Enhanced Triethylamine-Sensing Characteristics of SnS₂/LaFeO₃ Composite

Abstract

Triethylamine (TEA), a volatile organic compound (VOC), has important applications in industrial production. However, TEA has an irritating odor and potential toxicity, making it necessary to develop sensitive TEA gas sensors with high efficiency. This study focused on preparing LaFeO₃ nanoparticles modified by SnS₂ nanosheets (SnS₂/LaFeO₃ composite) using a hydrothermal method together with sol–gel technique. According to the comparison results of the gas-sensing performance between pure LaFeO₃ and SnS₂/LaFeO₃ composite with varying composition ratios, 5% SnS₂/LaFeO₃ sensor had a sensitivity for TEA that was 3.2 times higher than pure LaFeO₃ sensor. The optimized sensor operates at 140 °C and demonstrates strong stability, selectivity, and long-term durability. Detailed analyses revealed that the SnS₂ nanosheets enhanced oxygen vacancy (O_V) content and carrier mobility through heterojunction formation with LaFeO₃. This study provides insights into improving gas-sensing performance via p-n heterostructure design and proposes a novel LaFeO₃-based material for TEA detection.

1. Introduction

The release and leakage of volatile organic compounds (VOCs) have severely affected human survival and safety over the last couple of decades [1,2,3]. Triethylamine (TEA) is a hazardous VOC primarily serving as a preservative, catalyst, and solvent in the chemical industry [4,5]. As a toxic gas, it is colorless, is transparent, and has an irritating odor. Being exposed to a TEA environment for a long term possibly induces many health issues of headaches, nausea, and skin and respiratory irritation, and in severe cases, death [6,7]. In food safety, TEA is the primary characteristic malodorous gas produced during the spoilage of aquatic products, such as fish. Its concentration directly correlates with fish freshness, making it a critical biomarker for assessing aquatic product quality and enabling food safety monitoring [8,9]. The Occupational Safety and Health Administration has confirmed an allowable exposure concentration for triethanolamine in air not to exceed 10 ppm [10,11]. Although conventional gas detection techniques are effective in accurately identifying toxic gases, they have several limitations. Therefore, efforts need to be made to develop a gas sensor with a relatively simple operation and good performance for industrial and daily life applications.

Metal oxide semiconductor (MOS)-based nanostructured materials have emerged as innovative solutions to overcome these challenges, finding extensive applications across multiple technological domains with notable implementation in catalytic processes and chemical detection systems [12,13,14]. MOS gas sensors are characterized by simple operation and low synthesis cost, and they are capable of detecting low concentrations of toxic gases [15,16]. Perovskite-type ABO₃ compounds, characterized by their ternary oxide configuration comprising A- and B-site metal cations with distinct ionic radii, exhibit structurally robust crystalline frameworks that demonstrate considerable potential in gas sensor applications [17,18,19,20]. Recent advancements in LaFeO₃-based sensing materials have demonstrated varied performance characteristics under different synthetic conditions [21]. Wang et al. fabricated hollow LaFeO₃ microspheres with a yolk-shell structure that exhibited a gas response value of 25.5 to 100 ppm ethanol at 225 °C [22]. Li et al. fabricated Au-LaFeO₃ nanocomposites with a simple wet-chemical method. The optimally proportioned Au-LaFeO₃ sensor had a response value of 44 to 100 ppm ethanol at 200 °C, representing a 27-fold enhancement compared to the pristine LaFeO₃ sensor, with a recovery time reduced to 8 s [23]. Xiao et al. successfully synthesized uniform porous LaFeO₃ microspheres via a hydrothermal method. According to gas-sensing tests, the porous LaFeO₃ microspheres had a response value of 29 to 100 ppm acetone at 260 °C [24].

Two-dimensional SnS₂ with a nanosheet morphology exhibits a narrow band gap, excellent adsorption kinetics, and low gas adsorption energy, making it well applied in the gas-sensing field [25]. The SnS₂ sensor developed by Yan et al. demonstrates a sensitivity of 13,000% toward 9 ppm NO₂, a strong selectivity, and a low detection limit for NO₂ [26]. Dong et al. adopted a hydrothermal treatment process for synthesizing α-MoO₃@SnS₂ nanosheets, which exhibited a response value of 114.9 to 100 ppm TEA at 175 °C. The foam-like structure, with its excellent permeability, facilitates enhanced gas-sensing performance [27]. Xu et al. applied a hydrothermal method for synthesizing SnS₂/ZnS flower-like microspheres presenting a high specific surface area (SSA), achieving a response of ~11 toward 50 ppm TEA at 180 °C [28].

