Synthesis And Performance Investigation Of Cu2O Hollow Structures

Cuprous oxide is a p-type semiconductor which has a direct and narrow band gapenergy. When the scale of Cu₂O particles decreases to the level of nano-meter, Cu₂Oparticles display excellent and special performance of optics and electricity. Inaddition, the synthesis of Cu₂O is nontoxic and environmental; we can briefly controlthe experiment and the reactants are rich and cheap. Cu₂O nanoparticles are proved tohave potential applications in photovoltaic cell, photocatalyzing water to producthydrogen, the negative electrode material for Li-ion batteries and so on. Therefore,nano/micro Cu₂O particles with various morphologies have received extensiveattention due to the correlation of their facets with their distinctive properties.We have successfully developed a facile and environmentally friendly procedurefor the synthesis of solid Cu₂O hexagram and extended hexapod-shaped microcrystalby reducing the copper-citrate complex solution with glucose in water bath with thetemperature of80℃. We have systematically researched the parameters of reaction（including NaCl concentration, reaction time, and reactants concentration） which canaffect the shape of Cu₂O crystals. The concentration of NaCl plays a important role ofthe formations of the hexagram and extended hexapod-shaped particles. The {111}facets are favored at higher chloride concentrations. With the concentration ofchloride is higher, the growth speed of {111} facets can be faster. Therefore, the {111}facets disappear gradually and the shape of Cu₂O particles evolve to the truncatedoctahedron.Cu₂O hollow extended hexapod-shaped and hexagram-shaped microcrystalswere obtained in situ by oxidative etching the solid Cu₂O particles of hexagram andextended hexapod at room temperature. The formation process and mechanism of theCu₂O hollow structures were investigated in detail by characterizing the productsobtained after different aging times. During the whole etching process, some smallpits are firstly observed on the vertexes and crystal edges of the original structureswhich possess actives sites （defects, atom steps, and kinks） with higher surface energyand chemical activity. With increasing aging time, the interior of each solid particlebecomes increasingly empty, while the size of the hole in the surface starts toincrease. We have investigated adsorption abilities and photocatalytic activities ofas-prepared Cu₂O particles with different morphologies via the photodegradation ofMO solution under visible light irradiation. The order of photocatalytic activity ofCu₂O with different morphologies was as follows: hollow extended hexapod-shapedmorphology> hollow hexagram morphology> solid extended hexapod-shapedmorphology. The photocatalytic activities of the hollow structures can be much betterthan the solid particles.Various pure Cu₂O micro-or nanostructures were found to be a potential sensingmaterial for mainly two kinds of gases, including C2H5OH and H2S. In ours work, it isconsidered that polyhedral Cu₂O and the coexistent hollow structure may displaygood gas-sensing performance of C2H5OH and H2S. The optimal operatingtemperature of sensors to C2H5OH and H2S based on our all Cu₂O structures is210℃.The sensitivity of hollow extended hexapod-shaped Cu₂O is obviously higher thanthat of the hollow and solid hexagram Cu₂O particles. Increasing the ethanolconcentration, the difference among the sensors gradually increases, and the responseof sensor based on hollow extended hexapod-shaped Cu₂O shows the fastest increase.The hollow extended hexapod-shaped Cu₂O exhibits rapid response and recoverycharacteristics to ethanol. The three sequential cycles of response-recovery transientsto10ppm ethanol show a reversible, repeatable, yet stable characteristic of gas sensorbased on hollow extended hexapod-shaped Cu₂O for ethanol detection. Comparedwith that of other Cu₂O structures or results related to literatures, hollow extendedhexapod-shaped Cu₂O exhibits a significantly improved the gas-sensing behavior.We measure the electrochemical performance of the hollow hexagram andextended hexapod-shaped Cu₂O by the first galvanostatic discharge–charge andcycling curves. The electrochemical performance of hollow extended hexapod-shapedCu₂O is better than that of the other. The first discharge capacities and Coulombicefficiency of hollow extended hexapod-shaped Cu₂O are higher.The improved activities of hollow nanostructures result from their high surfacearea and the porous structures with the rapid and effective gas diffusion toward theentire reaction surfaces.