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Article

Electrostatic Self-Assembly of Heterostructured In2O3/Ti3C2Tx Nanocomposite for High-Selectivity NO2 Gas Sensing at Room Temperature

by
Yongjing Guo
1,
Zhengxin Zhang
1,
Hangshuo Feng
1,
Qingfu Dai
1,
Qiuni Zhao
1,*,
Zaihua Duan
2,
Shenghui Guo
1,*,
Li Yang
1,
Ming Hou
1 and
Yi Xia
1,*
1
Faculty of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, China
2
State Key Laboratory of Electronic Thin Films and Integrated Devices, School of Optoelectronic Science and Engineering, University of Electronic Science and Technology of China (UESTC), Chengdu 611731, China
*
Authors to whom correspondence should be addressed.
Chemosensors 2025, 13(7), 249; https://doi.org/10.3390/chemosensors13070249
Submission received: 6 June 2025 / Revised: 28 June 2025 / Accepted: 8 July 2025 / Published: 10 July 2025
(This article belongs to the Special Issue Functional Nanomaterial-Based Gas Sensors and Humidity Sensors)
Browse Figures
Versions Notes

Abstract

Owing to high electrical conductivity, layered structure, and abundant surface functional groups, transition metal carbides/nitrides (MXenes) have received enormous interest in the field of gas sensors at room temperature. In this work, we synthesize a heterostructured nanocomposite with indium oxide (In2O3) decorated on titanium carbide (Ti3C2Tx) nanosheets by electrostatic self-assembly and develop it for high-selectivity NO2 gas sensing at room temperature. Self-assembly formation of multiple heterojunctions in the In2O3/Ti3C2Tx composite provide abundant NO2 gas adsorption sites and high electron transfer activity, which is conducive to improving the gas-sensing response of the In2O3/Ti3C2Tx gas sensor. Assisted by rich adsorption sites and hetero interface, the as-fabricated In2O3/Ti3C2Tx gas sensor exhibits the highest response to NO2 among various interference gases. Meanwhile, a detection limit of 0.3 ppm, and response/recovery time (197.62/93.84 s) is displayed at room temperature. Finally, a NO2 sensing mechanism of In2O3/Ti3C2Tx gas sensor is constructed based on PN heterojunction enhancement and molecular adsorption. This work not only expands the gas-sensing application of MXenes, but also demonstrates an avenue for the rational design and construction of NO2-sensing materials.

