Whole-Process Mildly Prepared TiO₂@Ag Composite Material for Printed, Flexible, and Room-Temperature NH₃ Sensing

A processing strategy to prepare flexible gas sensors that can detect ammonia (NH3) gas at room temperature was proposed in this study. All of the procedures, including material preparation and sensor fabrication, were carried out at mild temperature of no more than 70 °C. Different proportions of silver nanoparticles (AgNPs) were doped on TiO2 nanoparticles to form TiO2@Ag composite materials from reactive silver precursors via a facile heating and stirring process. NH3 gas sensors with different sensitive patterns were produced by the additive printing process based on the ultrasonic resonance principle. Flexible poly(ethylene terephthalate) (PET) with interdigital electrodes (IDEs) was used as the substrate. Facile post-treatment of hot-pressing at a mild temperature of 70 °C was applied to improve the adhesion strength of the sensitive layer to the flexible substrate. Characterizations were carried out to confirm the morphological, elemental, crystal information, and elemental states of the TiO2@Ag composite material. Gas-sensing tests were implemented at different conditions to study the gas-sensing property and mechanism of the flexible sensor. The modified ASTM tape test was applied to inspect the adhesion strength of the sensitive layer on the PET substrate. The whole-process mild strategy of coupling printing technology with hot-press treatment can be extended to the preparation of various kinds of flexible gas sensors.