Construction of 2D TiO₂@MoS₂ Heterojunction Nanosheets for Efficient Toluene Gas Detection

Abstract

Monitoring trace toluene exposure is critical for early-stage lung cancer screening via breath analysis, yet conventional chemiresistive sensors face fundamental limitations, including compromised selectivity in complex VOC matrices and humidity-induced signal drift, with prevailing p–n heterojunction architectures suffering from inherent charge recombination and environmental instability. Herein, we pioneer a 2D core–shell n–n heterojunction strategy through rational design of TiO₂@MoS₂ heterostructures, where vertically aligned MoS₂ nanosheets are epitaxially grown on 2D TiO₂ derived from graphene-templated synthesis, creating built-in electric fields at the heterojunction interface that dramatically enhance charge carrier separation efficiency. At 240 °C, the TiO₂@MoS₂ sensor exhibits a superior response (R_a/R_g = 9.8 to 10 ppm toluene), outperforming MoS₂ (R_a/R_g = 2.8). Additionally, the sensor demonstrates rapid response/recovery kinetics (9 s/16 s), a low detection limit (50 ppb), and excellent selectivity against interfering gases and moisture. The enhanced performance is attributed to unidirectional electron transfer (TiO₂ → MoS₂) without hole recombination losses, methyl-specific adsorption through TiO₂ oxygen vacancy alignment, and steric exclusion of non-target VOCs via size-selective MoS₂ interlayers. This work establishes a transformative paradigm in gas sensor design by leveraging n–n heterojunction physics and 2D core–shell synergy, overcoming long-standing limitations of conventional architectures.

1. Introduction

Toluene is a common volatile organic compound (VOC) that can damage the central nervous system, causing headaches, dizziness, and liver and kidney toxicity with long-term exposure. High-concentration inhalation can lead to acute poisoning. Toluene also serves as a potential biomarker for diagnosing diseases like lung cancer and diabetes [1]. Traditional detection methods, such as gas chromatography–mass spectrometry (GC-MS), are accurate, but require expensive equipment and laboratory settings, preventing real-time monitoring. Electrochemical sensors face cross-interference issues, and photoionization detectors (PIDs) are costly to maintain. Therefore, developing high-sensitivity, low-cost, portable semiconductor toluene gas sensors through material innovation and intelligent design is crucial [2,3,4]. Such sensors could enable home health monitoring, industrial safety warnings, and early disease screening, promoting advancements in precision medicine and environmental governance [5].

Two-dimensional transition metal dichalcogenides (TMDs) have emerged as promising candidates for next-generation gas sensors, due to their atomic-scale thickness, tunable electronic properties, and high surface-to-volume ratios [6]. Molybdenum disulfide (MoS₂), a graphene-like layered TMD, has garnered significant attention. In its thermodynamically stable 2H phase, the crystal structure consists of S-Mo-S trilayers stacked via van der Waals interactions, with each Mo atom in trigonal prismatic coordination [7,8,9]. The hydrothermal synthesis of MoS₂ enables precise control over layer number (typically one to five layers) and defect density, yielding nanostructures with specific surface areas and direct bandgaps suitable for charge transfer-based gas sensors [10,11]. Notably, 2D MoS₂ nanosheets exhibit superior gas adsorption kinetics compared to their 0D quantum dot or 1D nanobelt due to their exposed basal planes (90% surface accessibility) and abundant edge sulfur vacancies, which serve as preferential adsorption sites [12]. Additionally, in the case of ultrathin MoS₂ layers, the sulfide terminations at MoS₂ edges can achieve maximal exposure. Thus, constructing heterostructures to vertically grow such thin 2D MoS₂ represents a viable strategy [13].

