Next Article in Journal
Development of a Moisture Pretreatment Device for the Accurate Quantitation of Water-Soluble Volatile Organic Compounds in Air
Next Article in Special Issue
The Application of Combined Visible and Ultraviolet Irradiation to Improve the Functional Characteristics of Gas Sensors Based on ZnO/SnO2 and ZnO/Au Nanorods
Previous Article in Journal
Macrocyclic Compounds Comprising Tris(3-Aminopropyl)Amine Units and Fluorophore Moieties: Synthesis and Spectroscopic Studies in the Presence of Metal Salts
Previous Article in Special Issue
Building a Sensor Benchmark for E-Nose Based Lung Cancer Detection: Methodological Considerations
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Chemosensors
Volume 11
Issue 3
10.3390/chemosensors11030187
chemosensors-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

Highly Sensitive p-SmFeO3/p-YFeO3 Planar-Electrode Sensor for Detection of Volatile Organic Compounds

by
Huiyang Liu
1,
Denghui Zhu
1,
Tingting Miao
1,
Weikang Liu
1,
Juan Chen
2,
Bin Cheng
1,
Hongwei Qin
1 and
Jifan Hu
1,*
1
State Key Laboratory for Crystal Materials, School of Physics, Shandong University, Jinan 250100, China
2
The Fifth Research Institute of China Aerospace Science and Technology Corporation, Beijing 100000, China
*
Author to whom correspondence should be addressed.
Chemosensors 2023, 11(3), 187; https://doi.org/10.3390/chemosensors11030187
Submission received: 19 February 2023 / Revised: 7 March 2023 / Accepted: 9 March 2023 / Published: 10 March 2023
(This article belongs to the Special Issue Chemical Sensors for Bio-Medical and Environmental Applications)
Browse Figures
Versions Notes

Abstract

:
Nanocomposites of SmFeO3/YFeO3 (1:0, 0.8:0.2, 0.6:0.4, 0.4:0.6, 0.2:0.8, and 0:1) with different molar proportions were prepared by the sol–gel method. The material’s properties were characterized by various test methods, such as scanning-electron microscopy (SEM) and X-ray photoelectron-diffraction spectrometry (XPS). The gas-sensing characteristics of the sensor were tested in darkness and under illumination using monochromatic light with various selected wavelengths. The test results show that the SmFeO3/YFeO3 sensor with the molar ratio of 0.4:0.6 had the highest gas response to volatile organic compound (VOC) gases and that the optimum operating temperature was lower (120 °C). The light illumination improved the sensor’s sensitivity to gas. Under the 370-nanometer light illumination, the sensor’s responses to 30 ppm of ethanol, acetone, and methanol gases were 163.59, 134.02, and 111.637, respectively, which were 1.35, 1.28, and 1.59 times higher, respectively, than those without light. The high gas sensitivity of the sensor was mainly due to the adsorption of oxygen on the material’s surface and the formation of a p–p heterojunction. The SmFeO3/YFeO3 sensor, which can respond to different VOC gases, can be used to detect the safety of unknown environments and provide a timely warning of the presence of dangerous gases in working environments.

1. Introduction

As society develops, increasing attention is paid to the harmful effects of VOC to the human body and the environment. Ethanol, acetone, methanol, and formaldehyde are all volatile organic compound gases. The impact of these gases on the human body has a negative effect on the respiratory system, and can even cause cancer, threatening human life [1,2,3]. Therefore, the preparation of sensors that can effectively detect VOC gases has received extensive attention. Semiconductor materials [4,5,6,7,8,9,10,11,12] are the most common gas-sensing materials due to their excellent physical and chemical properties. The detection of harmful gases by the semiconductor detector was shown by the resistance change of the sensor. Semiconductors such as WO3 [13], ZnO [14], and LaFeO3 [15], have been widely investigated as sensor materials for detecting various gases. In semiconductor materials, perovskite-type oxides of ABO3 have been widely studied [16,17,18,19,20,21,22,23,24,25,26,27,28]. There are many chemical elements to choose from for cations at the A and B positions in ABO3. Compared with traditional oxide-gas-sensing materials, perovskite materials are more stable, so they are expected to exhibit unique advantages in gas sensors.
As typical p-type-semiconductor perovskite materials, SmFeO3 nanomaterials have attracted wide attention, and have high sensitivity to various VOC gases [29,30,31]. However, pure SmFeO3 has some disadvantages, such as its high operating temperature and low response value. There are many ways to improve the gas-sensing performance of pure SmFeO3 perovskite sensors, such as by doping it with a noble metal [32,33,34,35,36]. The combination of these materials can overcome the shortages of pure metal materials and produce sensor materials with higher performance levels. In recent years, increasing attention has been paid in research to materials with heterojunction interfaces. Li et al. prepared a Co-Fe2O3/SmFeO3 p–n-heterojunction composite using the sol–gel method with molecular imprinting technology, and the sensor’s response to 5 ppm of methanol gas was 19.7 at 155 °C [37]. Zakie et al. synthesized a SmFeO3/ZnO nanocomposite by the thermal treatment method, and the SmFeO3/ZnO nanocomposite’s sensor had a response of 45 to 10 ppm acetone at 350 °C [38]. These previous studies proved that the construction of a heterojunction can improve the gas-sensing characteristics of sensors. However, it is still important to find sensor materials with lower operating temperatures, faster response speeds, and higher response value.
In this paper, we combined another YFeO3 rare-earth perovskite nanomaterial with SmFeO3 to prepare SmFeO3/YFeO3 (0.8:0.2, 0.6:0.4, 0.4:0.6, and 0.2:0.8) nanomaterials with a heterojunction interface and different molar ratios. The characteristics of the sensitivity of the sensor to VOC gases were studied in the dark and under multi-wavelength-light illumination. The test results show that the SmFeO3/YFeO3 composite sensor had a higher gas-sensing performance than the pure SmFeO3 and YFeO3 sensors, and the optimal operating temperature of the sensor was 120 °C. The multi-wavelength-light illumination improved the sensor’s response to the VOC gases. In addition, we also discuss the gas-sensing response mechanism of the SmFeO3/YFeO3 sensor.

2. Materials and Methods

2.1. Preparation of Nanomaterials

The SmFeO3/YFeO3 (e:f) nanomaterials with a heterojunction interface were prepared using the sol–gel method. In our previous research [39,40], we successfully prepared SmFeO3 and YFeO3 nanomaterials with different annealing temperatures (500–900 °C) using the sol–gel method. Previous studies proved that when the annealing temperature was 700 °C, SmFeO3 and YFeO3 nanomaterial sensors had the best gas-sensing properties. Consequently, we mixed the SmFeO3 and YFeO3 nanomaterials (700 °C) according to different molar ratios (0.8:0.2, 0.6:0.4, 0.4:0.6, and 0.2:0.8), and then ground and fully mixed them. The mixture was annealed at 700 °C for 3 h and then ground again. Finally, the SmFeO3/YFeO3 (e:f) nanomaterials with a heterojunction interface were obtained.

