications, including operations in the pharmaceutical, textile, and chemical industries; food processing and storage; water treatment; and purification of gases [1]. Furthermore, because of its bactericidal and virus inactivating activity, it has provided a satisfactory replacement for various ecologically damaging and physiologically noxious compounds. In contrast to some other oxidants, the ozone oxidation process does not produce toxic waste (only oxygen) [2]. However, when ozone exceeds a certain threshold level, exposure becomes hazardous to human health, causing headache, burning eyes, respiratory irritation, and lung damage [3]. In many developed countries, the maximum allowed safe concentration of ozone is 50 ppb for continuous exposure and 100 ppb for short-term exposure [4]. Accidental leakage and emission of ozone into the atmosphere can easily occur from certain processes. For example, the processes of UV irradiation and electric arc welding are generally accompanied by ozone generation [5]. Additionally, ozone is produced in office environments by photocopiers and laser printers [6]. Moreover, ozone in the atmosphere at low concentra-
∗ Corresponding author. E-mail addresses: [email protected], [email protected] (R.-J. Wu).
tions is colorless and odorless. It is therefore necessary to monitor the concentration of ozone in the atmosphere for reliable concentration control. Various technological methods, including gas sensing, electrochemical, impedance spectroscopic, amperometric, optical, resistive, work functional, and UV light photoreduction methods [7–14], have been employed to determine concentrations of ozone. Among these methods, gas sensing (based on solid-state sensors)—because of its many advantages over traditional chemical analysis techniques such as high sensitivity, short response times, low cost, low weight, simple design, online operation, low working temperature (25 ◦ C), ease of use, and low energy consumption [15–17]—has been widely used for the detection of trace amounts of ozone in the atmosphere. Recently, sensors based on metal oxide semiconductors, including ZnO, WO3 , SnO2 , In2 O3 , NiO, CuO, and SrTi0.85 Fe0.15 O3 [18–24], have been developed and extensively used for ozone detection. However, no experimental data regarding interference by other gases and stability tests of the sensors have been reported [18–23]. The SrTi0.85 Fe0.15 O3 sensor was used for 800 ppb ozone sensing at 250 ◦ C [24], the sensor response was 9.0, and the response and recovery times were determined as 28 s and 161 s, respectively. However, strong interference of NO2 gas was revealed, and no short or long term stability tests of the sensor were carried out [24]. Layered double hydroxides are a family of anionic
http://dx.doi.org/10.1016/j.snb.2016.10.012 0925-4005/© 2016 Elsevier B.V. All rights reserved.
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clay materials, represented by the general formula [M2+ 1−x M3+ x (OH)2 ]x+ (An− ) x/n ·mH2 O, where M2+ is a divalent metal ion, such as Mg2+ , Ca2+ , or Zn2+ ; M3+ is a trivalent metal ion, such as Al3+ , Cr3+ , Fe3+ , or Co3+; and An− is an anion, such as Cl− , CO3 2− , or NO3 − [25]. Layered double hydroxides have attracted considerable attention because of their high surface area, excellent electrical conductivity, low toxicity, inexpensiveness, ease of preparation, high ionic exchange capacity, environmental friendliness, and good thermal stability [26–28]. However, there are only a few studies about their gas sensing properties [29,30] and no reports about their ability to sense ozone. To fill this gap, the aim of this study was to develop an easy and cost-effective route for synthesizing a fast-response, highly sensitive, and selective ozone sensor based on Ni–Al layered double hydroxide (NiAl–LDH). The structural and microstructural properties of NiAl–LDH samples were characterized through X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) spectroscopy. We also investigated the ozone sensing properties of the gas sensor based on NiAl–LDH at atmospheric room temperature (25 ◦ C).
