Enhanced Performances of PbS Quantum-Dots-Modified MoS2 Composite for NO2 Detection at Room Temperature.

The modification of the material surface by the second-phase particles enables the electron interaction on the Fermi level or the energy band between different materials, which can achieve the improvement of gas-sensing properties. Herein, a novel composite of PbS quantum-dots-modified MoS2 (MoS2/PbS) is synthesized by combination of hydrothermal method with chemical precipitation and fabricated into the gas sensor to investigate its enhanced gas-sensing properties caused by the modification of PbS quantum dots at room temperature. It is found that the responsivity of MoS2/PbS is obviously higher than that of pure MoS2 gas sensor throughout the whole test range, and MoS2/PbS gas sensor has better selectivity compared with pure MoS2 gas sensor at room temperature. The response of MoS2/PbS gas sensor is about 50 times higher than that of MoS2 gas sensor at 100 ppm NO2 concentration. The recovery behavior is greatly improved, and the resistance of MoS2/PbS gas sensor can return completely with almost no drift (the recovery ratio is more than 99%). The enhanced gas-sensing properties of MoS2/PbS, which are superior to those of pure MoS2, are ascribed to the large surface area of MoS2 combined with the high responsivity of PbS quantum dots for NO2. The formation of heterojunctions leads to the competitive adsorption of the target gases, which can prevent MoS2 from being oxidized, further improving the stability of gas sensor. Furthermore, to profoundly discuss the enhanced performances and the sensing mechanism, the molecular models of adsorption systems are constructed to calculate the adsorption energies and the diffusion characters of NO2 via density functional theory. We expect that our work can offer a useful guideline for enhancing the gas-sensing properties at room temperature.