A New Breakthrough in SO2 Detection: TiO2/MoSe2 Composite Sensors

By Dr. Noopur JainReviewed by Bethan DaviesJan 17 2025

Air pollution is still a massive concern, with sulfur dioxide (SO₂) standing out as one of the most harmful pollutants. Generated largely by industrial emissions, SO₂ is a known contributor to respiratory illnesses and environmental degradation, including acid rain. Developing effective, reliable ways to monitor SO₂ levels is therefore crucial—and a recent study in Nanomaterials offers an exciting breakthrough.

Study: TiO₂ Nanosphere/MoSe₂ Nanosheet-Based Heterojunction Gas Sensor for High-Sensitivity Sulfur Dioxide Detection. Image Credit: Valeryia Zayats/Shutterstock.com

Researchers have developed a novel gas sensor using a composite of titanium dioxide (TiO₂) and molybdenum diselenide (MoSe₂). By combining these materials, the team achieved a significant leap in sensitivity and performance, making this composite sensor a promising solution for environmental monitoring.

Why TiO₂ and MoSe₂?

TiO₂ has long been a favorite for gas sensing due to its stability and reactivity. However, it has limitations, especially in detecting certain gases like SO₂ with high sensitivity. On the other hand, MoSe₂, a two-dimensional material with a high surface area and unique electronic properties, excels at adsorbing gas molecules.

By combining these two materials into a heterojunction structure, researchers hypothesized that the strengths of each would complement one another. TiO₂ would provide a stable foundation for gas sensing, while MoSe₂ would enhance sensitivity and gas adsorption. This synergy could lead to a sensor that outperforms existing options.

A Step-by-Step Look at the Sensor’s Development

The TiO₂/MoSe₂ composite sensor was developed using a carefully controlled process:

1. TiO₂ Synthesis: Titanium sulfate (Ti(SO₄)₂) and urea were dissolved in water and treated with ultrasonic waves for uniform mixing. The solution was heated to 180 °C in a sealed reactor for three hours, then purified through multiple centrifugation steps and dried at 60 °C to produce high-purity TiO₂ powder.
2. MoSe₂ Synthesis: Sodium molybdate (Na₂MoO⁴·2H₂O), selenium powder, and hydrazine hydrate were then combined and processed. After stirring, ultrasonic treatment, and heating at 200 °C for 48 hours, the mixture was purified and vacuum-dried. The dried material was calcined at 700 °C under argon gas for two hours, yielding MoSe₂ nanosheets.
3. Composite Formation: TiO₂ nanoparticles were uniformly distributed on MoSe2 nanosheets to create the final composite structure, ensuring effective interaction between the two materials.

Testing and Results

The sensor’s performance was evaluated using an automatic gas mixing system to measure its response to varying SO₂ concentrations (0.5–100 ppm). The sensor’s response was calculated as the ratio of its resistance in air (Ra) to its resistance in the presence of SO₂ (Rg). Recovery was facilitated by purging the chamber with argon gas.

Key findings include:

• High Sensitivity: The sensor exhibited a 59.3 % response at 100 ppm SO₂ with a detection limit as low as 0.25 ppm.
• Fast Response and Recovery Times: At an operating temperature of 175 °C, the sensor achieved a response time of 15 seconds and a recovery time of 13 seconds.
• Environmental Stability: The sensor demonstrated stable performance under controlled humidity, an essential factor for practical applications.

The enhanced performance of the TiO₂/MoSe₂ sensor is attributed to the unique properties of the composite. MoSe₂’s high surface area enhances the adsorption of SO₂ molecules, while TiO₂ facilitates efficient charge transfer. This combination amplifies the sensor’s resistance changes, leading to more precise and reliable detection.

Material characterization techniques such as transmission electron microscopy (TEM) and X-ray diffraction (XRD) confirmed that TiO₂ nanoparticles were evenly distributed on MoSe₂ nanosheets. This uniform structure is essential for maximizing gas interaction and ensuring consistent performance.

Implications and Future Directions

This study highlights the potential of combining two-dimensional materials like MoSe₂ with traditional semiconductors such as TiO₂ to create next-generation gas sensors. With its high sensitivity, rapid response, and durability, the TiO₂/MoSe₂ composite sensor could significantly improve the way we monitor SO₂ levels in industrial and environmental settings.

While the results are promising, the researchers see room for further improvement. Optimizing the sensor’s design, automating production processes, and testing its performance in real-world environments are key next steps.

Additionally, the principles demonstrated here could be applied to detect other harmful gases, broadening the sensor’s potential impact. With continued advancements, this technology could play a vital role in reducing air pollution and protecting public health.

Journal Reference

Zhou L., Niu C., et al. (2025). TiO₂ Nanosphere/MoSe₂ Nanosheet-Based Heterojunction Gas Sensor for High-Sensitivity Sulfur Dioxide Detection. Nanomaterials 15(1), 25. DOI:10.3390/nano15010025, https://www.mdpi.com/2079-4991/15/1/25