2.2. Materials Characterization

Using X-ray diffraction (XRD; 40 KV, 40 mA, Bruker D8 Advanced, Bruker Group, Billerca, MA, USA) with CuKα radiation, we measured the structural characteristics of the nanopowders. The microscopic morphology of the sample was observed by scanning-electron microscopy (SEM). The elemental composition and valence state of the samples were observed with an X-ray photoelectron-diffraction spectrometer (XPS; Thermo Scientific Escalab 250Xi, Thermo Fisher Scientific, Inc., Waltham, MA, USA). The ultraviolet–visible (UV–Vis) absorption spectra of the powder samples were tested by a UV–Vis–NIR spectrometer (UV–Vis–NIR, Cary 5000, Agilent, Palo Alto, CA, USA).

2.3. Fabrication and Measurement of Gas Sensors

The SmFeO3/YFeO3 (e:f) powder samples were mixed with a small amount of deionized water and ground into a paste. Next, they were coated on the 1.5 × 1-millimeter planar electrode to prepare the planar-electrode sensors. In our previous research [39,40], we used the same planar electrode. One side was the material coating surface, with two platinum electrodes (for measurement), and the other side was the heating layer, with two platinum electrodes (for heating). After the preparation, the sensor was placed on a 200 °C aging table and heated for 48 h to improve its stability.
We used the gas-sensitivity-test system produced by Zhengzhou Weisheng company (WS-30A, Weisheng Electronics Co., Ltd., Zhengzhou, China) to test the performance of the fabricated gas sensor. The system reflects the characteristics of the gas sensor by measuring the voltage of the load resistance in series with the gas sensor. The sensor’s response is defined as S = Rg/Ra, where Rg and Ra are the resistance of the sensor in target gas and in the air, respectively. The response time is the time it takes for the resistance to increase to 90% of the change. The recovery time is the time taken to reduce the sensor resistance to 10% of the change.

3. Results

3.1. Nanomaterial Characterization

Figure 1 shows the XRD patterns of the SmFeO3/YFeO3 (e:f) nanomaterials. The XRD pattern provides the crystallinity information of the nanostructures of the powder materials. The YFeO3 sample was a hexagonal lattice structure (PDF#48-0529) [41,42,43,44,45]. The peaks of the YFeO3 in Figure 1 mainly correspond to the (100), (101), (102), (104), (110), (106), and (114) crystal planes. The SmFeO3 sample had an orthogonal lattice structure (PDF#39-1490) [46,47,48], and the XRD diffraction peaks in the figure correspond to the (101), (111), (200), (121), (002), (210), (220), (022), (131), (202), (040), (212), (311), (321), (240), (042), (331), and (242) crystal planes. In the XRD spectra of the SmFeO3/YFeO3 nanocomposite materials with the ratios of 0.2:0.8, 0.4:0.6, 0.6:0.4, and 0.8:0.2, the characteristic peaks of the SmFeO3 and YFeO3 materials appeared at the same time, which signifies the coexistence of SmFeO3 and YFeO3 in the SmFeO3/YFeO3 composites. With the increase in the proportion of the YFeO3 material, the relative intensity of the (102) diffraction peak of the YFeO3 at 33.2° increased gradually, while the (121) diffraction peak of the SmFeO3 at 32.7° decreased gradually.
Figure 2 shows the SEM spectra of the SmFeO3/YFeO3 (e:f) nanomaterials. The particle sizes were spherical below 100 nm, and some particles were elliptical after aggregation. When the mixing ratio of the two materials was different, the particle-size distribution of the materials also changed. The average particle sizes of the SmFeO3/YFeO3 (1:0, 0.8:0.2, 0.6:0.4, 0.4:0.6, 0.2:0.8, and 0:1) nanomaterials were 34.8, 42.1, 41.8, 38, 23.55, and 20.55 nm, respectively. The average particle size first increased and then decreased.
Figure 3 shows the XPS spectra of the SmFeO3/YFeO3 (e:f) nanomaterials. The SmFeO3/YFeO3 nanomaterials mainly contained the characteristic peaks of Sm, Fe, Y, O, and C, without other impurity peaks, as shown in Figure 3a. It can be seen that the characteristic peaks of the Sm and Y elements changed significantly with the proportion of the materials. It is further proven that we successfully prepared SmFeO3/YFeO3 nanocomposite materials with different proportions. The Sm 3d spectra of the SmFeO3/YFeO3 were divided into 3d3/2 (1110.2 eV) and 3d5/2 (1083.2 eV) [46], as shown in Figure 3b. The peaks of Fe 2p at 724.5 ± 0.5 eV and 711 ± 0.2 eV corresponded to 2p1/2 and 2p3/2 [35], respectively, as shown in Figure 3c. Figure 3d shows the XPS spectra of the Y 3d, which were divided into two peaks of 3d3/2 (158.8 eV) and 3d5/2 (156.8 eV) [49].
Figure 4 shows the O 1s spectra analysis of the SmFeO3/YFeO3 nanomaterial. The XPS spectra of the O 1s were divided into three peaks, which correspond to three kinds of oxygen specification [50]. One corresponded to the lattice oxygen (529.4 ± 0.2 eV), one corresponded to the adsorbed oxygen (531.3 ± 0.5 eV), and one corresponded to the oxygen in the carbonate (532.5 ± 0.5 eV). The lattice oxygen and the oxygen in the carbonate did not react with the gas and had no effect on the carrier concentration on the material surface, so they did not affect the sensor performance. The adsorbed oxygen on the material surface reacted with the test gas, increasing the concentration of hole carriers, thus improving the response value of the sensor to the gas. The adsorbed oxygen contents on the surface of the SmFeO3/YFeO3 (e:f) nanomaterials were 28.19%, 31.34%, 37.58%, 39.94%, 32.15%, and 31.87% for the SmFeO3/YFeO3 nanomaterials with the proportions of 1:0, 0.8:0.2, 0.6:0.4, 0.4:0.6, 0.2:0.8, and 0:1, respectively. The changing trend is shown in Figure 5. The adsorbed oxygen content first increased and then decreased with the increase in the proportion of YFeO3, and the adsorbed oxygen content of the SmFeO3/YFeO3 (0.4:0.6) material was the highest.

