C-doped and N-doped reduced graphene oxide/TiO2 composites with exposed (0Â 0Â 1) and (1Â 0Â 1) facets controllably synthesized by a hydrothermal route and their gas sensing characteristics

Element doping and controllably facet exposing are efficient solutions for enhancing gas sensing performances of TiO2 nanomaterials. In this study, C-doped and N-doped reduced graphene oxide/TiO2 composites with special exposed facets C-RGO/TiO2 (with HF) and N-RGO/TiO2 (with HF) were controllably synthesized via a hydrothermal method using HF as the morphology-controlling agent at 180 °C for 12 h. The as-prepared composites were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and other measurements. Their gas sensing results demonstrate that the gas sensing performance of N-RGO/TiO2 (with HF) is much better than that of C-RGO/TiO2 (with HF), such as higher sensitivity, and shorter response and recovery time. The sensor based on N-RGO/TiO2 (with HF) exhibits the highest gas response toward isopropanol, ethanol, and acetone at a working temperature of 210, 240, and 270 °C, respectively. The lowest detection of these gases was 1 ppm. The gas sensing mechanism was also carefully analyzed. The TiO2 particles of composite with exposed facets generate electron-hole pairs efficiently. The N element dopant plays the roles of narrowing the band gap of TiO2 based composite, and strengthening the chemical binding between N-RGO and TiO2, which is of benefit to charge separation and electron mobility.