By reasonably building p-n heterojunctions in MOS nanomaterials to modulate the electron and hole concentration, gas-sensing performance can be effectively enhanced [29]. Shuai et al. successfully synthesized NiO/BiVO₄ p-n heterojunction microspheres via hydrothermal treatment. The 10% NiO-BiVO₄ sensor presented a gas response of 183.11 to 30 ppm TEA versus the pure BiVO₄ sensor [30]. Wu et al. synthesized In₂O₃-decorated Mn₂O₃ nanorod-based multidimensional nanostructures via a hydrothermal method, which exhibited an enhanced SSA. The In₂O₃/Mn₂O₃ composite with an In:Mn ratio of 1:0.12 demonstrated a response value of 44.3 toward 100 ppm TEA at 180 °C [31].

The study successfully synthesized SnS₂/LaFeO₃ composite by combining the hydrothermal method with high-temperature annealing treatment. In the SnS₂/LaFeO₃ composite material, the combination of p-type LaFeO₃ and n-type SnS₂ forms a p-n heterojunction. This creates a built-in electric field at the interface, enabling more efficient carrier separation and transport. The introduction of SnS₂ increases the specific surface area of the composite material, providing more reactive sites for the target gas and thereby enhancing gas-sensing performance. The 5% SnS₂/LaFeO₃ sensor demonstrates a response of 124.5 to 100 ppm TEA, along with excellent selectivity and long-term stability. Compared to similar sensors, the performance of our sensor significantly outperforms comparable counterparts. For example, Hao et al. fabricated a RuO₂/LaFeO₃ gas sensor exhibiting a response value of 60.4 towards 100 ppm TEA at 260 °C [32]. Ma et al. fabricated a WO₃-SnWO₄ nanorod-based gas sensor showing a response value of 80.2 towards 100 ppm TEA at 130 °C [33]. Zhao et al. fabricated a gas sensor based on WO₃-modified ErVO₄ nanoparticles. At its optimal operating temperature of 200 °C, the ErVO₄/WO₃ composite exhibited a response of 15.79 towards 100 ppm TEA [34]. The LaFeO₃/ZnO composite prepared by Ni et al. exhibited a response value of 50 to 100 ppm TEA at 200 °C [35].

2. Experiment

2.1. Preparation of LaFeO₃ Nanoparticles and SnS₂ Nanosheets

The preparation of LaFeO₃ nanoparticles was achieved by using the citric acid sol–gel method [36] by first dissolving Fe(NO₃)₃·9H₂O and La(NO₃)₃·6H₂O in 50 mL of deionized water (DW) to form an orange solution A and then dissolving citric acid (210.0 mg, 1 mmol) in 30 mL of DW to obtain a colorless transparent solution B. The two solutions were mixed under magnetic agitation, followed by 5 h of continuous stirring at 80 °C until obtaining a reddish-brown gel. After 12 h of drying treatment, the gel underwent 2 h of calcination at 350 °C and 4 h of calcination at 700 °C in succession to synthesize the LaFeO₃.

A one-step hydrothermal method was applied for synthesizing SnS₂ nanosheets [37]. Firstly, a colorless transparent solution was obtained by completely dissolving SnCl₄·5H₂O (17.5 mg, 0.05 mmol) and thiourea (22.8 mg, 0.3 mmol) in 50 mL of DW. The hydrothermal reaction proceeded for 12 h at 180 °C, followed by the collection of the generated yellow product.

2.2. Synthesis of SnS₂/LaFeO₃ Composite

LaFeO₃ powder (100 mg) was dissolved in a 40 mL ethylene glycol (EG) solution using 30 min of ultrasonication. SnS₂ powder with varying masses ultrasonically dispersed in 20 mL of EG solution was added dropwise into the LaFeO₃ solution before half an hour of stirring. The mixture underwent 12 h of hydrothermal heating at 160 °C to obtain a powder sample. The powder sample was sequentially rinsed using DW and ethanol and dried again. The SnS₂/LaFeO₃ composite with different contents (5 wt%, 10 wt%, and 20 wt%) could be made. The resulting materials were designated as 5% SnS₂/LaFeO₃, 10% SnS₂/LaFeO₃, and 20% SnS₂/LaFeO₃, respectively.

