Solid-state Chemical Synthesis And Gas-sensing Property Of ?-MoO₃ Nano-materials

Semiconductor oxide gas-sensing materials play an important role in the field of detection and monitoring of toxic, harmful, inflammable and explosive gases. The existing semiconductor oxide gas-sensing materials for a variety of gas has a very good response, but there are still some defects of high working temperature and poor stability, thus the development of new semiconductor oxide gas-sensing materials with excellent comprehensive performance have important significance. Current synthetic methods for oxides gas-sensing materials often required expensive experimental equipment, complex experiment process and harsh experimental conditions, so it is very necessary to develop some synthetic methods that only require simple equipment, less synthesis steps and mild condition. In recent years, as a new kind of gas-sensing material, MoO3 has attracted more and more attention. In this paper, we use simple, convenient, efficient and green solid-state reaction to synthesize?-MoO3 nanomaterials. The influence of different reactants, different reactant ratios and other conditions to the microstructure of ?-MoO3 nanomaterials were studied, and the relationship between the microstructure and gas-sensing properties were investigated. The gas-sensing properties of ?-MoO3 nanomaterials were modified by doping with rare earth elements and metal elements. This paper mainly includes the following contents:(1) ?-MoO3 nanomaterials were prepared by the calcination of precusors that were synthesized by solid-state chemical reaction between ammonium molybdate and organic acid at the room temperature. The influence of different reactants, reactant ratios, calcined temperature of precursor, and surfactants to morphology and gas-sensing performance of ?-MoO3 nanomaterials sand were investigated.Experimental results showed that the reactant, the reactant ratio, the calcination temperature, the surfactants have an effect on the morphology and the gas-sensing properties of the ?-MoO3 nanomaterials. The as-prepared samples have a smaller sizeand better gas sensing properties when the reactant was oxalic acid, the response value of the sample reached 11.4 to 100 ppm xylene; when the ratio of ammonium molybdate and oxalic was 1:5, the products had a smaller size and uniform morphology, and the response value reached 10.2 to 100 ppm xylene; when the calcined temperature for precursor was 450 oC, the as-prepared sample had a more appropriate nucleation and growth rate, and the sample has uniform morphology and better gas response; when we added PEG-400 to the reaction system, the microenvironment of solid-state reaction changed, the as-prepared sample displayed a array structure self-assembled by nanorods, and showed a bigger surface area and higher response, the response value of the sample reached 16.5 to 100 ppm xylene.(2) Three kinds of rare earth elements(Y, Yb, Pr) were doped to modify gas-sensing properties of ?-MoO3 nanomaterials. The influence of doping substances and amount on the gas-sensing properties of ?-MoO3 nanomaterials were investigated,and the gas-sensing mechanism was analyzed. The experiment results showed that the doping of Y, Yb and Pr can increased the response value. Compared with undoped samples, the sample of 1% Y-doped showed a higher response value, and the response value reached 30.2 to 100 ppm xylene, which was two times than that of undoped sample. The response value of 5% Yb-doped sample reached 23.2, and the response of 7 % Pr-doped sample also reached 21.2.(3) Six kinds of metal elements(Fe?Co?Ni?Zn?Sn?In) were doped to modify gas-sensing properties of ?-MoO3 nanomaterials. The influence of doping substances and amount on the gas-sensing properties of ?-MoO3 nanomaterials were investigated.Experimental results show that the doping of metal elements can not only decrease the working temperature of ?-MoO3 nanomaterials, from 370 oC to 340 oC, but also increase the response value of ?-MoO3 nanomaterials. The response value of 0.3%Fe-doped sample reached 26.4 at 340 oC to 100 ppm xylene. For 100 ppm xylene at the optimal working temperature of 340 oC, the response value of 0.5% Sn-dopedsample reached 25.2, the response value of 3% Co-doped sample reached 24.2, the response value of 0.7% Zn-doped sample was 21.2, the response value of 1%In-doped sample was 19.4, and the response value of 2% Ni-doped sample was 18.1.