Enhanced\nPerformances of PbS Quantum-Dots-Modified\nMoS₂ Composite for NO₂ Detection at Room Temperature

Abstract

The modification\nof the material surface by the second-phase particles\nenables the electron interaction on the Fermi level or the energy\nband between different materials, which can achieve the improvement\nof gas-sensing properties. Herein, a novel composite of PbS quantum-dots-modified\nMoS₂ (MoS₂/PbS) is synthesized by combination\nof hydrothermal method with chemical precipitation and fabricated\ninto the gas sensor to investigate its enhanced gas-sensing properties\ncaused by the modification of PbS quantum dots at room temperature.\nIt is found that the responsivity of MoS₂/PbS is obviously\nhigher than that of pure MoS₂ gas sensor throughout the\nwhole test range, and MoS₂/PbS gas sensor has better selectivity\ncompared with pure MoS₂ gas sensor at room temperature.\nThe response of MoS₂/PbS gas sensor is about 50 times higher\nthan that of MoS₂ gas sensor at 100 ppm NO₂ concentration.\nThe recovery behavior is greatly improved, and the resistance of MoS₂/PbS gas sensor can return completely with almost no drift\n(the recovery ratio is more than 99%). The enhanced gas-sensing properties\nof 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\nadsorption of the target gases, which can prevent MoS₂ from\nbeing oxidized, further improving the stability of gas sensor. Furthermore,\nto profoundly discuss the enhanced performances and the sensing mechanism,\nthe molecular models of adsorption systems are constructed to calculate\nthe adsorption energies and the diffusion characters of NO₂ via density functional theory. We expect that our work can offer\na useful guideline for enhancing the gas-sensing properties at room\ntemperature.