- Nano Express
- Open Access
Gas-Sensing Devices Based on Zn-Doped NiO Two-Dimensional Grainy Films with Fast Response and Recovery for Ammonia Molecule Detection
© Wang et al. 2015
Received: 21 June 2015
Accepted: 23 November 2015
Published: 1 December 2015
Zn-doped NiO two-dimensional grainy films on glass substrates are shown to be an ammonia-sensing material with excellent comprehensive performance, which could real-time detect and monitor ammonia (NH3) in the surrounding environment. The morphology and structure analysis indicated that the as-fabricated semiconductor films were composed of particles with diameters ranging from 80 to 160 nm, and each particle was composed of small crystalline grain with a narrow size about 20 nm, which was the face-centered cubic single crystal structure. X-ray diffraction peaks shifted toward lower angle, and the size of the lattice increased compared with undoped NiO, which demonstrated that zinc ions have been successfully doped into the NiO host structure. Simultaneously, we systematically investigated the gas-sensing properties of the Zn-doped NiO sensors for NH3 detection at room temperature. The sensor based on doped NiO sensing films gave four to nine times faster response and four to six times faster recovery speeds than those of sensor with undoped NiO films, which is important for the NiO sensor practical applications. Moreover, we found that the doped NiO sensors owned outstanding selectivity toward ammonia.
In recent years, air pollution have become one of the most serious problems that every country in the world is facing, which also have attracted considerable attention from a part of the scientific community to investigation of various atmospheric environmental issues [1–5]. Ammonia (NH3) is one of the toxic gases in the earth’s atmosphere and is considered as an artificial source for intensive livestock breeding with the decomposition process of manure and the chemical industry for the production of fertilizers and for refrigeration systems [6, 7]. Generally speaking, upon exposure to around 50 ppm (corresponding to about 40 μg/m3), NH3 is irritating to respiratory system, skin, and eyes and could cause acute poisoning or life-threatening situations [8–11]. Therefore, it became highly desirable to design and fabricate a portable sensing device with low cost and low power, which can real-time detect and monitor NH3 in air . Currently, some miniaturized chemical gas sensors based on nanoscale metal oxide semiconductor, which rely principally on monitoring the direct change in the conductance in adsorption and desorption of gas molecules, have been successfully obtained [13–15]. Gas-sensing performance strongly depends on the dimension, size, and morphology of the sensing materials. Thus, further research on sensing materials is still necessary for enhancing the sensing properties and continuing the expansion of the area of application of the sensor.
During the past several years, various semiconductor metal oxides such as WO3, CuO, TiO2, SnO2, ZnO, and In2O3 have been successfully prepared and their gas-sensing properties have been investigated from a part of the gas-sensing community [16–21]. Among these gas-sensing materials, naturally p-type NiO semiconductors with a wide band gap energy in the range of 3.6–4.0 eV have been recognized as an interesting and prosperous nanomaterials for the detection of gas molecules due to their simplicity of use, high compatibility with microelectronic processing, and environmental friendliness . Recently, one of the most significant breakthroughs in the domain of gas-sensing devices based on metal oxides was the preparation of the doped-nanomaterials [23–25]. Specifically, various catalysts (such as Pt, Ag, and NiO) have been loaded into metal oxide-sensing materials to improve gas-sensing performances. The doping contents, distribution, and size of catalysts are key parameters for enhancing gas molecules response/recovery speeds as well as selectivity . Therefore, doping metal ions in nanoscale NiO two-dimensional grainy films is considered as an effective and simple way to improve the gas-sensing properties (such as decreasing the response and recovering time) via forming micro area p-n junction (e.g., p-type NiO/n-type ZnO), which is very important for the application of gas sensors.
In our previous study, we developed a gas sensor based on pure NiO films for sensing NH3, which owned excellent stability and outstanding sensitivity performance . However, as being a product, the major issue is that the recovery speed is very poor at room temperature because the desorptions of gas molecules adsorbed on sensor need take a long time, and similar problem was proposed via other investigators [28–30]. To solve this problem, we would fabricate the nickel oxide two-dimensional grainy films and doping zinc ions forming in micro region, which enhanced the response and recovery speeds via improving electron transport and gas molecular diffusion in this special nanostructure. In the present work, we present a hydrothermal controllable route combined with high-temperature oxidation approach to prepare Zn-doped NiO films with well-controlled morphologies and systematically investigate Zn-doping effects on the gas-sensing performance of sensors at room temperature. The results showed that the response and recovery speed of NH3 can be remarkably improved via doping zinc ions in nanoscale NiO films as compared with pristine NiO films, which may provide a simple approach to fabricate excellent gas sensors based on metal oxides with desirable gas-sensing performance.