1. Introduction

With the development of global industrialization, atmospheric pollutants in the ecological environment have greatly restricted the development of social economy and become a serious problem for contemporary civilization [1,2,3]. Nitrogen dioxide (NO2), as a hazardous gas, is harmful to human health when its concentration exceeds 3 ppm [4,5]. Therefore, developing fast, highly sensitive, and highly selective NO2 gas sensors is crucial for protecting human health and monitoring the atmospheric environment [6,7,8].
Among numerous gas detection technologies, metal oxide semiconductor (MOS)-based gas sensors are widely used due to their advantages of low cost, small size, easy integration, and real-time monitoring [9,10,11,12]. Metal oxide-based gas-sensing materials mainly include tin dioxide (SnO2), zinc oxide (ZnO), tungsten trioxide (WO3), indium oxide (In2O3), and copper oxide (CuO) [13,14,15,16]. Among them, In2O3 is widely used in the manufacture of gas sensors due to its high sensitivity and fast response characteristics [17,18]. For instance, Zhang et al. [19], using the electrospinning method, prepared In2O3 nanowires for NO2 gas sensing under visible light irradiation (400–700 nm, 4.58 mW·cm−2). The In2O3 nanowire-based NO2 gas sensor exhibits a response value of 780 to 5 ppm NO2, with a response and recovery time of 200 s and 20 s, respectively. Most MOS-based gas sensors demand either elevated operating temperatures or light irradiation, leading to higher power consumption. Meanwhile, this type of sensor displays a broad-spectrum response to multiple gases (such as NO2, ammonia (NH3), hydrogen sulfide (H2S), sulfur dioxide (SO2), and volatile organic compounds (VOCs)), which leads to the insufficient selectivity of MOS-based gas sensors [20,21].
Two-dimensional (2D) materials (such as graphene, transition-metal dichalcogenides (TMDs), graphitic carbon nitride (g-C3N4)) have received tremendous attention as gas-sensing materials in recent years due to their high specific surface area, rich surface chemical bond, atomic-level thickness, and adjustable electrical properties. MXene is a group of transition metal carbides/nitrides/carbonitrides with a layered structure, discovered by Gogosti in 2011 [22]. Most MXene, such as titanium carbide (Ti3C2Tx), vanadium carbide (V2CTx), and niobium carbide (Nb2CTx), is synthesized by the selective etching out of the A layers from MAX phases, where A is mainly a group IIIA or IVA element, M represents an early transition metal, and X is carbon and/or nitrogen [23,24]. Thus, the surface of MXene is rich in defects, and the functional groups on its surface can be regulated by selecting the synthesis method [25]. In addition, the layered structure of MXene will provide abundant active sites for gas adsorption and surface reactions, and high carrier mobility of MXene is beneficial for reducing the signal noise of the gas sensors [26,27]. However, MXene-based gas-sensitive materials mainly suffer from oxidation by NO2, which leads to poor stability of the NO2 gas sensor due to MXene deterioration. Thus, forming a protective film on the surface of MXene by modification or composite is a common strategy to improve the stability of MXene. Classically, Ti3C2Tx/TiO2 nanocomposite are prepared by in situ growth, formation of Schottky barrier can effectively improve the performance of Ti3C2Tx-based NO2 gas sensors [28,29].
In this work, we investigated the achievement of decorating In2O3 on Ti3C2Tx nanosheets via electrostatic self-assembly to enhance gas-sensing response at room temperature. The morphology and chemical structure of composite are characterized, and the gas-sensing performances of In2O3/Ti3C2Tx gas sensors are investigated in this study. The formation of multiple heterojunctions in the In2O3/Ti3C2Tx composite provide abundant NO2 gas adsorption sites and high electron transfer activity, resulting in high response and selectivity of the In2O3/Ti3C2Tx gas sensor. Moreover, the enhanced NO2 gas-sensing mechanism is demonstrated based on heterojunction and molecular adsorption. This work expands the application of MXene in the field of gas sensor.

2. Materials and Methods

2.1. Sample Preparation

The reagents used in this study were purchased through standard commercial channels without further modification. Indium nitrate pentahydrate (In(NO3)3·5H2O), N, N-dimethylformamide (C3H7NO, DMF), urea (CH4N2O), lithium fluoride (LiF), hydrochloric acid (HCl), poly(diallyldimethylammonium chloride) (PDDA), and methanol were purchased from Shanghai Macklin Biochemical Technology Co., Ltd. (Shanghai, China). Titanium aluminum carbide (Ti3AlC2) was bought from Jilin 11 Technology Co., Ltd. (Changchun, Jilin, China). In this study, the In2O3/Ti3C2Tx composite was synthesized using hydrothermal and electrostatic self-assembly methods, as illustrated in Figure 1.
(1)
Synthesis of zero-dimensional In2O3 nanoparticles
The In2O3 nanoparticles were synthesized using the hydrothermal method [30]. Initially, 0.5 mmol (In(NO3)3·5H2O) was dissolved in 20 mL DMF. Subsequently, 0.01 mol urea was added to the solution and stirred for 1 h until the solution becomes transparent. The solution was transferred to a 25 mL polytetrafluoroethylene-lined autoclave and hydrothermally treated at 180 °C for 24 h. Upon completion of the reaction, a white precipitate was obtained, which was repeatedly washed multiple times via centrifugation using deionized water and ethanol. The washed product then dried in a vacuum oven at 60 °C for 12 h. After drying, the sample was placed in a tubular furnace and calcined at 500 °C for 2 h to obtain In2O3 nanoparticles.
(2)
Synthesis of 2D Ti3C2Tx
A 1.3 g measurement of LiF powder was dissolved in 80 mL hydrochloric acid (6 mol·L−1) and stirred at room temperature for 30 min. Then 2 g Ti3AlC2 was added slowly, and the mixture was stirred for an additional 30 min. The resulting solution was transferred to a 150 mL polytetrafluoroethylene-lined autoclave and heated in a constant-temperature oven at 120 °C for 5 days. After the reaction was completed, the autoclave was cooled to room temperature and taken out. The obtained precipitate was repeatedly centrifuged and washed several times with deionized water and ethanol until the pH was close to 7 and then placed in a 60 °C vacuum drying oven for drying to obtain black Ti3C2Tx powder.
(3)
Synthesis of In2O3/Ti3C2Tx Composite
The In2O3/Ti3C2Tx composite was synthesized via electrostatic self-assembly. Firstly, 1 g In2O3 nanoparticles was dispersed in 300 mL of 0.5 wt% PDDA solution and ultrasonic treatment for 3 h. Following filtration, the PDDA-modified In2O3 was rinsed with deionized water and dried in a drying oven at 70 °C for 12 h. Subsequently, 1 g of the PDDA-modified In2O3 powder was dispersed in 10 mL methanol. Ti3C2Tx with different mass (10 mg, 20 mg, and 50 mg) was added to the solution, and the mixture was stirred vigorously for 10 h. Finally, the suspension was washed with methanol several times and dried in a vacuum oven at 70 °C for 12 h to obtain the In2O3/Ti3C2Tx composite. For the convenience of description, the different In2O3/Ti3C2Tx composites are designated as IT1, IT2, and IT3, with Ti3C2Tx proportions of 1%, 2%, and 5%, respectively. The performance of the optimized IT2 is consistently referred to as In2O3/Ti3C2Tx composite in subsequent sections.