3.2. Gas-Sensing Characteristics

In semiconductor gas sensors, the working temperature has a great influence on the gas-sensing characteristics. We tested the gas-sensitivity response of the SmFeO3/YFeO3 (1:0, 0.8:0.2, 0.6:0.4, 0.4:0.6, 0.2:0.8, and 0:1) sensors to ethanol, acetone, methanol, and formaldehyde gases in the dark at 100–150 °C, as shown in Figure 6. The response values of the SmFeO3/YFeO3 (e:f) sensors to the four gases had similar trends with temperature. With the increase in the working temperature, the response value first increased and then decreased, reaching the maximum value at 120 °C, with the exception of the optimal temperature of the YFeO3 sensor, which was 110 °C. The reason for this trend was that, with the increase in the working temperature, the test gas overcame the energy barrier and encouraged the oxidation and reduction reaction on the material surface, so the sensor’s response value increased. However, the high operating temperature caused the gas-desorption efficiency on the material surface to be greater than the adsorption efficiency, so the sensor’s response value decreased. The sensor with the highest response value at 120 °C was SmFeO3/YFeO3 (0.4:0.6). The response values of the SmFeO3/YFeO3 (0.4:0.6) sensor to 30 ppm of ethanol, acetone, methanol, and formaldehyde were 120.76, 104.65, 70.43, and 9.21, respectively.
Figure 7 shows the curves of the SmFeO3/YFeO3 (0.4:0.6) sensor’s response value to VOC gases with the operating temperature under multi-wavelength (470, 420, and 370 nm) light illumination. It can be seen that under the light illumination, the response value of the sensor first increased and then decreased with the change in the operating temperature at 100–150 °C. The optimum operating temperature was 120 °C. Compared with the darkness, we did not measure the change in the optimal operating temperature under light illumination. The temperature interval during the test was 10 °C due to the limitations of the equipment. The light-excitation energy within the wavelength range of the available light source was insufficient to cause visible temperature changes. At 120 °C, the SmFeO3/YFeO3 (0.4:0.6) sensor’s response values to 30 ppm of ethanol, acetone, methanol, and formaldehyde under 370 nm of light illumination were 163.59, 134.02, 111.637, and 18.60, respectively, which were 1.35, 1.28, 1.59, and 2.02 times, respectively, those in the dark. Therefore, it was confirmed that the multi-wavelength light illumination improved the response value of the sensor.
The repeatability of the sensor was an important parameter in the reliability of the sensor in use. A verified sensor would be expected achieve similar results for multiple tests in the same environment. The detection results of the SmFeO3/YFeO3 (0.4:0.6) sensor for three gases at 120 °C were repeated under 370 nm of light illumination, as shown in Figure 8. The SmFeO3/YFeO3 (0.4:0.6) sensor displayed good repeatability with VOC gases.
We also tested the response/recovery time of the SmFeO3/YFeO3 (0.4:0.6) sensor under light illumination, as shown in Figure 9. Before the sensor contacted the target gas, the resistance was stable, and the log of R was about 6.55 Ω. After the target gas was introduced, the sensor’s resistance increased, conforming to the characteristic of the p-type semiconductor material. However, due to the different gas characteristics, the response/recovery time of the sensor to the different gases varied greatly. Under the 370-nanometer light illumination, the response/recovery times of the SmFeO3/YFeO3 (0.4:0.6) sensor to 30 ppm of ethanol, acetone, methanol, and formaldehyde were 37/129 s, 166/228 s, 69/94 s, and 83/237 s, respectively. The fastest response of the sensor was to the ethanol gas, and the slowest response was to the acetone gas. The combination of the response value and the response/recovery time can be used as a parameter index to judge gas during the application of sensors.
Figure 10 shows the dynamic-response curve and change curve of the SmFeO3/YFeO3 (0.4:0.6) sensor’s response to VOC gases at 120 °C with the change in concentration. When the concentrations of the ethanol, acetone, and methanol gases increased from 10 ppm to 50 ppm, the response value of the SmFeO3/YFeO3 (0.4:0.6) sensor increased gradually. After several cycles, the resistance of the SmFeO3/YFeO3 (0.4:0.6) sensor recovered to a level close to that in the air, as shown in Figure 10a–c. As can be seen from Figure 10d, the SmFeO3/YFeO3 (0.4:0.6) sensor’s response value increased with the gas concentration at 10–50 ppm. As shown in Figure 10e, we tested the linear relationship between the response value of the SmFeO3/YFeO3 (0.4:0.6) sensor and the gas concentration (0.5–10 ppm). The SmFeO3/YFeO3 (0.4:0.6) sensor demonstrated a good linear relationship with the three gases at low concentrations. The slopes of the linear relationship between the sensor and the concentrations of the three gases were 7.765, 5.126, and 2.833. According to the linear relationship, the detection limit of the sensor for the ethanol, acetone, and methanol gases can be calculated as 0.38, 0.42, and 0.67ppm, respectively. Therefore, the sensor has not only a high response value but also a low detection limit.
At an optimum operating temperature of 120 °C, the gas-sensing characteristics of the SmFeO3/YFeO3 (0.4:0.6) sensor under 370 nm of light illumination were tested at different humidity levels, as shown in Figure 11. Figure 11a shows that the SmFeO3/YFeO3 (0.4:0.6) sensor’s dynamic-response curve to 30 ppm of the ethanol gas gradually decreased with the increase in humidity. When the humidity decreased from 30%RH to 80%RH, the response value of the sensor decreased by about 20%. Under different humidity conditions, the resistance of the SmFeO3/YFeO3 (0.4:0.6) sensor recovered to close to the initial value after the gas desorption. The variation curves of the SmFeO3/YFeO3 (0.4:0.6) sensor’s response to the ethanol, acetone, and methanol gases with relative humidity are shown in Figure 11b, and it can be seen that the response value decreased with the increase in relative humidity. The relative humidity in the air is high in summer, so the measurement results of the sensor were low during this season.
The power parameters of the light sources were set by adjusting the corresponding voltage on the LED light-source device. Figure 12 shows the dynamic-response curves of the SmFeO3/YFeO3 (0.4:0.6) sensor to the VOC gases (ethanol, acetone, methanol, and formaldehyde) under multi-wavelength light illumination (with different optical powers) at 120 °C. Under the same wavelength of light illumination, the greater the optical power (30, 50, and 98 mW), the higher the response value of the SmFeO3/YFeO3 (0.4:0.6) sensor. When the optical power was the same, the shorter the wavelength of the light source (470, 420, and 370 nm), the higher the response value of the SmFeO3/YFeO3 (0.4:0.6) sensor.
Figure 13a shows the response histogram of the SmFeO3/YFeO3 (0.4:0.6) sensor to the VOC gases at 120 °C under 370 nm of light illumination. The response value of the sensor to 30 ppm ethanol was the highest. Although the sensor’s response values to the acetone and methanol gases were lower than those for the ethanol, the response values were still high. Therefore, the SmFeO3/YFeO3 (0.4:0.6) sensor can detect various gases. Figure 13b shows the stability-test curves of the SmFeO3/YFeO3 (0.4:0.6) sensor for the VOC gases at 120 °C under 370 nm of light illumination over 35 days. The value of the SmFeO3/YFeO3 (0.4:0.6) sensor’s response to the VOC gases changed little and had good stability.
Table 1 shows a comparison of the gas-sensing characteristics between the SmFeO3/YFeO3 (0.4:0.6) sensor and other sensors. It can be seen that the optimal operating temperature of the SmFeO3/YFeO3 (0.4:0.6) sensor was lower and the gas-response value was higher.
This kind of planar-electrode sensor has a small size, low optimal working temperature, high response value, and good stability, and detects various VOC gases. In the future, it will be possible to use them in portable or wearable gas sensors, which can detect the environment and warn users about the occurrence of dangerous gases in a timely manner.