2.3. Control Experiment: In Situ Synthesis of SnS₂/LaFeO₃ Composite

LaFeO₃ powder (100 mg) was dissolved in a 40 mL ethylene glycol (EG) solution using 30 min of ultrasonication. Afterwards, specific quantities of SnCl₄·5H₂O (0.025, 0.05, and 0.075 mmol) and thiourea (0.15, 0.3, and 0.45 mmol) were completely dissolved in 20 mL of ethylene glycol and then added dropwise to the LaFeO₃ solution under magnetic stirring. The mixture underwent 12 h of hydrothermal heating at 160 °C to obtain a powder sample. The powder sample was sequentially rinsed using DW and ethanol and dried again. The obtained SnS₂/LaFeO₃ composite with different molar ratios are designated as SnS₂/LaFeO₃-1, SnS₂/LaFeO₃-2, and SnS₂/LaFeO₃-3.

2.4. Characterizations of Gas-Sensitive Materials

X-ray diffraction (XRD) was employed to analyze the composition, crystal type, and grain size of the samples. The model of the diffractometer used in this study was a SHIMADZU XRD-7000S (SHIMADZU, Kyoto, Japan). The scanning 2θ angle range during testing was 5–80°, with a scanning speed of 5°/min. Field-emission scanning electron microscopy (SEM) was used to observe the microscopic morphology of the synthetic material precursors and target samples. The model of the SEM used in this study was an FEI Nova NanoSEM450 (FEI, Hillsboro, OR, USA). Prior to testing, high-purity ethanol, clean silicon wafers, conductive adhesive, and other materials were prepared, and the accelerating voltage was set to 18 kV. To test the specific surface area, pore volume, and pore size distribution of the samples, a fully automated physical adsorption instrument produced by Beijing JWGB Technology Co., Ltd. (Beijing, China), model BK100C, was used to analyze the experimental materials. Before testing, cleaned BET tubes and a certain amount of liquid nitrogen were prepared. To determine the chemical composition, elemental valence states, and their percentages on the surface of the target samples, X-ray photoelectron spectroscopy (XPS) was performed using an X-ray photoelectron spectrometer manufactured and designed by Thermo Fisher Scientific (Waltham, MA, USA), model ESCALABTM 250Xi.

2.5. Fabrication of the Gas Sensors

Gas sensors were constructed and measured following a previous description [38]. Initially, a specific amount of pure LaFeO₃, pure SnS₂, and SnS₂/LaFeO₃ composite was dispersed in DW. This suspension was then used to prepare a slurry with the appropriate viscosity for coating onto the ceramic tube for fabricating the sensors (Figure 1). A CGS-8 intelligent gas-sensitive analysis system (Beijing Elite Technology, Beijing, China) was employed for testing the sensor’s sensitivity (R_a/R_g or R_g/R_a). R_a and R_g denote the resistance values of the sensor in air and the target gas, respectively. The response and recovery time denote the duration necessary for the sensor to achieve 90% of the total resistance variation in the target gas and air.

3. Results and Discussion

3.1. Structural and Morphological Characteristics

Figure 2 presents the microscopic morphology and elemental distribution of pure SnS₂, pure LaFeO₃, and the 5% SnS₂/LaFeO₃ composite. As shown in Figure 2a, LaFeO₃ primarily consists of aggregated nanoparticle structures, while SnS₂ in Figure 2b exhibits a well-defined hexagonal morphology. Figure 2c,d reveal that SnS₂ nanosheets in the 5% SnS₂/LaFeO₃ composite are randomly and densely anchored onto the LaFeO₃ nanoparticle framework, with no significant alterations in their original dimensions or morphology after composite formation. Elemental mapping images (Figure 2e–j) demonstrate a homogeneous spatial distribution of Sn, S, La, Fe, and O components, further confirming the successful synthesis of the SnS₂/LaFeO₃ composite.

According to Figure 3, the SnS₂/LaFeO₃ composite with varying content ratios has diffraction peaks corresponding to the pure LaFeO₃ crystal phase (JCPDS Card No. 75-0541) [39]. With rising SnS₂ content, the intensities of the diffraction peaks at 15.02° and 41.87° in the SnS₂/LaFeO₃ composite gradually become more pronounced, matching those of pure SnS₂ crystals (JCPDS Card No. 83-1705) [40]. The SnS₂/LaFeO₃ composite is successfully synthesized, as evidenced by the impurity peaks not being detected in the patterns.

The results from Figure 4 and

Table 1. Samples’ textural parameters from BET analysis.

