Highly Selective H₂S Gas Sensor Based on Ti₃C₂Tₓ MXene–Organic Composites

Cost-effective and high-performance H₂S sensors are required for human health and environmental monitoring. 2D transition-metal carbides and nitrides (MXenes) are appealing candidates for gas sensing due to good conductivity and abundant surface functional groups but have been studied primarily for detecting NH₃ and VOCs, with generally positive responses that are not highly selective to the target gases. Here, we report on a negative response of pristine Ti₃C₂Tₓ thin films for H₂S gas sensing (in contrast to the other tested gases) and further optimization of the sensor performance using a composite of Ti₃C₂Tₓ flakes and conjugated polymers (poly[3,6-diamino-10-methylacridinium chloride-co-3,6-diaminoacridine-squaraine], PDS-Cl) with polar charged nitrogen. The composite, preserving the high selectivity of pristine Ti₃C₂Tₓ, exhibits an H₂S sensing response of 2% at 5 ppm (a thirtyfold sensing enhancement) and a low limit of detection of 500 ppb. In addition, our density functional theory calculations indicate that the mixture of MXene surface functional groups needs to be taken into account to describe the sensing mechanism and the selectivity of the sensor in agreement with the experimental results. Thus, this report extends the application range of MXene-based composites to H₂S sensors and deepens the understanding of their gas sensing mechanisms.