2.2. Characterization Method

The crystalline phase of the In2O3/Ti3C2Tx composite was analyzed by X-ray diffraction (XRD, Rigaku D/max-2500, Rigaku, Tokyo, Japan). The microstructure of In2O3/Ti3C2Tx composite was characterized by field emission scanning electron microscopy (FESEM JSM-7100F, JEOL, Tokyo, Japan) and high-resolution transmission electron microscopy (HRTEM, Tecnai G2 F30-S-Twin, FEI, Hillsboro, OR, USA). The EDS spectrum of In2O3/Ti3C2Tx composite was obtained by energy dispersive spectrometer (EDS, Hitachi S-4800, Hitachi, Tokyo, Japan). The different elemental compositions and chemical states of In2O3/Ti3C2Tx composite were analyzed by scanning imaging photoelectron spectroscopy (XPS, PHI5000 Versaprobe-II, ULVAC-PHI, Tokyo, Japan). The direct band gap energy of In2O3 and In2O3/Ti3C2Tx composite was obtained by UV-visible spectroscopy. N2 isothermal adsorption–desorption test was used to obtain the specific surface area of the samples. An F-7000 spectrophotometer (Hitachi, Tokyo, Japan) was used to collect the room-temperature photoluminescence (PL) spectra of the samples.

2.3. Fabrication of Gas Sensors and Tests

The measuring electrode was fabricated on the basis of an alumina substrate (6 × 30 mm). The gear-shaped electrode had a width of 0.42 mm, with an inter-electrode gap of 0.42 mm between the adjacent gear-shaped electrodes. The samples were prepared for the gas-sensing studies using the following procedures: First, platinum sizing agent was printed on the alumina (Al2O3) substrate by using screen printing. The alumina matrixes were subsequently dried at 80 °C for 40 min. Subsequent calcination was performed at 350 °C and 850 °C for 20 min at each temperature. The In2O3/Ti3C2Tx paste sensing materials were printed on the alumina matrix by using screen printing method. Finally, the as-products were annealed at 350 °C for 1 h under argon atmosphere to remove the organic solvent. According to our previous test result [30], the thickness of the gas-sensing film is about 4 μm.
This work mainly focuses on the enhancement of the gas-sensing performance of the In2O3/Ti3C2Tx composite material, characterizing the morphology and chemical state of the composite, and studying and discussing the gas-sensing performance and mechanism. The gas-sensing performance of the sensor was evaluated using a commercial four-channel test system (SD101, Wuhan HuachuangRuike Tech. Co., Ltd., Wuhan, China). The testing apparatus includes three main components: a computer for data acquisition, a precision gas flow controller, and a multi-channel test chamber. All measurements were conducted at room temperature. For each test, the measuring electrode was placed in a closed chamber filled with air until a stable resistance baseline was established. Subsequently, target gases with different concentrations were introduced. A minimum of three identical samples were tested for each condition, and the average response values were calculated. The response value of the materials to NO2 can be determined using the following equation:
Response = Rg/Ra
where Ra is the sample resistance in air, and Rg is the sample resistance in the presence of NO2 gas.

