Next Article in Journal
Effect of Random Nanostructured Metallic Environments on Spontaneous Emission of HITC Dye
Next Article in Special Issue
Nanostructured Gas Sensors: From Air Quality and Environmental Monitoring to Healthcare and Medical Applications
Previous Article in Journal
Biotransformation of Food-Grade and Nanometric TiO2 in the Oral–Gastro–Intestinal Tract: Driving Forces and Effect on the Toxicity toward Intestinal Epithelial Cells
Previous Article in Special Issue
Effect of the Morphology and Electrical Property of Metal-Deposited ZnO Nanostructures on CO Gas Sensitivity
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Nanomaterials
Volume 10
Issue 11
10.3390/nano10112133
nanomaterials-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Enhanced High-Temperature (600 °C) NO2 Response of ZnFe2O4 Nanoparticle-Based Exhaust Gas Sensors

by
Adeel Afzal
1,*,
Adnan Mujahid
2,
Naseer Iqbal
1,
Rahat Javaid
3 and
Umair Yaqub Qazi
1,4
1
Department of Chemistry, College of Science, University of Hafr Al Batin, P.O. Box 1803, Hafr Al Batin 39524, Saudi Arabia
2
Institute of Chemistry, University of Punjab, Quaid-i-Azam Campus, Lahore 54590, Pakistan
3
Renewable Energy Research Center, Fukushima Renewable Energy Institute, National Institute of Advanced Industrial Science and Technology, AIST, 2-2-9 Machiikedai, Koriyama, Fukushima 963-0298, Japan
4
Division of Nanomaterials and Chemistry, Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei 230026, China
*
Author to whom correspondence should be addressed.
Nanomaterials 2020, 10(11), 2133; https://doi.org/10.3390/nano10112133
Submission received: 7 September 2020 / Revised: 18 October 2020 / Accepted: 21 October 2020 / Published: 27 October 2020
(This article belongs to the Special Issue Nanostructured Gas Sensors Synthesis and Applications)
Browse Figures
Versions Notes

Abstract

:
Fabrication of gas sensors to monitor toxic exhaust gases at high working temperatures is a challenging task due to the low sensitivity and narrow long-term stability of the devices under harsh conditions. Herein, the fabrication of a chemiresistor-type gas sensor is reported for the detection of NO2 gas at 600 °C. The sensing element consists of ZnFe2O4 nanoparticles prepared via a high-energy ball milling and annealed at different temperatures (600–1000 °C). The effects of annealing temperature on the crystal structure, morphology, and gas sensing properties of ZnFe2O4 nanoparticles are studied. A mixed spinel structure of ZnFe2O4 nanoparticles with a lattice parameter of 8.445 Å is revealed by X-ray diffraction analysis. The crystallite size and X-ray density of ZnFe2O4 nanoparticles increase with the annealing temperature, whereas the lattice parameter and volume are considerably reduced indicating lattice distortion and defects such as oxygen vacancies. ZnFe2O4 nanoparticles annealed at 1000 °C exhibit the highest sensitivity (0.13% ppm–1), sharp response (τres = 195 s), recovery (τrec = 17 s), and linear response to 100–400 ppm NO2 gas. The annealing temperature and oxygen vacancies play a major role in determining the sensitivity of devices. The plausible sensing mechanism is discussed. ZnFe2O4 nanoparticles show great potential for high-temperature exhaust gas sensing applications.

1. Introduction

Hazardous exhaust gases such as nitrogen dioxide (NO2) and sulfur dioxide (SO2) are the major atmospheric pollutants [1]. The European Union’s (E.U.) ambient air quality directives have set the hourly NO2 concentration threshold as 200 µg/m3 [2]. According to the European Environment Agency (EEA) report published in 2016, NO2 pollution was responsible for 71,000 premature deaths in the E.U. [3]. Thus, it is important to detect the emission and subsistence of NO2 in indoor and outdoor air. The main source of NO2 pollution is the exhaust emissions as a result of the combustion processes in motor vehicles and manufacturing industries [4]. The direct inspection of the exhaust emissions requires devices that can detect NO2 at high temperatures, i.e., usually ≥500 °C [5]. In this regard, metal oxide-based electronic gas sensors are the most sought-after devices for applications in harsh environments [6,7,8].
According to a recent review of high-temperature gas sensors, Ghosh et al. [9] noted the majority of the metal oxide-based gas sensors work at moderately high temperatures only, while the sensitivity of metal oxides is substantially influenced at temperatures above 350 °C. Albeit a large number of metal oxide-based NO2 gas sensors are reported [10,11,12,13], only a few work at high temperatures, i.e., ≥600 °C. For instance, Miura et al. [14] reported Yt-stabilized zirconia and spinel ZnFe2O4 sensing electrodes for the electrochemical detection of NOx at 600–700 °C. However, chemiresistive-type NO2 gas sensors for high-temperature applications are rarely reported [13,15,16]. Therefore, the fabrication of high-temperature NO2 gas sensors for harsh environments is highly desired due to their widespread applications in all types of combustion systems.
This article reports the first high-temperature thick film chemiresistive gas sensor for NO2 detection at 600 °C. The sensor is based on highly stable spinel zinc ferrite (ZnFe2O4) nanoparticles prepared via a solid-state, high-energy ball-milling (HEBM) process followed by high-temperature thermal annealing at different temperatures (600, 800, and 1000 °C). ZnFe2O4 nanoparticles have been used for the detection of toxic organic vapors and gases such as acetone at 260 [17] and 275 °C [18], ethanol at 27 [19] and 220 °C [20], toluene at 300 °C [21], H2S at 85 °C [22] and 135 °C [23], and O2 at 180 °C [24]. Recently, Runa et al. [25] fabricated a chemiresistive NO2 gas sensor using ZnO/ZnFe2O4 composites with p-n heterostructure, which revealed excellent selectivity and high gas response toward 0.1–20 ppm NO2 compared to pure ZnO. However, the gas response diminished rapidly at temperatures of ≥220 °C [25]. In this work, the effects of high-temperature annealing on the crystal structure and NO2 gas sensing properties are studied. The cubic spinel ZnFe2O4 nanoparticles are stable at high temperatures and demonstrate excellent NO2 sensing capability at 600 °C with fast response and recovery times.

