Research On Enhanced Photocatalytic Activity With Surface Modification Of Titanium Dioxide

As global energy consumptions continue,it is very promising to use semiconductors photocatalytic water splitting to convert solar energy into clean and efficient hydrogen energy.Titanium dioxide（TiO₂）is materials of semiconductors that find extensive application in the field of photocatalytic due to its favorable properties such as highly photo-activity,chemical stability,non-toxicity and low price.However,TiO₂ has response weak sunlight（only 5%of the ultraviolet region of sunlight can be absorbed）and its wide band-gap with 3.0eV,which greatly limits efficiency of photocatalytic hydrogen evolution of TiO₂.In this work,the photocatalytic enhancement mechanism of surface modification of TiO₂ was researched by the way of theoretical calculation and experiments.And the main results are as follows.The electronic structures and optical properties of noble metal atoms M（Run,Rhn,Pdn）（n=1-2）and Au nano-clusters adsorbed onto the facet（101）of anatase TiO₂ have been calculated,based on the density functional theory（DFT）with Cambridge Serial Total Energy Package（CASTEP）and plane-wave pseudopotential.Two configurations of noble metal M atom adsorption on the facet（101）of the anatase TiO₂ were stabilized by adjusting the adsorption energies and mulliken charge.In the single configuration,the formation of M-O₂c chemical bond by single M atoms with O₂c of TiO₂（101）facets.In the double configuration,double M atoms formed M-O₂c-Ti5c chemical bond with O₂c and Ti5c of TiO₂（101）facets.Associated with the potential distribution and migration of charge,the results of the average electrostatic potential indicated that electric field line pointed from the noble metal M and Au nano-clusters atoms layer to the TiO₂（101）facet layer in noble metal M and Au modified TiO₂,which accelerated the separation of the photo-carriers.Associated with the difference charge density and the transfer of charge in the interface,the difference charge density certified that the existence of electron enrichment region around noble metal M and Au nano-clusters atoms,as photo-electron traps on the TiO₂（101）facet,retarded the recombination of photo-carriers.Similarly,the results of density of states proved that the valence band（VB）and conduction band（CB）predominantly composed of O-2p states and Ti-3d states,and the appearance of M-4d and Au-5d electronic impurity states near Fermi level effect of the top of VB and the bottom of CB,formation of degenerate energy level to narrow the band gap and increase the optical absorption for visible region.Ru and Au nano-clusters were deposited on the surface of nano-particle anantse TiO₂,by photo-reduction method,respectively.The characterization results confirmed that formation of Ru,Au-O-Ti chemical bond after Ru and Au clusters deposited TiO₂ facets by X-ray diffraction（XRD）,Transmission electron microscopy（TEM）,Raman and X-ray photoelectron spectroscopy（XPS）.And the absorption capacity of TiO₂ in the visible region was enhanced and red shift of absorbed edge with the evidence of ultraviolet-visible spectroscopy（UV-Vis）,while retarded recombination of photo-generated electron-hole pairs from analysis of steady-state fluorescence emission spectroscopy and results of photocatalytic H2 evolution performance.It is certified that the enhancement of the response for visible light and the acceleration of the separation of photo-carriers were owe to the elecltron aggregation of formed Au-O-Ti and the effect of the surface plasmon resonance（SPR）of Au nano-clusters.The photocatalytic activity of Au@TiO₂ exhibits a greatly boosted evolution rates of H2（114.67pmol·g-1·-h-1）,compared with that of Ru@TiO₂（40.78 μmol-g-1-·h-1）.