Preparation Of N/S-TiO₂ Films And Its Photoelectrocatalytic Degradation Performance For Methyl Orange

TiO₂ is a well known photocatalyst that can effectively purify dye wastewater,but the poor utilization of sunlight always leads to the problem of low wastewater treatment efficiency.In addition,the preparation method of TiO₂ film is often complicated in the current study,which hinders its further practical application.Therefore,finding a simple and effective method for preparing TiO₂ films and enabling them to rapidly degrade dye wastewater under sunlight has become the key of this research field.Ammonium persulfate aqueous solution was used as a source of N and S,and anatase phase NO_x/S⁶⁺-TiO₂ film with high activity was successfully prepared by electro-assisted oxidation process,and the film could quickly decolorize methyl orange（MO）in sunlight.The films’morphology,optical properties and photoelectrochemical activity were characterized.In addition,the effects of MO initial concentration,degradation process,external bias,different light sources and other external factors on MO degradation were discussed.Through free radical quenching experiment,the possible mechanism of photocatalytic degradation of MO was proposed.The main conclusions are as follows:（1）In the preparation conditions,when the concentration of ammonium persulfate and the electro-voltage increasing,the MO degradation effect of TiO₂ film under simulated sunlight was better.Other factors such as assisted oxidation time have no significant on the decolorization efficiency of MO.（2）XRD,XPS,and UV-vis-NIR measurements showed that:when the auxiliary voltage increased,the crystal had greater cracks and the"flower-like"and"holes"were formed on the surface of the TiO₂ film.The less active rutile gradually disappeared,the crystal phase changed to anatase with a higher active site;The N and S concentrations gradually increased with increasing voltage,up to 3.44%and 0.68%,respectively;the light absorption range was enhanced,and the bandgap become narrower,thereby directly improving the films’photoelectrocatalytic activity.（3）Further analysis of the NO_x/S⁶⁺-TiO₂ film through TEM and XPS,this research suggested that:the"flower-like"structure was formed by disorderly accumulation of small particle crystals,the surface spacing of the lattice fringe was 0.35nm,which exhibited good crystallinity with single crystal structure.Element S was independent of the TiO₂ lattice by the weak force field between S⁶⁺and Ti-O bond,and N with the forms of Ti-O-N and NO bond were attached to the pores or combined with TiO₂ lattice.The NO_x/S⁶⁺-TiO₂ film had a high photocurrent density under simulated sunlight that was 0.46 m A/cm².Combining EIS and PL,it can be concluded that the film remarkably reduced the recombination of electron-hole pairs and rapid separation and transport of photogenerated electrons.（4）The decolorization of MO using NO_x/S⁶⁺-TiO₂ film reached 98.71%under simulated sunlight after 20 minutes.The mineralization rate reached 59.44%,and the reaction rate was 0.2422 min^-1.Repeating the same experiment 10 times,the MO decolorization rate hardly decreased.The influence of external factors on the photoelectrocatalytic degradation was studied:the electrochemical enhancement efficiency gradually increased with increasing the external bias,when the applied voltage was 2 V,the electrochemical enhancement efficiency could be as high as 96.59%.Free radical quenching experiments showed that the synergistic effect of·OH,h⁺and·O₂^-promoted the decolorization and degradation of MO in the photoelectrocatalytic process.