Fabrication And Properties Of Highly Efficient Photocatalytic Metal Oxide Hollow Spheres

Metal oxide hollow spheres have attracted considerable interests due to their large surface area, large internal space, nanoscale thickness of the shell and wide range of potential applications, such as solar cells, photocatalysis and lithium-ion batteries. A large number of researches show that the hard template method is the most universal method. As a new star of the hard templates, carbon spherules provide a possibility in the preparation of single and multiple shells metal oxide hollow spheres. It becomes a necessary and meaningful work to look for a facile route for preparing carbon spherules and explore the optimum synthesis conditions for synthesis of hollow spheres using carbon spherules.The carbon spherules are directly prepared by the solvothermal method of glucose solution and phenol auxiliary in this paper. The influence of the synthesis condition on the shape of the carbon spherules has been explored and then the ZnO, TiO2 and Fe2O3 multi-shelled hollow spheres have been prepared though direct adsorption. With an emphasis on the multi-shelled ZnO hollow spheres, the influence of the process conditions on the structural, morphological, electrical and photocatalytic properties of ZnO hollow spheres are investigated by XRD, SEM, TEM and photo-catalytic reactor method, respectively. Based on the synthesis of ZnO hollow spheres, the TiO2、Fe2O3、 Mn2O3 multi-shelled hollow spheres and TiO2 nanoparticles are fabricated and the morphology and properties of those are also studied. The main results are listed as follows:1. Uniform and monodispersed carbon spherules are synthesized directly through a solvothermal route with glucose solution. The SEM images show that the concentration of the glucose and reaction time has a significant influence on the diameters of the spherules. The dimension of carbon spherules increases with increasing concentration of the glucose and reaction time, and a maximum dimension of 10μm has been observed. The main reason for this can be attributed to the improvement of the degree of dehydration and polymerization of the glucose. Based on this, monodispersed carbon spherules are prepared with the help of phenol. Compared to the addition of phenol and catechol, the dimension and production of carbon spherules are much larger with the addition of phloroglucinol. We believe it is mainly because the phloroglucinol has more hydroxyl groups, which have positive effect on the polymerization of glucose.2. Furthermore, single-, double-, and triple-shelled ZnO hollow microspheres are prepared by using carbonaceous saccharide microspheres (CMSs) as sacrificial templates and the relation between the number of shells of ZnO hollow microspheres and the diameters of carbonaceous saccharide microspheres are also explored. The results improve that the number of shells of ZnO hollow microspheres increases as the diameters of carbonaceous saccharide microspheres increased. It is easy to understand that when the carbonaceous microspheres are larger, more zinc ions are absorbed inside their inner core, which lead to hollow spheres with more shells. The photocatalytic activities of the ZnO hollow spheres and ZnO nanoparticles are measured. ZnO nanoparticles degrade 70% MO within 1 h, while all the ZnO hollow microspheres degrade more than 90% MO within 1 h. The triple-shelled ZnO hollow microspheres exhibit the best photodegradation activity. The reason for this is attributed to the multiple-shelled hollow microsphere structure can enable multiple light reflection and scattering between the outer spherical shell and the two interior shells compared with the nanoparticles and single-shelled hollow spheres and provide a more efficient way to enhance light-harvesting efficiency, supply more specific surface area for adsorbing dye molecules, and also have the better photo-induced charge separation efficiency.3. By utilizing carbon spheres as template, single and multiple shells hollow spheres of TiO2 and Fe2O3 are also fabricated. The relationships between the concentration of metal ion and number of shell of TiO2 and Fe20.3 hollow spheres are studied, and we find that the number of the shell of TiO2 and Fe2O3 hollow sphere increases with increasing concentration of TiCl3 and FeCl3. The photocatalytic performance of TiO2 multiple shell hollow spheres is examined. The degradation effect of TiO2 multiple shell hollow spheres to RhB (10 mg L-1) reaches 90% after 70 min. The magnetic property of Fe2O3 hollow spheres is also studied. The saturation magnetizations of single shell and multiple shells Fe2O3 hollow spheres are 2.8 and 13.7 emu g-1,respectively. In addition, the coercivity values are 93.2 and 237.1 Oe.4. TiO2 nanoparticles are synthesized directly by solvothermal method of the mixture solution of glucose and TiCl3. The size of the nanoparticles is less than 10 nm. The degradation effect of these TiO2 nanoparticles to RhB (10 mg L-1) reaches 90% after 20 min which is superior to P25. Finally, Mn2O3 multiple shell hollow spheres are synthesized by the direct solvothermal method of the mixture solution of glucose and Mn(NO3)2-The lithium electric behavior of the Mm2O3 multiple shell hollow spheres exhibits good cycle performance and rate capability when acted as negative electrode materials, which is owing to the large specific surface area, excellent electrical conductivity and the special structure of Mn2O3 multiple shell hollow spheres.