Engineering three-dimensionally ordered mesoporous structure of TiO2 for the fast responsive NH3 gas sensor at ambient conditions

Abstract

Engineering TiO2 nanostructures with a unique fast responsive property for NH3 detection under ambient conditions remains a great challenge in the sensor industry as TiO2 is active at an elevated temperature of more than 200 °C. Despite this obstacle, in this work, the hierarchical three-dimensional ordered mesostructured (3DOM) of TiO2 with designed morphology and pore orientation was developed for the NH3 gas sensor at room temperature. The hybrid TiO2 templates, polymethyl methacrylate (PMMA) and pluronic 123 (P123), were employed during an evaporation-induced self-assembly synthesis. The 3DOM TiO2 was identified to be in a pure anatase phase and showed a honeycomb-like morphology with the walls made of well-connected fine TiO2 particles. The micelle formation time of P123 and the size of PMMA affected the thickness of well-connected nanoparticles of 3DOM TiO2. The optimized micelle formation time for producing the highest sensitivity to the NH3 gas of the P123 and the PMMA size was 15 h and 250 nm, respectively. The NH3 gas sensors were further engineered by laminating the suspended 3DOM TiO2 on a Cu screen printing chip. Interestingly, the low detection limit of 0.1 ppm of NH3 gas sensing was obtained at ambient conditions. Moreover, the systematic gas diffusion pathway with fast response and the grain-controlled transducer process were enhanced when using the 3DOM TiO2 compared to the pristine TiO2 nanoparticles. This work clearly demonstrates that the engineering-designed hierarchical 3DOM structure could provide a fast responsive and low detection limits NH3 sensors at ambient conditions.