2. Materials and Methods

Iron(III) oxide (Fe2O3 nanopowder) and zinc oxide (ZnO nanopowder) obtained from MilliporeSigma (Merck KGaA, Darmstadt, Germany) were used to prepare ZnFe2O4 nanoparticles. ZnFe2O4 nanoparticles were synthesized by high-energy ball milling (HEBM) process using a SPEX™ 8000M Mixer/Mill™ (SPEX® SamplePrep, New Jersey, NJ, USA). The ball mill was equipped with a 500-cc stainless steel vessel containing stainless steel balls for mechanical milling of Fe2O3 and ZnO. The mass ratio of steel balls and chemical powders was fixed at 50:1. HEBM was performed under ambient conditions for 2 h at 600 rpm. The product was subsequently vacuum annealed at 600, 800, and 1000 °C for 2 h, and characterized. Corresponding to the annealing temperature (600–1000 °C), the samples were abbreviated as ZnFe2O4-600, ZnFe2O4-800, and ZnFe2O4-1000, respectively.
The crystal structure of the annealed ZnFe2O4 nanoparticles was studied with a STOE STADI P X-ray diffractometer (XRD) (STOE & Cie GmbH, Darmstadt, Germany) using a Cu Kα irradiation source (λ = 1.5406 Å). The samples were scanned in the 2θ range of 10°–90° with a scan rate of 2°/min. The crystallite size (D) is determined by the Scherrer’s formula [26] (D = Kλ/Bcosθ), where K is a numerical factor referred to as the crystallite-shape factor with an approximate value of 0.89, λ is the wavelength of the X-rays, B is full-width at half-maximum of the most intense (311) diffraction peak in radians, and θ is the Bragg angle. The experimental lattice parameter (a), X-ray density (ρxrd), and the specific surface area (SA) are also calculated from the XRD data of annealed ZnFe2O4 nanoparticles, as described elsewhere [27,28].
The microstructure and surface morphology of ZnFe2O4 nanoparticles were studied with a JEOL JSM-6510 scanning electron microscope (SEM) (JEOL Ltd., Tokyo, Japan). The elemental composition of ZnFe2O4 nanoparticles was determined with the energy-dispersive X-ray spectroscopy (EDS) (JEOL Ltd., Tokyo, Japan).
Thick-film chemiresistor-type gas sensors were fabricated by mixing an appropriate amount of ZnFe2O4-600, ZnFe2O4-800, and ZnFe2O4-1000 nanoparticles with absolute ethanol to make a thick slurry, which was subsequently drop-coated onto alumina micro-hotplates with vapor-deposited platinum (Pt) contacts. The devices were placed in a vacuum oven at 80 °C for 2 h to dry and stabilize the sensing element. The chemiresistor-type devices were installed in a gas sensing chamber fitted with the electrical connections and the gas inlet and outlet. The measurements were performed with a Keithley 6517A electrometer. The sensor responses were measured simultaneously at 600 °C for 100–400 ppm of NO2 gas. The sensor response (S) is defined as S(%) = (Rg – Ra) × 100/Ra, where Ra and Rg are the resistances in air and (100–400 ppm) NO2 gas.

