Preparation And Gas Sensing Properties Of Bismuth Tungstate-based Nanomaterials

Hydrogen sulfide is often found in poorly ventilated areas,and is very harmful to the environment and health because it is highly toxic.Therefore,it is very important to study sensitive materials that can quickly detect H₂S gas at low temperature.Bismuth tungstate is a representative composite metal oxide.Its typical Aurvillius-type layered structure is beneficial to gas contact with the material,thereby improving the gas sensitivity of the material.In this paper,flaky Bi₂W₂O₉ materials were synthesized,and modified by loading precious metals and complex oxides respectively.Using scanning electron microscope(SEM),transmission electron microscope(TEM),X-ray powder diffraction(XRD),X-ray photoelectron spectroscopy(XPS),etc.analyzed the morphology and composition of the material,and studied the gas sensitivity of the materials before and after modification to H₂S gas.This paper is mainly divided into the following three parts:(1)Bi₂W₂O₉ sheets were synthesized by solvothermal method using bismuth nitrate as bismuth source,tungsten chloride as tungsten source and methanol as solvent.The gas sensitivity test of the material shows that the material can detect H₂S at a low temperature of 92?,with a detection limit of 200 ppb,and the sensor has good reproducibility,humidity resistance and long-term stability.In addition,XPS and gas chromatography-mass spectrometry(GC-MS)were used to explore the sensitive mechanism of the flake Bi₂W₂O₉ material to H₂S gas.(2)On the basis of the sheet-shaped Bi₂W₂O₉ material,the Ag/Bi₂W₂O₉ material was assembled into a gas sensor by the method of ultraviolet light reduction and the gas sensitivity test was carried out.The results show that the Ag loading can improve the gas sensitivity of the material.When the Ag loading is 8 wt%,the material can detect100 ppb H₂S(S=1.6)at 92?,and the sensitivity to 100 ppm H₂S is 76.82,which is 1.5times of that of pure Bi₂W₂O₉,and the response time is only 8 s.Moreover,the change of Ag/Bi₂W₂O₉ material before and after contact with H₂S was analyzed by XPS and GC-MS.(3)A simple solvothermal method was used to synthesize a two-dimensional flake WO₃/Bi₂W₂O₉ composite by adjusting the ratio of bismuth nitrate and tungsten chloride.The composite material has a sensitivity of 84.14 to 100 ppm H₂S at 92°C,which is1.64 and 1.1 times that of the pure phase Bi₂W₂O₉ and 8 wt%Ag/Bi₂W₂O₉,respectively,the response time is 2 s,and the detection limit drops to 10 ppb(S=1.47).It has a good linear relationship for both high concentration and low concentration H₂S.While XPS and GC-MS were used to study the changes before and after the material was in contact with H₂S,the Kelvin probe and ultraviolet diffuse reflection were used to discussed the composition of n-n heterojunction and the influence of heterostructure on gas-sensing performance.