3.3. Mechanism Discussion

We studied the light-absorption ability of SmFeO3, YFeO3, and SmFeO3/YFeO3 composite materials with different molar-mass ratios by UV–visible absorption spectroscopy, as shown in Figure 14a. As demonstrated in to Figure 14a, we obtained the (ahv)2–(hv) curves of the SmFeO3, and YFeO3 samples, which are shown in Figure 14b. After the calculation, the band energies of the SmFeO3 and YFeO3 materials were 2.009 and 1.837 eV, respectively. The calculation formula is as follows:
ahv = A(hv − Eg)1/2
where A is a constant, hv is the photon energy, Eg is the band-gap energy of the material, and a is the absorbance.
The photon energies of the light sources with the wavelengths of 470, 420, and 370 nm were 2.638, 2.952, and 3.351 eV, respectively. The photon energies of the light sources with different wavelengths were higher than the band energies of the SmFeO3, YFeO3, and nanomaterials with heterogeneous interfaces. Therefore, the light illumination caused the electronic transition on the material surface. The electronic transit to a higher energy level improved the conductivity and reduced the resistance. Photoexcitation produces photo-generated electrons and holes, which can react with oxygen to produce more adsorbed oxygen ions, so the sensor reacts with more gases to improve its performance. Therefore, the light illumination improved the response of the SmFeO3/YFeO3 sensor due to the photoelectric effect.
The gas-sensing mechanism of the SmFeO3/YFeO3 (e:f) sensor under light illumination can be explained by the depletion layer and p–p heterojunction. In the SmFeO3/YFeO3 (e:f) nanomaterials, a p–p-heterojunction interface formed between the SmFeO3 and YFeO3 materials. The charge transfer led to a change in the barrier height. The p–p heterojunctions on the SmFeO3/YFeO3 interface acted as tunable resistors, resulting in differences in the sensor’s resistance at different temperatures.
O2 (gas) → O2 (ads)
O2 (ads)+e− → O2− (ads)
O2− (ads)+e→ → 2O− (ads)
C2H5OH (gas)+6O− (ads) → 2CO2+3H2O+6e−
CH3COCH3 (gas)+8O− (ads) → 3CO2+3H2O+8e−
CH3OH (gas)+3O− (ads) → CO2+2H2O+3e−
The SmFeO3 and YFeO3 materials are p-type semiconductors. After the contact between the two semiconductors, since the Fermi energy level of the SmFeO3 was higher than that of the YFeO3, the electrons flowed from the conduction band of the SmFeO3 to the conduction band of the YFeO3 material, resulting in the formation of energy-band bending [56,57,58] and a depletion layer, until the Fermi energy level reached the equilibrium state, as shown in Figure 15a. Under the light illumination, photo-generated electrons and holes were generated in the p–p heterojunction. At the same time, the built-in electric field generated between the heterojunctions inhibited the recombination of photo-generated electron–hole pairs. Therefore, there were more photo-generated electrons and holes on the surface of the material, which were able to react with oxygen to generate more adsorbed oxygen ions.
When the SmFeO3/YFeO3 nanomaterials were exposed to air, the oxygen molecules in the air made full contact with the materials’ surfaces, capturing electrons in the materials’ conduction bands to form oxygen ions, as shown in Formulas (2)–(4). Due to the presence of the electron-depletion layer, the sensor’s resistance in the air was relatively low.
When the SmFeO3/YFeO3 sensors were in contact with the VOC gases, the gas molecules reacted with the oxygen ions and released electrons, as shown in Formulas (5)–(7). The electrons combated the holes in the materials, and the presence of electron–hole pairs reduced the hole density in the nanocomposites and broke the dynamic-carrier balance between the SmFeO3 and YFeO3 materials. The hole transfer of the SmFeO3 and YFeO3 further reduced the thickness of the electron-depletion layer on the SmFeO3 surface, so the resistance of the SmFeO3/YFeO3 sensor increased, as shown in Figure 15b. The dynamic-response curves of the resistance (Figure 9) of the SmFeO3/YFeO3 sensor to the VOC gases show that the sensor’s resistance increased after its contact with the VOC gases, confirming the reliability of the sensing mechanism above.

4. Conclusions

In this study, SmFeO3/YFeO3 (e:f) nanocomposite materials with different proportions were prepared using the sol–gel method. A planar electrode measuring 1.5 × 1 mm was used to prepare the small-size planar-electrode sensor. The optimal working temperature of the SmFeO3/YFeO3 (e:f) planar-electrode sensor was 120 °C. Additionally, multi-wavelength light illumination improved the gas sensitivity of the sensor. Under the 370-nanometer light illumination, the values of the responses of the SmFeO3/YFeO3 (0.4:0.6) sensor to 30 ppm of the ethanol, acetone, methanol, and formaldehyde gases were 163.59, 134.02, 111.637, and 18.60, respectively, which were 1.35, 1.28, 1.59, and 2.02 times, respectively, those found in the dark. In addition, the gas-sensing mechanism of the sensor was explained by analyzing the p–p heterojunction. This planar-electrode sensor, with its small size, low operating temperature, and high gas-sensitivity-response value, has major potential for future use a portable gas sensor to detect VOC gases and warn users about potential dangers in unknown environments.

Author Contributions

Conceptualization, H.L., D.Z. and T.M.; methodology, H.L., W.L., J.C., B.C. and H.Q.; software, H.L., W.L. and J.C.; validation, T.M. and W.L.; formal analysis, D.Z.; investigation, H.L. and D.Z.; resources, T.M., W.L. and J.C.; data curation, H.L.; writing—original draft preparation, H.L.; writing—review and editing, H.L., J.H., J.C., B.C. and H.Q.; visualization, W.L.; supervision, J.H.; project administration, J.H.; funding acquisition, B.C., H.Q. and J.H. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China, grant numbers 51772174 (Jifan Hu), 51472145 (Hongwei Qin), and 11904204 (Bin Cheng).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (grant numbers: 51772174, 51472145, and 11904204).

