Synthesis Of Schwertmannite Based Catalysts And Their Performance In Photo-fenton Reaction

Schwertmannite,a type of Fe?III?-oxyhydroxysulfate mineral always in a metastable state,mainly exists in acid mine drainage and acid sulphate soil and can also be prepared through simple artificial method.Schwertmannite is cheap,environmentally friendly,and highly reactive,and it can efficiently absorb pollutants like heavy metal and oxygen-bearing acid radical.Therefore,Schwertmannite is a kind of environmental pollution control material with good applications.In recent years,Schwertmannite has attracted wide attentions in terms of its applications in heterogeneous Fenton degradation of pollutants.This work firstly studied the activity of Schwertmannite in photo-Fenton degradation of organic pollutant.Then to futher improve the activity of Schwertmannite in a photo-Fenton process,it was combined with TiO₂ and g-C₃N₄,two semiconductors with different width of band gap,and positions of conduction band and valence band.The catalytic performance and the related mechanism of the two catalysts in a photo-Fenton reaction were further studied.The obtained results in this work may provide theoretical basis for future preparation of efficient Schwertmannite-based photo-Fenton catalysts.The following results of this study were obtained:?1?Schwertmannite can degrade organic pollutant Rhodamine B in a photo-Fenton process.The degradation of Rhodamine B?RhB?under Fenton reaction,photo reaction and photo-Fenton reaction by Schwertmannite were respectively examined,and only under photo-Fenton condition can Schwertmannite decolorize RhB within 120 min,but with a mineralization rate less than 10%.?2?Schwertmannite?Sh?was coupled with TiO₂?P25?through mechanochemical milling to synthesize TiO₂/Sh catalyst with outstanding catalytic activity and good stability,The obtained TiO₂/Sh can efficiently degrade RhB,and the catalytic activity can be affected by various factors such as TiO₂ content and soluion pH.With increasing the content of TiO₂,the reaction rate constant of TiO₂/Sh firstly increased,and then it decreased after the content of TiO₂ exceeded 20%.Using the optimized sample,RhB can be totally decolorized within 20 min with the reaction rate constant of 0.157 min-1.Under experimental pH conditions?pH=3-6?,better catalytic performance was obtained at lower solution pH.At pH 3,the reaction rate of 20%TiO₂/Sh is 2.1 times as fast as that of M-Sh.TiO₂/Sh can efficiently degrade RhB due to the transfer of electrons between TiO₂ and Schwertmannite,which not only helps the separation of photo-induced electrons andholes of TiO₂ but also can accelerate the regeneration of Fe2+.?3?Novel photo-Fenton catalyst of Sh/C₃N₄ was prepared by combining Schwertmannite with g-C₃N₄ through an in situ synthesis method,and the obtained catalyst showed high photo-Fenton activity and good stability in degradating caffeine and RhB.Synergistic effect of these two components in Sh/C₃N₄ were observed,and the optimal content of Sh is 42%.In this case,the reaction rate is 12.4 times and 23.2 times as fast as that of Sh and g-C₃N₄,respectively,in degradating caffeine.In the Sh/C₃N₄photo-Fenton catalytic reaction system,the detected active species are mainly main ·OH and O₂·-.During the photo-Fenton catalytic process,that photo-induced electrons from g-C₃N₄ on one hand can reduce O₂ to O₂·-,and on the other hand can transfer to Schwertmannite,accelerating the regeneration of Fe2+and increasing the photo-Fenton reaction rate.Moreover,this migration process of the photo-induced electrons also promoted the separation of photo-induced electrons and holes,which can aiso improve the catalytic activity of g-C₃N₄.