Preparation Of Two-dimensional Molybdenum Trioxide By Liquid Phase Stripping And Its Gas Sensing Properties

With the application of graphene in various sectors like optical sensors, nano-electronic devices, solar cells, the scientific community has put more and more attention to other two-dimensional layer materials, such as transition metal dichalcogenides, transition metal oxides and other 2D materials. Such materials span the entire range of electronic structures, from insulator to metal, and display interesting properties. These include the topological insulator effect, superconductivity, and thermoelectricity etc. Gas sensor technology is one of the most important key technologies in the future, which is being widely used in our daily life. There are an increasing number of sensors applying to the process of production monitoring, sanitation detection, and detection of medical health care as well as disaster prevention. However, owning a larger specific surface area and surface activity,2D nanomaterials expose more surface atoms, which has resulted in the shortage of surface atom ligands and the increase of active sites, thus significantly improving the performance of gas sensor. MoO3 belongs to wide bandgap semiconductor, with 2D layered structure like graphene. It not only has a good sensor response to a variety of volatile organic compounds, but also can be used as precursors to synthesize functional composite materials with organic polymers. Nevertheless, to prepare large areas of 2D layered materials with high quality in general, the physical and chemical methods are of great difficulty. This paper mainly focuses on the process of exfoliation of the bulk MoO3 crystals into nanosheets by combining grinding and sonication, the exploration of the effects of ultrasonic solvent on the product, and the presentation of ion-exchange method and hydrothermal synthesis method in preparing MoO3/polymer composite materials.Firstly, a combination of grinding and sonication was used to cause exfoliation of the bulk MoO3 crystals into nanosheets. The whole operation is quite simple and preparation conditions are relatively easy, in which material characterizations are adopted, including UV-Vis-NIR spectroscopy, XRD, Raman, FESEM, TEM and AFM. It is found that the 2D-MoO3 nanosheets are far more effective than the bulk MoO3 powder for chemical sensor application. At the optimum working temperature, the response of the present sensor using the 2D-MoO3 nanosheets increases from 8 to 33,3 times higher than the value of the bulk MoO3. More specifically, the response time is reduced to 21 seconds from 27 seconds for the reference; meanwhile, the recovery time sharpened from 26 to 10 seconds. This is mainly attributed to that the high specific surface area of the gas sensitive material can offer more reactive sites for material surface, provide a bigger place for gas adsorption and make for the target gas molecule adsorption and transmission, hence significantly enhancing the gas sensitive performance of the sensor.Secondly, we have carried out a study on the effect of solvent in liquid exfoliation method on the product appearance. In the first place, we demonstrated a versatile mixed-solvent strategy to obtain highly dispersed suspensions of 2D-MoO3 nanosheets. By using appropriate solvent, highly stable MoO3 suspensions can be obtained in low-boiling solvent. The 50 vol% ethanol/water solution is more effective to disperse the MoO3 nanosheets than other solvents, with the highest concentration 0.182 mg/ml harvested. Meanwhile, we found that the solvent is effective not only in dispersing but also in exfoliating the MoO3 nanosheets. And it is far more effective for chemical sensor application. Both DMSO and DMF solvents are difficult to remove during the fabrication of MoO3 nanosheet device. The remaining solvents can cause aggregation during the slow solvent evaporation, leading to lower sensor response.Finally, we combined ion-exchange method and hydrothermal synthesis method. We adopt MoO3 as the inorganic subject and organic monomer as object, taking dodecyl-amine as good organic intercalation agent, to modify the MoO3 interlayer. At last the similar polarity of Dimethyl sulfoxide and N,N-Dimethylformamide are inserted into the layer to prepare MoO3/polymer composite materials successfully.