Ultrafast and Sensitive Hydrophobic QCM Humidity Sensor by Sulfur Modified Ti3C2Tx MXene

MXenes, 2-D transition metal carbides, nitrides, and carbonitrides, have developed to be attractive nanomaterials for humidity-sensitive materials due to their abundant active sites, tunable surface chemistry, and outstanding stability. Nevertheless, metallic conductivity also makes it hard to extract the signal change from semiconductor resistive gas sensors. Here, we introduce quartz crystal microbalance (QCM) as a humidity sensor platform to collect the signal of MXene mass change directly replacing electronic signal detection. Surface modification was taken place for changing the surface functional groups during hydrofluoric acid (HF) etching for enhancing more humidity sensing performance of Ti3C2Tx MXene. Sulfurized Ti3C2Tx MXene QCM sensors show the highest humidity sensing performance than as-synthesized Ti3C2Tx MXene from 6 Hz/% up to 105 Hz/% with an ultrafast response and recovery time (13/6 s). Also, it was calculated up to 20 times more water absorption ratio compared to mass change of the as-synthesized Ti3C2Tx MXene, showing potential for high-performance and fast humidity sensors.