In situ synthesis of polyoxometalate-derived MoS2/phosphomolybdic acid composites for highly sensitive NO2 detection

MoS2 is a promising gas sensing material due to its low resistance and low operating temperature. But the sensitivity of MoS2 is limited by fast electron-hole complexation. In this work, phosphomolybdic acid (PMo12) was used as precursor. After sulfurizing by one-step hydrothermal method, the generated MoS2 and unspent PMo12 can in-situ form MoS2/PMo12 composite nanospheres. The gas sensing performances of the composite were comprehensively investigated. By adjusting hydrothermal reaction temperature, optimized sensitivity (MoS2/PMo12-240) to NO2 gas can be gained. At a low operating temperature of 80°C, the optimized response value to 100 ppm NO2 gas is 2.466, which is higher than most reported MoS2-based NO2 sensors. Moreover, MoS2/PMo12-240 composite also exhibits good selectivity, repeatability, long-term stability and humidity resistance. The mechanism of sensing performance enhancement was also analyzed and discussed. As a semiconductor-like material, PMo12 can form heterojunction together with MoS2. The valence band of PMo12 can capture the holes in MoS2 and effectively suppresses electron-hole complexation. Thus the sensing performance can be improved. This work provides a new strategy for designing and constructing high performance sulfide composite gas sensors by introducing POMs.