2. Experimental 2.1. Fabrication of NiAl–LDH The NiAl–LDH was fabricated using a hydrothermal process. NiSO4 ·6H2 O (0.26 g), Al2 (SO4 )3 (0.17 g), and urea (0.21 g) were dissolved in deionized water (20 mL) to form a clear solution that was then transferred into a 100 mL Teflon-lined stainless steel autoclave. Hydrothermal treatment was performed for a period of at least 24 h at a temperature of at least 100 ◦ C. Subsequently, the obtained product was separated using a centrifuge, washed thoroughly with deionized water several times, and dried in an oven at 80 ◦ C for 12 h. 2.2. Characterization of NiAl–LDH The morphology and structure of the NiAl–LDH were investigated through TEM (JEM-2100F), energy dispersive spectrometry (EDX; JEM-2100F), and SEM (Nova TM NanoSEM 230). The crystal structures of the NiAl–LDH were characterized using an XRD-6000 Shimadzu X-ray diffractometer with Cu K␣ radiation at 40 kV and 30 mA between 10◦ and 70◦ (2), with the scanning rate being 2◦ /min. The infrared spectrum of NiAl–LDH was measured on a Nicolet Nexus 870 FTIR spectroscope in the frequency range
400–4000 cm−1 . The sample was pulverized and dispersed in KBr pellets before recording the spectrum. 2.3. Fabrication of the NiAl–LDH sensor A sensing material was fabricated by mixing the prepared sample and a binder of 90 wt% ethyl alcohol. The sensing film was fabricated by dip-coating it on a pair of comb-like gold electrodes existing on an alumina substrate with dimensions of 10 mm × 5 mm. The sensing film was placed in a room temperature (25 ◦ C) environment for 24 h to wait for the ethyl alcohol to volatilize. 2.4. Gas sensing properties of the NiAl–LDH sensor The ozone response measurement was conducted in a dynamic flow system, in which the sensors were housed in a glass cover chamber (gas sensing chamber), shown in Fig. 1. The diameter of the glass cover was 12.3 cm. The ozone gas was produced by an ozone generator (TCA 158, Tsun Cheng Co., Taiwan), was diluted with air to 15–3580 ppb by adjusting two mass flow controllers, and was monitored with a commercial ozone sensor (MIL-RAM 01-2313). The commercial ozone sensor was calibrated according to the standard concentration by the Center for Measurement Standards/Industrial Technology Research Institute (CMS/ITRI) in Taiwan. The NOx concentration was measured by the CMS/ITRI as less than 420 ppb. The total flow rate of the testing gas (ozone/air) was fixed at 400 cm3 /min during measurements and the temperature of the sensor device was controlled at 25 ± 2 ◦ C, with relative humidity (RH) maintained at 50 ± 5%. The RH varied among 12%, 20%, 30%, 40%, 50%, 60%, 70%, 80% and 90% ± 5% by divided flow system. The sensor response (S) was defined as S = Rair /Rozone , where Rozone is the electrical resistance of the sensor in ozone gas, and Rair is its electrical resistance in air. The response time (t90 ) was defined as the time taken for the saturation value to increase from 10% to 90%, whereas the recovery time (tr90 ) was the reverse of the response time. Other gas inference tests were performed under the same conditions. Interference gases of CH3 OH (700 ppb), C2 H5 OH (700 ppb), NO2 (700 ppb), CH3 COCH3 (700 ppb), and H2 (700 ppb) were employed for the sensing system. The sensor response (S) of reducing gas and oxidizing gas was defined as S1 = Rg /Rair and S = Rair /Rg , respectively, where Rg is the resistance in an environment containing gas. The sensor process in the interference tests was the same as that in the ozone gas condition. The gas sensing resistance measurements were performed using a Jiehan 5000 data acquisition system, a simple voltage circuit was used to measure the sensor resistance with an input DC voltage of 2 V, and a
Fig. 1. Ozone detection system. (a) Ozone generator, (b) air pump, (c) mass flow controller and power box, (d) drying tube, (e) pipe tee, (f) UV ozone detector, (g) gas control valve, (h) glass cover and ozone sensor device, (i) power supply, (j) circuits, (k) data acquisition system, and (l) computer.
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Fig. 2. XRD patterns of NiAl–LDH.
