| As environmental pollution and energy depletion problems are getting more and more serious today, people become to pay more attention to the environmental protection and the development new energy. That why most of the scientific community research on metal oxides are focus on these two points. To design a gas sensor to NH3 gas which can work in atmosphere at room temperature, we chose Co3O4 because of its fine conductivity, good catalytic reactivity and noteworthy chemical stability. As the properties of the sensor strongly depend on their morphologies and structure, we synthesized two different kinds of Co3O4 sensors which are named as 3D hierarchical porous Co3O4 materials（HPCo） and Co3O4/PEI-GO composite materials.In first part, 3D hierarchical porous Co3O4 materials（HPCo） were synthesized via a PS spheres templated transformation route. This novel 3D structure contained not only plenty of interconnecting macropores and mesopores, but also a large amount of irregular structure defects. The HPCo has a large specific surface area of 58.75 m2·g-1 and a average particle size of 20 nm. It also presents excellent sensing performance to NH3 gas at room temperature with the highest sensitivity（146.2% to 100 ppm）, fast response time（2 s to 100 ppm）, and a low detection limit of 0.5 ppm. Such superior properties are attributed to the unique hierarchical porous structure, large specific surface area, excellent chemisorbed ability to oxygen species and good catalytic activity of Co3O4 nanomaterials.In second part, Co3O4/PEI-GO composite materials via a hydrothermal route. In this work, the PEI was used as a load-directing agent to the final Co3O4 particles grow on the graphite oxide along the branched PEI chains. The synthesized Co3O4/PEI-GO composite materials has a p-p heterojunction and presents excellent sensing performance to NH3 gas at room temperature with the highest sensitivity（65.7% to 1000 ppm）, fast response time（2.3 s to 1000 ppm）. |
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