Photo-Assisted Selective and Reversible Acetone Sensors Based on 2-D MoSe₂ Nanoflakes
Flourishing industrialization and urbanization have led to the release of hazardous gases and volatile organic compounds (VOCs) into the atmosphere, posing an immediate and lasting threat to human health. High levels of VOCs, such as acetone, can severely impact renal and nervous health with prolonged exposure. On the other hand, human metabolism naturally produces small amounts of VOCs, which serve as biomarkers, reflecting metabolic health and potentially indicating deteriorated conditions. Previous studies have shown that abnormal presence of acetone in breath can be a signal of diseases, such as diabetes, lung cancer, and heart failure. Hence, ultrasensitive and inexpensive detection of acetone is essential for monitoring environmental and human health.
Two-dimensional (2D) Transition metal dichalcogenides have garnered significant attention due to the tunability offered by their layer-dependent chemical and optical properties, which makes them appealing in numerous fields of application. With a high surface-to-volume ratio, increased carrier mobility, high adsorption energy with varying affinity for different molecules, and environmental stability, these materials exhibit strong potential for room temperature sensing.
This paper explores the acetone sensing capabilities of 2D MoSe2 nanoflakes at room temperature. Chemically exfoliated MoSe2 was deposited on an ITO-coated glass substrate to fabricate the sensor. The sensing parameters of this device are checked using a home-built gas sensing setup, and measurements were initially conducted in the dark and at room temperature. This sensor exhibits a sensitivity of 6.87%/ppm for acetone along with a response time of 290 s. High selectivity for acetone compared to other VOCs is a key feature of this sensor. The limit of detection (LOD) for this sensor is statistically estimated to be 6.84 ppb. With minimal hysteresis (~0.993%), this sensor exhibits excellent reversibility, a highly desirable property for practical implementation. However, after the withdrawal of acetone, the recovery time of this sensor is quite extensive, which is further modified by photo-assisted gas sensing.
Photo-assisted gas sensing is a prevalent approach to enhance sensing parameters of room temperature detection, characterized by low power consumption, enhanced safety, and improved longevity, thereby mitigating the degradation issues owing to diffusion and sintering effects associated with high-temperature operations. 2D TMDs such as MoSe2 nanoflakes demonstrate phenomenal optoelectronic properties, making it easier to modulate their gas sensing mechanism by external optical stimuli.
We have used low-irradiance LEDs with wavelengths ranging from UV to NIR. Under UV- illumination (wavelength ~ 375 nm), the recovery time of this sensor is reduced to half of that in the dark. This is attributed to the flat-band absorption feature characteristics of these types of nanomaterials, where a large number of photo-generated hot electron-hole pairs accelerates the recovery process in the absence of acetone. This phenomenon is known as photo-stimulated desorption (PSD). However, this improvement comes at the cost of reduced sensing response percentage. This is ascribed to the p-type nature of MoSe2 nanoflakes, where holes are the majority carriers.
Our device shows promise for high-performance acetone detection, based on metrics like LOD, hysteresis error, selectivity, and recovery rate. Simple device design, room temperature sensing, along with the facile photo-assistance technique, further ensure economical sustainability. Its ultrasensitive detection capabilities, cost-effectiveness, and low power requirements make this sensor promising for real-time applications.