3. Results and Discussion

Figure 1 shows the XRD pattern of as-synthesized ball-milled ZnFe2O4 nanoparticles, referred to as BM-ZnFe2O4. The HEBM process yields crystalline BM-ZnFe2O4 nanoparticles with a cubic spinel lattice structure as indicated by the presence of characteristic (311) diffraction at 35.22° (2θ) position. The crystallite size (D) of as-synthesized BM-ZnFe2O4 nanoparticles is 9.30 nm. The lattice parameter (a) is calculated to be 8.445 Å, which is in agreement with the values reported for spinel ZnFe2O4 nanostructures in the literature and the standard value of bulk ZnFe2O4 (a = 8.441 Å) [29,30,31]. The lattice parameter of as-synthesized BM-ZnFe2O4 nanoparticles is slightly higher (~0.05%) than the standard value that may be inherent to the ball-milling process because an increase in the lattice parameter of ball-milled ZnFe2O4 samples has been reported earlier [32,33,34].
Theoretically, the cation distribution in a perfect normal spinel ZnFe2O4 unit cell is (Zn2+)tet[Fe3+]octO4, i.e., the tetrahedral (A) and octahedral (B) sites are solely occupied by Zn2+ and Fe3+ cations, respectively [35]. However, in nanocrystalline ZnFe2O4 the contrary distributions of Zn2+ and Fe3+ cations on both A and B sites are observed [36,37], which form mixed (or random) spinel structure. According to Chinnasamy et al. [32], the slight increase in the lattice parameter is attributed to the lattice expansion caused by the occupation of B sites by Zn2+ ions. Thus, the XRD pattern of as-synthesized BM-ZnFe2O4 nanoparticles indicates the formation of a mixed cubic spinel lattice. Nonetheless, BM-ZnFe2O4 nanoparticles are annealed at different temperatures to examine the effect of annealing on the crystal structure evolution, lattice parameter, crystallite size, and morphology of ZnFe2O4 nanoparticles.
High-temperature annealing is an important step in the fabrication of ZnFe2O4 nanoparticles, as it renders stability and improves the physical properties of ZnFe2O4 [38,39]. Figure 2 shows the XRD patterns of ZnFe2O4 nanoparticles annealed at 600, 800, and 1000 °C for 2 h. XRD patterns are refined using Match! (version 3.11.1.183) and FullProf programs for phase identification from X-ray powder diffraction. All samples exhibit a crystalline structure with the characteristic diffractions corresponding to the following miller indices: (111), (220), (311), (222), (400), (422), (511), (440), (620), and (533), which conform to the crystallography open database card number 230–0615 [40]. XRD results substantiate the formation of the cubic spinel ferrite structure with the Fd-3m space group. Also, the XRD patterns align well with the reported literature for ZnFe2O4 nanoparticles [30,41,42]. The absence of additional diffraction peaks corresponding to the impurities or unreacted oxides also reveals the formation of a single-phase cubic spinel lattice [40].
Figure 3a–c shows the most intense diffractions of the characteristic (311) plane in ZnFe2O4 nanoparticles annealed at different temperatures. The XRD data were used to calculate the crystallite size (D), lattice parameter (a), interplanar distance (d311), volume (V), X-ray density (ρxrd), and specific surface area (S) of the annealed ZnFe2O4 nanoparticles. Table 1 presents these structural parameters for different samples. The effect of annealing is obvious because of the changes in position and breadth of (311) diffraction peak as a function of the annealing temperature, which reveal variations in the crystallite size and lattice parameter. The position of (311) shifts to a higher 2θ value as the annealing temperature increases.
As shown in Figure 3d, the crystallite size of ZnFe2O4 nanoparticles increases with the annealing time, which is certainly comprehensible because annealing results in grain growth, and the higher the temperature, the greater is the crystallite size [43,44,45]. The annealing at 600 °C doubles the crystallite size of ZnFe2O4@600 nanoparticles compared to as-synthesized BM-ZnFe2O4 nanoparticles. While annealing at 800 °C results in a further increase in the crystallite size, the crystallite sizes of ZnFe2O4@800 and ZnFe2O4@1000 nanoparticles are comparable. Thus, the little difference in the crystallites sizes of samples treated at 800 and 1000 °C means the rate or degree of annealing decreases with the increasing crystallite size [46].
On the other hand, the lattice parameter decreases with the increase in annealing temperature, as shown in Figure 3e. Although this is contrary to the findings reported earlier that demonstrate an increase in the lattice parameter upon high-temperature annealing [47,48,49], the lattice parameter and crystal structure essentially depend on the processing method and conditions. As discussed above, in the starting sample, as-synthesized BM-ZnFe2O4 nanoparticles exhibit a random spinel structure with a certain degree of inversion that is inherently observed for the ball-milled ZnFe2O4 nanoparticles [32,33]. The reduction in the lattice parameter of annealed ZnFe2O4 nanoparticles can be explained by the redistribution of cations and crystal defects (oxygen vacancies).
During the high-temperature annealing process, both Zn2+ and Fe3+ cations may alter positions that influence the crystal structure. For instance, Lemine et al. [50] demonstrated that a decrease in the lattice parameter (from 8.448 to 8.427 Å) was caused by the redistribution of cations within the interstitial sites. However, this can also be attributed to the crystal defects [39,51]. It is a well-known fact that high-temperature annealing induces lattice defects and distortions. Furthermore, in the case of nanocrystalline ZnFe2O4, it is believed that Zn2+ ions due to their volatile nature escape from the lattice during thermal treatment that successively results in oxygen vacancies [39,52]. Thus, a decrease in the lattice parameter (from 8.445 Å for BM-ZnFe2O4 to 8.420 Å for ZnFe2O4@1000) is attributed to the cationic redistribution (distortion) and lattice compression caused by escaping Zn2+ ions and oxygen vacancies.
Consequently, the interplanar distance and the volume of the annealed ZnFe2O4 nanoparticles are reduced as a function of the annealing temperature. On the other hand, the X-ray density increases (from 5.321 g cm–3 for BM-ZnFe2O4 to 5.368 g cm–3 for ZnFe2O4@1000) with the increase in annealing temperature. However, as shown in Table 1, the specific surface area is reduced to 48 m2 g–1 due to an increase in the crystallite size of the annealed ZnFe2O4 nanoparticles. These results demonstrate that ZnFe2O4@1000 and ZnFe2O4@800 nanoparticles have bigger crystallite size and smaller specific surface area, but the greatest number of defect sites (as oxygen vacancies) and a geometrically frustrated [53] or distorted cubic spinel crystal structure compared to as-synthesized BM-ZnFe2O4 nanoparticles.
Figure 4a–c shows the SEM images of ZnFe2O4 nanoparticles annealed at different temperatures. An increase in the annealing temperature (to 1000 °C) results in a more compact surface, as shown in Figure 4c: the micrograph of ZnFe2O4@1000 nanoparticles. On the other hand, ZnFe2O4@600 nanoparticles annealed at 600 °C (Figure 4a) show less compact surface morphology with smaller particle size and relatively less aggregation of nanoparticles into clusters. The ZnFe2O4@800 nanoparticles demonstrate a similar surface morphology with slightly larger aggregates of nanoparticles, as shown in Figure 4b.
The image analysis of the scanning electron micrographs (via WSxM freeware [54]) shows the size distribution of ZnFe2O4 nanoparticles and the respective histograms are presented as insets in Figure 4a–c. ZnFe2O4@600 nanoparticles exhibit narrow size distribution with an average aggregate size of 100.2 nm, while ZnFe2O4@800 and ZnFe2O4@1000 nanoparticles reveal a relatively broad size distribution and an average aggregate size of 143.8 and 146.5 nm, respectively.
Figure 5 shows three-dimensional surface micrographs and topographic profiles of the sensing layers composed of ZnFe2O4 nanoparticles annealed at different temperatures. ZnFe2O4@600 surface exhibits a relatively smooth profile and roughness (Figure 5a). On the other hand, ZnFe2O4@800 (Figure 5b) and ZnFe2O4@1000 (Figure 5c) nanoparticles demonstrate higher roughness, greater particle size, and cluster formation. Thus, both X-ray diffraction and microscopic results indicate that ZnFe2O4 nanoparticles annealed at 800 and 1000 °C exhibit bigger crystallite size and a compact surface microstructure compared to those annealed at 600 °C.
Table 2 presents the elemental composition of the annealed ZnFe2O4 nanoparticles. Compared to theoretically calculated values (wt.% or at.%), annealed ZnFe2O4 nanoparticles exhibit variations. As the annealing temperature increases, the relative percentage of Fe increases while the proportions of Zn and O decrease. A decrease in the oxygen content with increasing temperature is attributed to the oxygen vacancies and lattice defects. In addition, the atomic ratio of Fe/Zn is found to be 2.07, 2.20, and 2.21 for ZnFe2O4@600, ZnFe2O4@800, and ZnFe2O4@1000 nanoparticles, respectively. The increase in the Fe/Zn ratio as a function of annealing temperature may be attributed to the volatile nature of Zn2+ ions [39], as discussed earlier. Thus, the results are consistent and exhibit the microstructure evolution in the annealed ZnFe2O4 nanoparticles as a function of annealing temperature.
Figure 6 demonstrates the NO2 gas response of ZnFe2O4 nanoparticles annealed at different temperatures. The sensor measurements are performed at 600 °C. The as-synthesized BM-ZnFe2O4 nanoparticles based chemiresistive devices are not stable at 600 °C and do not show a measurable response to NO2 gas. On the other hand, all the annealed ZnFe2O4 samples show a significant measurable response to 100–400 ppm NO2, as shown in Figure 6. The sensor responses are generally saturated after ~4 min of exposure to the different concentrations of NO2 gas. ZnFe2O4@1000 nanoparticles exhibit the highest NO2 gas response, which is attributed to their greater stability at elevated temperatures and the presence of a large number of lattice defects. ZnFe2O4@600 and ZnFe2O4@800 nanoparticles also exhibit significant gas response at 600 °C. Peng et al. [55] recently demonstrated that the gas sensing properties of ZnFe2O4 nanoparticles could be enhanced by controlling the oxygen vacancies and that ZnFe2O4 nanoparticles with more oxygen vacancies revealed superior gas (acetone vapors) sensing performance at 280 °C. Thus, the higher NO2 response of ZnFe2O4@1000 nanoparticles may be attributed to the oxygen vacancies resulting from high-temperature annealing of nanoparticles.
Figure 7 shows the calibration curves obtained by plotting the maximum gas response of the annealed ZnFe2O4 nanoparticles as a function of gas concentration. All ZnFe2O4 samples exhibit a linear response in the concentration range of 100–400 ppm as demonstrated by the straight lines in Figure 7. The sensitivity of ZnFe2O4-based chemiresistive devices can be calculated from the slope of a straight line. The sensitivity of NO2 sensors follows the order: ZnFe2O4@1000 > ZnFe2O4@800 > ZnFe2O4@600, which describes the effect of annealing temperature on sensor performance. An increase in annealing temperature improves the NO2 sensing properties of ZnFe2O4 nanoparticles. Therefore, ZnFe2O4@1000 nanoparticles exhibit 2.0-fold and 3.2-fold high sensitivity compared to ZnFe2O4@800 and ZnFe2O4@600 nanoparticles, respectively.
Figure 8 shows the kinetics of ZnFe2O4-based chemiresistive gas sensors. The response (τres) and recovery (τrec) times of the annealed ZnFe2O4 nanoparticles are estimated from their response to 300 ppm NO2 gas. All samples show fast response and recovery times. The response times are in the range of 145–195 s and follow the order: ZnFe2O4@800 > ZnFe2O4@600 > ZnFe2O4@1000. Thus, ZnFe2O4@1000 nanoparticles exhibit slightly longer response (τres) times compared to ZnFe2O4@600 and ZnFe2O4@800 nanoparticles. The recovery times are sharp (i.e., ≤20 s) for all samples and all sensors exhibit 100% recovery to their original state. At elevated temperatures, the recovery times are generally faster [10]. Overall, ZnFe2O4@1000 nanoparticles exhibit excellent NO2 gas sensing properties such as high sensitivity, good response kinetics, and linear response in the tested concentration range.
The chemiresistive gas sensors function on the principles of changes in resistance of the sensing element when test gas molecules interact with the semiconductor surface [9]. Figure 9 demonstrates the gas sensing mechanism of ZnFe2O4 nanoparticles. ZnFe2O4 is an n-type semiconductor [56]. In principle, when the ZnFe2O4-based chemiresistive device is exposed to air at elevated temperatures, active oxygen species are adsorbed on the surface of ZnFe2O4 nanoparticles. As shown in Figure 9a, O2 molecules are physisorbed (O2−) at low temperatures (<200 °C) and subsequently chemisorbed (O– and O2–) at elevated temperatures (>200 °C) by capturing mobile electrons (e–) from the surface. This leads to the formation of a charge depletion layer on the surface of ZnFe2O4 nanoparticles. Afterward, the surface is exposed to different concentrations of NO2 gas and NO2 being an electron-withdrawing molecule [57] further extracts mobile e− from the surface or interacts with the chemisorbed oxygen species, as shown in Figure 9b. Consequently, the density of major charge carriers (e−) decreases, and the thickness of the depletion region increases, which increases the resistance of the device. The redox reactions taking place on the surface of ZnFe2O4 nanoparticles are depicted in Figure 9.
Considering the mechanism described above, it is important to understand the behavior of ZnFe2O4 nanoparticles annealed at different temperatures. It is believed that semiconducting metal oxides with more oxygen vacancies adsorb a large number of active oxygen species, which in turn facilitates the surface redox reactions with the target gas molecules and improves the gas response [55]. Thus, oxygen vacancies and lattice defects play a major role in determining the gas response of ZnFe2O4 nanoparticles. Therefore, ZnFe2O4@1000 nanoparticles exhibit the best NO2 gas sensing properties despite their slightly bigger crystallite size and smaller specific surface area. Table 3 shows a comparison of ferrite-based chemiresistive NO2 sensors. The results demonstrate the potential of stable ZnFe2O4@1000 nanoparticles for high-temperature gas sensing applications.

