Anatase porous titania nanosheets for resonant-gravimetric detection of ppb-level NO2 at room-temperature

Abstract

The trace-level detection of harmful NO₂ gas at room-temperature is very important for environmental protection and public health. This paper reports the resonant-gravimetric detection of ppb-level NO₂ at room-temperature using two-dimensional porous TiO₂ nanosheets (PTNSs) as highly active sensing materials. They are synthesized by a facile high-temperature calcination approach based on a graphene oxide self-sacrificial template. The PTNS sample prepared at 500 °C (TiO₂-500 °C) show an anatase structure, while the sample prepared at 800 °C (TiO₂-800 °C) contains an impurity rutile phase. By loading pure anatase PTNSs onto resonant microcantilevers, the sensors exhibit high sensitivity to NO₂ gas with a limit of detection as low as 15 ppb. Compared with the TiO₂-800 °C sample, the much higher sensitivity of the TiO₂-500 °C sample can be attributed to the bigger adsorption enthalpy (–ΔH°) of pure anatase TiO₂ to NO₂ gas molecules (21.7 and 57.8 kJ mol⁻¹, respectively). Density functional theory calculations further demonstrate that the existence of the rutile impurity phase in the TiO₂-800 °C sample results in its significantly decreased adsorption activity to NO₂. This work approves the great application potential of anatase PTNSs for the highly sensitive resonant-gravimetric detection of NO₂ gas at room-temperature.