Ti₃C₂T<i>_x</i> MXene Functionalized via Boron Doped MoS₂ Quantum Dots: A Synergy of Heterojunctions and Doping Effect Enabling Ultrasensitive SO₂ Detection at Room Temperature

The design of mixed-dimensional heterostructures has emerged to be a new frontier of research as it induces exciting physical/chemical properties that extend beyond the fundamental properties of single dimensional systems. Therefore, rational design of heterostructured materials with novel surface chemistry and tailored interfacial properties appears to be very promising for the devices such as the gas sensors. Here, a highly sensitive gas sensor device is constructed by employing heterostructures of boron doped molybdenum disulfide quantum dots (B-MoS₂ Qdots) assembled into the matrix of Ti₃C₂T_x MXene. Functionalization of MXene surface with B-MoS₂ Qdots as a result of strong electrostatic attraction leads to improved charge migration behavior, active site exposure and abundant specific surface area. As a result, the Ti₃C₂T_x/B-MoS₂ sensor device shows ultra-high response (28,998.3% @ 3 ppm), ultra-fast response rate (23.1% s^-1), sub-ppm (10 ppb lowest) detection of sulfur dioxide (SO₂) gas and excellent reversibility at room temperature. Density functional theory-based calculations indicate that enhanced SO₂ sensing performance results from synergy of the 2D-0D heterostructure formation and preferential adsorption of SO₂, induced by doped boron (B) heteroatoms in Qdots. Finally, a portable and wireless SO₂ monitoring system is demonstrated for real-time detection of SO₂ leakage and quantification under certain circumstances.