Construction And Catalytic Degradation Of Dyes Based On γ-Fe₂O₃ Bentonite Photo-fenton System

Advanced oxidation process（AOPs）can produce hydroxyl radical（·OH）with strong oxidation ability,which has made some progress in the treatment of organic wastewater.In AOPs process,Fenton(H₂O₂+Fe²⁺/Fe³⁺)has attracted wide attention due to its strong ability to oxidize and degrade organic pollutants.However,Fenton reaction has some disadvantages,such as high cost of H₂O₂,narrow acidic pH range,catalyst recovery difficult and easy to produce iron sludge during reaction.In order to overcome these shortcomings,heterogeneous photo-Fenton is developed to replace Fenton reaction,including iron ion,iron cluster or iron oxide fixation.Therefore,the selection of catalyst supports is the most important during the preparation of stable,highly active and inexpensive heterogeneous catalysts is the key to this technique.Bentonite is an ideal catalyst supports because of its rich reserves,friendly environment,large specific surface area and high adsorption capacity.In this paper,we successfully synthesized theγ-Fe₂O₃ pillared bentonite（γ-Fe₂O₃-P-Bent）catalyst using a simple cationic exchange method,and then based onγ-Fe₂O₃-P-Bent constructing optical system of Fenton.Rhodamine B（RhB）,simulating organic pollutant wastewater,was selected to investigate the photo-Fenton degradation activities ofγ-Fe₂O₃-P-Bent composite under UV irradiation.The main results and conclusions are as follows:（1）γ-Fe₂O₃-P-Bent magnetic composite was prepared by cationic exchange method,and the degradation properties of Rh B under UV light were also investigated.Introduction of CTAB into the synthetic system,as a template accelerated the hydrolysis and condensation of the Fe source,which promotedγ-Fe₂O₃ formation during calcination.In addition,the CTAB as an expansive agent organic modified bentonite and improve the specific surface area of bentonite.The magnetic catalyst prepared by this method has the advantages of simple operation,high catalytic activity,good long-term stability and high photocatalytic activityin in a wide range of pH 3.28-9.17.Under the best conditions（RhB 20 mg/L,pH 4.25,γ-Fe₂O₃-P-Bent 0.20 g/L,H₂O₂ 10 mM）,97.8%degradation rate and 79.3%TOC removal of Rh B within 30min.The degradation rate of RhB solution was 90.5%after the catalyst was reused for five cycles,which showed that the magnetic catalyst possessed very stable,highly reactive.The saturation magnetization values ofγ-Fe₂O₃-P-Bent was 10 emu/g,and easy to separate using an external magnetic field.（2）The visible light responsive semiconductor catalyst BiVO₄ was introduced into heterogeneous Fenton reaction to prepare BiVO₄/γ-Fe₂O₃-P-Bent（Bi-Fe-Bt）catalyst with different BiVO₄ loading by hydrothermal method,and the performance of RhB degradation under visible light was studied.With the addition of visible light BiVO₄,the visible region ofγ-Fe₂O₃-P-Bent increases.The composite photocatalyst has better visible light photocatalytic activity.The results show that the catalyst exhibits excellent catalytic property toward Rh B when the concentration of BiVO₄ is10%wt.Under the same conditions（10%Bi-Fe-Bt 0.20 g/L,pH 5.6,H₂O₂ 10 mM）,compared with theγ-Fe₂O₃-P-Bent,10%Bi-Fe-Bt showed a higher photocatalytic activity.Almost 93.2%degradation rate of RhB could obtained within 20 min and almost completely degraded after 120 min.The degradation rate of Rh B solution was98%after the catalyst was reused for five cycles,which showed that the magnetic catalyst possessed very stable,highly reactive.The saturation magnetization values of10%Bi-Fe-Bt was 8.71 emu/g,which can be rapidly separated from the solution by external magnetic field.（3）Using polyvinyl alcohol as the skeleton,the conductive polymer polypyrrole into heterogeneous Fenton reaction,and combined of cycle freezing/thawing method and freeze-drying method,PPy-Bi-Fe-Bt aerogel-based Photo-Fenton catalyst prepared and we have studied the performance of the catalyst for degradation of RhB under solar light.The composite catalyst was prepared into aerogel by using conductive polymer aerogel as the carrier,which can not only increase the specific surface area of the catalyst,but also increase the contact area between catalyst and pollutant surface.At the same time,the aerogel can be recovered without external force.The catalyst can be separated in one step,which solves the difficult problem of recovery photocatalyst in practical application.Under the optimum conditions（T 20^oC,pH 4.5,H₂O₂ 5 mM）,almost 97.5%degradation rate of RhB could obtained within30 min and almost completely degraded after 60 min.The degradation rate of RhB solution was 79%after the catalyst was reused for five cycles,which showed that the catalyst possessed good catalytic stability.