Selective Detection of NH₃ Gas by Ti₃C₂T Sensors with the PVDF-ZIF-67 Overlayer at Room Temperature

In the realm of NH₃ gas-sensing applications, the electrically conductive nature of Ti₃C₂T MXene, adorned with surface terminations such as -O and -OH groups, renders it a compelling material. However, the inherent challenges of atmospheric instability and selectivity in the presence of gas mixtures have prompted the exploration of innovative solutions. This work introduces a strategic solution through the deposition of a mixed-matrix membrane (MMM) composed of poly(vinylidene fluoride) (PVDF) as the matrix and zeolitic imidazolate framework-67 (ZIF-67) as the filler. This composite membrane acts as a selective filter, permitting the passage of a specific gas, namely NH₃. Leveraging the hydrophobic and chemically inert nature of PVDF, the MMM enhances the atmospheric stability of Ti₃C₂T by impeding water molecules from interacting with the MXene. Furthermore, ZIF-67 is selective to NH₃ gas via acid-base interactions within the zeolite group and selective pore size. The Ti₃C₂T sensor embedded in the MMM filter exhibits a modest 1.3% change in the sensing response to 25 ppm of NH₃ gas compared to the response without the filter. This result underscores the filter's effectiveness in conferring selectivity and diffusivity, particularly at 35% relative humidity (RH) and 25 °C. Crucially, the hydrophobic attributes of PVDF impart heightened stability to the Ti₃C₂T sensor even amidst varying RH conditions. These results not only demonstrate effective NH₃ detection but also highlight the sensor's adaptability to diverse environmental conditions, offering promising prospects for practical applications.