Heterojunction engineering effectively enhances sensing performance by lowering operating temperatures and improving sensitivity, selectivity, and humidity resistance in nanomaterials [14,15]. Due to the band structure mismatch between two sensing materials, energy bands bend to form electron- depletion layers (EDLs) or hole accumulation layers (HALs) when the Fermi levels equilibrate [16,17]. Furthermore, a hierarchical composite structure can provide additional active adsorption sites for target gases and exhibit superior catalytic activity compared to single metal oxides. Thus, heterostructures are critical for optimizing the gas-sensing properties of metal oxides [18,19]. Hermawan et al. [20] reported a p–n CuO@SnO₂ heterojunction that achieved a remarkable toluene response (R_a/R_g = 540 at 75 ppm) with exceptional selectivity. The enhanced performance was attributed to the synergistic effects of the p–n heterojunction, high surface area, and porous architecture. Notably, in situ formation of metallic Cu under high toluene concentrations disrupted the p–n junction and established Ohmic contact with the n-type SnO₂, further amplifying the sensing response. Liu et al. [21] fabricated a porous Co₃O₄–Fe₃O₄ composite with p–n heterojunctions by functionalizing Fe₃O₄ with ZIF-67-derived Co₃O₄. The Co₃O₄ derived from ZIF-67 exhibited a higher specific surface area than Fe₃O₄, leading to a 20-fold improvement in toluene response at 225 °C. Additionally, the sensor demonstrated a low detection limit (0.1 ppm, response = 1.68), excellent selectivity, and long-term stability. This enhancement primarily stemmed from the p–n heterojunction, increased surface area, and optimized oxygen vacancy (O_V) concentration. Therefore, heterojunction construction provides a viable pathway for developing highly sensitive and practical gas sensors based on nanostructured metal oxides. The integration of vertically aligned ultrathin MoS₂ nanosheets with a wide-bandgap metal oxide semiconductor (MOS) core constructs a 2D core–shell n–n heterojunction, where the MOS core acts as an electron donor and the MoS₂ shell serves as an electron acceptor [14]. A built-in electric field forms at the heterointerface through type II band alignment, significantly enhancing carrier separation efficiency, while the core–shell structure achieves specific gas recognition through the synergistic interface coupling effect between MOS and MOS₂ components [6].

Here, we report a unique 2D heterostructure TiO₂@MoS₂ nanosheet. Two-dimensional TiO₂ nanosheets were synthesized via a graphene sacrificial template method, followed by the hydrothermal growth of fish scale-like MoS₂ nanosheets on their surfaces. By adjusting the hydrothermal reaction time, MoS₂ layers with controlled thicknesses were achieved, exhibiting an average lateral size of 193 ± 21 nm. Compared to pristine MoS₂ nanosheets, the TiO₂@MoS₂ heterostructure demonstrated a superior toluene response (R_a/R_g = 9.8@10 ppm) at 240 °C, along with rapid response/recovery kinetics (9 s/16 s), excellent stability, durability, and high humidity resistance. The enhanced gas-sensing performance is attributed to the n–n heterojunction and high specific surface area. The synergistic interaction between the two components and the unique core–shell hierarchical architecture with self-assembled nanostructures collectively amplify the sensor’s capabilities. This study provides a rational material design strategy, offering a promising candidate for efficient detection of toluene gas.

2. Materials and Methods

2.1. Synthesis of Sensor Materials

Synthesis of TiO₂ Nanosheets: TiO₂ precursor was synthesized using a graphene oxide (GO) sacrificial template method. Specifically, 100 mg of GO was dispersed in 200 mL of ethanol and ultrasonicated for 1 h. Subsequently, 2.5 mmol of titanium butoxide (TBOT) was added dropwise under continuous stirring, and the mixture was stirred overnight (18 h) to obtain a gray suspension. The product was thoroughly washed three times with deionized water and ethanol, followed by drying at 80 °C overnight. Finally, the dried powder was calcined in a muffle furnace at 500 °C for 2 h with a heating rate of 2 °C/min, yielding white TiO₂ nanosheets.

Synthesis of TiO₂@MoS₂ Nanocomposites: 0.1 mmol of ammonium heptamolybdate tetrahydrate (NH₄)₂MoO₄·4H₂O) was dissolved in 10 mL of deionized water under vigorous stirring. A predetermined amount of the as-prepared TiO₂ nanosheets was added to the solution, and the mixture was incubated at room temperature for 12 h and dried at 80 °C for 12 h. Separately, 0.1 mmol of (NH₄)₂MoO₄·4H₂O and 3.05 mmol of thiourea (CH₄N₂S) were dissolved in 40 mL of deionized water. The (NH₄)₂MoO₄·4H₂O-loaded TiO₂ nanosheets were then added to the solution, and the mixture was stirred at room temperature for 1 h. The homogeneous suspension was transferred to a 50 mL Teflon-lined stainless-steel autoclave and heated at 200 °C for 8 h. After cooling to room temperature, the black precipitate was collected, washed three times with deionized water and ethanol, and dried at 60 °C overnight to obtain TiO₂@MoS₂-8 nanosheets. By adjusting the reaction time to 4 h and 12 h under identical conditions, samples labeled TiO₂@MoS₂-4 and TiO₂@MoS₂-12 were prepared. For comparison, pure MoS₂ nanosheets were synthesized using the same procedure without the addition of TiO₂ nanosheets.

