Study On Bulk/surface Doping Structure Regulation Of Wide-bandgap Semiconductor And Photoelectriccatalytic Process Synergy Effects

As one of the most potential wastewater treatment technologies,photocatalytic oxidation technology has drawn much attention and became a hot spot of researching because of its simple process,high efficiency,energy saving,non-second contamination and absolutely mineralization.However,the applications of photocatalysts mainly involving TiO2 wide-bandgap semiconductors were greatly limited because of low photocatalytic activities under visible light irradiation.So,how to improve the efficiency of photocatalysis of wide-bandgap semiconductors through the method of band gap narrowing has become the key problem to be solved in the field of photo catalysis research Based on the above mentioned problem,the synergy between doping structure regulation and photoelectriccatalytic process was detailed studied and discussed in this article.The detailed works and main results are described as follows.1?Li-doped TiO2/SO42-nanoparticles was successfully synthesized via a simple calcinination process in a vacuum environment using Ti(SO4)2 and LiBr as precursors,and were characterized by TEM,XRD,IR,DLS,XPS and UV-vis DRS.Li doping can reduce the diameters of TiO2 nanoparticles and affect the surface chemical forms and structures.The as-prepared photo catalysts with different LiBr contents exhibited notably enhanced degradation efficiency for methylene blue,and exhibited the highest photocatalytic activity under UV light when the molar doping ratio of Li was 0.0125.Moreover,the most photocatalytically efficient sample also showed much higher activity for eliminating methylene blue under visible light by applying a negative bias than P25 and the control samples without applying a negative bias.The introduced negative bias electrostatic fields could not only render TiO2 responsive to visible light,but was also able to increase the lifetime of the photo-excited charges in the doped semiconductor.This provides a facile,fast and universal method to rapidly degrade organic materials based on the Franz-Keldysh effect and the synergetic effects of the electrostatic force.2?A series of boron-doped TiO2/SO42-photocatalysts were successfully prepared by the solid-phase thermolysis method.Several technologies including X-ray powder diffraction(XRD),Fourier transform infrared spectroscopy(FT-IR),UV-vis diffuse reflectance spectra(UV-vis DRS)and X-ray photoelectron spectroscopy(XPS)were employed to investigate the phase structures,diffuse reflectance spectroscope(DRS)and surface chemical states.The photo catalytic properties of B-doped TiO2 were evaluated by degrading methylene blue(MB)under UV irradiation and visible-light irradiation Results showed that B species have been doped into the crystal lattice of TiO2 with B doped in the form of substitutional and interstitial B,and can affect the surface chemical forms and structures of surface hydroxyl groups and SO42-groups.The exqperimental results of UV-vis DRS further indicate that the as-prepared photocatalysts with different B contents exhibited the stronger absorption in the visible light region and UV region.Compared to P25,B-doped TiO2 samples showed better activities for degradation of methylene blue(MB)under UV irradiation and visible light irradiation,and exhibited the highest photocatalytic activity when the molar doping ratio of B was 0.25.The superior performance is ascribed to the synergy and interplay among the decrease of the optical energy gap,efficient charge separation and surface hydroxyl groups.3?We report a simple thermal decomposition synthesis route of C-N-S co-doped TiO2 mischcrystal with isobandgap property for visible light application by using urea as carbon,nitrogen sources and Ti(SO4)2 as sulfur sources.The C-N-S co-doped TiO2 mischcrystal exhibited unique isobandgap characteristic,prominent red-shift in the UV-visible absorption spectrum and much narrower band gap(2.42 and 1.39 eV)due to defects and impurity levels confirmed by powder X-ray diffraction,diffuse reflectance spectroscopy(DRS),photo luminescence(PL),Raman spectroscopy and X-ray photoelectron spectroscopy(XPS).The excellent photocatalytic performance of the C-N-S co-doped TiO2 mischcrystal samples was demonstrated by degradation of MB under visible light.The apparent rate of black TiO2 is 4-7 times higher than that of C-N-S co-doped TiO2(anatase and rutile)under visible light irradiation.The valence band XPS and DRS results were carefully examined to understand the band gap reduction of C-N-S co-doped TiO2.This study confirms that the band gap structure of C-N-S co-doped TiO2 is determined by mixed crystalline structure,impurity energy levels and defective cores on the surface of TiO2.We present a new idea that will be useful for the design of band gap structure for photocatalysts with higher photocatalytic activities under visible light irradiatio.4?Surface modification studies on SiC to improve photocatalytic performance are presented in this work.The surfece of SiC was treated by the etching process to thin oxide layers.The surface configuration and chemical composition of SiC during the etching process were determined by XRD,TEM,UV-vis DRS,XPS and FT-IR.The results demonstrated that the crystal structure,morphology and optical band gap did not change significantly,but reactions make the chemical bond rupture and the oxide scale thin.The photoelectrocatalytic performance of SiC was evaluated in the degradation experiment of MB.Compared with the raw SiC sample,SiC was chemically treated with NaOH solution to enhance photoelectrocatalytic activity in the UV light region;the kinetic constant of resulted M-SiC is 30-120 higher than that of SiC.