3. Results and Discussion

3.1. Characterization

XRD patterns are presented in Figure 2a, the diffraction peak of Ti3AlC2 at 2θ = 9.63° corresponds to the (002) crystal plane [31]. After etching with HCl and LiF, the (002) peak shifts to a lower diffraction angle (from 2θ = 9.5° to 5.8°), and its intensity broadens. This shift indicates an increase in the interlayer spacing, consistent with selective removal of the Al atom layers [32]. These results confirm the successful synthesis of Ti3C2Tx. The diffraction peaks of In2O3 located at 2θ of 21.5°, 30.5°, 35.4°, and 51.0° and 60.6° correspond to the (211), (222), (400), (440), and (600) planes of In2O3 phase, respectively (JCPDS card No. 89-4595). Comparing the XRD patterns of the In2O3/Ti3C2Tx composite with those of the pristine In2O3 and Ti3C2Tx, the XRD characteristic peaks of In2O3 and Ti3C2Tx appear simultaneously in the In2O3/Ti3C2Tx, indicating the presence of In2O3 and Ti3C2Tx in the composite.
SEM was employed to analyze the morphologies of pristine In2O3, Ti3C2Tx, and In2O3/Ti3C2Tx composites. As shown in Figure 2b, the In2O3 nanoparticles exhibit consistent morphology and size distribution, with dense surface, good crystallinity, and uniform dispersion. Figure 2c illustrates that Ti3C2Tx has a micron-scale size and presents an accordion-like multilayer nanosheet structure. This indicates that the Al atom layer in the Ti3AlC2 precursor structure is selectively etched, resulting in a typical 2D layered structure, which makes it possible for In2O3 nanoparticles to be inserted into deep regions of Ti3C2Tx. Figure 2d reveals that numerous In2O3 nanoparticles are attached to the surface of Ti3C2Tx, and some In2O3 nanoparticles penetrate into the gaps between the layers of Ti3C2Tx. This structure creates favorable conditions for the formation of heterojunction, which enhances the adsorption and diffusion of gas molecules on the surface of the composite, thereby promoting the gas-sensitive performances of the In2O3/Ti3C2Tx composite sensor. Figure 2e presents TEM images of the In2O3/Ti3C2Tx composite, confirming that In2O3 nanoparticles are attached to the surface of Ti3C2Tx, consistent with the SEM observations. The HRTEM image in inset shows a lattice fringe spacing of 0.29 nm, corresponding to the (222) planes of In2O3, agreement with the XRD pattern. This confirms the favorable crystallinity of the In2O3/Ti3C2Tx composite. EDS was employed to further confirm the elemental distribution and contents in the In2O3/Ti3C2Tx composite materials. Figure 2f demonstrates a uniform distribution of In, O, C, and Ti elements, further illustrating the successful incorporation of In2O3 into the Ti3C2Tx structure.
XPS analysis was applied to confirm the chemical states and elemental compositions in the In2O3/Ti3C2Tx composite. In Figure 3a, the spectral peak of C 1s are located at 282.6 eV, 284.5 eV, 286.2 eV, and 288.3 eV, respectively, belonging to the C-Ti, C-C, C-O, and C-F bonds [33]. As shown in Figure 3b, the Ti 2p peaks of Ti3C2Tx located at 455.4 eV, 456.0 eV, 457.5 eV, and 459.1 eV can be attributed to Ti-C, TixOy, Ti-x, and TiO2, respectively [34]. XPS analysis of the O 1s region (Figure 3c) exhibits three characteristic peaks at 529.9 eV, 531.4 eV, and 533.2 eV, corresponding to lattice oxygen (OL), oxygen vacancy (OV), and adsorbed oxygen (OC), respectively. The OC refers to the oxygen species bound on the material surface through physical or chemical actions. This oxygen may come from air exposure, surface reactions, or treatment processes. The OL refers to the oxygen atoms in the crystal structure that are periodically arranged and occupy fixed lattice positions and combine with the metal ions inside the oxide. The OV refers to point defects formed in crystalline materials due to the absence of oxygen atoms. The existence of oxygen vacancies can enhance the carrier transport rate, thereby improving the gas sensitivity performance. The oxidized Ti states observed in Ti 2p spectrum correlate with the OL in O 1s spectrum of In2O3/Ti3C2Tx. Figure 3d shows the In 3d spectra of In2O3/Ti3C2Tx. The peaks of In 3d 5/2 and In 3d 3/2 are 444.4 eV and 452 eV, respectively, which are In-O bonds in In2O3, consistent with the presence of In3+ [35].
The band gap values of In2O3 and In2O3/Ti3C2Tx are calculated to be 2.55 eV and 2.04 eV according to the Tauc plot (Figure 3e), respectively [36]. The narrower direct band gap of In2O3/Ti3C2Tx indicates that less energy is required to excite electrons to the conduction band, which enhances the electron transfer rate. This observation further clarifies why the performance of the In2O3/Ti3C2Tx composite is significantly better than that of pristine In2O3 nanoparticles [37]. As shown in Figure 3f, the photoluminescence intensity of the In2O3/Ti3C2Tx composite is lower than that of the In2O3 nanoparticles. This effect originates from the interaction between Ti3C2Tx and In2O3. Additionally, the reduced photoluminescence intensity suggests enhanced electron mobility in the In2O3/Ti3C2Tx composite, which generally facilitates improved electron transport, thereby enhancing the gas-sensing performance of the sensor [38].