2.2. Gas-Sensing Performance Measurement

The as-prepared TiO₂ NSs, TiO₂@MoS₂ NSs, and MoS₂ NSs were mixed with deionized water to form a homogeneous paste. Each paste was uniformly coated onto a ceramic substrate equipped with a pair of gold electrodes using a fine brush (Figure S1). The operating temperature of the sensor was controlled by adjusting the heating current applied to the embedded heating electrode. The gas-sensing performance was evaluated using a static test system (Elite Technology Co., Ltd. Suzhou, China). Target gas concentrations were generated via a static gas distribution method.

The gas-sensing performance was evaluated using a custom-built static testing system, where sensor resistance was monitored continuously with a source meter under controlled conditions. Target analytes were introduced into the 20 L test chamber by injecting liquid toluene with a microsyringe and vaporizing it on a hotplate. The volume Q can be determined by:

$$Q={\displaystyle \frac{VCM}{22.4D\rho }}\times {10}^{-9}\times {\displaystyle \frac{273+T_R}{273+T_B}}$$

(1)

Here, V, C, M, d, ρ, T_R, and T_B are the test chamber volume (L), vapor concentration (ppm), molecular mass (g/mol), liquid density (kg/m³), liquid purity (%), environmental temperature (°C), and temperature (°C) in the testing chamber, respectively.

Sensitivity (S), a critical performance metric of gas sensors, is quantified as the resistance ratio under distinct gaseous environments. For n-type semiconductors, sensitivity is defined as:

$$S=R_a/R_g(N-type)\left(oxidizinggases\right)$$

(2)

$$S=R_g/R_a(N-type)\left(reducinggases\right)$$

(3)

where R_a denotes the baseline resistance in dry air and R_g represents the steady-state resistance upon exposure to the target analyte. Conversely, p-type semiconductors exhibit inverse trends.

3. Results and Discussion

3.1. Morphology and Structure Characterization

As demonstrated in Figure 1, TiO₂ nanosheets were synthesized via a graphene oxide sacrificial template method followed by annealing at 500 °C. Subsequently, fish scale-like MoS₂ nanosheet arrays were uniformly grown on the TiO₂ surfaces through a controlled hydrothermal reaction (Figure 1). Optimizing precursor concentration and hydrothermal reaction time was crucial for MoS₂ growth. The thickness of MoS₂ nanostructures could be effectively tuned by adjusting the hydrothermal duration. The facile and reproducible synthesis protocol offers significant advantages for scalable production.

To characterize the morphology and structure of TiO₂@MoS₂ composites, SEM and low-magnification TEM analyses were performed. As shown in Figure 2a, ultrathin TiO₂ nanosheets (~2.1 ± 0.3 nm thickness) were successfully synthesized via the graphene oxide sacrificial template method. In contrast, pristine MoS₂ formed spherical aggregates with an average diameter of 530 ± 12 nm (Figure 2b). Figure 2c–e reveal the hierarchical heterostructure, where vertically aligned MoS₂ nanosheets (193 ± 21 nm lateral size) uniformly coat TiO₂ surfaces, forming an n–n heterojunction. The MoS₂ coverage density exhibited a positive correlation with hydrothermal duration, enabling thickness-controlled growth. TEM characterization (Figure 2f) further confirmed the 2D–2D interfacial architecture. HR-TEM analysis (Figure 2g) resolved distinct lattice spacings of 0.250 nm, corresponding to the (102) plane of MoS₂ [22,23,24,25]. The polycrystalline nature was verified by selective electron diffraction (SAED) patterns showing concentric diffraction rings (Figure 2h). Energy dispersion spectrum (EDS) elemental mapping (Figure 2i) demonstrated homogeneous spatial distribution of Ti, Mo, S, and O, conclusively confirming the formation of well-integrated TiO₂@MoS₂ heterostructures.

