Mesoporous Co₃O₄Synthesized By Hard Templating Method And Their Gas Sensing Properties

Mesoporous metal oxides are considered promising candidates in thedevelopment of gas sensors, due to their high specific surface area, high pore volumeand tunable pore size. There are a lot of mesoporous materials, considering MCM、SBA、FSM、HMS、AMS and so on. There are also many kinds of constructs, likethree-dimensional hexagonal, two-dimensional hexagonal, cubic, stratiform and so on.Especially sba-15is two-dimensional hexagonal and KIT-6has three-dimensionalchannels. There are two kinds of method synthesizing mesoporous metal oxidematerials, soft and hard templating method. Compared with soft templating method,in the synthesis of target oxide, mesoporous structure using hard templating method isnot easier to collapse, and retain relatively complete. So we usually using hardtemplating method in the synthesis of metal oxidesCobalt oxide （Co₃O₄） regarded as a model for p-type semiconductor has wideapplications such as catalyst, anode materials in Li-ion rechargeable batteries,solid-state sensors, electrochromic devices, solar energy absorbers, and pigments.Recent works have demonstrated that Co₃O₄is also a promising functional materialfor chemoresistive-type gas sensors.Co₃O₄-k and Co₃O₄-s were synthesized by using KIT-6and SBA-15and onetime impregnated. The results of small angle X-ray diffraction, nitrogenadsorption–desorption demonstrate that the Co₃O₄-k and Co₃O₄-s are mesoporousmaterial. Through the static testing system, the responses of Co₃O₄-k and Co₃O₄-s toCO are both higher than the previous report, and Co₃O₄-k is also higher than Co₃O₄-s.Mesoporous Co₃O₄-k and Co₃O₄-s have been successfully synthesized by twiceimpregnated and using cubic KIT-6and hexagonal SBA-15as the hard templates,respectively. By investigating the reaction of HF and hard templates, Co₃O₄-k-HF-60and Co₃O₄-s-HF-60were choosen to test to the next gas sensing test. The results ofsmall angle X-ray diffraction, nitrogen adsorption–desorption and transmissionelectron microscopy demonstrate that the Co₃O₄-k-HF-60and Co₃O₄-s-HF-60display three-dimensional cubic mesoporous structures and two-dimensional hexagonalmesostructures, respectively. The sensing properties of mesoporous Co₃O₄-k-HF-60and Co₃O₄-s-HF-60for ethanol were investigated. The sensor utilizingCo₃O₄-k-HF-60exhibits more excellent response and recovery behavior and muchhigher sensitivity to ethanol, compared to that based on Co₃O₄-s-HF-60. Althoughboth samples possess the similar specific surface area, three-dimensional intersectedchannels in Co₃O₄-k-HF-60accommodating large number of target gas molecularleads to high utilization of sensing materials, which coupled with high electronmobility in the interconnected framework of Co₃O₄-k-HF-60result in its superiorsensing performance than that of Co₃O₄-s-HF-60containing two-dimensional straightchannels. Because of the different morphology and pore structure, when the gassensor is exposed to gas molecules, pore structure of mesoporous material becomes animportant factor to affect the adsorption process. In the adsorption process, highlybicontinuous pore structure and large and uniform pore size both provide better masstransfer dynamic.