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Boots, A.W.; van Berkel, J.J.; Dallinga, J.W.; Smolinska, A.; Wouters, E.F.; van Schooten, F.J. The versatile use of exhaled volatile organic compounds in human health and disease. J. Breath. Res. 2012, 6, 027108. [Google Scholar] [CrossRef]
  2. Park, A.S.; Ritz, B.; Ling, C.; Cockburn, M.; Heck, J.E. Exposure to ambient dichloromethane in pregnancy and infancy from industrial sources and childhood cancers in California. Int. J. Hyg. Environ. Health 2017, 220, 1133–1140. [Google Scholar] [CrossRef]
  3. Int Panis, L.; de Geus, B.; Vandenbulcke, G.; Willems, H.; Degraeuwe, B.; Bleux, N.; Mishra, V.; Thomas, I.; Meeusen, R. Exposure to particulate matter in traffic: A comparison of cyclists and car passengers. Atmos. Environ. 2010, 44, 2263–2270. [Google Scholar] [CrossRef]
  4. Jiang, Q.; Guo, X.; Wang, C.; Jia, L.; Zhao, Z.; Yang, R.; Wang, P.; Deng, Q. Polyvinylpyrrolidone-mediated Co3O4 microspheres assembled in size-tunable submicron spheres with porous core-shell structure for high-performance gases sensing. J. Alloys Compd. 2023, 935, 167976. [Google Scholar] [CrossRef]
  5. Jin, Z.; Wang, C.; Wu, L.; Liu, H.; Shi, F.; Zhao, J.; Liu, F.; Fu, K.; Wang, F.; Wang, Z.; et al. Construction of Pt/Ce-In2O3 hierarchical microspheres for superior triethylamine detection at low temperature. Colloids Surf. A 2023, 659, 130738. [Google Scholar] [CrossRef]
  6. Sun, B.; Shi, G.; Tang, Z.; Zhang, P.; Guo, Y.; Zhu, S.; Liu, J. Rapid gas-sensing detection of carbon disulfide by a CdS/SnS nanocomposite-based cataluminescence sensor. Chemosensors 2023, 11, 10. [Google Scholar] [CrossRef]
  7. Liu, M.; Xue, L.; Feng, Q.; Wang, Y.; Liu, J.; Zhang, S.; Hu, W. Facile preparation of Co3O4 hollow dodecahedron with superior peroxidase-like activity for selective detection of cholesterol. Chemosensors 2023, 11, 27. [Google Scholar] [CrossRef]
  8. Cui, X.; Lu, Z.; Wang, Z.; Zeng, W.; Zhou, Q. Highly sensitive SF6 decomposition byproducts sensing platform based on CuO/ZnO heterojunction nanofibers. Chemosensors 2023, 11, 58. [Google Scholar] [CrossRef]
  9. Torai, S.; Ueda, T.; Kamada, K.; Hyodo, T.; Shimizu, Y. Effects of addition of CuxO to porous SnO2 microspheres prepared by ultrasonic spray pyrolysis on sensing properties to volatile organic compounds. Chemosensors 2023, 11, 59. [Google Scholar] [CrossRef]
  10. Li, J.; Jin, Z.; Chao, Y.; Wang, A.; Wang, D.; Chen, S.; Qian, Q. Synthesis of graphene-oxide-decorated porous ZnO nanosheet composites and their gas sensing properties. Chemosensors 2023, 11, 65. [Google Scholar] [CrossRef]
  11. Ur Rahman, Z.; Shah, U.; Alam, A.; Shah, Z.; Shaheen, K.; Bahadar Khan, S.; Ali Khan, S. Photocatalytic degradation of cefixime using CuO-NiO nanocomposite photocatalyst. Inorg. Chem. Commun. 2023, 148, 110312. [Google Scholar] [CrossRef]
  12. Chen, Y.; Qin, H.; Cao, Y.; Zhang, H.; Hu, J. Acetone sensing properties and mechanism of SnO2 thick-films. Sensors 2018, 18, 3425. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  13. Li, J.; Wu, J.; Yu, Y. DFT exploration of sensor performances of two-dimensional WO3 to ten small gases in terms of work function and band gap changes and I-V responses. Appl. Surf. Sci. 2021, 546, 149104. [Google Scholar] [CrossRef]
  14. Castello Lux, K.; Fajerwerg, K.; Hot, J.; Ringot, E.; Bertron, A.; Collière, V.; Kahn, M.L.; Loridant, S.; Coppel, Y.; Fau, P. Nano-structuration of WO3 nanoleaves by localized hydrolysis of an organometallic Zn precursor: Application to photocatalytic NO2 abatement. Nanomaterials 2022, 12, 4360. [Google Scholar] [CrossRef] [PubMed]
  15. Chumakova, V.; Marikutsa, A.; Platonov, V.; Khmelevsky, N.; Rumyantseva, M. Distinct roles of additives in the improved sensitivity to CO of Ag- and Pd-modified nanosized LaFeO3. Chemosensors 2023, 11, 60. [Google Scholar] [CrossRef]
  16. Sheng, H.; Ma, S.; Han, T.; Yun, P.; Yang, T.; Ren, J. A highly sensitivity and anti-humidity gas sensor for ethanol detection with NdFeO3 nano-coral granules. Vacuum 2022, 195, 110642. [Google Scholar] [CrossRef]
  17. Rajaitha, P.M.; Hajra, S.; Padhan, A.M.; Panda, S.; Sahu, M.; Kim, H.J. An electrochemical sensor based on multiferroic NdFeO3 particles modified electrode for the detection of H2O2. J. Alloys Compd. 2022, 915, 165402. [Google Scholar] [CrossRef]
  18. Zhang, H.; Xiao, J.; Chen, J.; Zhang, L.; Zhang, Y.; Jin, P. Au modified PrFeO3 with hollow tubular structure can be efficient sensing material for H2S detection. Front. Bioeng. Biotechnol. 2022, 10, 969870. [Google Scholar] [CrossRef]
  19. Cai, Z.; Park, S. A superior sensor consisting of porous, Pd nanoparticle–decorated SnO2 nanotubes for the detection of ppb-level hydrogen gas. J. Alloys Compd. 2022, 907, 164459. [Google Scholar] [CrossRef]
  20. Bhardwaj, R.; Hazra, A. Pd functionalized SrTiO3 hollow spheres for humidity-tolerant ethanol sensing. Sens. Actuators B 2022, 372, 132615. [Google Scholar] [CrossRef]
  21. Yin, Y.; Shen, Y.; Zhao, S.; Bai, J.; Qi, Y.; Han, C.; Wei, D. Effect of noble metal elements on ethanol sensing properties of ZnSnO3 nanocubes. J. Alloys Compd. 2021, 887, 161409. [Google Scholar] [CrossRef]
  22. Han, T.; Ma, S.; Xu, X.; Cao, P.; Liu, W.; Xu, X.; Pei, S. Electrospinning synthesis, crystal structure, and ethylene glycol sensing properties of orthorhombic SmBO3 (B. = Fe, Co) perovskites. J. Alloys Compd. 2021, 876, 160211. [Google Scholar] [CrossRef]
