Synthesis And Characterizations Of TiO₂Photocatalysts With High-energy Facets Dominated And Their Photocatalytic Performance

It is well known that the surface morphology of Ti_O2have a critical impact on itsphotocatalytic properties. Therefore, the Ti_O2with high-energy crystal facets dominatedbecome a hot research topic for their potential high performance in photocatalysis. Wesuccessful synthesized the Ti_O2with high energy facets with the assistance of the additiveNaBF4and NaF, which are non-toxic and easy to operate. the main work is as follows:(1) Using HCl and NaBF4as the hydrolysis control agent and capping agent,respectively, the growth of the crystal facets of anatase Ti_O2could easily be controlled by thetunning of the concentration of NaBF4under the acidic conditions, thus, we have successfullysynthesized the mirco-sized anatase Ti_O2with different crystal facets by a hydrothermalmethod. The results showed that a appropriate amount of NaBF4could lead to thedisappearing of low energy {101} facet, thus anatase Ti_O2wholly faceted with {100} and{001} planes could be prepared, and the proportion of {100} and {001} facet could be adjustby the reaction conditions. The analysis of X-ray photoelectron spectroscopy showed thatthere were F-Ti species and lattice F on the surface of the samples synthesized with theassistance of NaBF4. Density functional theory (DFT) calculations showed that the formationof the lattice F was responsible for the elimination of {101} facets. Photocatalytic activitytests showed that the anatase Ti_O2with exclusive {100} and {001} facets displayed a superiorphotoreactivity compared with the common anatase Ti_O2with {101} and {001} facets.(2) Considering that NaBF4can be decomposed in the acidic solution under hightemperature to produce F-as a controlled release fluorine source, which can lower the reactionrate to some extent and is in favor of the generation of surface lattice F. Therefore, we simplyreplaced the NaBF4by NaF and much smaller anatase Ti_O2particles with wholly {100} and{001} facets could be prepared at a lower reaction temperature of100oC. Field emissionscanning electron microscopy (FESEM) and electron diffraction (SAED) further confirmedthe crystal facets of the samples and the existence of surface lattice F. Through theinvestigation of the reaction temperature, the concentration of HCl and the concentration ofNaF, it was revealed that the mechanism using NaF is the same to that of NaBF4. Thephotocatalytic activity test showed that the as-synthesized anatase Ti_O2photocatalysts withexclusive {100} and {001} facets possessed excellent performance, and the photocatalyticactivity per unit surface area was seven times of that of the commercial titanium dioxide P25.(3) The rutile Ti_O2with {110} and {111} facets have successfully prepared by ahydrothermal method at high temperature. The low energy {110} facet could be eliminated by the adjust of the concentrations of HCl and NaF, thus we could get a rutile Ti_O2particle withalmost100%{111} facet exposed. XPS characterization showed that the F-Ti species existingon the surface had a crucial influence on the growth of the {110} and {111} facets. Furtherstudy showed that the annealing temperature and atmosphere played an important role on theformation of surface species. The UV–vis absorption spectra of as-synthesized samplesrevealed that these rutile Ti_O2samples had strong visible light absorption, indicating thepotential visible light photocatalytic activity.