Rb2CO3-decorated In2O3 nanoparticles for the room-temperature detection of sub-ppm level NO2

•A facile manufacturing process of new Rb2CO3-decorated In2O3 sensor.•The Rb2CO3/In2O3 composite sensor detecting 100 ppb level NO2 gas at room temperature under visible light illumination.•Propose the mechanism for the high sensing performance realized by high rate of electron supply to the receptor.•Good sensing performance of high selectivity, stability, repeatability, linearity, with discussion of the humidity effect.