4. Conclusions

In summary, this study presents the effects of annealing temperature on the microstructure evolution and gas sensing properties of ZnFe2O4 nanoparticles. A high-energy ball-milling procedure is used to prepare pure ZnFe2O4 nanoparticles that are annealed at different temperatures (600–1000 °C). ZnFe2O4 nanoparticles exhibit a random spinel lattice structure that is distorted during high-temperature annealing. The XRD results show an increase in the crystallite size, but a reduction in the lattice parameter and volume that is attributed to the presence of lattice defects as oxygen vacancies. The oxygen vacancies play a major role in controlling the sensitivity of ZnFe2O4 nanoparticles. Thus, ZnFe2O4@1000 nanoparticles (annealed at 1000 °C) reveal the superior gas sensing properties with the highest sensitivity, good response kinetics, and linear response toward 100–400 ppm NO2 gas. This is the first example of a ZnFe2O4@1000-based chemiresistive device showing significant gas response and stable sensor performance at 600 °C.

Author Contributions

Conceptualization, A.A.; methodology, A.A. and A.M.; validation, A.M. and N.I.; formal analysis, A.M., N.I. and R.J.; investigation, A.M. and N.I.; data curation, N.I., R.J. and U.Y.Q.; writing—original draft preparation, A.A.; writing—review and editing, A.A., A.M. and N.I.; visualization, A.M., R.J. and U.Y.Q.; project administration, A.A.; funding acquisition, A.A. All authors have read and agreed to the published version of the manuscript.

Funding

This research and the APC were funded by the Deanship of Scientific Research, University of Hafr Al Batin [grant number. G-107-2020].

Acknowledgments

The authors extend their appreciation to the Deanship of Scientific Research, University of Hafr Al Batin for funding this work through the research group project number G-107-2020.

