Preparation Anclphotoeatalyitc Activity Of Co-Doped Titania Hollow Microspheres

Titania has attracted much attention in the field of sewage treatment, air purificationand solar energy batteries due to its high photocatalytic efficiency, stable chemicalreaction, low cost and non-toxic. However, the wide band gap nature of most ofnanometer titania makes it absorb only ultraviolet light, low quantum efficiency andmore agglomerate, which limits its application. In order to improve the light energyutilization efficiency and reactive activity, we have many methods to reach this purpose.Here, micrometer titania hollow microspheres were designed and fabricated viaelectrostatic self-assembly method, and the titania hollow microspheres modified withmetal&nonmetal co-doping was investigated, which extend visible-light respondingregion.The monodispersed cationic polystyrene （PS） microspheres were prepared throughdispersion polymerization by using styrene （St） and methacryloyloxethyltrimethylammonium chloride （DMC） as monomer in a suitable condition, and thestructure of the cationic PS microspheres were characterized by means of FT-IR,1HNMR. The effects of monomer, initiator, disperser and the composition of the reactionmedia on the cationic PS microspheres size and the size distribution were studied. Theresults shows that when the temperature is70℃, St mass fraction is10%, AIBN massfraction is0.2%, PVP mass fractions is1.5%, DMC mass fraction is0.3%, and volumeratio of ethanol and H₂O is9, the average size of cationic microspheres is1.38μm, thedispersion coefficient reaches0.005and the zeta potential is about+40mV.Titania hollow microspheres were prepared with monodispersed cationicpolystyrene microspheres as template by using the electrostatic self-assembly method.The surface characteristics have been evaluated by FT-IR, SEM, TEM and XRDanalysis, and the effect of calcination temperatures was investigated on photocatalyticproperties of mesoporous titania hollow microspheres. The experimental results indicatethat the monodispersed titania hollow microspheres with the average diameters of1.23μm possess a thin shell （30nm）. The titania hollow microspheres calcined at500℃exhibit better photocatalytic activity and stability compare to P25.For the enhancement of visible-light-driven photocatalytic activity of mesoporoustitania hollow microspheres. N-doped titania hollow microspheres were prepared by theelectrostatic self-assembly method using triethylamine as nitrogen source. Themorphology and structure of N doped titania hollow microspheres were characterizedby SEM, XRD, XPS and UV-vis DRS analysis. Meantime, the effect of dopingconcentration and calcination temperatures was investigated on photocatalyticproperties of mesoporous titania hollow microspheres. It turned out that the titaniamicrosphere has a well defined hollow structure. The doping effects of N can changethe oxidized state of N or O bonds in crystal cavities. This indicates that using thesynthesized method indeed leads to the substitution of some oxygen sites by atomic N. The visible-light responding region was extended by N doping because the doping of Ncould introduce crystal cavities into titania hollow microspheres and reduce its energyband gap, thus result in the red-shift of absorption edge and increase the photocatalyticactivity responding to visible light. When the optimum mass ratio of triethylamine totetrabutyl orthotitante was about2:1, respectively, the N-doped titania hollowmicrospheres calcined at450℃exhibit better photocatalytic activity.In order to get a better efficiency in optimizing the photocatalytic activity of titaniamicrospheres. N/Mo co-doping titania hollow microspheres were prepared by theelectrostatic self-assembly method using triethylamine as nitrogen source andammonium molybdate as molybdenum source. The morphology and structure of N/Moco-doped titania hollow spheres were characterized by SEM, XPS, XRD and UV-visDRS analysis. Meantime, the effect of doping concentration and calcinationtemperatures was investigated on photocatalytic properties of N/Mo co-doped titaniahollow microspheres. The experimental results indicate that titania microsphere has awell defined hollow structure, N has replaced O in crystal structure to form Ti-N band.Meantime, Mo6+has replaced Ti4+in crystal structure to form Ti-O-Mo band. N/Mocodoped tiania hollow microspheres exhibited better absorption performance tovisible-light, which was understood by the synergistic effect due to N and Mo doping.However, best photocatalytic activity for degrading methylene blue （MB） was obtainedin the1.0%Mo/N codoped titania hollow microspheres calcined at400℃.