3.2. Gas-Sensing Performances

Figure 4a presents the response values of pristine In2O3, IT1, IT2, and IT3 to 100 ppm NO2 at room temperature. The pristine In2O3 exhibits a relatively low response value of 7.9, while all composites demonstrate significantly enhanced responses. Notably, the IT2 composite achieves the maximum response value of 55.9. These results suggest that an optimal combination of Ti3C2Tx enhances the gas-sensing performance of the sensors, while excessive Ti3C2Tx will inhibit the responses. Figure 4b displays the resistance response curve of In2O3/Ti3C2Tx sensor to 0.3–100 ppm NO2, while the inserted image shows the response–recovery curve of the gas sensors to 0.3 ppm NO2. The response value increases with the increase of NO2 concentration. It is clearly seen that the response curve exhibits an increase in resistance followed by its decrease, particularly for 100 ppm NO2. We propose the following several possibilities: (i) Fluctuations in airflow during the flow-switching process of the test equipment. At the moment when the gas flow rate switches, the actual gas flow rate may be higher than the actual set value for an instant. At this time, the resistance changes significantly. As the gas flow rate drops to a stable state, the resistance value gradually decreases. (ii) When the test gas is switched from air to NO2, the gas has not yet fully filled the test chamber. At this stage, the gas diffusion rate is relatively high, and the gas-sensitive reaction is intense, leading to a significant increase in resistance. As NO2 gradually fills the chamber, the diffusion rate decreases, and the gas-sensitive reaction process becomes less intense, resulting in a gradual reduction in the amplitude of resistance change. The logarithmic linear fitting curves of In2O3 and In2O3/Ti3C2Tx gas sensors are shown in Figure 4c, where the response value data of the pristine In2O3 to different concentrations of NO2 at room temperature are derived from previously published papers [39]. Compared with In2O3 gas sensor, In2O3/Ti3C2Tx sensor shows a sensitivity of 0.86 with a linearity of R2 = 0.98. Figure 4d displays the response/recovery time of the In2O3/Ti3C2Tx composite gas sensor to 25 ppm NO2, the calculation results show that the response/recovery times are 198/94 s. According to our previous study [39], the resistance of pure In2O3 is approximately 100 kΩ. The addition of Ti3C2Tx reduces the resistance of the composite gas sensor to 2 kΩ. This remarkable reduction in resistance originates from the excellent electrical conductivity of Ti3C2Tx, which facilitates efficient electron transport when combined with In2O3, ultimately leading to the observed reduction in overall composite resistance.
To assess the impact of different gas selectivity on sensor performance in complex environments, the response performance of In2O3/Ti3C2Tx composite sensor to carbon monoxide (CO), methanol (CH3OH), ethanol (C2H5OH), and toluene (C7H8) are also tested at room temperature. The response value of the materials to the above four gases can be determined using the following equation:
Response = Ra/Rg
where Ra is the sample resistance in air, and Rg is the sample resistance in the presence of CO, CH3OH, C2H5OH, or C7H8 gas. Figure 4e shows the response of the In2O3/Ti3C2Tx sensor to 100 ppm of each of the four gases at room temperature. The response values for CO, CH3OH, C7H8, and C2H5OH gases are 1, 1.1, 1.2, and 1, respectively. Obviously, the response value of the In2O3/Ti3C2Tx composite sensor to NO2 is significantly higher than that of the other gases. The gas-sensing performance of the In2O3/Ti3C2Tx composite was tested once a day for ten consecutive days at room temperature. Figure 4f demonstrates that the response of the In2O3/Ti3C2Tx gas sensor to NO2 exhibits a fluctuation with an absolute deviation of 6.8% over a 10-day period, indicating that it has good stability. Although the humidity-related NO2 sensing performances have not been tested, it is speculated, based on existing studies, that humidity interference will reduce the NO2 sensing performances [40,41,42,43]. As shown in Table 1 [40,44,45,46,47], the proposed In2O3/Ti3C2Tx sensor is competitive compared with the previously reported oxide-based NO2 gas sensors in terms of working temperature and response value. Therefore, the In2O3/Ti3C2Tx can be a highly responsive and selective sensing material for practical NO2 sensors.

