Microwave-assisted Carbon-induced Preparation And Performance Regulation Of Metal Oxide Gas-sensitive Material

In this paper,normal-pressure microwave-assisted method is used to uniformly load metal oxides on carbon nanomaterials to induce the preparation of metal oxide@C composites or metal oxide structured materials.The gas sensing properties of the obtained materials were systematically researched for realizing effective regulation of low concentration,low temperature and high-performance detection of toxic and harmful gases.And the relevant gas-sensing mechanism was analyzed.The main contents are as follows:（1）In₂O₃/rGO nanocomposites were synthesized via a normal-pressure microwave-assisted method and an in-situ growth technology with graphene oxide（GO）as matrix.The In₂O₃ nanoparticles are uniformly distributed on rGO surfaces with particle sizes of 3～26 nm.The gas sensing performance of the In₂O₃/rGO sensors with different In₂O₃ contents were tested,and the results show that the 20-In₂O₃/rGO composite with indium nitrate mass ratio of 20 to GO has the highest response and the best selectivity to NO gas as a gas sensitive sensor.The response of the 20-In₂O₃/rGO sensor to 50 ppm NO at the optimum operating temperature of 150℃is 30.6,which is 6 times higher than the pure In₂O₃sensor（5.2）.The enhanced NO sensing properties of In₂O₃/rGO nanocomposite can be attributed to the synergistic effect of In₂O₃ particles and rGO sheets.（2）α-Fe₂O₃ hollow chains（α-Fe₂O₃ HCs）nanostructure,consisting of porousα-Fe₂O₃thin layers,was prepared by normal-pressure microwave-assisted method and subsequent calcination heat treatment with carbon chains as a template.The carbon chains were prepared by hydrothermal method.Carbon spheres,which composed of the carbon chains,have a diameter range of 100～160 nm,and the average diameter is 125 nm.After removing the carbon template by calcination,the diameter of obtainedα-Fe₂O₃ HCs is 110～190 nm with an average diameter of 150 nm.The size of the second-levelα-Fe₂O₃ nanoparticles ranges from 7 to 33nm.The gas-sensing test shows that theα-Fe₂O₃ HCs sensor has high response,low operating temperature,high selectivity and good stability to HCHO vapor.The response of theα-Fe₂O₃HCs sensor is up to 96 to 5 ppm HCHO at the optimum operating temperature of 150℃.The improved HCHO-sensing performance of theα-Fe₂O₃ HCs sensor at low temperature（≤150℃）can be attributed to the second-level porousα-Fe₂O₃ structure,which is induced by the uniformly dispersed Fe（OH）₃@C chains,and is rich in oxygen vacancy defects.（3）Porousα-Fe₂O₃ nanosheets composed of interconnectedα-Fe₂O₃ nanoparticles were synthesized via a normal-pressure microwave-assisted method and subsequent calcination heat treatment by using GO as template.The particle sizes of secondaryα-Fe₂O₃ nanoparticles is 20～35 nm.The gas-sensing test shows that the porousα-Fe₂O₃ nanosheets sensor has low operating temperature,high selectivity and good stability to H₂ gas.The response of the porousα-Fe₂O₃ nanosheets sensor is up to 17.9 to 10 ppm H₂ at the optimum operating temperature of 150℃.The enhanced H₂-sensing performance of the porousα-Fe₂O₃ nanosheets can be attributed to the special structure of porousα-Fe₂O₃ nanosheets composed of second-levelα-Fe₂O₃ nanoparticles.