Conflicts of Interest

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

References

  1. Sun, Y.; Zwolińska, E.; Chmielewski, A.G. Abatement technologies for high concentrations of NOx and SO2 removal from exhaust gases: A review. Crit. Rev. Environ. Sci. Technol. 2016, 46, 119–142. [Google Scholar] [CrossRef]
  2. Air Quality Standards: 2008/50/EC Directive on Ambient Air Quality and Cleaner Air for Europe. Available online: https://www.eea.europa.eu/themes/air/air-quality-concentrations/air-quality-standards (accessed on 28 April 2020).
  3. Casquero-Vera, J.A.; Lyamani, H.; Titos, G.; Borrás, E.; Olmo, F.J.; Alados-Arboledas, L. Impact of primary NO2 emissions at different urban sites exceeding the European NO2 standard limit. Sci. Total Environ. 2019, 646, 1117–1125. [Google Scholar] [CrossRef] [PubMed]
  4. Kaplan, G.; Avdan, Z.Y.; Avdan, U. Spaceborne Nitrogen Dioxide Observations from the Sentinel-5P TROPOMI over Turkey. Proceedings 2019, 18, 4. [Google Scholar] [CrossRef] [Green Version]
  5. Afzal, A.; Andersson, M.; Di Franco, C.; Ditaranto, N.; Cioffi, N.; Scamarcio, G.; Lloyd Spetz, A.; Torsi, L. Electrochemical deposition of gold on indium zirconate (InZrOx with In/Zr atomic ratio 1.0) for high temperature automobile exhaust gas sensors. J. Solid State Electrochem. 2015, 19, 2859–2868. [Google Scholar] [CrossRef]
  6. Liu, F.; Wang, B.; Yang, X.; Guan, Y.; Sun, R.; Wang, Q.; Liang, X.; Sun, P.; Lu, G. High-temperature stabilized zirconia-based sensors utilizing MNb2O6 (M: Co, Ni and Zn) sensing electrodes for detection of NO2. Sens. Actuators B Chem. 2016, 232, 523–530. [Google Scholar] [CrossRef]
  7. Liu, F.; Wang, B.; Yang, X.; Guan, Y.; Wang, Q.; Liang, X.; Sun, P.; Wang, Y.; Lu, G. High-temperature NO2 gas sensor based on stabilized zirconia and CoTa2O6 sensing electrode. Sens. Actuators B Chem. 2017, 240, 148–157. [Google Scholar] [CrossRef]
  8. Dai, L.; Shi, M.; Han, W.; Meng, W.; He, Z.; Zhu, L.; Wang, L. High-temperature NO2 sensor based on aluminum/indium co-doped lanthanum silicate oxyapatite electrolyte and cobalt-free perovskite oxide sensing electrode. Sens. Actuators B Chem. 2017, 250, 629–640. [Google Scholar] [CrossRef]
  9. Ghosh, A.; Zhang, C.; Shi, S.Q.; Zhang, H. High-Temperature Gas Sensors for Harsh Environment Applications: A Review. CLEAN Soil Air Water 2019, 47, 1800491. [Google Scholar] [CrossRef]
  10. Afzal, A.; Cioffi, N.; Sabbatini, L.; Torsi, L. NOx sensors based on semiconducting metal oxide nanostructures: Progress and perspectives. Sens. Actuators B Chem. 2012, 171–172, 25–42. [Google Scholar] [CrossRef]
  11. Dey, A. Semiconductor metal oxide gas sensors: A review. Mater. Sci. Eng. B 2018, 229, 206–217. [Google Scholar] [CrossRef]
  12. Barsan, N.; Schierbaum, K. Gas Sensors Based on Conducting Metal Oxides: Basic Understanding, Technology and Applications; Elsevier: Amsterdam, The Netherlands, 2018; ISBN 978-0-12-811225-0. [Google Scholar]
  13. Afzal, A. β-Ga2O3 nanowires and thin films for metal oxide semiconductor gas sensors: Sensing mechanisms and performance enhancement strategies. J. Mater. 2019, 5, 542–557. [Google Scholar] [CrossRef]
  14. Miura, N.; Zhuiykov, S.; Ono, T.; Hasei, M.; Yamazoe, N. Mixed potential type sensor using stabilized zirconia and ZnFe2O4 sensing electrode for NOx detection at high temperature. Sens. Actuators B Chem. 2002, 83, 222–229. [Google Scholar] [CrossRef]
  15. Wetchakun, K.; Samerjai, T.; Tamaekong, N.; Liewhiran, C.; Siriwong, C.; Kruefu, V.; Wisitsoraat, A.; Tuantranont, A.; Phanichphant, S. Semiconducting metal oxides as sensors for environmentally hazardous gases. Sens. Actuators B Chem. 2011, 160, 580–591. [Google Scholar] [CrossRef]
  16. Joshi, N.; Hayasaka, T.; Liu, Y.; Liu, H.; Oliveira, O.N.; Lin, L. A review on chemiresistive room temperature gas sensors based on metal oxide nanostructures, graphene and 2D transition metal dichalcogenides. Microchim. Acta 2018, 185, 213. [Google Scholar] [CrossRef] [PubMed]
  17. Li, L.; Tan, J.; Dun, M.; Huang, X. Porous ZnFe2O4 nanorods with net-worked nanostructure for highly sensor response and fast response acetone gas sensor. Sens. Actuators B Chem. 2017, 248, 85–91. [Google Scholar] [CrossRef]
  18. Lv, L.; Wang, Y.; Cheng, P.; Zhang, B.; Dang, F.; Xu, L. Ultrasonic spray pyrolysis synthesis of three-dimensional ZnFe2O4-based macroporous spheres for excellent sensitive acetone gas sensor. Sens. Actuators B Chem. 2019, 297, 126755. [Google Scholar] [CrossRef]
  19. Khurshid, R.; Ali, F.; Afzal, A.; Ali, Z.; Qureshi, M.T. Polyol-mediated coprecipitation and aminosilane grafting of superparamagnetic, spinel ZnFe2O4 nanoparticles for room-temperature ethanol sensors. J. Electrochem. Soc. 2019, 166, B258–B265. [Google Scholar] [CrossRef]
  20. Nemufulwi, M.I.; Swart, H.C.; Mdlalose, W.B.; Mhlongo, G.H. Size-tunable ferromagnetic ZnFe2O4 nanoparticles and their ethanol detection capabilities. Appl. Surf. Sci. 2020, 508, 144863. [Google Scholar] [CrossRef]
  21. Dong, C.; Liu, X.; Xiao, X.; Du, S.; Wang, Y. Monodisperse ZnFe2O4 nanospheres synthesized by a nonaqueous route for a highly slective low-ppm-level toluene gas sensor. Sens. Actuators B Chem. 2017, 239, 1231–1236. [Google Scholar] [CrossRef]
  22. Gao, X.; Sun, Y.; Zhu, C.; Li, C.; Ouyang, Q.; Chen, Y. Highly sensitive and selective H2S sensor based on porous ZnFe2O4 nanosheets. Sens. Actuators B Chem. 2017, 246, 662–672. [Google Scholar] [CrossRef]