Preparation of the Gas-Sensing Materials
Assembling of the Gas-Sensing Devices
The crystallinity and crystalline nature of each synthesized crystal were identified via X-ray powder diffraction (XRD) using a 18-kW advanced X-ray diffractometer (D8 ADVANCE, Bruker, Germany) in a two theta range from 30 to 90° with a Cu Kα (λ = 0.154056 nm) rotating anode point source operating at 40 kV and 40 mA. The specific surface morphology and elemental composition of as-prepared samples were investigated using a field emission scanning electron microscopy (FESEM, Zeiss Ultra 55, Germany) combined with energy-dispersive spectroscopy (EDS) at accelerating voltage of 5 and 20 kV, respectively. In addition, high-resolution transmission electron microscopy (HRTEM) images were recorded in a JEM-2010 transmission electron microscope operating at 200 kV. The electrical signal of the gas-sensing devices was monitored using the Agilent 4156C. The gas-sensing properties of sensor were evaluated via the resistance change at a working voltage of 1 V.
Results and Discussion
Structure and Morphology of Gas-Sensing Materials
Zn-doped NiO films on glass substrate were fabricated via the hydrothermal reaction combined with subsequent high-temperature oxidation method, as shown in Fig. 1. In the first stage of synthesis of gas-sensing materials, a controlled hydrazine reduction approach has been developed to synthesize Ni(1 − x)Znx films on a substrate in a flask. In the second stage, Ni(1 − x)Znx films were transformed Ni(1 − x)ZnxO films via situ chemical oxidation route in open air. The specific chemical reactions for the synthesis can be expressed as follows:
In order to understand the internal microstructure of the doped film in more detail, further HRTEM images recorded from a particle in film are shown in Fig. 4c, d, which shows the crystal lattice structure. The images with no visible or planar defects show the high crystallinity of the Zn-doped NiO film. The inter-planar distance of the fringes in Fig. 4c was measured to be 0.245 (approx. 2.5) nm, which is slightly larger than that for the (111) plane of intrinsic cubilc NiO crystal (0.24120 nm). In the meantime, the interspacing in Fig. 4d was determined to be 0.212 (approx. 2.1) nm, which is also slightly larger than that for the distance of intrinsic NiO (200) plane (0.20890 nm). These results indicate lattice expansion, which implied that zinc atoms might form substitution atoms in NiO film to a great extent.
Gas-Sensing Performances of the Sensors
As well as we know, the stoichiometric NiO crystal is an insulator, however, typical NiO exhibits a reasonable electrical conductivity due to nickel vacancies or interstitial oxygen atoms in NiO crystal (p-type semiconductor) . As-synthesized Zn-doped NiO film exhibited oxygen-rich stoichiometry (see Fig. 5A2–C2), such as the atomic ratio O/Ni of 0 mol% Zn-NiO was about 51.16/48.84. Ammonia-sensing devices based on doped NiO films were fabricated via connecting the gas-sensing materials to the testing sockets using homemade silver paste combined with subsequent sputtering pure Au, as shown in Fig. 2. In our testing experiments, the conductance between the positive and negative electrodes was measured with a precision semiconductor parameter analyzer (Agilent 4156C) to investigate the response of gas-sensing devices. The sensor response is defined via the equation (ΔG/G0 = (G–G0)/G0), where G0 and G are the conductance of sensing films when exposed to the air and target gas with 25 % of relative humidity, respectively. The response time (τresponse) and recovery time (τrecovery) are defined as the time needed to reach 90 % of the final steady state conductance upon exposure to the testing gas and air, respectively .
In summary, semiconductor Zn-doped NiO gas-sensing films on glass substrates have been successfully fabricated via a chemical reaction combined with subsequent high-temperature oxidation method. SEM observations revealed that the doped NiO film composed of nanoscale particles with diameters ranging from 80 to 160 nm, which was larger than the crystalline grain size (about 20 nm) calculated from X-ray diffraction peaks; and Zn-doping concentrations had no influence on the growth of the gas-sensing films. In XRD and HRTEM characterization of doped NiO films, we found that all the XRD peaks shifted toward lower angle and the size of the lattice increased compared with undoped NiO samples, which is assigned to the successful incorporation of zinc ions in the NiO host structure. Significantly, the gas-sensing devices based on as-fabricated Zn-doped NiO films exhibited the short response/recovery time, excellent sensitivity, and selectivity toward ammonia over other organic gases, such as chloroform, dichloromethane, ethylacetate, formaldehyde, heptane, iso-propanol, and toluene. It is suggested that the approach demonstrated here could also be extended to other element-doped sensing films for corresponding gas-sensing devices, which realize gas detection at room temperature.