  23. Yang, T.T.; Ma, S.Y.; Cao, P.F.; Xu, X.L.; Wang, L.; Pei, S.T.; Han, T.; Xu, X.H.; Yun, P.D.; Sheng, H. Synthesis and characterization of ErFeO3 nanoparticles by a hydrothermal method for isopropanol sensing properties. Vacuum 2021, 185, 110005. [Google Scholar] [CrossRef]
  24. Meng, F.; Hu, J.; Liu, C.; Tan, Y.; Zhang, Y. Highly sensitive and low detection limit of acetone gas sensor based on porous YbFeO3 nanocrystallines. Chem. Phys. Lett. 2021, 780, 138925. [Google Scholar] [CrossRef]
  25. Aranthady, C.; Jangid, T.; Gupta, K.; Mishra, A.K.; Kaushik, S.D.; Siruguri, V.; Rao, G.M.; Shanbhag, G.V.; Sundaram, N.G. Selective SO2 detection at low concentration by Ca substituted LaFeO3 chemiresistive gas sensor: A comparative study of LaFeO3 pellet vs thin film. Sens. Actuators B 2021, 329, 129211. [Google Scholar] [CrossRef]
  26. Chen, Y.; Wang, D.; Qin, H.; Zhang, H.; Zhang, Z.; Zhou, G.; Gao, C.; Hu, J. CO2 sensing properties and mechanism of PrFeO3 and NdFeO3 thick film sensor. J. Rare Earth 2019, 37, 80–87. [Google Scholar] [CrossRef]
  27. Zhang, H.; Qin, H.; Cheng, B.; Cao, Y.; Chen, Y.; Xie, J.; Liu, W.; Gao, C.; Zhou, G.; Hu, J. Pd:LaFe0.9Mg0.1O3: Planar type acetone sensor with high sensitivity. Mater. Sci. Semicond. Process. 2019, 96, 91–98. [Google Scholar] [CrossRef]
  28. Zhang, P.; Qin, H.; Zhang, H.; Lv, W.; Hu, J. CO2 gas sensors based on Yb1−xCaxFeO3 nanocrystalline powders. J. Rare Earth 2017, 35, 602–609. [Google Scholar] [CrossRef]
  29. Zhang, H.; Xiao, J.; Wang, Y.; Zhang, L.; Zhao, G.; Yang, H.; Wang, H. A portable acetone detector based on SmFeO3 can pre-diagnose diabetes through breath analysis. J. Alloys Compd. 2022, 922, 166160. [Google Scholar] [CrossRef]
  30. Han, T.; Ma, S.Y.; Xu, X.L.; Xu, X.H.; Pei, S.T.; Tie, Y.; Cao, P.F.; Liu, W.W.; Wang, B.J.; Zhang, R.; et al. Rough SmFeO3 nanofibers as an optimization ethylene glycol gas sensor prepared by electrospinning. Mater. Lett. 2020, 268, 127575. [Google Scholar] [CrossRef]
  31. Tasaki, T.; Takase, S.; Shimizu, Y. Improvement of sensing performance of impedancemetric C2H2 sensor using SmFeO3 thin-films prepared by a polymer precursor method. Sensors 2019, 19, 773. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  32. Zhang, H.; Xiao, J.; Chen, J.; Zhang, L.; Zhang, Y.; Pei, X. Pd-modified SmFeO3 with hollow tubular structure under light shows extremely high acetone gas sensitivity. Rare Met. 2023, 42, 545–557. [Google Scholar] [CrossRef]
  33. Han, T.; Ma, S.; Yun, P.; Sheng, H.; Xu, X.; Cao, P.; Pei, S.; Alhadi, A. Synthesis and characterization of Ho-doped SmFeO3 nanofibers with enhanced glycol sensing properties. Vacuum 2021, 191, 110378. [Google Scholar] [CrossRef]
  34. Zhang, H.; Qin, H.; Zhang, P.; Hu, J. High sensing properties of 3wt% Pd-doped SmFe1-xMgxO3 nanocrystalline powders to acetone vapor with ultralow concentrations under light illumination. ACS Appl. Mater. Interf. 2018, 10, 15558–15564. [Google Scholar] [CrossRef] [PubMed]
  35. Li, L.; Qin, H.; Zhang, L.; Hu, J. Ultrasensitive sensing performances to sub-ppb level acetone for Pd-functionalized SmFeO3 packed powder sensors. RSC Adv. 2016, 6, 6967–6974. [Google Scholar]
  36. Zhang, H.; Qin, H.; Zhang, P.; Chen, Y.; Hu, J. Low concentration acetone gas sensing properties of 3 wt% Pd-doped SmCoxFe1-xO3 nanocrystalline powders under UV light illumination. Sens. Actuators B 2018, 260, 33–41. [Google Scholar] [CrossRef]
  37. Li, K.; Chen, M.; Rong, Q.; Zhu, Z.; Liu, Q.; Zhang, J. High selectivity methanol sensor based on Co-Fe2O3/SmFeO3 p-n heterojunction composites. J. Alloys Compd. 2018, 765, 193–200. [Google Scholar] [CrossRef]
  38. Anajafi, Z.; Naseri, M.; Neri, G. Acetone sensing behavior of p-SmFeO3/n-ZnO nanocomposite synthesized by thermal treatment method. Sens. Actuators B 2020, 304, 127252. [Google Scholar] [CrossRef]
  39. Liu, H.; Cao, Y.; Liu, W.; Chen, J.; Hu, J. Gas response of SmFeO3 planar electrode sensor to volatile organic compounds gases under light illumination. Mater. Lett. 2022, 326, 133009. [Google Scholar] [CrossRef]
  40. Liu, H.; Miao, T.; Liu, W.; Chen, J.; Cheng, B.; Qin, H.; Hu, J. Highly sensitive acetone gas sensor based on YFeO3 planar electrode under multi-wavelength light illumination. Mater. Lett. 2023, 333, 133596. [Google Scholar] [CrossRef]
  41. Wang, M.; Wang, T.; Song, S.; Tan, M. Structure-controllable synthesis of multiferroic YFeO3 nanopowders and their optical and magnetic properties. Materials 2017, 10, 626. [Google Scholar] [CrossRef] [Green Version]
  42. Liu, Y.; Kuo, Y.; Liu, W.; Chou, W. Photoelectrocatalytic activity of perovskite YFeO3/carbon fiber composite electrode under visible light irradiation for organic wastewater treatment. J. Taiwan Inst. Chem. Eng. 2021, 128, 227–236. [Google Scholar] [CrossRef]
  43. Guo, Y.; Zhang, N.; Huang, H.; Li, Z.; Zou, Z. A novel wide-spectrum response hexagonal YFeO3 photoanode for solar water splitting. RSC Adv. 2017, 7, 18418–18420. [Google Scholar] [CrossRef] [Green Version]
  44. Zhang, R.; Chen, C.; Jin, K.; Niu, L.; Xing, H.; Luo, B. Dielectric behavior of hexagonal and orthorhombic YFeO3 prepared by modified sol-gel method. J. Electroceram. 2014, 32, 187–191. [Google Scholar] [CrossRef]
  45. Liu, J.; He, F.; Chen, L.; Qin, X.; Zhao, N.; Huang, Y.; Peng, Y. Novel hexagonal-YFeO3/α-Fe2O3 heterojunction composite nanowires with enhanced visible light photocatalytic activity. Mater. Lett. 2016, 165, 263–266. [Google Scholar] [CrossRef]