Fig. 3. FTIR spectra of NiAl–LDH.
computer was used to perform data acquisition and processing. An inductance–capacitance–resistance meter (HIOKI 3532-50) was used to measure the complex impedance (Z) of the sensors in a test chamber (frequency = 1 kHz, applied voltage = 1 V) under various humidity conditions (RH = 12–90%). 3. Results and discussion 3.1. Structure characterization In Fig. 2, the peaks corresponding to the (003), (006), (012), (015), and (018) planes, respectively, are attributed to the characteristic reflections of the NiAl–LDH structure [31], and no other crystalline phase is evident. Moreover, the typical doublet of the d (110)–d (113) planes of NiAl–LDH can be clearly observed in the zone around 2 = 60–62◦ . The XRD pattern for NiAl–LDH is similar to those reported in the literature [31], indicating that NiAl–LDH of high purity was successfully prepared. IR spectra of NiAl–LDH between 400 and 4000 cm−1 are shown in Fig. 3. NiAl–LDH has a broad band centered at 3363 cm−1 , which is attributed to the stretching mode of the OH group with hydrogen bonding and that of interlayer water molecules. The peak at 1646 cm−1 can be attributed to the bending mode of water molecules. The peaks at 1140 cm−1 and 1072 cm−1 can be assigned to the 1 (SO4 )2− symmetric and 3 (SO4 )2− antisymmetric stretching modes, respectively. In addition, the bands recorded at the low
Fig. 4. (a) SEM image of NiAl–LDH, (b) TEM image of NiAl–LDH, (c) EDS spectrum of NiAl–LDH.
frequency region (below 700 cm−1 ) are ascribed to M O vibrations and M O H bending (M = Ni, Al). The morphology of the NiAl–LDH was characterized through SEM and TEM. The SEM image of the NiAl–LDH is shown in Fig. 4a, indicating that the NiAl–LDH consists of platelets stacked upon each other and forming solid agglomerates with a flower-like structure. Furthermore, the NiAl–LDH exhibits a flake-like morphology with a larger lateral dimension than the longitudinal one, which is the typical feature of layered materials, as illustrated in Fig. 4b. Moreover, the EDX spectrum of the NiAl–LDH can be observed in Fig. 4c.
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Table 1 Sensing properties of various kinds of sensing materials to 700 ppb ozone at room temperature. Various kinds of sensing materials
S
t90 /s
tr90 /s
RH (%)
Ni(OH)2 Al(OH)3 NiAl-LDH
1.56 1.10 1.84
8 36 8
244 22 74
50 50 50
Fig. 6. (a) Resistance and (b) sensor response of NiAl–LDH upon exposure to three cycle tests at ozone concentrations of 45, 350, 610, and 2000 ppb at room temperature.
Fig. 5. (a) Resistance and (b) sensor response of NiAl–LDH to 540 ppb ozone at room temperature.
According to the EDX data, Ni, Al, O, and S elements are the major components. In addition, the Ni/Al molar ratio is calculated to be 1, which is close to the designated ratio. This result implies that the interlayer anions of NiAl–LDH are possibly sulphate ions. 3.2. Ozone-response properties of NiAl–LDH The sensing properties of Ni(OH)2 , Al(OH)3 , and NiAl–LDH sensors were studied at room temperature (25 ◦ C) under exposure to 700 ppb ozone, and the sensing properties are listed in Table 1. The sensor response of NiAl–LDH, 1.84, is higher than those of the other sensing materials. Table 1 also reveals that the response times of NiAl–LDH and Ni(OH)2 are both 8 s, shorter than that of Al(OH)3 . According to Fig. 5 (a), the sensor resistance is decreasing of introducing ozone gas and sensor resistance increasing by removing ozone gas. This NiAl-LDH sensor is a p-type semiconductor gas sensor. As illustrated in Fig. 5 (b), the response of the NiAl–LDH sensor was increased by the introduction of 540 ppb ozone and reduced by opening an air inlet. Additionally, the sensor response (S) of the NiAl–LDH sensor to 540 ppb ozone was calculated as 1.74. Moreover, the NiAl–LDH sensor clearly exhibited total reversibility and good stability of the baseline after 15 cycle tests, and the response and recovery were fairly reproducible and quick. To further investigate the stability of the NiAl–LDH sensor, the sensor response was tested under various ozone concentration levels, as shown in Fig. 6 (a) and (b). The NiAl–LDH sensor retained the original response with no significant change after three cycle tests
Fig. 7. Stability test of the ozone sensor based on NiAl–LDH to 540 ppb ozone at room temperature.
