Regulation Of Electron Transport And Attenuation Of Cr（Ⅵ）in Mesoporous TiO_2-x@PDA Photocatalysis

Since the 21st century,with the rapid development of industry,the problem of heavy metal pollution has become increasingly serious.Cr（Ⅵ）is a recognized highly toxic heavy metal,which has"three properties",and the efficient and energy-saving treatment of chromium-containing wastewater has become a current research difficulty.Compared with the traditional ion exchange method,adsorption method,chemical precipitation method and other technologies,photocatalytic technology,as an emerging modern green environmental protection technology,has become a research hotspot in the field of environmental pollution control.The commonly used photocatalytic material Ti O₂ still has problems such as small visible light response range,low quantum yield,and difficulty in electron-hole separation,which greatly limits its industrial application.In this paper,by modifying and compounding polydopamine（PDA）and doping Fe components,the photoresponse range of Ti O₂-based photocatalysts is broadened,Fe heterojunction components are introduced to regulate the Fermi level of photocatalysts,and shallow defects are constructed.The recombination of photogenerated electrons and holes is delayed,and the excellent electrical conductivity of PDA is used to synergistically regulate the electron transport properties through polymer bridging.In this paper,titanium sulfate was used as titanium source,urea was used as alkali source,surfactant F127 was used as template agent,and dopamine（DA）was used as bridging agent to prepare PDA@Ti O₂ by inorganic-organic self-assembly method.On this basis,a series of mesoporous composite photocatalysts Ti O_2-x@PDA were prepared by doping Fe heterogeneous components to construct structural defects.The characterization results show that:（1）The series of composite materials Ti O_2-x@PDA are all mesoporous and spherical in shape,the size of the spheres is not uniform and there is agglomeration,and local defects are generated after the introduction of Fe components,and still have anatase type Ti O₂ crystal structure,and compared with pure Ti O₂ and PDA@Ti O₂,5%Fe（S）-PDA@Ti O₂ exhibits the largest specific surface area of 312.407m²/g;（2）The introduced Fe components are based on Fe²⁺and Fe³⁺Form exists,changing the binding energy position of O 1s and Ti 2p,bringing shallow defects,and showing a stronger absorption peak in the ultraviolet band than pure Ti O₂,and a new absorption peak in the visible band,which broadens the photoresponse range;（3）PL,I-T,and EIS characterization methods prove that the modified 5%Fe（S）-PDA@Ti O₂ photocatalyst has the lowest photogenerated electron-hole recombination rate,the highest cycle response photocurrent and the smallest interfacial charge transfer resistance,It shows a more excellent separation and transport effect of photogenerated carriers.The results of photocatalytic reduction of Cr（Ⅵ）surface:（1）5%Fe（S）-PDA@Ti O₂ shows that the optimal reaction condition is p H=4.0,the dosage is 1.20g/L,and the initial Cr（Ⅵ）concentration is The highest ability to reduce and attenuate Cr（Ⅵ）at 20mg/L is 99.61%;（2）The removal rate of dark reaction 150min only reaches 40%,and the reduction reaction in the light process is that Cr（Ⅵ）is finally attenuated and fixed It is the main reason for Cr（Ⅲ）;（3）Adding potassium persulfate to capture electrons will inhibit the reaction,and adding methanol to consume holes will shorten the time for the reaction to reach equilibrium;（4）There is a large change in p H before and after the reaction,It shows that the reaction of reducing Cr（Ⅵ）needs the participation of H⁺,and mesoporous 5%Fe（S）-PDA@Ti O₂ has good stability for reducing Cr（Ⅵ）.The fitted photocatalytic reduction of Cr（Ⅵ）conforms to the first-order kinetic equation,and the apparent overall reaction constant k under different reaction conditions is calculated.Finally,the mechanism of reduction and removal of Cr（Ⅵ）under visible light was discussed.