孔隙结构可调的Cu2O球状纳米结构及其NO2气体传感性质

Cavity-Tunable Cu2O Spherical Nanostructures and Their NO2 Gas Sensing Properties

We report the preparation of cavity-controlled Cu₂O nanospheres, having various mesoporous, hollow, and solid structures, by simply adjusting the OH^- concentration and the release rate of Cu²⁺ with the assistance of polyvinyl pyrrolidone (PVP). It indicates that the OH^- diffusion kinetics is the key factor that determines the morphology of the products. For OH^-] > 0.05 mol·L^-1, the high chemical potential made them rapidly diffuse into the PVP micelle interiors. Adsorbed Cu²⁺ on the PVP produced Cu(OH)₂, which was subsequently reduced to Cu₂O. After re-crystallization, Cu₂O solid spheres formed. For OH^-] < 0.025 mol·L^-1, the OH^- diffusion rate was reduced, and the Cu(OH)₂ layer on the PVP micelles blocked diffusion into the interior. After re-crystallization, Cu₂O hollow spheres had large cavities (~220 nm). For 0.025 mol·L^-1 < OH^-] < 0.05 mol·L^-1, hollow spheres with smaller cavities (30-60 nm) formed. When an aqueous NH₃ solution was the OH^- source, although the concentration of OH^- is low, the small amount of Cu(OH)₂ formed with the limited Cu²⁺ was not enough to block OH^- diffusion into the micelles. The free NH₃ and the low OH^- concentration did not promote re-crystallization; thus, mesoporous Cu₂O spheres were formed. We characterized NO₂ gas sensing of the three structures. The porous structures exhibited more sensitivity than did the hollow or solid structures. Together with the specific surface area data, the improved gas sensitivity suggests that the open structure of the mesoporous spheres facilitates NO₂ diffusion and O₂ adsorption.