空氣污染是目前全球最關注的環保議題之一，對人類健康、生態系統和氣候造成不利影響。如NO₂、NO、N₂O、NH₃和CO₂等，這些主要由工廠和汽車所排放的氣體，會增加罹患呼吸系統疾病的風險。其中，NO₂是一種眾所周知的有害氣體，對其識別與濃度測量非常重要。當NO₂濃度超過0.053 ppm時，過度暴露有可能會使呼吸道系統受損。因此，能夠準確檢測低濃度NO₂氣體，對於人類健康和環境保護至關重要。
二維材料具有高比表面積與豐富的表面活化反應點，是作為氣體感測材料不錯的研究對象，其中，具半導體特性的MoS2是目前討論最多的感測材料之一，據文獻結果顯示，室溫下，以MoS2作為感測NO2材料時，由於感測響應訊號過低，感測響應時間與重新回復時間也太長，甚至往往需要適當升溫，才能感測到較低濃度與得到較好的感測結果。因此，本研究通過在二硫化鉬 (MoS₂)中加入MXene形成混合粉末，來做為感測器的材料。 MXene 也是一種二維材料，其高比表面積、高導電性和豐富的表面官能團，能夠有效提升電子傳導和氣體吸附能力，藉以改善MoS2材料在低濃度狀態下很好的感測性能。
該材料合成流程簡單，透過不同水熱氧化溫度與混合比例的變化，找到最佳的製作條件，形成最佳的異質混合結構。從材料分析的結果明顯看到層狀結構經過水熱氧化法後，MXene表面的官能團鍵結從Ti-OH轉換成富含Ti-O鍵結狀態，而非形成TiO2，即C-Ti-O的形式。加入MXene同時提升MoS2混合粉末的導電性，且隨著MXene濃度的增加。導電度也隨之增加。
從孔隙度分析的結果，加入MXene後形成的異質結構，使感測材料整體的比表面積提升達4倍以上，吸收氣體量也大幅增加。在NO2 10ppm條件下， MoS2中加入MXene可以使感測響應從原本的2% 提升到8%；另一方面，可感測的最低濃度值也從純MoS2 的3ppm下降到 0.05 ppm，即50ppb。室溫下感測50 ppb最快響應時間與回復時間僅分別需要100秒與136秒，經過多次循環感測實驗，此混合材料展現優異的可重複性與穩定性。

Air pollution is one of the most pressing environmental issues globally. When concentrations of harmful substances in the atmosphere exceed natural levels, they can negatively impact human health, ecosystems, and climate. These pollutants may include gases, particulate matter, or biological contaminants. Exposure to gases such as NO₂, NO, N₂O, NH₃, and CO₂—primarily emitted by factories and vehicles—increases the risk of respiratory diseases. Among these gases, NO₂ is a well-known harmful pollutant, making its detection and measurement crucial. When NO₂ concentrations exceed 0.053 ppm, prolonged exposure may lead to respiratory system damage. Therefore, accurate detection of NO₂ at low concentrations is essential for both human health and environmental protection.
Two-dimensional (2D) materials, characterized by their high surface area and abundant surface-active sites, are promising candidates for gas sensing. MoS₂, a semiconductor material, is commonly studied for this purpose. However, according to existing research, using MoS₂ as a sensing material for NO₂ at room temperature often results in low sensing response signals, long response and recovery times, and frequently requires heating to achieve effective detection at low concentrations. In this study, we address these limitations by incorporating MXene into MoS₂ to form a composite powder. MXene, also a 2D material, offers high surface area, excellent conductivity, and abundant surface functional groups, enhancing electron transport and gas adsorption capabilities, which in turn stabilizes sensing performance even at low NO₂ concentrations.
The synthesis process is simple. By adjusting hydrothermal oxidation temperatures and mixing ratios, optimal fabrication conditions were determined, leading to the formation of an ideal heterogeneous composite structure. Material analysis results show that after hydrothermal oxidation synthesis, the surface functional group of MXene transited from Ti-OH to Ti-O rich bonds. Adding MXene also enhances the composite film’s conductivity. The more MXene concentration was added the higher current was observed. Porosity analysis indicates that adding MXene not only increases the materials’ specific surface area by more than four times but also enhances the amount of gas absorption capability. Sensing response at a concentration of 10 ppm improved from 2% to 8%. Furthermore, the lowest detection limit obviously improved from 3 ppm to 0.05 ppm. That is, 50 ppb. The response time and recovery time of 50ppb were to 100s and 136s, respectively. Finally, cyclic NO2 sensing testing demonstrated excellent repeatability and stability at room temperature.

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