Sample	Surface Area (m2 g−1)	Pore Volume (cm3 g−1)	Average Pore Size (nm)
LaFeO3	10.165	0.075	29.434
5% SnS2/LaFeO3	12.433	0.086	27.582
10% SnS2/LaFeO3	12.768	0.078	24.544
20% SnS2/LaFeO3	11.295	0.077	25.339

show that specific surface areas (SSAs) of LaFeO₃ and 5% SnS₂/LaFeO₃ are 10.165 m²/g and 12.433 m²/g, respectively. Incorporating SnS₂ elevates the material’s SSA. A larger SSA offers more reactive sites, contributing to improved gas-sensing performance. Although the sample of 10% SnS₂/LaFeO₃ has the largest SSA, there are still other key factors that affect the gas-sensing performance, such as the sensors’ baseline resistances in air, which is discussed later.

The XPS analysis results revealed the chemical states of various elements in pure SnS₂, pure LaFeO₃, and SnS₂/LaFeO₃ composite with different ratios. As shown in Figure 5a, the doublet peaks at 487.2 and 495.7 eV are assigned to the Sn⁴⁺ 3d_5/2 and Sn⁴⁺ 3d_3/2 orbitals of SnS₂ [41]. Compared with pure SnS₂, the Sn⁴⁺ 3d_5/2 and Sn⁴⁺ 3d_3/2 peaks in the SnS₂/LaFeO₃ composite exhibited a 0.9 eV shift to lower binding energies. Similarly, the doublet peaks at 162.2 and 163.4 eV in Figure 5b are assigned to the S²⁻ 2p_3/2 and S²⁻ 2p_1/2 orbitals of SnS_2, respectively [41]. These S²⁻ 2p peaks in the SnS₂/LaFeO₃ composite also showed a 0.9 eV negative shift relative to those in pure SnS₂. The observed binding energy shifts of the elements demonstrate a strong electronic interaction between SnS₂ and LaFeO₃, ultimately promoting SnS₂/LaFeO₃ heterojunctions to be formed.

In Figure 5c, the peaks located at 833.7, 838.2, 850.6, and 855.0 eV are assigned to the La³⁺ 3d_5/2 and La³⁺ 3d_3/2 orbitals in pure LaFeO₃, accompanied by three satellite peaks. Compared to pure LaFeO₃, the La 3d peaks in the SnS₂/LaFeO₃ composite exhibit a shift toward higher binding energy by approximately 0.1–0.2 eV [42]. In Figure 5d, the peaks at 710.0 and 723.7 eV target the Fe³⁺ 2p_3/2 and 2p_1/2 orbitals, while those at 712.2 and 725.5 eV target the Fe⁴⁺ 2p_3/2 and 2p_1/2 orbitals [43,44]. Binding energy presents a slight shift resulting from the heterostructure effect at the interface of the SnS₂/LaFeO₃ composite.

In Figure 6, the O 1s binding energy peak is deconvoluted into three peaks located at 529.3, 531.25, and 532.8 eV, targeting lattice oxygen (O_L), oxygen vacancies (O_V), and chemisorbed oxygen (O_C), respectively [45,46], with relevant peak area ratios displayed in

Table 2. XPS O1s peak area ratios of varying oxygen species.

Sample	OL (%)	OV (%)	OC (%)
LaFeO3	66.17	26.67	7.16
5% SnS2/LaFeO3	65.17	31.33	3.50
10% SnS2/LaFeO3	65.32	28.84	5.84
20% SnS2/LaFeO3	65.75	27.74	6.51

. The 5% SnS₂/LaFeO₃ composite exhibit a higher O_V content than pure LaFeO₃. Oxygen vacancies (O_V) are active sites for surface oxygen adsorption, capable of accelerating surface redox reactions [47]. Generally, a higher O_V content more remarkably strengthens gas-sensing performance.

According to the analyses from XRD, SEM, EDS, and XPS, the synthesis of the SnS₂/LaFeO₃ composite was successfully accomplished.

3.2. Gas-Sensing Properties of the Nanomaterials

The optimal operating temperature is a critical indicator in gas sensor testing. According to Figure 7a,b, these sensors exhibit two distinct optimal operating temperatures and demonstrate significantly divergent response behaviors to TEA gas. The pure SnS₂-based sensor achieves optimal performance at 80 °C, with a response value of 14.2 to 100 ppm TEA. Comparatively, LaFeO₃-based sensors reach their optimal working temperature at 140 °C. Notably, the 5% SnS₂/LaFeO₃ sensor delivers a response value of 124.5 to 100 ppm TEA, representing an approximately three-fold enhancement compared to the pure LaFeO₃ sensor. According to Figure 7c,d, as temperature increases, the semiconductor’s thermal excitation effect dominates, inducing a monotonic decline in baseline resistance with rising temperature. With the increased addition of SnS₂, the baseline resistance of the SnS₂/LaFeO₃ composite starts to increase. Meanwhile, the difference in R_g/R_a gradually decreases, thus reducing the sensitivity.