To determine the phase composition and interfacial interactions in the TiO₂@MoS₂ heterostructure, X-ray diffraction (XRD) and Raman analyses were performed. The XRD pattern of TiO₂@MoS₂ (Figure 3a) revealed distinct diffraction peaks at 25.3° (101), 37.8° (004), and 48.0° (200), corresponding to anatase TiO₂ (JCPDS #97-002-4276), alongside peaks at 31.6° (102) and 45.5° (110), attributed to MoS₂ (JCPDS #97-064-4259). A noticeable shift in the (004) peak of TiO₂ and the (110) peak of MoS₂ was observed, indicative of lattice strain arising from the intimate interfacial coupling in the heterojunction.

To analyze the structural advantages of the TiO₂@MoS₂ nanocomposite, nitrogen adsorption–desorption measurements were conducted to determine its specific surface area and pore distribution using BET theory and BJH methods. As shown in Figure 3b, all three materials (TiO₂, MoS₂, TiO₂@MoS₂-8) exhibit type IV isotherms with H3-type hysteresis loops in the relative pressure (P/P₀) range of 0.6–1.0, characteristic of mesoporous structures. The average pore diameters determined by BJH analysis were 2.4 nm (TiO₂), 3.1 nm (MoS₂), and 8.3 nm (TiO₂@MoS₂-8). Notably, the TiO₂@MoS₂-8 composite demonstrated the highest BET surface area of 87.48 m²/g, significantly surpassing that of pristine TiO₂ nanosheets (9.04 m²/g) and MoS₂ nanosheets (19.68 m²/g), confirming the heterojunction’s role in enhancing porosity (Figure 3c).

X-ray photoelectron spectroscopy (XPS) was employed to investigate the surface composition and chemical states of TiO₂, MoS₂, and TiO₂@MoS₂-8 nanocomposites. As shown in Figure 4a, the survey spectra confirm the coexistence of Ti, Mo, S, and O in the TiO₂@MoS₂-8 heterostructure, consistent with EDS, XRD, and HRTEM results, with no impurity peaks except for residual carbon (C 1s). High-resolution Ti 2p spectra (Figure 4b) reveal characteristic peaks at 459.08 eV (Ti 2p_3/2) and 464.87 eV (Ti 2p_1/2) for TiO₂@MoS₂-8, with a spin–orbit splitting of 5.79 eV, typical of Ti⁴⁺ in TiO₂. Notably, a 0.40 eV positive binding energy shift compared to pure TiO₂ (458.68 eV and 464.47 eV) indicated electron transfer from TiO₂ to MoS₂. The Mo 3d spectrum (Figure 4c) exhibited peaks at 228.65 eV (Mo 3d_5/2) and 231.87 eV (Mo 3d_3/2), with a corresponding S 2s peak at 225.90 eV, while a 0.60 eV negative shift relative to pure MoS₂ further confirmed interfacial charge redistribution. Similarly, the S 2p peaks (Figure 4d) at 162.06 eV (S 2p_3/2) and 163.16 eV (S 2p_1/2) show a 0.15 eV shift, corroborating strong electronic interactions. Deconvolution of O 1s spectra (Figure 4e) identifies three components: lattice oxygen (O_lat, 529.5 ± 0.6 eV), oxygen vacancies (O_def, 531.6 ± 0.4 eV), and adsorbed oxygen species (O_ads, 532.5 ± 0.6 eV). TiO₂@MoS₂-8 demonstrates elevated O_def (22.72%) and O_ads (4.58%) concentrations compared to TiO₂, which aligns with its enhanced ESR signal intensity (Figure 4f) reflecting higher oxygen vacancy density. These synergistic effects of enhanced charge transfer and oxygen-mediated surface activity collectively improved toluene-sensing performance by promoting gas adsorption and redox reactions at the heterojunction interface.