3.3. Gas-Sensing Mechanism

The sensing mechanism of the In2O3/Ti3C2Tx composite is exhibited in Figure 5a. The detection mechanism for NO2 in semiconductors is based on changes in surface resistance. Upon exposure to air, a large number of O2 molecules are adsorbed onto the surface of the In2O3/Ti3C2Tx composite, resulting in the formation of chemisorbed oxygen (O2−). This process leads to the development of an electron depletion layer. Once the oxidizing NO2 gas interacts with the surface of the In2O3/Ti3C2Tx, it reacts with the e−, forming NO2− (NO2 + e− → NO2−), and continues to extract electrons from the In2O3/Ti3C2Tx, thereby causing the electron depletion layer to expand. In this process, the transfer of electrons is hindered, the electron mobility is reduced, and the resistance of the material is increased [37].
Figure 5b shows the band structure diagram of the In2O3/Ti3C2Tx composite. The work function and band gap of In2O3 and Ti3C2Tx are Wf = 4.4 eV and 3.59 eV, Eg = 2.55 eV and 1.4 eV, respectively [48]. When In2O3 and Ti3C2Tx make contact, a heterojunction is formed, improving the activity of the charge transfer, which further enhances the gas-sensing properties of the composite. To achieve Fermi-level equilibrium, the energy band of In2O3 and Ti3C2Tx bend, which cause the electrons to move from Ti3C2Tx to In2O3. As a result of this electron transfer, an electron depletion layer is established at the interface of In2O3 to Ti3C2Tx. In NO2, the depletion region widens after the adsorbed gas molecules capture electrons, the free-moving electrons in n-type In2O3/Ti3C2Tx reducing, thereby increasing the In2O3/Ti3C2Tx sensor resistance.