We thank for the financial support from Key Scientific Research Fund of Xihua University (No. z1320110), Xihua University Young Scholars Training Program (No. 01201418), Chunhui Project of Education Ministry of China (No. Z2011074), and the Open Research Subject of Key Laboratory (Research Base) of Special Materials Preparation and Control (Xihua University, No. szjj2014-059).
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
- Richards-Kortum R, Oden M (2013) Engineering. Devices for low-resource health care. Science 342:1055–7View ArticleGoogle Scholar
- Leclaire J, Husson G, Devaux N, Delorme V, Charles L, Ziarelli F et al. (2010) CO2 binding by dynamic combinatorial chemistry: an environmental selection. J Am Chem Soc 132:3582–93View ArticleGoogle Scholar
- Henschler D (1973) Toxicological problems relating to changes in the environment. Angew Chem Int Ed 12:274–83View ArticleGoogle Scholar
- Yang H, Flower RJ, Thompson JR (2013) Pollution: China’s new leaders offer green hope. Nature 493:163View ArticleGoogle Scholar
- Rumyantseva MN, Gaskov AM, Rosman N, Pagnier T, Morante JR (2005) Raman surface vibration modes in nanocrystalline SnO2: correlation with gas sensor performances. Chem Mater 17:893–901View ArticleGoogle Scholar
- Narducci D (2011) Biosensing at the nanoscale: there’s plenty of room inside. Sci Adv Mater 3:426–35View ArticleGoogle Scholar
- Bekyarova E, Kalinina I, Itkis ME, Beer L, Cabrera N, Haddon RC (2007) Mechanism of ammonia detection by chemically functionalized single-walled carbon nanotubes: in situ electrical and optical study of gas analyte detection. J Am Chem Soc 129:10700–6View ArticleGoogle Scholar
- Lin CW, Chen HI, Chen TY, Huang CC, Hsu CS, Liu RC et al. (2011) On an indium-tin-oxide thin film based ammonia gas sensor. Sens Actuators B 160:1481–4View ArticleGoogle Scholar
- Xu X, Fang X, Zeng H, Zhai T, Bando Y, Golberg D (2010) One-dimensional nanostructures in porous anodic alumina membranes. Sci Adv Mater 2:273–94View ArticleGoogle Scholar
- Close IG, Catlin FI, Cohn AM (1980) Acute and chronic effects of ammonia burns on the respiratory tract. Arch Otolaryngol 106:151–8View ArticleGoogle Scholar
- Timmer B, Olthuis W, van den Berg A (2005) Ammonia sensors and their applications-a review. Sens Actuators B 107:666–7View ArticleGoogle Scholar
- Wang J, Yang P, Wei XW (2015) High-performance, room-temperature, and no-humidity-impact ammonia sensor based on heterogeneous nickel oxide and zinc oxide nanocrystals. ACS Appl Mater Interfaces 7:3816–24Google Scholar
- Wang F, Gu HW, Swager TM (2008) Carbon nanotube/polythiophene chemiresistive sensors for chemical warfare agents. J Am Chem Soc 130:5392–3View ArticleGoogle Scholar
- Wang J, Wei LM, Zhang LY, Zhang J, Wei H, Jiang CH et al. (2012) Zinc-doped nickel oxide dendritic crystals with fast response and self-recovery for ammonia detection at room temperature. J Mater Chem 22:20038–47View ArticleGoogle Scholar
- Kong LT, Wang J, Luo T, Meng FL, Chen X, Li MQ et al. (2010) Novel pyrenehexafluoroisopropanol derivative-decorated single-walled carbon nanotubes for detection of nerve agents by strong hydrogen-bonding interaction. Analyst 135:368–74View ArticleGoogle Scholar
- Polleux J, Gurlo A, Barsan N, Weimar U, Antonietti M, Niederberger M (2006) Template-free synthesis and assembly of single-crystalline tungsten oxide nanowires and their gas-sensing properties. Angew Chem Int Ed 45:261–5View ArticleGoogle Scholar
