Study On The Fabrication And Properties Of Carbon-based Chemical Sensor

Due to the excellent physical and chemical properties,carbon materials have become one of the hot spots in the field of materials science and electronic devices.Among them,graphene possesses high carrier mobility and large specific surface area,it can detect NO₂ and other gases at room temperature.Graphene not only has the advantages of simple preparation process and low cost,but also can improve the power consumption of traditional semiconductor oxide gas sensors.It is a new type of room temperature gas sensing material with great application prospect.However,the shortcomings of pure graphene-based NO₂ sensors,such as low sensitivity and long response time and recovery time,have become the bottleneck to hinder its further development.The analysis of the effect of the microstructure of graphene on its gas sensing properties can not only clarify the sensing mechanism of the sensor,but also provide a theoretical basis for the development of graphene gas sensors with excellent performance,which has important research significance.As environmental problems become increasingly serious,researchers have focused on developing a green,environmentally friendly way to synthesize carbon materials.Natural biomass has the advantages of renewable,low pollution and abundant resources,it can be used as an effective substitute for traditional chemical reagents to prepare porous carbon materials,and has a certain research value in the field of electrochemistry.In this paper,we have constructed the reduced graphene oxide?rGO?-based NO₂sensor and biomass-derived N and P co-doped porous carbon materials for H₂O₂sensing,respectively.The relationship between the microstructure of graphene and the gas sensing performance,and the electrochemical properties of biomass-derived functional carbon material-based to H₂O₂ have been studied.And the sensing mechanism were also analyzed.First,in the process of preparation of GO by a modified Hummers'method,the oxidation temperature was controlled to 65oC,75oC,85oC and 95oC,respectively.The rGO-65,rGO-75,rGO-85 and rGO-95 with different oxygen content were prepared by one-step hydrothermal reduction method.The results of the gas sensing test show that the rGO-85 has higher sensitivity?36.7%?,faster response time?628 s?and recovery time?1575 s?at room temperature towards 5 ppm NO₂,and this characteristic is obviously superior to the other three rGO samples,which can be attributed to the high C-O content in rGO-85.The results show that the C-O bonds in rGO can promote the adsorption of NO₂ molecules,while the C=O bonds were not conducive to the desorption of NO₂ molecules.Subsequently,in order to further study the effect of graphene structure control on the sensing properties of NO₂ sensor at room temperature,the GO sample was used as precursor,five rGO materials with increasing reduction degree were prepared by controlling the hydrothermal reduction temperature?the reduction temperature were120oC,140oC,160oC,180oC and 200oC,respectively?.The results of gas sensing test showed that the rGO-200 sample prepared by reduction at 200oC showed a higher sensitivity to 5 ppm NO₂ at room temperature?43.4%?,but the recovery time was longer?8163 s?.The experimental results show that the more oxygen-containing functional groups in graphene are not the better,and the unsaturated carbon on the non-hexagonal ring has a great effect on the adsorption of NO₂.Moreover,the crumpled structure on the surface of graphene can provide more adsorption sites for the adsorption of NO₂ molecules.Therefore,the sensing properties of graphene towards NO₂ can be improved by properly adjusting the defects and crumpled structure on the surface of graphene.Finally,nitrogen and phosphorusco-doped micro/mesoporous carbon?N,P-MMC?was prepared by thermal treatment of freeze-dried okra.The results of electrochemical measurement of H₂O₂ showed that the N,P-MMC/GCE had a lower detection limit?6.8?M?and a wide linear range?0.1-10 mM and 20-200 mM?of H₂O₂.The reason of the material exhibits good electrochemical properties for H₂O₂,on the one hand,the micropore and mesoporous structure is beneficial to the molecular transfer between electrolyte and electrode material.On the other hand,the co-doped of N and P can reduce the resistance of the solid-liquid interface,which is beneficial to the transfer of electrons.In this paper,we have investigated the structure control of graphene and the effect on the gas sensing properties of the NO₂ sensor at room temperature,firstly.It is proved that the proper adjustment of the structure of graphene can effectively improve the sensing properties of the graphene to the NO₂,and provides a new idea for the development of room temperature NO₂ sensors.Secondly,the electrochemical properties of biomass-derived functional carbon materials for H₂O₂ were studied,and the preparation of carbon materials from biomass opens a new way for the preparation of porous carbon materials.