Synthesis And Sensing Properties Of Doped α-MoO₃ Nanocrystaland MoO₃ Nanocomposite

Pure one dimensional (ID) orthorhombic molybdenum trioxide (α-MoO3) nanobelts with width of 200～800 nm and length of several micrometers have been successfully synthesized by a facile and low temperature (120℃) hydrothermal method without any surfactant or template. For the sake of improving the sensing properties of the α-MoO3, the doping of Cd was used to modify the α-MoO3. The crystal structure and morphology of the α-MoO3 were characterized by XRD, FT-IR, Raman and FESEM. The sensing measurements reveal that the samples annealed at 300℃ not only exhibit high response to H2S but also small cross-sensing to other reducing gases. The change of intrinsic defects in Cd-doped sample is responsible for the enhancement of the sensing properties, which has been confirmed by the room temperature PL, UV/visible, Raman spectra and XPS. The response transients of the sensor under different gas concentrations were measured and modeled using L-H heterogeneous reaction mechanism. Origin and mechanism of the enhanced gas sensing for 5 wt% Cd-doped sample were analyzed in detail according to the characteristic of PL and XPS.The hetero-junction hybrids of 1D molybdenum trioxide nanorods/ reduced graphene oxide (MoO3/rGO) with different contents of rGO have been prepared through in-situ one-step microwave hydrothermal method. The morphology, structure and composition of the hybrids were characterized by FESEM, TEM, XRD, FT-IR, XPS, Raman and TG analysis, respectively. The sensing test results show that the novel hybrid with the optimum content of rGO not only exhibit enhanced sensitivity, good selectivity, fast response and recovery compared to that of pure MOO3 but also exhibit long-term stability and reproducibility to ppm-level H2S at low operating temperature of 110℃. The sensing mechanism of MoO3/rGO to H2S is also proposed. The enhancement of sensing performance can be attributable to the formation of hetero-j unction at the interface in hybrid, which renders the surface of the MoO3 nanorods more n-type, meantime facilitates the migration of electrons due to the incorporating of rGO. The study will promote extensive application in efficient H2S gas sensors.