An ultra-sensitive NH gas sensor enabled by an ion-in-conjugated polycroconaine/TiCT core-shell composite.

MXenes are emerging sensing materials due to their metallic conductivity and rich surface chemistry for analytes; they, however, suffer from poor stability. Incorporation with functional polymers can largely prevent the performance decay and enhance the sensing performance. Herein, we demonstrate a core-shell composite, TiCT@croconaine (poly(1,5-diaminonaphthalene-croconaine), PDAC) prepared by a facile polymerization reaction, suitable for NH detection. Compared to pristine TiCT, the sensor made of a TiCT-polycroconaine composite exhibits a significantly enhanced sensitivity of 2.8% ppm and an estimated achievable limit of detection of 50 ppb. The improved sensing performance could be attributed to the presence of PDAC facilitating the adsorption of NH and changing the tunneling conductivity between TiCT domains. Density functional theory (DFT) calculations reveal that the adsorption energy of NH on PDAC is the highest among the tested gases, which supports the selectivity of the sensor to this analyte. Benefiting from the protection conferred by the PDAC shell, the composite has a reliable operation period of at least 40 days. In addition, we demonstrated a flexible paper-based sensor of the TiCT@PDAC composite, without attenuated performance upon mechanical deformation. This work proposed a novel mechanism and a feasible methodology to synthesize MXene-polymer composites with improved sensitivity and stability for chemical sensing.