  23. Zhang, H.-J.; Meng, F.-N.; Liu, L.-Z.; Chen, Y.-J.; Wang, P.-J. Highly sensitive H2S sensor based on solvothermally prepared spinel ZnFe2O4 nanoparticles. J. Alloys Compd. 2018, 764, 147–154. [Google Scholar] [CrossRef]
  24. Fareed, S.; Jamil, A.; Afsar, F.; Sher, F.; Li, C.; Xu, X.; Rafiq, M.A. Selective Oxygen Sensor Prepared Using Ni-doped Zinc Ferrite Nanoparticles. J. Electron. Mater. 2019, 48, 5677–5685. [Google Scholar] [CrossRef]
  25. Runa, A.; Zhang, X.; Wen, G.; Zhang, B.; Fu, W.; Yang, H. Actinomorphic flower-like n-ZnO/p-ZnFe2O4 composite and its improved NO2 gas-sensing property. Mater. Lett. 2018, 225, 73–76. [Google Scholar] [CrossRef]
  26. Holzwarth, U.; Gibson, N. The Scherrer equation versus the “Debye-Scherrer equation”. Nat. Nanotechnol. 2011, 6, 534. [Google Scholar] [CrossRef]
  27. Satalkar, M.; Kane, S.N. On the study of Structural properties and Cation distribution of Zn 0.75-x Ni x Mg 0.15 Cu 0.1 Fe 2 O 4 nano ferrite: Effect of Ni addition. J. Phys. Conf. Ser. 2016, 755, 012050. [Google Scholar] [CrossRef]
  28. Afzal, A.; Abuilaiwi, F.A.; Javaid, R.; Ali, F.; Habib, A. Solid-state synthesis of heterogeneous Ni0.5Cu0.5-xZnxFe2O4 spinel oxides with controlled morphology and tunable dielectric properties. J. Mater. Sci. Mater. Electron. 2020, 31, 14261–14270. [Google Scholar] [CrossRef]
  29. Gomes, J.A.; Azevedo, G.M.; Depeyrot, J.; Mestnik-Filho, J.; da Silva, G.J.; Tourinho, F.A.; Perzynski, R. ZnFe2O4 nanoparticles for ferrofluids: A combined XANES and XRD study. J. Magn. Magn. Mater. 2011, 323, 1203–1206. [Google Scholar] [CrossRef]
  30. Manikandan, A.; Judith Vijaya, J.; Sundararajan, M.; Meganathan, C.; Kennedy, L.J.; Bououdina, M. Optical and magnetic properties of Mg-doped ZnFe2O4 nanoparticles prepared by rapid microwave combustion method. Superlattices Microstruct. 2013, 64, 118–131. [Google Scholar] [CrossRef] [Green Version]
  31. Ferrari, S.; Kumar, R.S.; Grinblat, F.; Aphesteguy, J.C.; Saccone, F.D.; Errandonea, D. In-situ high-pressure x-ray diffraction study of zinc ferrite nanoparticles. Solid State Sci. 2016, 56, 68–72. [Google Scholar] [CrossRef] [Green Version]
  32. Chinnasamy, C.N.; Narayanasamy, A.; Ponpandian, N.; Chattopadhyay, K. The influence of Fe3+ ions at tetrahedral sites on the magnetic properties of nanocrystalline ZnFe2O4. Mater. Sci. Eng. A 2001, 304–306, 983–987. [Google Scholar] [CrossRef]
  33. Ehrhardt, H.; Campbell, S.J.; Hofmann, M. Structural evolution of ball-milled ZnFe2O4. J. Alloys Compd. 2002, 339, 255–260. [Google Scholar] [CrossRef]
  34. Fella, O.O.; Tamine, M.; Randrianantoandro, N.; Grenèche, J.M. Microstructural Studies of Milled and Annealed ZnFe2O4 Nanostructures Using X-Ray Diffraction and Mössbauer Spectroscopy. Nanosci. Nanoeng. 2013, 1, 1–6. [Google Scholar]
  35. Goldman, A. Crystal Structure of Ferrites. In Handbook of Modern Ferromagnetic Materials; Goldman, A., Ed.; The Springer International Series in Engineering and Computer Science; Springer US: Boston, MA, USA, 1999; pp. 207–227. ISBN 978-1-4615-4917-8. [Google Scholar]
  36. Qin, M.; Shuai, Q.; Wu, G.; Zheng, B.; Wang, Z.; Wu, H. Zinc ferrite composite material with controllable morphology and its applications. Mater. Sci. Eng. B 2017, 224, 125–138. [Google Scholar] [CrossRef]
  37. Fritsch, D. Electronic and optical properties of spinel zinc ferrite: Ab-initio hybrid functional calculations. J. Phys. Condens. Matter 2018, 30, 095502. [Google Scholar] [CrossRef] [Green Version]
  38. Li, G.; Zhu, X.; Song, W.; Yang, Z.; Dai, J.; Sun, Y.; Fu, Y. Annealing Effects on Semitransparent and Ferromagnetic ZnFe2O4 Nanostructured Films by Sol–Gel. J. Am. Ceram. Soc. 2011, 94, 2872–2877. [Google Scholar] [CrossRef]
  39. Yadav, R.S.; Kuřitka, I.; Vilcakova, J.; Urbánek, P.; Machovsky, M.; Masař, M.; Holek, M. Structural, magnetic, optical, dielectric, electrical and modulus spectroscopic characteristics of ZnFe2O4 spinel ferrite nanoparticles synthesized via honey-mediated sol-gel combustion method. J. Phys. Chem. Solids 2017, 110, 87–99. [Google Scholar] [CrossRef]
  40. Solano, E.; Frontera, C.; Puig, T.; Obradors, X.; Ricart, S.; Ros, J. Neutron and X-ray diffraction study of ferrite nanocrystals obtained by microwave-assisted growth. A structural comparison with the thermal synthetic route. J. Appl. Crystallogr. 2014, 47, 414–420. [Google Scholar] [CrossRef]
  41. Zhang, J.; Song, J.-M.; Niu, H.-L.; Mao, C.-J.; Zhang, S.-Y.; Shen, Y.-H. ZnFe2O4 nanoparticles: Synthesis, characterization, and enhanced gas sensing property for acetone. Sens. Actuators B Chem. 2015, 221, 55–62. [Google Scholar] [CrossRef] [Green Version]
  42. Xu, X.; Xiao, L.; Haugen, N.O.; Wu, Z.; Jia, Y.; Zhong, W.; Zou, J. High humidity response property of sol–gel synthesized ZnFe2O4 films. Mater. Lett. 2018, 213, 266–268. [Google Scholar] [CrossRef]
  43. Sintering and Grain Growth. In Ceramic Materials: Science and Engineering; Carter, C.B.; Norton, M.G. (Eds.) Springer: New York, NY, USA, 2007; pp. 427–443. ISBN 978-0-387-46271-4. [Google Scholar]
  44. Ranjith Kumar, E.; Arunkumar, T.; Prakash, T. Heat treatment effects on structural and dielectric properties of Mn substituted CuFe2O4 and ZnFe2O4 nanoparticles. Superlattices Microstruct. 2015, 85, 530–535. [Google Scholar] [CrossRef]