3.2. Gas-Sensitive Property

TiO₂@MoS₂ nanocomposites show great potential as chemiresistive gas sensors due to their high surface area and hierarchical 2D structures. The operating temperature affects surface resistance by altering adsorbed oxygen species and reaction kinetics. This is due to faster surface reactions at higher temperatures competing with reduced gas molecule adsorption because of fewer available active sites [26]. Temperature-dependent sensing tests were conducted from 200 to 280 °C for MoS₂, TiO₂@MoS₂-4, TiO₂@MoS₂-8, and TiO₂@MoS₂-12. The temperature-dependent response exhibited a characteristic volcano profile (Figure 5a), peaking at 240 °C. Below this temperature, inadequate thermal activation hindered oxygen ionosorption and toluene oxidation. Beyond 240 °C, accelerated desorption prevailed over surface reactions, reducing sensor response value [27]. The TiO₂@MoS₂-8 composite achieved a maximum response of 9.8@10 ppm toluene, representing a 3.5-fold enhancement over pristine MoS₂ (2.8), primarily due to oxygen vacancy-mediated toluene adsorption. Notably, TiO₂@MoS₂-8 exhibited rapid response/recovery kinetics (9 s/16 s, Figure 5b), outperforming other samples (MoS₂: 4.1 s/18 s; TiO₂@MoS₂-4: 10 s/17 s; TiO₂@MoS₂-12: 12 s/20 s), benefiting from its optimized mesoporous structure facilitating gas diffusion. Selectivity tests against xylene, benzene, triethylamine, acetone, methanol, ethanol, and ammonia (Figure 5c) revealed superior toluene selectivity. Even under simulated exhaled breath conditions containing mixed interferents (Figure 5d), the sensor maintained stable toluene detection, confirming its robustness in complex environments. These critical attributes of high sensitivity, rapid reaction kinetics, and selective discrimination collectively establish TiO₂@MoS₂ nanocomposites as promising materials for toluene detection applications.

Figure 5e illustrates the dynamic response of TiO₂@MoS₂-based sensors to varying concentrations of toluene gas, ranging from 50 ppb to 10 ppm. The sensor response demonstrates stepwise enhancement with increasing concentration, with TiO₂@MoS₂ composites exhibiting superior sensitivity compared to pristine MoS₂, particularly at higher concentrations. A limit of detection (LOD) of 50 ppb was achieved for the optimal TiO₂@MoS₂-8 sensor. As shown in Figure 5f, all samples maintain linear responses across the 0.05–10 ppm range, validating quantitative detection capability. Repeatability tests (Figure 5g) revealed stable performance over five cycles at 10 ppm, with response variations below ±5.2%. Under humidity challenges (25%–75% RH, Figure 5h), the response attenuation remained <20%, underscoring robust moisture resistance. Long-term stability assessments (30 days exposure to 10 ppm toluene, Figure 5i) showed <8% signal drift, confirming durability for practical deployment.

Table 1. Comparison of sensor-based toluene gas detection characteristics with different detection materials.

Materials	T (°C)	Concentration (ppm)	Detection Limit (ppm)	Tres/Trec (s)	Ref.
Pd/PdO-decorated SnO2	285	100	0.05	50/138	[28]
V2C MXene	25	200	0.047	14/34	[29]
SnO2-decorated NiO	100	250	0.01	-	[30]
MoS2-Fe3O4	25	20	5	58/23	[7]
ZnO@Co3O4	290	100	5	11.2/12.5	[16]
NiO/ZnO	100	300	0.1	2/33	[17]
TiO2@MoS2	240	10	0.05	9/16	This work

shows the comparison of sensor-based toluene gas detection characteristics with different detection materials, further confirming the great potential of TiO₂@MoS₂-based material as a toluene sensor due to its lower detection limit and rapid response/recovery time.

As shown in Figure 6a, time-resolved in situ Fourier transform infrared (in situ FTIR) spectroscopy was employed to analyze intermediate products during toluene sensing. Peaks observed in the 1450–1600 cm⁻¹ range originate from C=C aromatic ring vibrations, with increasing intensity over time indicating progressive aromatic compound accumulation. Absorption bands between 1370–1450 cm⁻¹ correspond to C-H bending modes of methyl groups directly bonded to the benzene ring, confirming toluene decomposition. Concurrently, diminishing toluene-specific peaks and emerging signals at 3000–3100 cm⁻¹ (aromatic C-H stretching) suggest catalytic conversion pathways where toluene transforms into benzene derivatives. Resistance changes in TiO₂@MoS₂ nanocomposites arise from oxygen-mediated surface interactions: at 240 °C, chemisorbed oxygen species (O₂⁻, O⁻) populate oxygen vacancies, forming electron-depletion layers that reduce baseline resistance in air (Equation (4)) [31]. Upon toluene exposure, adsorbed oxygen species react with methyl groups via stepwise dehydrogenation (Equations (5)–(8)), modulating conductivity through electron transfer between the semiconductor and reaction intermediates. This mechanistic framework aligns with the observed spectral evolution and sensor response dynamics.