Figure 8a–c shows the gas sensors’ time-varying response–recovery curves to 100 ppm TEA concentration. In terms of response time, the 5% SnS₂/LaFeO₃ sensor does not show a significant response advantage, and with regard to the recovery time, the pure LaFeO₃ and pure SnS₂ sensor have a recovery time of 165 and 175 s, respectively, while the 5% SnS₂/LaFeO₃ sensor has a recovery time elevated to 64 s, which is significantly faster than that of the two single material sensors. Figure 8b illustrates the resistance response variation curves of different sensors to 100 ppm TEA at the optimal working temperature.

Selectivity is also a fundamental criterion for gas sensors. The sensors were used to test the selectivity at 140 °C to 100 ppm of acetone, ethanol, n-propanol, isopropanol, methanol, xylene, acetic acid, hexane, formaldehyde, ammonia, and other gases (Figure 9a). Compared to other tested gases (such as acetone with a C=O bond energy of 728 kJ/mol and methanol with an O-H bond energy of 458.8 kJ/mol), the 5% SnS₂/LaFeO₃ sensor exhibits significantly enhanced response characteristics toward TEA. This superiority primarily stems from the lower bond energy (305 kJ/mol) of the C-N bond in TEA molecules. The disparity in bond energy facilitates easier surface interfacial reactions between TEA and the gas-sensitive material, thereby enhancing the gas selectivity.

These sensors present excellent stability and reproducibility (Figure 9b). Notably, the 5% SnS₂/LaFeO₃ gas sensor exhibits more prominent response and recovery characteristics at 1 ppm TEA, achieving a response value of 10.2 (Figure 9c). This result indicates that the 5% SnS₂/LaFeO₃ gas sensor possesses a lower detection limit. In addition, in Figure 8d, a linear fitting was conducted for all sensors in 1–100 ppm. The 5% SnS₂/LaFeO₃ sensor exhibited the fitting equation of $\mathrm{y}=10.838+10109\mathrm{x}$ (R² = 0.998), demonstrating a strong linear relationship.

Relative humidity (RH) also critically affects the sensor performance. Figure 10a illustrates the humidity resistance tests of four gas sensors toward 100 ppm TEA. With the RH rising from 20% to 80%, the 5% SnS₂/LaFeO₃ sensor has a response declining from 123.4 to 9.6. This decline arises due to water molecules in the air competing with the target gas for active sites on the material surface, impeding the formation of adsorbed oxygen species. Consequently, the baseline resistance increases, leading to reduced gas-sensing performance [48]. Figure 10b shows a continuous 30-day gas sensitivity test of the 5% SnS₂/LaFeO₃ gas sensor, which maintains a stable response value to 100 ppm TEA at 140 °C, providing excellent long-term stability. Additionally, anti-interference tests were conducted using mixed gases containing 50 ppm TEA and 50 ppm interfering gases (formaldehyde, acetic acid, methanol, ammonia, and hexane), as shown in Figure 10c. The 5% SnS₂/LaFeO₃ sensor displays minimal response variations to the mixed gases, confirming its superior anti-interference capability.

To demonstrate that the hydrothermal method of combining SnS₂ and LaFeO₃ materials is simple and that the synthesized SnS₂/LaFeO₃ composites have excellent properties, we conducted a control experiment of the in situ synthetic method. Figure 11a presents a control experiment on the sensing properties of in situ-grown SnS₂ on LaFeO₃. The SnS₂/LaFeO₃-2 composite shows a response of 26.2 to 100 ppm TEA at 140 °C and 40% RH. Compared to pure LaFeO₃, there is no significant improvement in gas-sensing performance. Figure 11b shows the resistance variation curves of the three sensors. As the SnS₂ loading content increases, the baseline resistance demonstrates an upward trend (Figure 11c).