  46. Hu, Q.; Yue, B.; Yang, D.; Zhang, Z.; Wang, Y.; Liu, J. Electrochemical and magnetic properties of electrospun SmFeO3 and SmCoO3 nanofibers. J. Am. Ceram. Soc. 2022, 105, 1149–1158. [Google Scholar] [CrossRef]
  47. Zhang, Y.; Zou, H.; Peng, J.; Duan, Z.; Ma, M.; Xin, X.; Li, W.; Zheng, X. Enhanced humidity sensing properties of SmFeO3-modified MoS2 nanocomposites based on the synergistic effect. Sens. Actuators B 2018, 272, 459–467. [Google Scholar] [CrossRef]
  48. Alizadeh, A.; Shariatinia, Z. Unveiling the influence of SmFeO3-TiO2 nanocomposites as high performance photoanodes of dye-sensitized solar cells. J. Mol. Liq. 2022, 348, 118070. [Google Scholar] [CrossRef]
  49. Nand, M.; Tripathi, S.; Rajput, P.; Kumar, M.; Kumar, Y.; Mandal, S.K.; Urkude, R.; Gupta, M.; Dawar, A.; Ojha, S.; et al. Different polymorphs of Y doped HfO2 epitaxial thin films: Insights into structural, electronic and optical properties. J. Alloys Compd. 2022, 928, 167099. [Google Scholar] [CrossRef]
  50. Cao, E.; Qin, Y.; Cui, T.; Sun, L.; Hao, W.; Zhang, Y. Influence of Na doping on the magnetic properties of LaFeO3 powders and dielectric properties of LaFeO3 ceramics prepared by citric sol-gel method. Ceram. Int. 2017, 43, 7922–7928. [Google Scholar] [CrossRef]
  51. Hao, P.; Qu, G.; Song, P.; Yang, Z.; Wang, Q. Synthesis of Ba-doped porous LaFeO3 microspheres with perovskite structure for rapid detection of ethanol gas. Rare Met. 2021, 40, 1651–1661. [Google Scholar] [CrossRef]
  52. Haryadi, H.; Suprayoga, E.; Suhendi, E. An analysis of electronic properties of LaFeO3 using density functional theory with generalized gradient approximation-perdew-burke-ernzerhof method for ethanol gas sensors. Mater. Res. 2022, 25, 554. [Google Scholar] [CrossRef]
  53. Cao, Y.; Zhou, C.; Qin, H.; Hu, J. High-performance acetone gas sensor based on ferrite–DyFeO3. J. Mater. Sci. 2020, 55, 16300–16310. [Google Scholar] [CrossRef]
  54. Ma, L.; Ma, S.Y.; Shen, X.F.; Wang, T.T.; Jiang, X.H.; Chen, Q.; Qiang, Z.; Yang, H.M.; Chen, H. PrFeO3 hollow nanofibers as a highly efficient gas sensor for acetone detection. Sens. Actuators B 2018, 255, 2546–2554. [Google Scholar] [CrossRef]
  55. Pei, S.; Ma, S.; Xu, X.; Xu, X.; Almamoun, O. Modulated PrFeO3 by doping Sm3+ for enhanced acetone sensing properties. J. Alloys Compd. 2021, 856, 158274. [Google Scholar] [CrossRef]
  56. Lou, Z.; Li, Y.; Zhu, L.; Xie, W.; Niu, W.; Song, H.; Ye, Z.; Zhang, S. The crystalline/amorphous contact in Cu2O/Ta2O5 heterostructures: Increasing its sunlight-driven overall water splitting efficiency. J. Mater. Chem. A 2017, 5, 2732–2738. [Google Scholar] [CrossRef]
  57. Bai, S.; Tian, K.; Han, N.; Guo, J.; Luo, R.; Li, D.; Chen, A. A novel rGO-decorated ZnO/BiVO4 heterojunction for the enhancement of NO2 sensing properties. Inorg. Chem. Front. 2020, 7, 1026–1033. [Google Scholar] [CrossRef]
  58. Bai, S.; Tian, K.; Meng, J.C.; Zhao, Y.; Sun, J.; Zhang, K.; Feng, Y.; Luo, R.; Li, D.; Chen, A. Reduced graphene oxide decorated SnO2/BiVO4 photoanode for photoelectrochemical water splitting. J. Alloys Compd. 2021, 855, 156780. [Google Scholar] [CrossRef]
Chemosensors 11 00187 g001 550
Figure 1. The X-ray diffraction patterns of SmFeO3/YFeO3 (e:f) powder nanomaterials.
Figure 1. The X-ray diffraction patterns of SmFeO3/YFeO3 (e:f) powder nanomaterials.
Chemosensors 11 00187 g001
Chemosensors 11 00187 g002 550
Figure 2. The SEM images of SmFeO3/YFeO3 (e:f) nanomaterials: (a) 1:0, (b) 0.8:0.2, (c) 0.6:0.4, (d) 0.4:0.6, (e) 0.2:0.8, and (f) 0:1.
Figure 2. The SEM images of SmFeO3/YFeO3 (e:f) nanomaterials: (a) 1:0, (b) 0.8:0.2, (c) 0.6:0.4, (d) 0.4:0.6, (e) 0.2:0.8, and (f) 0:1.
Chemosensors 11 00187 g002
Chemosensors 11 00187 g003 550
Figure 3. The XPS characterization of SmFeO3/YFeO3 (e:f) nanomaterials: (a) overall spectra, (b) Sm 3d, (c) Fe 2p, and (d) Y 3d.
Figure 3. The XPS characterization of SmFeO3/YFeO3 (e:f) nanomaterials: (a) overall spectra, (b) Sm 3d, (c) Fe 2p, and (d) Y 3d.
Chemosensors 11 00187 g003
Chemosensors 11 00187 g004 550
Figure 4. High-resolution XPS spectra of O 1s in SmFeO3/YFeO3 nanomaterials: (a) SmFeO3, (b) 0.8:0.2, (c) 0.6:0.4, (d) 0.4:0.6, (e) 0.2:0.8, and (f) YFeO3.
Figure 4. High-resolution XPS spectra of O 1s in SmFeO3/YFeO3 nanomaterials: (a) SmFeO3, (b) 0.8:0.2, (c) 0.6:0.4, (d) 0.4:0.6, (e) 0.2:0.8, and (f) YFeO3.
Chemosensors 11 00187 g004
Chemosensors 11 00187 g005 550
Figure 5. Change trend of the adsorbed oxygen content of SmFeO3/YFeO3 (e:f) nanomaterials.
Figure 5. Change trend of the adsorbed oxygen content of SmFeO3/YFeO3 (e:f) nanomaterials.
Chemosensors 11 00187 g005
Chemosensors 11 00187 g006 550
Figure 6. Response curves of the SmFeO3/YFeO3 (e:f) sensor to VOC gases in the dark with temperature: (a) ethanol, (b) acetone, (c) methanol, and (d) formaldehyde.
Figure 6. Response curves of the SmFeO3/YFeO3 (e:f) sensor to VOC gases in the dark with temperature: (a) ethanol, (b) acetone, (c) methanol, and (d) formaldehyde.
Chemosensors 11 00187 g006
Chemosensors 11 00187 g007 550
Figure 7. Response curves of the SmFeO3/YFeO3 (0.4:0.6) sensor to VOC gases under multi-wavelength light illumination with temperature: (a) ethanol, (b) acetone, (c) methanol, and (d) formaldehyde.
Figure 7. Response curves of the SmFeO3/YFeO3 (0.4:0.6) sensor to VOC gases under multi-wavelength light illumination with temperature: (a) ethanol, (b) acetone, (c) methanol, and (d) formaldehyde.
