Facile synthesis of ZnIn2S4/Cu2O hierarchical heterostructures for enhanced selectivity and sensitivity of NH3 gas at room temperature

The development of an effective and reliable sensor with the capability to detect ammonia (NH3) gas at room temperature exerts a significant influence on the sensor industry. The gas sensing performance is notably improved by the formation of a heterostructure between metal oxide with metal sulfides. In this study, pure ZnIn2S4 (ZIS), Cu2O and heterostructures of ZIS with 5, 10 and 20 wt% of Cu2O were successfully prepared using hydrothermal, co-precipitation and heat treatment methods, respectively. A thorough investigation has been carried out to examine the sensing capabilities of all the materials upon exposure to NH3 with different concentrations (1, 5, 10, 15, 20, 25 and 50 ppm) at room temperature (RT). Impressively, the composite material 0.9ZnIn2S4/0.1Cu2O (ZIS-10) has exhibited remarkable gas sensitivity compared to pristine ZIS and Cu2O towards 25 ppm NH3, low limit of detection (1 ppm) with fast response/recovery times (37/25 sec). The improved performance of the ZIS-10 composite sensor may be ascribed to the synergistic effect between ZIS and Cu2O, which facilitates the electron transfer from ZIS to the Cu2O at the interface. The plausible gas-sensing mechanism and the pathways responsible for enhanced sensing are also discussed in detail.