Figure 12a presents the selectivity tests of the three sensors based on the in situ synthesized samples toward eight different gases. The SnS₂/LaFeO₃-2 sensor exhibits relatively high responses to gases such as acetone, n-propanol, and iso-propanol, but shows no significant selective advantage for the target analyte. Figure 12b displays the cyclic stability test results, where the response values remain essentially unchanged over multiple cycles. Notably, the sensing performance improved during testing due to a decrease in ambient humidity to approximately 35% RH. Figure 12c,d show the concentration-dependent response curves of the three sensors to TEA from 1 ppm to 100 ppm. The SnS₂/LaFeO₃-2 composite demonstrates superior gas response values, with its concentration–response relationship following the linear fitting equation (y = 4.254 + 0.214x, R² = 0.962).

3.3. Gas-Sensing Mechanism

During the high-temperature annealing treatment of the LaFeO₃ sol–gel precursor in air, cation vacancies (La and Fe) generated under high-temperature conditions induce hole formation, triggering a p-type LaFeO₃ semiconductor. The equations below interpret the corresponding defect reaction [49,50]:

$$V_{La} \to V_{La}^{‴}+3h^{\dot{}}$$

(1)

$$V_{Fe} \to V_{Fe}^{‴}+3h^{\dot{}}$$

(2)

It is allowed to explain the sensing mechanism by examining the reversible conductivity variation of the sensing layer attributed to the process through which the sensing material interacts with adsorbed gas molecules [51]. The equations below interpret the overall steps:

$$O_{2\left(gas\right)}\to O_{2\left(ads\right)}$$

(3)

$$O_{2\left(ads\right)}+e^{-}\to O_{2\left(ads\right)}^{-}\left(T<100 °\mathrm{C}\right)$$

(4)

$$O_{2\left(ads\right)}^{-}+e^{-}\to 2O_{\left(ads\right)}^{-}\left(100 °\mathrm{C}<T<300 °\mathrm{C}\right)$$

(5)

$${\left(C_2{H}_5\right)}_3{N}_{\left(gas\right)}+39O_{\left(ads\right)}^{-}\leftrightarrow N_{2\left(gas\right)}+12{CO}_{2\left(gas\right)}+15H_2{O}_{\left(gas\right)}+39e^{-}$$

(6)

Upon the exposure of the LaFeO₃ to atmospheric air, oxygen molecules (O₂) adsorbed onto the surface are converted to $O_{2\left(ads\right)}^{-}$ and $O_{\left(ads\right)}^{-}$ through capturing electrons from the conduction band, forming a hole accumulation layer (HAL) on the LaFeO₃ surface and reducing the electronic resistance of LaFeO₃. Upon the exposure to TEA gas, the reaction between the TEA molecules and the adsorbed oxygen species present on the LaFeO₃ surface promoted the release of electrons back into the materials, increasing the resistance.

As shown in Figure 13, LaFeO₃ is a p-type semiconductor [52], and SnS₂ is an n-type semiconductor [53]. Affected by their different work functions, the electrons of LaFeO₃ can flow to SnS₂ and the holes of SnS₂ flow to LaFeO₃ until the Fermi level achieves equilibrium [54,55]. This charge transfer can be verified by XPS characterization (Figure 5).

This further increases the hole concentration in LaFeO₃ and thickens the HAL in an air atmosphere, thereby reducing the electronic resistance R_a and providing the potential for a lager change between R_a and R_g. As shown in Figure 7b, a small amount (5%) of SnS₂-composition significantly reduces the resistance value of R_a. Moreover, the p-n heterojunction improves the charge transport during the reaction process on the surface, enhancing the sensing response. The 5% SnS₂/LaFeO₃ composite exhibits the highest content of O_V and O_C. This promotes the participation of more target gas molecules in surface redox reactions. Furthermore, BET surface area measurements indicate that the introduction of SnS₂ effectively increases the specific surface area of the material. This provides more active sites and accelerates the redox reaction process, thus enhancing the gas-sensing performance.

4. Conclusions

In conclusion, the SnS₂/LaFeO₃ composites were successfully synthesized by a high-temperature annealing treatment and hydrothermal method. The 5% SnS₂/LaFeO₃ sensor demonstrates a response of 124.5 to 100 ppm TEA at 140 °C, 3.2 times higher than the pure LaFeO₃ sensor. Furthermore, for the SnS₂/LaFeO₃ sensor, the sensor response exhibits a linear relevance to the gas concentration, anti-interference capability, and long-term stability. Furthermore, the formed heterojunction elevates the O_V content and expands the HAL on the surface, thereby improving the TEA-sensing property. The findings in the study will assist researchers in designing and synthesizing MOS gas sensors for TEA detection.