Chemosensors 11 00187 g007
Chemosensors 11 00187 g008 550
Figure 8. Repeatability test of sensitivity of the SmFeO3/YFeO3 (0.4:0.6) sensor to VOC gases in 5 cycles under 370 nm of light illumination.
Figure 8. Repeatability test of sensitivity of the SmFeO3/YFeO3 (0.4:0.6) sensor to VOC gases in 5 cycles under 370 nm of light illumination.
Chemosensors 11 00187 g008
Chemosensors 11 00187 g009 550
Figure 9. Response/recovery time of the SmFeO3/YFeO3 (0.4:0.6) sensor to VOC gases under 370 nm of light illumination: (a) ethanol, (b) acetone, (c) methanol, and (d) formaldehyde.
Figure 9. Response/recovery time of the SmFeO3/YFeO3 (0.4:0.6) sensor to VOC gases under 370 nm of light illumination: (a) ethanol, (b) acetone, (c) methanol, and (d) formaldehyde.
Chemosensors 11 00187 g009
Chemosensors 11 00187 g010 550
Figure 10. The dynamic-response curve of the SmFeO3/YFeO3 (0.4:0.6) sensor to (a) ethanol, (b) acetone, and (c) methanol gases with different gas concentrations; (d) change curves of the SmFeO3/YFeO3 (0.4:0.6) sensor’s response with concentration at 120 °C; (e) the linear-fit curves of the gas responses for SmFeO3/YFeO3 (0.4:0.6) sensor.
Figure 10. The dynamic-response curve of the SmFeO3/YFeO3 (0.4:0.6) sensor to (a) ethanol, (b) acetone, and (c) methanol gases with different gas concentrations; (d) change curves of the SmFeO3/YFeO3 (0.4:0.6) sensor’s response with concentration at 120 °C; (e) the linear-fit curves of the gas responses for SmFeO3/YFeO3 (0.4:0.6) sensor.
Chemosensors 11 00187 g010
Chemosensors 11 00187 g011 550
Figure 11. (a) Dynamic-response curve under different humidity levels of the SmFeO3/YFeO3 (0.4:0.6) sensor for ethanol gas; (b) variation curves with humidity of the SmFeO3/YFeO3 (0.4:0.6) sensor for VOC gases under 370 nm of light illumination.
Figure 11. (a) Dynamic-response curve under different humidity levels of the SmFeO3/YFeO3 (0.4:0.6) sensor for ethanol gas; (b) variation curves with humidity of the SmFeO3/YFeO3 (0.4:0.6) sensor for VOC gases under 370 nm of light illumination.
Chemosensors 11 00187 g011
Chemosensors 11 00187 g012 550
Figure 12. Dynamic-response curves under different optical powers of the SmFeO3/YFeO3 (0.4:0.6) sensor for VOC gases under multi-wavelength light illumination: (a) ethanol, (b) acetone, (c) methanol, and (d) formaldehyde.
Figure 12. Dynamic-response curves under different optical powers of the SmFeO3/YFeO3 (0.4:0.6) sensor for VOC gases under multi-wavelength light illumination: (a) ethanol, (b) acetone, (c) methanol, and (d) formaldehyde.
Chemosensors 11 00187 g012
Chemosensors 11 00187 g013 550
Figure 13. (a) Response histogram of the SmFeO3/YFeO3 (0.4:0.6) sensor for VOC gases at 120 °C; (b) stability curves of the SmFeO3/YFeO3 (0.4:0.6) sensor for VOC gases at 120 °C within 35 days.
Figure 13. (a) Response histogram of the SmFeO3/YFeO3 (0.4:0.6) sensor for VOC gases at 120 °C; (b) stability curves of the SmFeO3/YFeO3 (0.4:0.6) sensor for VOC gases at 120 °C within 35 days.
Chemosensors 11 00187 g013
Chemosensors 11 00187 g014 550
Figure 14. (a) The UV–visible absorption spectrum of SmFeO3/YFeO3 (e:f) powder samples; (b) the (ahv)2–(hv) curves of SmFeO3 and YFeO3 powder samples.
Figure 14. (a) The UV–visible absorption spectrum of SmFeO3/YFeO3 (e:f) powder samples; (b) the (ahv)2–(hv) curves of SmFeO3 and YFeO3 powder samples.
Chemosensors 11 00187 g014
Chemosensors 11 00187 g015 550
Figure 15. Schematic diagram of the energy band of the SmFeO3/YFeO3 composite material (a) in air and (b) VOC gases.
Figure 15. Schematic diagram of the energy band of the SmFeO3/YFeO3 composite material (a) in air and (b) VOC gases.
Chemosensors 11 00187 g015
Table
Table 1. Comparison of gas-sensing performance between SmFeO3/YFeO3 (0.4:0.6) sensor and other perovskite sensors.
Table 1. Comparison of gas-sensing performance between SmFeO3/YFeO3 (0.4:0.6) sensor and other perovskite sensors.
MaterialsGasTem. (°C)Con. (ppm)Res.Refs.
NdFeO3ethanol250100150[16]
La0.98Ba0.02FeO3ethanol20010079.3[51]
Au-LaFeO3ethanol20010044[52]
SmFeO3acetone21015.92[29]
Pd-SmFeO3acetone220110.73[32]
SmFeO3/ZnOacetone3501045[38]
YFeO3acetone11030128.1[40]
DyFeO3acetone19023.81[53]
PrFeO3acetone180106[54]
Sm-PrFeO3acetone2705044.94[55]
Co-Fe2O3/SmFeO3methanol155519.7[37]
SmFeO3methanol1203026.41[39]
SmFeO3/YFeO3ethanol12030163.593this work
SmFeO3/YFeO3acetone12030134.023this work
SmFeO3/YFeO3methanol12030111.637this work
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Liu, H.; Zhu, D.; Miao, T.; Liu, W.; Chen, J.; Cheng, B.; Qin, H.; Hu, J. Highly Sensitive p-SmFeO3/p-YFeO3 Planar-Electrode Sensor for Detection of Volatile Organic Compounds. Chemosensors 2023, 11, 187. https://doi.org/10.3390/chemosensors11030187

AMA Style

Liu H, Zhu D, Miao T, Liu W, Chen J, Cheng B, Qin H, Hu J. Highly Sensitive p-SmFeO3/p-YFeO3 Planar-Electrode Sensor for Detection of Volatile Organic Compounds. Chemosensors. 2023; 11(3):187. https://doi.org/10.3390/chemosensors11030187

Chicago/Turabian Style

Liu, Huiyang, Denghui Zhu, Tingting Miao, Weikang Liu, Juan Chen, Bin Cheng, Hongwei Qin, and Jifan Hu. 2023. "Highly Sensitive p-SmFeO3/p-YFeO3 Planar-Electrode Sensor for Detection of Volatile Organic Compounds" Chemosensors 11, no. 3: 187. https://doi.org/10.3390/chemosensors11030187

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