at ozone concentrations of 45, 350, 610 and 2000 ppb, demonstrating its suitability for measuring different ozone concentrations. Furthermore, the short term stability of the NiAl–LDH sensor was measured at 700 ppb ozone for 19 days, as shown in Fig. 7. Notably, the sensor exhibited almost constant sensor signals during the test, with responses of 1.75, 1.73, 1.72, 1.78, and 1.76 on days 0, 1, 7, 13, and 19, respectively, indicating that the NiAl–LDH sensor has excellent short term stability. Selectivity is a crucial parameter for evaluating the performance of the NiAl–LDH sensor. To investigate the selectivity of the NiAl–LDH sensor, a series of interference tests was conducted. The responses of the NiAl–LDH sensor to 700 ppb hydrogen gas (H2 ), acetone (CH3 COCH3 ), methanol (CH3 OH), ethanol (C2 H5 OH), and nitrogen dioxide (NO2 ) are presented in Table 2. The response value of the NiAl–LDH sensor to ozone is 1.84, which is considerably higher than those to other gases at the same concentrations. Therefore, the NiAl–LDH sensor exhibits excellent selectivity to ozone at room temperature (25 ◦ C). Table 3 reveals that the sensor response increased from 1.41 to 1.97 as the RH increased from 10% to 90% to 400 ppb ozone. This variation of sensor response is due to water vapor, and the
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Table 2 Sensor response of various gases at room temperature. Various kinds of reducing gases
Concentration (ppb)
S1
t90 /s
tr90 /s
RH (%)
Hydrogen (H2 ) Acetone (CH3 COCH3 ) Methanol (CH3 OH) Ethanol (C2 H5 OH)
700 700 700 700
1.00 1.02 1.21 1.02
— 2 210 2
— 2 80 2
50
Various kinds of oxidizing gases
Concentration (ppb)
S
t90 /s
tr90 /s
RH (%)
Nitrogen dioxide (NO2 ) Ozone (O3 )
700 700
1.00 1.84
— 8
— 74
50 50
50 50
Table 3 Sensor response of 400 ppb ozone concentrations under various humidity condition at room working temperature. RH (%)
S
t90 /s
tr90 /s
10% 30% 50% 70% 90%
1.41 1.50 1.69 1.86 1.97
20 18 8 6 5
25 30 30 30 35
Table 4 Sensor impedance under various humidity condition at room working temperature on NiAl-LDH. RH (%)
Sensor impedance (M)
12% 20% 30% 40% 50% 60% 70% 80% 90%
14.94 15.06 15.08 15.42 15.68 15.42 15.17 14.87 14.85
Fig. 8. Sensor response versus various ozone concentrations from 15 to 3580 ppb on NiAl–LDH at room temperature.
Z (10%): Sensor impedance under relative humidity 10%. Z (10%) = 14.94 M. Z (50%): Sensor impedance under relative humidity 50%. Z (50%) = 15.68 M. Z (90%): Sensor impedance under relative humidity 90%. Z (90%) = 14.85 M.
Table 5 Sensor response of ozone concentrations from 15 to 3580 ppb on NiAl-LDH at room working temperature. Ozone (ppb)
S
t90 /s
tr90 /s
RH (%)
15 35 70 140 240 340 540 740 1740 3580
1.22 1.35 1.53 1.56 1.65 1.67 1.75 1.86 2.02 2.20
4 6 8 8 8 8 8 8 8 8
4 6 8 8 8 16 36 124 168 212
50 50 50 50 50 50 50 50 50 50
response time is faster on higher relative humidity condition in Table 3. Specifically, water and ozone molecules were adsorbed at the sites of NiAl–LDH (higher RH) and took part in the sensing reaction. We obtained the change in sensor impedance to relative humidity from 12% to 90% at 25 ◦ C in Table 4, in order to evaluate the interference from water vapor under no ozone gas condition. As the standard humidity condition of the ozone gas sensing system is RH = 50%. We calculated the low humidity interference by ratio of Z(50%)/Z(10%) = 1.05, and also estimated the high humidity interference by ratio of Z(50%)/Z(90%) = 1.06 from Table 4. Therefore, it is no significant interference of low and high humidity conditions. The relationship between sensor response and concentration of ozone is shown in Fig. 8 and Table 5. The sensor response increased