4. Conclusions

In this study, the In2O3/Ti3C2Tx composites were successfully synthesized through a facile electrostatic self-assembly method. The gas-sensing properties of the In2O3/Ti3C2Tx NO2 sensor were investigated at room temperature. The In2O3/Ti3C2Tx composite containing 2% Ti3C2Tx exhibited the best NO2 sensing performance with a response value of 55.9, and fast response and recovery (198 s and 94 s). Finally, a NO2 sensing mechanism of a In2O3/Ti3C2Tx gas sensor is constructed based on p-n heterojunction enhancement and molecular adsorption. This work provides a new way for a rational design of MXene-based gas sensors, and further demonstrates a pathway for the systematic development of NO2-sensing materials.

Author Contributions

Conceptualization, Z.Z., Q.Z., L.Y. and Y.X.; methodology, Y.G., H.F. and Z.Z.; validation, Y.G., H.F. and Z.Z.; formal analysis, H.F., Q.D., Z.D. and M.H.; investigation, H.F., Z.Z. and Y.X.; data curation, Y.G., H.F., Z.Z., Q.D. and S.G.; writing—original draft preparation, Y.G.; writing—review and editing, Q.Z., Z.D., M.H. and Y.X.; supervision, L.Y.; project administration, L.Y. and S.G.; funding acquisition, L.Y. and S.G. All authors have read and agreed to the published version of the manuscript.

Funding

This work is supported by Yunnan Fundamental Research Projects (grant NO. 202401BE070001-005, 202501CF070183, 202401BE070001-021), the Natural Science Foundation of China (grant NO. 52364051, 52304400, 62101225, 22368029), Central Guidance Local Scientific and Technological Development Funds (grant NO. 202407AB110022), Yunnan Major Scientific and Technological Projects (No. 202302AG050002), the Key Technology Research and Development Program of Shandong Province (No. 2023CXGC010903), the open project (KJS2306) of Jiangsu Key Laboratory for Carbon-Based Functional Materials and Devices, Soochow University and Central guidance local scientific and technological development funds (202407AB110022). The authors (Shenghui Guo, Yunling Scholar; Li Yang, Industrial Innovation Scholar) would like to acknowledge the Yunnan Province Xingdian Talent Support Plan Project.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data is contained within this article.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Schematic illustration of the synthesis of the In2O3/Ti3C2Tx composite.
Figure 1. Schematic illustration of the synthesis of the In2O3/Ti3C2Tx composite.
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Figure 2. (a) XRD patterns of pristine In2O3 nanoparticles, Ti3AlC2, pristine Ti3C2Tx, and In2O3/Ti3C2Tx composite; SEM images of (b) In2O3 nanoparticles, (c) Ti3C2Tx, and (d) In2O3/Ti3C2Tx composite; (e) TEM and HRTEM images of In2O3/Ti3C2Tx; (f) EDS mapping analysis of In, O, C, and Ti elements in In2O3/Ti3C2Tx composite.
Figure 2. (a) XRD patterns of pristine In2O3 nanoparticles, Ti3AlC2, pristine Ti3C2Tx, and In2O3/Ti3C2Tx composite; SEM images of (b) In2O3 nanoparticles, (c) Ti3C2Tx, and (d) In2O3/Ti3C2Tx composite; (e) TEM and HRTEM images of In2O3/Ti3C2Tx; (f) EDS mapping analysis of In, O, C, and Ti elements in In2O3/Ti3C2Tx composite.
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Figure 3. XPS spectra of In2O3/Ti3C2Tx composite: (a) C 1s, (b) Ti 2p, (c) O 1s, and (d) In 3d; (e) Tauc plot and (f) PL spectra of In2O3 nanoparticles and In2O3/Ti3C2Tx composite.
Figure 3. XPS spectra of In2O3/Ti3C2Tx composite: (a) C 1s, (b) Ti 2p, (c) O 1s, and (d) In 3d; (e) Tauc plot and (f) PL spectra of In2O3 nanoparticles and In2O3/Ti3C2Tx composite.
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Figure 4. (a) Response values of In2O3/Ti3C2Tx sensors with different contents to 100 ppm NO2 at room temperature; (b) dynamic response/recovery curves of the In2O3/Ti3C2Tx gas sensor to 0.3–100 ppm NO2 at room temperature; (c) logarithmic linear fitting curves of In2O3 [31] and In2O3/Ti3C2Tx composite gas sensors; (d) amplified response curve of In2O3/Ti3C2Tx gas sensor to 25 ppm NO2; (e) selective responses for the In2O3/Ti3C2Tx gas sensor to various gases; (f) responses of the In2O3/Ti3C2Tx gas sensor to 25 ppm NO2 in 10 days.
Figure 4. (a) Response values of In2O3/Ti3C2Tx sensors with different contents to 100 ppm NO2 at room temperature; (b) dynamic response/recovery curves of the In2O3/Ti3C2Tx gas sensor to 0.3–100 ppm NO2 at room temperature; (c) logarithmic linear fitting curves of In2O3 [31] and In2O3/Ti3C2Tx composite gas sensors; (d) amplified response curve of In2O3/Ti3C2Tx gas sensor to 25 ppm NO2; (e) selective responses for the In2O3/Ti3C2Tx gas sensor to various gases; (f) responses of the In2O3/Ti3C2Tx gas sensor to 25 ppm NO2 in 10 days.
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Figure 5. (a) Schematic illustration of the sensing mechanism of the In2O3/Ti3C2Tx composite; (b) energy band structure of In2O3/Ti3C2Tx composite in air and NO2 atmospheres.
Figure 5. (a) Schematic illustration of the sensing mechanism of the In2O3/Ti3C2Tx composite; (b) energy band structure of In2O3/Ti3C2Tx composite in air and NO2 atmospheres.
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Table 1. Comparisons of the proposed In2O3/Ti3C2Tx NO2 sensor with the reports NO2 sensors.
Table 1. Comparisons of the proposed In2O3/Ti3C2Tx NO2 sensor with the reports NO2 sensors.
MaterialsWorking Temperature (°C)Response
(Resistance Ratio)		Detection Range (ppm)Selectivity RatioRef.
In2O3 micro flower12519.6 (5ppm)-~21.7[44]
Pt decorated In2O330011 (200 ppm)-~11.2[45]
VS2/Ti3C2Tx/TiO2 nanocomposites1804.73 (50 ppm)10–50-[40]
ZnO nanorod1506.7 (100 ppm)-~12.4[46]
WO3 Nanorod20024 (100 ppm)-~15.6[47]
In2O3/Ti3C2TxRoom temperature55 (100 ppm)0.3–10045.8This work
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Guo, Y.; Zhang, Z.; Feng, H.; Dai, Q.; Zhao, Q.; Duan, Z.; Guo, S.; Yang, L.; Hou, M.; Xia, Y. Electrostatic Self-Assembly of Heterostructured In2O3/Ti3C2Tx Nanocomposite for High-Selectivity NO2 Gas Sensing at Room Temperature. Chemosensors 2025, 13, 249. https://doi.org/10.3390/chemosensors13070249

