Composite Modification Of Titanium Dioxide And Its Photocatalytic Degradation Of Organic Substances

TiO₂semiconductor is considered to be one of the most promising photocatalysts due to its high chemical stability,strong oxidation ability,low cost and easy availability.However,the two inherent defects of TiO₂greatly limit its practical application.For one thing,TiO₂has a wide band gap,which can only be excited by ultraviolet light,and it has a low utilization rate of sunlight.For another,its photogenerated carriers are easily recombined in the photocatalytic process,which makes its low quantum yield and photoactivity.In addition,due to the difficulty of separation and recovery of powdered TiO₂during use,this paper used the sol–gel method and the dipping–withdrawing method to prepare the easy–to–recover pure TiO₂and composite modified films.Aiming at the inherent defects of TiO₂,this article used semiconductor recombination and ions doping to modify it to improve its utilization of visible light and inhibit the recombination rate of photogenerated carriers,thereby enhancing its photocatalytic performance.The specific research work is as follows:1.Study on the photocatalytic performance of TiO₂/Sn O₂composite filmThe semiconductor Sn O₂was used for composite modification of TiO₂,because it has a band structure similar to that of TiO₂.According to the degradation rate of TiO₂/Sn O₂composite film to methyl green under ultraviolet light,it was determined that TiO₂/Sn O₂composite film had the best photocatalytic activity when the Sn/Ti molar ratio is 5%.In addition,the TiO₂/Sn O₂composite film was characterized by ultraviolet–visible diffuse reflectance spectroscopy and photoluminescence spectroscopy.The results show that the type II heterojunction formed between TiO₂and Sn O₂can effectively reduce the band gap energy,inhibit the recombination rate of photogenerated carriers,and improve the photocatalytic activity of TiO₂.2.Study on photocatalytic performance of ions doped TiO₂/Sn O₂composite filmsThe ions were doped on the TiO₂/Sn O₂composite film with the optimal molar ratio,mainly including:metal ions—Fe,Co,Ag,La,Y and non–metal ions—B,F.The photocatalytic performance of films was evaluated by the degradation rate of methyl green solution under ultraviolet light,and the optimal concentration and combination of ions doping were determined.Firstly,the TiO₂/Sn O₂composite film was doped with single ions（as mentioned above）,and the result show that the best single doped ion is Y with a concentration of 5×10^–3mol/L.Secondly,the second ion was doped on the basis of Y doped TiO₂/Sn O₂composite film,and the result show that the best combination of codoping is Y and F ions,and the concentration of F is 7×10^–3mol/L.Finally,the third ion was doped on the basis of Y/F codoped TiO₂/Sn O₂composite film,and the result show that the best combination is Y,F,and Ag ions tridoped TiO₂/Sn O₂composite film,and the concentration of Ag is 5×10^–3mol/L.3.Characterization and photocatalytic mechanism of Y/F/Ag tridoped TiO₂/Sn O₂composite filmThe structure,composition and surface morphology of Y/F/Ag tridoped TiO₂/Sn O₂composite film（Y/F/Ag–TS）were characterized by X–ray diffraction spectroscopy（XRD）,differential thermal and thermogravimetric curve（DTA–TG）,field emission scanning electron microscope（SEM）,high–resolution transmission electron microscopy（TEM）,X–ray photoelectron spectroscopy（XPS）,specific surface and pore size analysis（BET）,ultraviolet–visible diffuse reflectance spectroscopy（UV–vis DRS）and photoluminescence spectroscopy（PL）.The XRD and DTA–TG results show that the Y/F/Ag–TS is a mixed phase composed of anatase,rutile,and chlorargyrite,which is conducive to improve the photoactivity of TiO₂.The SEM,TEM,and BET results indicate that the Y/F/Ag–TS film has smaller grain size,larger surface area,and narrower pore diameter than TiO₂film.The XRD and TEM results manifest that some Y ions can enter the TiO₂lattice to cause lattice distortion.The XPS results confirm that Y mainly exists in the form of Y³⁺state and Ag mainly exists in the form of Ag Cl（Ag⁺）in the Y/F/Ag–TS sample,and F^–can be doped into the lattice of TiO₂to form Ti–F bonds.The Y³⁺ions act as electron traps to accelerate the separation of electrons and holes.The UV–vis DRS results show that the Y/F/Ag–TS film has a narrower bandgap（2.57 e V）and an obvious red shift at the absorption edge compared with TiO₂film.The PL results reveal that the Y/F/Ag–TS film has the higher separation efficiency of photogenerated electrons and holes and transfer efficiency of charges than TiO₂and TiO₂/Sn O₂film.The photocatalytic activity of the Y/F/Ag–TS film was evaluated by the degradation of methyl green,oxytetracycline and formaldehyde under ultraviolet or visible light conditions.The results indicate that the Y/F/Ag–TS film has high cycling stability and excellent visible light photocatalytic performance.The possible synergistic photocatalytic mechanism of Y/F/Ag–TS films was also discussed in this article.