Construction And Enhanced Gas Sensing Properties Of Three-dimensional Structured Metal Oxide Nanomaterials

Among many oxide materials,three-dimensional nanomaterials are suitable for gas-sensing semiconductor sensors because of their fine structure and large specific surface area.Three-dimensional nanomaterials include assembly structure,mesoporous material and multi-shell structure.The essence of semiconductor gas sensing is the change of resistance of gas sensing material during redox process.Therefore,it is theoretically feasible to synthesize high catalytic activity monoatomic material and apply it to gas sensing.Based on the above deduction,Bi₂WO₆ and Co-ZnO nanomaterials with three-dimensional structure were prepared by assembly method and oxidation etching method.Pt single-atoms were anchored on WO₃ using defect engineering strategy.The synthesis and gas sensitization mechanism of these materials were explored and studied.The main research results were as follows:1.Bi₂WO₆ nanoflowers with multistage structure were prepared by restricting crystallization and assembling Bi₂WO₆ with cetyltrimethylammonium chloride?CTAC?.The assembly unit consists of a crystalline-amorphous composite phase with a thickness of 6.5 nm.The order of feeding and the role of CTAC in the synthesis process were discussed.It was found that Bi₂WO₆ assembled with CTAC had a good response to 50 ppm ethanol?Ra/Rg=60.8?,while bismuth tungstate without CTAC had a response of only 5.7 under the same conditions.The gas sensing properties of bismuth tungstate were enhanced by the combined factors of ultrathin film,hierarchical assembly structure and composite crystal phase.2.Co-doped ZnO with polyhedral double-shell structure was obtained by annealing in the air after substituting part of Zn²⁺into ZIF-8 coordination junction.In the annealing process,Co²⁺is oxidized to Co³⁺,which catalyzes the oxidation and decomposition of ZIF-8,enabling it to complete the crystallization of ZnO at a lower temperature.At the same time,Co element will be doped into ZnO.In the process of gas sensing test,polyhedral double-shell structure provides large specific surface area and transmission channel.At the same time,the doping of Co makes the sensitivity and selectivity of ZnO to CO improved significantly.3.The precursor of yellow tungstic acid nanosheets was synthesized by oxalic acid intercalation,and then annealed to yield WO₃ nanosheets.Non-stoichiometric blue WO_3-x was obtained by using H₂/Ar to etch WO₃ surface and then use it to adsorb chloroplatinic acid.After reduction of chloroplatinic acid,single-atomic Pt-supported WO_3-x was obtained.In the gas sensing test of single-atomic Pt/WO_3-x,the response to5 ppm acetone was found to be R_a/R_g=43.4,which was significantly higher than that of Pt nanoparticles loaded WO_3-x and WO_3-x itself.In this work,the chemical principle of synthesis and the role of Pt single atom in the process of gas sensing enhancement were discussed.It also proves the feasibility of using single-atomic materials for the field of gas sensor.