- Chen JJ, Wang K, Hartman L, Zhou WL (2008) H2S detection by vertically aligned CuO nanowires array sensors. J Phys Chem C 112:16017–21View ArticleGoogle Scholar
- Francioso L, Taurino AM, Forleo A, Siciliano P (2008) TiO2 nanowires array fabrication and gas sensing properties. Sens Actuators B 130:70–6View ArticleGoogle Scholar
- Nayral C, Ould-Ely T, Maisonnat A, Chaudret B, Fau P, Lescouzères L, Peyre-Lavigne A (1999) A Novel Mechanism for the Synthesis of Tin/Tin Oxide Nanoparticles of Low Size Dispersion and of Nanostructured SnO2 for the Sensitive Layers of Gas Sensors. Adv Mater 11:61-3Google Scholar
- Zhang J, Wang SR, Xu MJ, Wang Y, Zhu BL, Zhang SM et al. (2009) Hierarchically porous ZnO architectures for gas sensor application. Cryst Growth Des 9:3532–7View ArticleGoogle Scholar
- Zhang YD, Zheng Z, Yang FL (2010) Highly sensitive and selective alcohol sensors based on Ag-doped In2O3 coating. Ind Eng Chem Res 49:3539–43View ArticleGoogle Scholar
- Wei ZP, Arredondo M, Peng HY, Zhang Z, Guo DL, Xing GZ et al. (2010) A template and catalyst-free metal-etching-oxidation method to synthesize aligned oxide nanowire arrays: NiO as an example. ACS Nano 4:4785–91View ArticleGoogle Scholar
- Ahsan M, Tesfamichael T, Ionescu M, Bell J, Motta N (2012) Low temperature CO sensitive nanostructured WO3 thin films doped with Fe. Sens Actuators B 162:14–21View ArticleGoogle Scholar
- Chen X, Guo Z, Xu WH, Yao HB, Li MQ, Liu JH et al. (2011) Templating synthesis of SnO2 nanotubes loaded with Ag2O nanoparticles and their enhanced gas sensing properties. Adv Funct Mater 21:2049–56View ArticleGoogle Scholar
- Sun P, You L, Sun YF, Chen NK, Li XB, Sun HB et al. (2012) Novel Zn-doped SnO2 hierarchical architectures: synthesis, characterization, and gas sensing properties. Cryst Eng Comm 14:1701–8View ArticleGoogle Scholar
- Cho NG, Woo HS, Lee JH, Kim ID (2011) Thin-walled NiO tubes functionalized with catalytic Pt for highly selective C2H5OH sensors using electrospun fibers as a sacrificial template. Chem Commun 47:11300–02View ArticleGoogle Scholar
- Wang J, Yang P, Wei XW (2015) Preparation of NiO two-dimensional grainy films and their high-performance gas sensors for ammonia detection. Nanoscale Res Lett 10:119View ArticleGoogle Scholar
- Zhu GX, Xu H, Liu YJ, Xu X, Ji ZY, Shen XP et al. (2012) Enhanced gas sensing performance of Co-doped ZnO hierarchical microspheres to 1,2-dichloroethane. Sens Actuators B 166:36–43View ArticleGoogle Scholar
- Russo PA, Donato N, Leonardi SG, Baek S, Conte DE, Neri G et al. (2012) Room-temperature hydrogen sensing with heteronanostructures based on reduced graphene oxide and tin oxide. Angew Chem Int Ed 51:11053–7View ArticleGoogle Scholar
- Soleimanpour AM, Jayatissa AH (2012) Preparation of nanocrystalline nickel oxide thin films by sol-gel process for hydrogen sensor applications. Mat Sci Eng C-Mater 32:2230–4View ArticleGoogle Scholar
- Soleimanpour AM, Jayatissa AH, Sumanasekera G (2013) Surface and gas sensing properties of nanocrystalline nickel oxide thin films. Appl Surf Sci 276:291–7View ArticleGoogle Scholar
- Franke ME, Koplin TJ, Simon U (2006) Metal and metal oxide nanoparticles in chemiresistors: does the nanoscale matter? Small 2:36–50View ArticleGoogle Scholar
- Kim HR, Haensch A, Kim ID, Barsan N, Weimar U, Lee JH (2011) Role of NiO doping in reducing the humidity impact on the performance of SnO2-based gas sensors: synthesis strategies, phenomenological and spectroscopic studies. Adv Funct Mater 21:4456–63View ArticleGoogle Scholar