Study On Synthesis And Gas Sensing Properties Of RGO/CoTiO₃ Composites

Cobalt titanate?CoTiO₃?,as a semiconductor gas sensing material,has advantages of high sensitivity,fast response and good stability.However,the application of CoTi O₃ has been limited owing to its high working temperature,which causes energy consumption and complicates the sensing devices.Therefore,how to effectively improve its gas sensing properties,especially reduce the working temperature,becomes important research problem of this topic.In this work,Co TiO₃ nanocrystal,mesoporous CoTiO₃ nanocrystal and porous CoTiO₃ microrods were firstly prepared by sol-gel method via using Co?NO₃?₂·6H₂O and Co?CH₃COO?₂·4H₂O as cobalt source,Ti?OC₄H₉?₄ as titanium source.Then,different microstructural rGO/CoTiO₃ heterogeneous gas sensing materials were obtained by compositing CoTiO₃ with graphene oxide?GO?.The influence of different preparation parameters on the structure,morphology and gas sensing performance of composites were studied in details,which can draw the following conclusions:?1?The CoTiO₃ nanocrystal with average diameter of 100 nm was prepared by using cobalt nitrate and butyl titanate with molar ration of 1:1.The sol pH value was fixed at 2⁵,and the annealing temperature was 650°C for 2 h.Mesoporous CoTiO₃ nanocrystal was prepared by adding P123 as template agent.The hexagonal porous CoTiO₃ microrods with average size of 3?m were synthesized by using ethylene glycol as solvent,annealing at 700°C.The response to 10 ppm ethanol of CoTiO₃ nanocrystal,mesoporous CoTiO₃nanocrystal and porous CoTi O₃ microrods was 2.2,6.22 and 7.23 respectively.The response and recovery time were 1 s/10 s,1 s/7 s and 1 s/1 s.And the optimal working temperature of the three materials was 360°C,322°C and334°C.?2?The content of graphene oxide,the ultrasonic power and the dosage of NMP solvent have important effects on the microstructure and properties of rGO/Co Ti O₃ nanocrystal composites which prepared by sol-gel method.With the increase of GO content,the conductivity of composites significantly improved.And the ethanol sensing response of composites firstly increased then decreased.The solvent affected the combination form and interaction of rGO and CoTiO₃.Ultrasound treatment facilitates rGO sheets dispersion.And Co Ti O₃ can uniformly distributed on the surface of rGO sheet,which is in favor of the improvement of gas sensitivity.The most sensing rGO/CoTi O₃ nanocrystal composite was prepared by using 3.9 wt%GO composited with Co Ti O₃,20 mL NMP as solvent and ultrasonic power of 240 W.The working temperature of as-prepared rGO/CoTiO₃ composite was 195°C.The response to 10 ppm ethanol was 5.5,and both the response and recovery time were 1 s.Compared to the pure Co TiO₃ nanocrystal,the working temperature reduced 165°C,response value increased nearly 1.5 times,and recovery time was shortened 8 s.?3?The composite consisting of rGO and hexagnol porous CoTi O₃microrods was obtained by improving the compound technology of CoTiO₃ and rGO.The optimal working temperature was 295°C,the response to 10 ppm ethanol was 32.2,and the response/recovery time was only 1 s.Compared to porous CoTiO₃ microrods,its working temperature reduced 39°C,response value increased nearly 3.5 times.?4?The excellent ethanol sensing perpformance of rGO/CoTiO₃ composite was attributed to following aspects.1)the high conductivity of graphene at relatively low temperature;2)the catalytic effect of Ti³⁺on gas adsorption/desorption and redox reaction in the process of gas sensing;3)the Co-O-C bond played a key role in fast carrier transport;4)The p-p heterojunction facilitated effective separation of electron-hole and promoted the carriers'transportation;5)The porous structure provided a large specific surface area and more active adsorption sites for gas adsorption/desorption.