  45. Van Hoang, N.; Hung, C.M.; Hoa, N.D.; Van Duy, N.; Van Hieu, N. Facile on-chip electrospinning of ZnFe2O4 nanofiber sensors with excellent sensing performance to H2S down ppb level. J. Hazard. Mater. 2018, 360, 6–16. [Google Scholar] [CrossRef] [PubMed]
  46. Wilder, D.R.; Fitzsimmons, E.S. Further Study of Sintering Phenomena. J. Am. Ceram. Soc. 1955, 38, 66–71. [Google Scholar] [CrossRef]
  47. Yadav, R.S.; Havlica, J.; Masilko, J.; Tkacz, J.; Kuřitka, I.; Vilcakova, J. Anneal-tuned structural, dielectric and electrical properties of ZnFe2O4 nanoparticles synthesized by starch-assisted sol–gel auto-combustion method. J. Mater. Sci. Mater. Electron. 2016, 27, 5992–6002. [Google Scholar] [CrossRef]
  48. Kombaiah, K.; Vijaya, J.J.; Kennedy, L.J.; Bououdina, M. Studies on the microwave assisted and conventional combustion synthesis of Hibiscus rosa-sinensis plant extract based ZnFe2O4 nanoparticles and their optical and magnetic properties. Ceram. Int. 2016, 42, 2741–2749. [Google Scholar] [CrossRef]
  49. Kombaiah, K.; Vijaya, J.J.; Kennedy, L.J.; Bououdina, M. Optical, magnetic and structural properties of ZnFe2O4 nanoparticles synthesized by conventional and microwave assisted combustion method: A comparative investigation. Optik 2017, 129, 57–68. [Google Scholar] [CrossRef]
  50. Lemine, O.M.; Bououdina, M.; Sajieddine, M.; Al-Saie, A.M.; Shafi, M.; Khatab, A.; Al-Hilali, M.; Henini, M. Synthesis, structural, magnetic and optical properties of nanocrystalline ZnFe2O4. Phys. B Condens. Matter 2011, 406, 1989–1994. [Google Scholar] [CrossRef]
  51. Nikolic, M.V.; Vasiljevic, Z.Z.; Lukovic, M.D.; Pavlovic, V.P.; Krstic, J.B.; Vujancevic, J.; Tadic, N.; Vlahovic, B.; Pavlovic, V.B. Investigation of ZnFe2O4 spinel ferrite nanocrystalline screen-printed thick films for application in humidity sensing. Int. J. Appl. Ceram. Technol. 2019, 16, 981–993. [Google Scholar] [CrossRef] [Green Version]
  52. Sivakumar, N.; Narayanasamy, A.; Ponpandian, N.; Govindaraj, G. Grain size effect on the dielectric behavior of nanostructured Ni0.5Zn0.5Fe2O4. J. Appl. Phys. 2007, 101, 084116. [Google Scholar] [CrossRef]
  53. Salcedo Rodríguez, K.L.; Stewart, S.J.; Mendoza Zélis, P.M.; Pasquevich, G.A.; Rodríguez Torres, C.E. Role of defects on the magnetic behaviour of the geometrically frustrated spinel ZnFe2O4. J. Alloys Compd. 2018, 752, 289–295. [Google Scholar] [CrossRef] [Green Version]
  54. Horcas, I.; Fernández, R.; Gómez-Rodríguez, J.M.; Colchero, J.; Gómez-Herrero, J.; Baro, A.M. WSXM: A software for scanning probe microscopy and a tool for nanotechnology. Rev. Sci. Instrum. 2007, 78, 013705. [Google Scholar] [CrossRef]
  55. Peng, S.; Wang, Z.; Liu, R.; Bi, J.; Wu, J. Controlled oxygen vacancies of ZnFe2O4 with superior gas sensing properties prepared via a facile one-step self-catalyzed treatment. Sens. Actuators B Chem. 2019, 288, 649–655. [Google Scholar] [CrossRef]
  56. Jeseentharani, V.; George, M.; Jeyaraj, B.; Dayalan, A.; Nagaraja, K.S. Synthesis of metal ferrite (MFe2O4, M = Co, Cu, Mg, Ni, Zn) nanoparticles as humidity sensor materials. J. Exp. Nanosci. 2013, 8, 358–370. [Google Scholar] [CrossRef] [Green Version]
  57. Valero, E.L. Advanced Nanomaterials for Inexpensive Gas Microsensors: Synthesis, Integration and Applications; Elsevier: Amsterdam, The Netherlands, 2019; ISBN 978-0-12-814828-0. [Google Scholar]
  58. Rathore, D.; Mitra, S.; Kurchania, R.; Pandey, R.K. Physicochemical properties of CuFe2O4 nanoparticles as a gas sensor. J. Mater. Sci. Mater. Electron. 2018, 29, 1925–1932. [Google Scholar] [CrossRef]
  59. Li, K.; Luo, Y.; Liu, B.; Gao, L.; Duan, G. High-performance NO2-gas sensing of ultrasmall ZnFe2O4 nanoparticles based on surface charge transfer. J. Mater. Chem. A 2019, 7, 5539–5551. [Google Scholar] [CrossRef]
  60. Waghmare, S.D.; Raut, S.D.; Ghule, B.G.; Jadhav, V.V.; Shaikh, S.F.; Al-Enizi, A.M.; Ubaidullah, M.; Nafady, A.; Thamer, B.M.; Mane, R.S. Pristine and palladium-doped perovskite bismuth ferrites and their nitrogen dioxide gas sensor studies. J. King Saud Univ. Sci. 2020, 32, 3125–3130. [Google Scholar] [CrossRef]
  61. Bagade, A.A.; Rajpure, K.Y. Development of CoFe2O4 thin films for nitrogen dioxide sensing at moderate operating temperature. J. Alloys Compd. 2016, 657, 414–421. [Google Scholar] [CrossRef]
  62. Wu, R.-A.; Wei Lin, C.; Tseng, W.J. Preparation of electrospun Cu-doped α-Fe2O3 semiconductor nanofibers for NO2 gas sensor. Ceram. Int. 2017, 43, S535–S540. [Google Scholar] [CrossRef]
  63. Yamada, Y.; Seno, Y.; Masuoka, Y.; Yamashita, K. Nitrogen oxides sensing characteristics of Zn2SnO4 thin film. Sens. Actuators B Chem. 1998, 49, 248–252. [Google Scholar] [CrossRef]
Nanomaterials 10 02133 g001 550
Figure 1. (a) X-ray diffraction pattern of the as-synthesized, ball-milled zinc ferrite (BM-ZnFe2O4) nanoparticles. (b) The characteristic (311) plane diffraction of cubic spinel BM-ZnFe2O4 nanoparticles.
Figure 1. (a) X-ray diffraction pattern of the as-synthesized, ball-milled zinc ferrite (BM-ZnFe2O4) nanoparticles. (b) The characteristic (311) plane diffraction of cubic spinel BM-ZnFe2O4 nanoparticles.
Nanomaterials 10 02133 g001
Nanomaterials 10 02133 g002 550
Figure 2. X-ray diffraction patterns of ZnFe2O4 nanoparticles annealed at different temperatures: (a) 600, (b) 800, and (c) 1000 °C.
Figure 2. X-ray diffraction patterns of ZnFe2O4 nanoparticles annealed at different temperatures: (a) 600, (b) 800, and (c) 1000 °C.