from 1.22 to 2.20 when the ozone concentration increased from 15 to 3580 ppb. Fig. 8 illustrates that the slope of the response curve is higher for a low ozone concentration than for a high ozone concentration. This shows that the sensor possesses the ability to sense a low ozone concentration. The sensor exhibited a sensor response of 1.22 to 15 ppb ozone, and the response and recovery times of the sensor were measured as 4 s and 4 s (Table 5), respectively. In addition, for all concentrations, the response time was not greater than 8 s. 3.3. Probable gas sensing mechanism Fig. 9a reveals that the NiAl–LDH sensing materials possess NiAl–LDH, and low concentration ozone gas is easily attracted to the surface. Because ozone is an oxidative molecule, it quickly captures an electron from Ni2+ on the NiAl–LDH structure as shown in Fig. 9b, and Ni3+ and adsorbed O3 − are then formed according to equation (1) [22]. The adsorbed O3 − is decomposed to oxygen gas and adsorbed O− (Eq. (2)). Eq. (3) shows that an adsorbed O− can easily react with Ni3+ to form Ni2+ and an adsorbed oxygen atom for attracting positive Ni3+ and a negative oxygen ion. Surfaceadsorbed oxygen atoms carry on combination reactions to yield oxygen gas according to Eq. (4). O3 + Ni2+ → Ni3+ + O3 − (ad) O3
−
(ad)
→ O
−
(ad)
+ O2
(1) (2)
O− (ad) + Ni3+ → O(ad) + Ni2+
(3)
2O(ad) → O2
(4)
The short response and recovery times (Table 4) arise from the high charge transfer speed between Ni2+ and Ni3+ in the NiAl–LDH structure (Eqs. (1) and (3)) [28]. Ozone can easily penetrate the NiAl–LDH structure (Fig. 9a and 9b) to approach Ni2+ ; thus, the reversible cycle between Ni2+ and Ni3+ in the NiAl–LDH sensor is
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Fig. 9. (a) Simple representation of ozone gas on NiAl–LDH structure. (b) Scheme of the simple sensing mechanism.
easily obtained. The unique characteristic of selective ozone sensing is that ozone has a strong oxidative property and can perform the M2+ and M3+ cycle reversibly in a NiAl–LDH sensor (Fig. 9b). 5. Conclusion In this study, we successfully synthesized NiAl–LDH for use as a sensor for ozone. The obtained NiAl–LDH sensor exhibits high sensitivity to ozone at parts per billion levels, total reversibility, good reproducibility, and good stability, indicating that it is a promising sensing material for the detection of ozone. References [1] R.J. Wu, Y.C. Chiu, C.H. Wu, Y.J. Su, Application of Au/TiO2 –WO3 material in visible light photoreductive ozone sensors, Thin Solid Films 574 (2015) 156–161. [2] G. Korotcenkov, B.K. Cho, Ozone measuring: what can limit application of SnO2 -based conductometric gas sensors, Sens. Actuators B: Chem. 161 (2012) 28–44. [3] L.S.R. Rocha, C.R. Foschini, C.C. Silva, E. Longo, A.Z. Simões, Novel ozone gas sensor based on ZnO nanostructures grown by the microwave-assisted hydrothermal route, Ceram. Int. 42 (2016) 4539–4545. [4] L. Berry, J. Brunet, Oxygen influence on the interaction mechanisms of ozone on SnO2 sensors, Sens. Actuators B: Chem. 129 (2008) 450–458. [5] Z.-M. Qi, H.-S. Zhou, I. Honma, K. Itoh, H. Yanangi, A disposable ozone sensor based on a grating-coupled glass waveguide coated with a tapered film of copper tetra-t-butylphtalocyanine, Sens. Actuators B: Chem. 106 (2005) 278–283. [6] Y. Hosoya, Y. Itagaki, H. Aono, Y. Sadaoka, Ozone detection in air using SmFeO3 gas sensor, Sens. Actuators B: Chem. 108 (2005) 198–201. [7] T.C.E. Marcus, M.H. Ibrahim, N.H. Ngajikin, A.I. Azmi, Optical path length and absorption cross section optimization for high sensitivity ozone concentration measurement, Sens. Actuators B: Chem. 221 (2015) 570–575.
[8] D. Ebeling, V. Patel, M. Findlay, J. Stetter, Electrochemical ozone sensor and instrument with characterization of the electrode and gas flow effects, Sens. Actuators B: Chem. 137 (2009) 129–133. [9] A. Labidi, C. Jacolin, M. Bendahan, A. Abdelghani, J. Guérin, K. Aguir, M. Maaref, Impedance spectroscopy on WO3 gas sensor, Sems. Actuators B: Chem. 106 (2005) 713–718. [10] M. Zimmer, M. Burgmair, K. Scharnagl, A. Karthigeyan, T. Doll, I. Eisele, Goldand platinum as ozone sensitive layer in work-function gas sensors, Sens. Actuators B: Chem. 80 (2001) 174–178. [11] A. Gaddari, F. Berger, M. Amjoud, J.B. Sanchez, M. Lahcini, B. Rhouta, D. Mezzane, C. Mavon, E. Beche, V. Flaud, A novel way for the synthesis of tin dioxide sol–gel derived thin films: application to O3 detection at ambient temperature, Sens. Actuators B: Chem. 176 (2013) 811–817. [12] S. Christoulakis, M. Suchea, E. Koudoumas, M. Katharakis, N. Katsarakis, G. Kiriakidis, Fast-response ozone sensor with ZnO nanorods grown by chemical vapor deposition, Appl. Surf. Sci. 252 (2006) 5351–5354. [13] Z. Zhu, J.L. Chang, R.J. Wu, Fast ozone detection by using a core-shell Au@TiO2 sensor at room temperature, Sens. Actuators B: Chem. 214 (2015) 56–62. [14] S. Addanki, J. Jayachandiran, K. Pandian, D. Nedumaran, Development of optical sensors for the quantitative detection of ozone using gold and silver thin film nanoislands, Sens. Actuators B: Chem. 210 (2015) 17–27. [15] S. Vallejos, V. Khatko, K. Aguir, K.A. Ngo, J. Calderer, I. Gràcia, C. Cané, E. Llobet, X. Correig, Ozone monitoring by micro-machined sensors with WO3 sensing films, Sens. Actuators B: Chem. 126 (2007) 573–578. [16] F.S.S. Chien, C.R. Wang, Y.L. Chan, H.L. Lin, M.H. Chen, R.J. Wu, Fast- response ozone sensor with ZnO nanorods grown by chemical vapor deposition, Sens. Actuators B: Chem. 144 (2010) 120–125. [17] M. Acuautla, S. Bernardini, L. Gallais, T. Fiorido, L. Patout, M. Bendahan, Ozone flexible sensors fabricated by photolithography and laser ablation processes based on ZnO nanoparticles, Sens. Actuators B: Chem. 203 (2014) 602–611. [18] I. Kortidis, K. Moschovis, F.A. Mahmoud, G. Kiriakidis, Structural analysis of aerosol spray pyrolysis ZnO films exhibiting ultra low ozone detection limits at room temperature, Thin Solid Films 518 (2009) 1208–1213. [19] W. Belkacem, A. Labidi, J. Guérin, N. Mliki, K. Aguir, Cobalt nanograins effect on the ozone detection by WO3 sensors, Sens. Actuators B: Chem. 132 (2008) 196–201. [20] G. Korotcenkov, I. Blinov, M. Ivanov, J.R. Stetter, Ozone sensors on the base of SnO2 films deposited by spray pyrolysis, Sens. Actuators B: Chem. 120 (2007) 679–686. [21] D. Klaus, D. Klawinski, S. Amrehn, M. Tiemann, T. Wagner, Light-activated resistive ozone sensing at room temperature utilizing nanoporous In2 O3 particles: influence of particle size, Sens. Actuators B: Chem. 217 (2015) 181–185. [22] R. Kumar, C. Baratto, G. Faglia, G. Sberveglieri, E. Bontempi, L. Borgese, Tailoring the textured surface of porous nanostructured NiO thin films for the detection of pollutant gases, Thin Solid Films 583 (2015) 233–238. [23] A. Bejaoui, J. Guerin, J.A. Zapien, K. Aguir, Theoretical and experimental study of the response of CuO gas sensor under ozone, Sens. Actuators B: Chem. 190 (2014) 8–15. [24] L.F. da Silva, V.R. Mastelaro, A.C. Catto, C.A. Escanhoela Jr., S. Bernardini, S.C. Zílio, E. Longo, K. Aguir, Ozone and nitrogen dioxide gas sensor based on a nanostructured SrTi0.85 Fe0.15 O3 thin film, J. Alloys Compd. 638 (2015) 374–379. [25] S. Senapati, R. Thakur, S.P. Verma, S. Duggal, D.P. Mishra, P. Das, T. Shripathi, M. Kumar, D. Rana, P. Maiti, Layered double hydroxides as effective carrier for anticancer drugs and tailoring of release rate through interlayer anions, J. Control. Release 224 (2016) 186–198. [26] M.F. Shao, F.Y. Ning, Y.F. Zhao, J.W. Zhao, M. Wei, D.G. Evans, X. Duan, Core–shell layered double hydroxide microspheres with tunable interior architecture for supercapacitors, Chem. Mater. 24 (2012) 1192–1197. [27] J. Xu, S.L. Gai, F. He, N. Niu, P. Gao, Y.J. Chen, P.P. Yang, Reduced graphene oxide/Ni1-x Cox Al-layered double hydroxide composites: preparation and high supercapacitor performance, Dalton Trans. 43 (2014) 11667–11675. [28] J. Wang, Y.C. Song, Z.S. Li, Q. Liu, J.D. Zhou, X.Y. Jing, M.L. Zhang, Z.H. Jiang, In situ Ni/Al layered double hydroxide and its electrochemical capacitance performance, Energy Fuel 24 (2010) 6463–6467. [29] Y. Guo, Y.P. Xiao, L.M. Zhang, Y.F. Song, Fabrication of (calcein–ZnS)n ordered ultra thin films on the basis of layered double hydroxide and its ethanol sensing behavior, Ind. Eng. Chem. Res. 51 (2012) 8966–8973. [30] Y.L. Ge, K. Kan, Y. Yang, L. Zhou, L.Q. Jing, P.K. Shen, L. Li, K.Y. Shi, Highly mesoporous hierarchical nickel and cobalt double hydroxide composite: fabrication, characterization and ultrafast NOx gas sensors at room temperature, J. Mater. Chem. A 2 (2014) 4961–4969. [31] L. Qiao, Y.M. Guo, X. Sun, Y.C. Jiao, X.Y. Wang, Electrochemical immunosensor with NiAl-layered double hydroxide/graphene nanocomposites and hollow gold nanospheres double-assisted signal amplification, Bioprocess Biosyst. Eng. 38 (2015) 1455–1468.
Biographies Guiying Kang received a B.Sc. from the Department of Applied Chemistry, College of Petrochemical Engineering, Lanzhou University of Technology in 2013. She is now entering a master’s program in the Department of Applied Chemistry, College of
Please cite this article in press as: G. Kang, et al., Rapid detection of ozone in the parts per billion range using a novel Ni–Al layered double hydroxide, Sens. Actuators B: Chem. (2016), http://dx.doi.org/10.1016/j.snb.2016.10.012
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Petrochemical Engineering, Lanzhou University of Technology. Her current scientific interests are Li battery and chemical sensor technology. Zhen Zhu received a B.Sc. and an M.E. from Tianjin Polytechnic University, China, and a Ph.D. in physical chemistry from Nankai University in 2014. He is now working in the School of Environmental Science and Safety Engineering at Tianjin University of Technology, Tianjin. His current scientific interests are photocatalysis, nanoscience, recourse recycling technology, and chemical sensor technology. Bing-Hong Tang received a B.Sc. from the Department of Applied Chemistry at Providence University, Taiwan in 2015. He is now entering a master’s program in the Department of Applied Chemistry at Providence University, Taiwan. His current scientific interests are dye-sensitized solar cell and chemical sensor technology.
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Chun-Han Wu received an M.S. degree from the Department of Applied Chemistry at Providence University, Taiwan in 2013. He is now enrolled in a Ph.D. program in the Department of Applied Chemistry at Providence University, Taiwan. His current scientific interests are dye-sensitized solar cells and chemical sensor technology. Ren-Jang Wu received a B.Sc. in Chemistry from National Tsinghua University in 1986, an M.S. in Chemistry from National Taiwan University in 1988, and a Ph.D. in Chemistry from National Tsinghua University in 1995. He is now a full professor in the Department of Applied Chemistry at Providence University, Taiwan. Ren-Jang is interested in chemical sensors, photocatalysis, nanoscience, and chemical standards technology.
Please cite this article in press as: G. Kang, et al., Rapid detection of ozone in the parts per billion range using a novel Ni–Al layered double hydroxide, Sens. Actuators B: Chem. (2016), http://dx.doi.org/10.1016/j.snb.2016.10.012