$${\mathrm{O}}_2\left(\mathrm{g}\right)\to {\mathrm{O}}_2\left(\mathrm{a}\mathrm{d}\mathrm{s}\right)$$

(4)

$${\mathrm{O}}_2\left(\mathrm{a}\mathrm{d}\mathrm{s}\right)+{\mathrm{e}}^{-}\to {\mathrm{O}}_2^{-}\left(\mathrm{a}\mathrm{d}\mathrm{s}\right)$$

(5)

$${\mathrm{O}}_2^{-}\left(\mathrm{a}\mathrm{d}\mathrm{s}\right)+{\mathrm{e}}^{-}\to 2{\mathrm{O}}^{-}\left(\mathrm{a}\mathrm{d}\mathrm{s}\right)$$

(6)

$${\mathrm{C}}_7{\mathrm{H}}_8\left(\mathrm{g}\right)+3{\mathrm{O}}^{-}\left(\mathrm{a}\mathrm{d}\mathrm{s}\right)\to {\mathrm{C}}_6{H}_6\left(\mathrm{g}\right)+{CO}_2+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right)+3{\mathrm{e}}^{-}$$

(7)

$${\mathrm{C}}_6{\mathrm{H}}_6\left(\mathrm{g}\right)+15{\mathrm{O}}^{-}\left(\mathrm{a}\mathrm{d}\mathrm{s}\right)\to 6{CO}_2+{3\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right)+15{\mathrm{e}}^{-}$$

(8)

The enhanced toluene-sensing performance of the 2D stacked MoS₂@TiO₂ heterostructure compared to pristine MoS₂ and TiO₂ nanosheets arises from three synergistic mechanisms, as follows.

(I) Hierarchical architecture and surface engineering. Gas–solid interactions in chemiresistive sensors critically depend on surface-mediated oxygen adsorption and target gas diffusion. The MoS₂@TiO₂ heterostructure exhibits a superior specific surface area, providing abundant active sites for oxygen chemisorption. The vertically aligned MoS₂ nanosheets on TiO₂ substrates prevent nanosheet restacking while creating interconnected nanochannels that enhance toluene diffusion kinetics.

(II) Interface charge redistribution in n–n heterojunctions. The work function disparity between MoS₂ (Φ = 4.05 eV) and TiO₂ (Φ = 4.77 eV), determined by ultraviolet photoelectron spectroscopy (UPS, Figure S3), drives interfacial electron transfer from TiO₂ to MoS₂ [32,33]. This creates a built-in electric field at the heterointerface, forming an electron-depletion layer, which lowers the oxygen adsorption activation energy and facilitates hole–electron separation efficiency [34]. Band alignment analysis (Figure S2) reveals heterojunction characteristics with MoS₂ and TiO₂ bandgaps of 3.20 eV and 0.85 eV, respectively [35,36,37]. The conduction band offset promotes electron trapping by adsorbed oxygen species (O₂⁻/O⁻), amplifying resistance modulation upon toluene exposure.

(III) Influence by oxygen species. Compared with TiO₂ nanosheets, TiO₂@MoS₂ has the highest ESR intensity and the highest relative concentration of oxygen vacancy. Therefore, the TiO₂@MoS₂ hierarchical structure can provide additional O_ads and O_def, which is conducive to the reaction of the target gas with oxygen, while increasing the surface active site, which is conducive to the sensing performance of toluene [38,39].

4. Conclusions

In summary, TiO₂@MoS₂ core–shell heterostructures were fabricated by assembling MoS₂ nanosheet arrays onto TiO₂ nanosheets prepared via a sacrificial template method. The unique 2D hierarchical heterojunction structure resulted in a larger specific surface area and increased generation of oxygen vacancies. Compared with individual TiO₂ nanosheets and MoS₂ nanosheets, the TiO₂@MoS₂ composite demonstrated the highest response (R_a/R_g = 9.8@10 ppm toluene) at 240 °C. Furthermore, the hierarchical TiO₂@MoS₂ core–shell structure exhibited fast response/recovery times (9 s/16 s), a low detection limit (50 ppb), excellent selectivity, and robust stability in humid environments. The enhanced gas-sensing performance is attributed to the synergistic effects between the two components and the distinctive core–shell hierarchical architecture with self-assembled nanostructures. This work provides a rational material structure design strategy, offering a promising candidate for detecting toluene gas, thereby demonstrating significant potential value for advancing environmental or disease diagnosis detection.