AMA Style

Guo Y, Zhang Z, Feng H, Dai Q, Zhao Q, Duan Z, Guo S, Yang L, Hou M, Xia Y. Electrostatic Self-Assembly of Heterostructured In2O3/Ti3C2Tx Nanocomposite for High-Selectivity NO2 Gas Sensing at Room Temperature. Chemosensors. 2025; 13(7):249. https://doi.org/10.3390/chemosensors13070249

Chicago/Turabian Style

Guo, Yongjing, Zhengxin Zhang, Hangshuo Feng, Qingfu Dai, Qiuni Zhao, Zaihua Duan, Shenghui Guo, Li Yang, Ming Hou, and Yi Xia. 2025. "Electrostatic Self-Assembly of Heterostructured In2O3/Ti3C2Tx Nanocomposite for High-Selectivity NO2 Gas Sensing at Room Temperature" Chemosensors 13, no. 7: 249. https://doi.org/10.3390/chemosensors13070249

APA Style

Guo, Y., Zhang, Z., Feng, H., Dai, Q., Zhao, Q., Duan, Z., Guo, S., Yang, L., Hou, M., & Xia, Y. (2025). Electrostatic Self-Assembly of Heterostructured In2O3/Ti3C2Tx Nanocomposite for High-Selectivity NO2 Gas Sensing at Room Temperature. Chemosensors, 13(7), 249. https://doi.org/10.3390/chemosensors13070249

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