Nanomaterials 10 02133 g002
Nanomaterials 10 02133 g003 550
Figure 3. The characteristic (311) plane diffractions of cubic spinel ZnFe2O4 nanoparticles annealed at (a) 600, (b) 800, and (c) 1000 °C. (d) The crystallite size, and (e) lattice parameter of ZnFe2O4 nanoparticles as a function of annealing temperature.
Figure 3. The characteristic (311) plane diffractions of cubic spinel ZnFe2O4 nanoparticles annealed at (a) 600, (b) 800, and (c) 1000 °C. (d) The crystallite size, and (e) lattice parameter of ZnFe2O4 nanoparticles as a function of annealing temperature.
Nanomaterials 10 02133 g003
Nanomaterials 10 02133 g004 550
Figure 4. Scanning electron microscopy images of ZnFe2O4 nanoparticles annealed at (a) 600, (b) 800, and (c) 1000 °C. The respective histograms are given in the inset. (d) Energy-dispersive X-ray spectrum of ZnFe2O4 nanoparticles annealed at 1000 °C.
Figure 4. Scanning electron microscopy images of ZnFe2O4 nanoparticles annealed at (a) 600, (b) 800, and (c) 1000 °C. The respective histograms are given in the inset. (d) Energy-dispersive X-ray spectrum of ZnFe2O4 nanoparticles annealed at 1000 °C.
Nanomaterials 10 02133 g004
Nanomaterials 10 02133 g005 550
Figure 5. Three-dimensional micrographs and surface profiles showing the surface morphology, roughness, and topography of the sensitive element–ZnFe2O4 nanoparticles annealed at (a) 600, (b) 800, and (c) 1000 °C.
Figure 5. Three-dimensional micrographs and surface profiles showing the surface morphology, roughness, and topography of the sensitive element–ZnFe2O4 nanoparticles annealed at (a) 600, (b) 800, and (c) 1000 °C.
Nanomaterials 10 02133 g005
Nanomaterials 10 02133 g006 550
Figure 6. Time-dependent sensor response of the annealed ZnFe2O4 nanoparticles toward 100–400 ppm NO2 gas at 600 °C.
Figure 6. Time-dependent sensor response of the annealed ZnFe2O4 nanoparticles toward 100–400 ppm NO2 gas at 600 °C.
Nanomaterials 10 02133 g006
Nanomaterials 10 02133 g007 550
Figure 7. The calibration curves for different ZnFe2O4 samples showing NO2 sensitivity of the chemiresistive devices.
Figure 7. The calibration curves for different ZnFe2O4 samples showing NO2 sensitivity of the chemiresistive devices.
Nanomaterials 10 02133 g007
Nanomaterials 10 02133 g008 550
Figure 8. The response and recovery times of ZnFe2O4 nanoparticles annealed at (a) 600, (b) 800, and (c) 1000 °C calculated from their respective responses to 300 ppm NO2.
Figure 8. The response and recovery times of ZnFe2O4 nanoparticles annealed at (a) 600, (b) 800, and (c) 1000 °C calculated from their respective responses to 300 ppm NO2.
Nanomaterials 10 02133 g008
Nanomaterials 10 02133 g009 550
Figure 9. The gas sensing mechanism of ZnFe2O4 nanoparticles-based chemiresistive gas sensors.
Figure 9. The gas sensing mechanism of ZnFe2O4 nanoparticles-based chemiresistive gas sensors.
Nanomaterials 10 02133 g009
Table
Table 1. The structural properties of ZnFe2O4 nanoparticles, annealed at different temperatures (T).
Table 1. The structural properties of ZnFe2O4 nanoparticles, annealed at different temperatures (T).
SampleT (°C)D (nm)a (Å)V (Å3)d311 (Å)ρxrd (g/cm3)S (m2/g)
BM-ZnFe2O4-9.308.445602.32.5465.321121.24
ZnFe2O4@60060018.718.430599.02.5425.35059.94
ZnFe2O4@80080023.038.424597.82.5405.36148.59
ZnFe2O4@1000100023.258.420597.02.5395.36848.07
Table
Table 2. The chemical composition of ZnFe2O4 nanoparticles annealed at different temperatures.
Table 2. The chemical composition of ZnFe2O4 nanoparticles annealed at different temperatures.
SampleZnFeO
(wt.%)(at.%)(wt.%)(at.%)(wt.%)(at.%)
ZnFe2O4@60026.6114.0847.1529.1726.2456.75
ZnFe2O4@80025.6013.5148.0429.6426.3656.85
ZnFe2O4@100025.6513.6848.6730.3425.6955.98
Table
Table 3. A comparison of the sensing properties of chemiresistive-type NO2 gas sensors.
Table 3. A comparison of the sensing properties of chemiresistive-type NO2 gas sensors.
MaterialFabrication MethodTemperature (°C)Detection Range (ppm)Response † (S)Response Time (s)Recovery Time (s)Reference
CuFe2O4Coprecipitation2720–24072%85[58]
ZnFe2O4Hydrothermal1251–10248 ‡6.511[59]
Pd-doped BiFeO3Sol-gel14050–350093%60100[60]
CoFe2O4Spray pyrolysis15020–8095%5114[61]
ZnO/ZnFe2O4Wet chemical2000.1–20~ 300 ‡715[25]
Cu-doped α-Fe2O3Electrospinning 3005–502 ‡118258[62]
ZnFe2O4Ball-milling600100–40011%19517This work
Sb-doped Zn2SnO4Sputtering 60050–300~ 4 ‡--[63]
† The response (S) is reported for the highest tested concentration of NO2 gas: S(%) = (Rg – Ra) × 100/Ra. ‡ If not reported as S(%), the response is measured as: S = Rg/Ra.
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

Afzal, A.; Mujahid, A.; Iqbal, N.; Javaid, R.; Qazi, U.Y. Enhanced High-Temperature (600 °C) NO2 Response of ZnFe2O4 Nanoparticle-Based Exhaust Gas Sensors. Nanomaterials 2020, 10, 2133. https://doi.org/10.3390/nano10112133

AMA Style

Afzal A, Mujahid A, Iqbal N, Javaid R, Qazi UY. Enhanced High-Temperature (600 °C) NO2 Response of ZnFe2O4 Nanoparticle-Based Exhaust Gas Sensors. Nanomaterials. 2020; 10(11):2133. https://doi.org/10.3390/nano10112133

Chicago/Turabian Style

Afzal, Adeel, Adnan Mujahid, Naseer Iqbal, Rahat Javaid, and Umair Yaqub Qazi. 2020. "Enhanced High-Temperature (600 °C) NO2 Response of ZnFe2O4 Nanoparticle-Based Exhaust Gas Sensors" Nanomaterials 10, no. 11: 2133. https://doi.org/10.3390/nano10112133

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop