Synthesis of SnO2/rGO/g-C3N4 composite nanomaterials with efficient charge transfer for sensitive optoelectronic detection of NO2 gas

The sensitivity improvement of g-C3N4 based gas sensor is still limited by the low charge separation and scarce adsorption sites. Here, reduced graphene oxide (rGO) was assembled on g-C3N4 and then ultrasmall tin oxide (SnO2) nanocrystals were decorated on the rGO/g-C3N4 by a facile hydrothermal method for fabricating SnO2/rGO/g-C3N4 composite nanomaterials. The optimized nanocomposite sensor exhibits an ultralow detection limit of 5 ppb with 117-time enhancement response to 1 ppm NO2 than bare g-C3N4 at room temperature, along with high selectivity. This is attributed to the enhanced charge separation by the electron transfer from g-C3N4 to SnO2 at the aid of rGO and the promoted adsorption of NO2 from SnO2 nanocrystals as site-selectively centers based on the time-resolved photophysical spectra and temperature-programmed desorption curves. This work provides an efficient route to improve the sensing performance of g-C3N4 at room temperature.