TiO2 nanotubes/g-C3N4 quantum dots/rGO Schottky heterojunction nanocomposites as sensors for ppb-level detection of NO2

As a strong oxidizing pollutant, NO2 can cause fire or even explosion. People living in atmosphere containing NO2 for a long time will significantly affects human health. In this work, we developed a Schottky heterojunction sensor modified by g-C3N4 quantum dots (g-C3N4QDs) and rGO deposited on TiO2 nanotubes (TNTs) arrays. This sensor showed high response and extremely fast response/recovery time as well as excellent detection of ppb level of NO2 at room temperature. TNTs were obtained using a one-step anodic oxidation process. TNTs were modified with g-C3N4QDs and rGO using quasi-CVD method and cyclic voltammetry during in situ electrodeposition, respectively. TNTs/g-C3N4QDs/rGO Schottky heterojunction sensor exhibited high sensitivity to 10 ppm of NO2 (response equal to 15982) at room temperature. Below 15 ppb, sensing response also can reach 127. Sensor response was very fast and increased to 15982 in just 2 s when exposed to 10 ppm of NO2 after which it recovers 90% within 1.16 s. This work clarified the influence of abundant oxygen vacancies (VO·) in TNTs and photogenerated electrons on TNTs/g-C3N4QDs/rGO nanostructures as well as their sensing performances. Our experimental details demonstrated that Schottky barrier was established between TNTs and rGO, which was very beneficial for ppb-level NO2 detection at room temperature.