Enhanced catalytic activity of SnO2 quantum dot films employing atomic ligand-exchange strategy for fast response H2S gas sensors

Colloidal quantum dots (CQDs) are considered as one of the ideal materials candidates for next-generation electronics and optoelectronics. Their large surface-to-volume ratio with exchangeable surface ligands offers a versatile freedom for the regulation of the semiconductor gas sensors. Here we demonstrated an atomic-ligand exchange strategy to construct highly sensitive and selective SnO2 quantum dot gas sensors. Both the cations and anions of the atomic ligands were engineered to enhance the gas adsorption and carrier transport via a film-level atomic ligand exchange treatment, among which the CuCl2-treated SnO2 CQD gas sensors exhibiting highest response of 1755 toward 50 ppm H2S with a fast response and recovery time (48 s/35 s) at 70 °C. The Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS) and UV-vis absorption spectra suggest that the long-chain organic ligands capping on the SnO2 CQDs were successfully exchanged by the atomic ligands and the quantum confinement of the CQDs were well conserved, which is favorable to preserve the catalytic activities of QD materials in real gas-sensing devices. Simultaneously, the copper (II) introduced on the surface of SnO2 CQD films can also act as a catalytic promoter by forming p-CuO/n-SnO2 heterojunctions, thereby enhancing the H2S-sensing performance at relatively low temperatures.