Preparation Of Bismuth Oxide Bromide/Cyclodextrin Resin Composite And Its Photocatalytic Degradation Performance Of Azo Dye In Water

Azo dye is a widely used dye compound,which is difficult to biodegrade and has a variety of toxic effects,causing serious water pollution problems.The combination of adsorption-photocatalysis and the technology based advanced oxidation（AOP）based on sulfate（SO4·-）promotes refractory organic pollution through the synergistic effect of adsorption,photocatalysis and visible light activation of dipersulfate（PMS）.The coupling technology for the decomposition of substances has the advantages of high degradation rate,low economic cost,and no secondary pollution.Acid Orange 7（AO7）is a kind of azo dyes,in this paper,AO7 is selected as the model pollutant.Through the combination of amphiphilic super-crosslinked porous cyclodextrin resin（PBCD-BD）and bismuth oxybromide（Bi OBr）,a composite material with dual functions of adsorption and photocatalysis is prepared,and Coupled with AOP based on SO₄^·-realizes the purification of AO7 in water and provides technical means for the treatment of azo dye wastewater.The main findings are as follows:（1）Using potassium bromide,bismuth nitrate pentahydrate and PBCD-B-D as raw materials,a Bi OBr/PBCD-B-D（BOP）composite material was constructed through a one-step solvothermal method.A variety of characterization methods are used to study the morphology,structure and chemical composition of BOP materials.The analysis results of scanning electron microscope（SEM）found that the morphology of BOP is a three-dimensional（3D）three-dimensional spherical flower,and with the continuous increase of PBCD-BD loading,the material diameter continues to increase（from 1μm to 2.5μm）.Energy spectrum,transmission electron microscope（TEM）,X-ray photoelectron spectroscopy（XPS）and other instruments show that BOB and PBCD-BD coexist in BOP materials,and PBCD-B-D is evenly dispersed.X-ray diffraction spectroscopy（XRD）shows that the BOP material has good crystallinity and high purity;（2）The system evaluated the effect of BOP materials with different PBCD-B-D loadings on the removal of azo dye AO7 through adsorption and photocatalysis.In 60minutes（min）,the adsorption capacity of BOP-24 on AO7 is 40.1 mg g^-1.With the increase of PBCD-B-D loading,the adsorption capacity of different BOP samples showed an upward trend.Among various prepared catalysts,the Bi OBr（BOP-24）composite with 24%PBCD-BD showed the highest AO7 removal performance（360min,93.2%）.Its reaction rate constant（k）was 2.13 times of BOB.Gradient degradation experiments at different concentrations showed that low-concentration AO7（0.1 m M）showed better adsorption and photocatalytic effects.The p H effect experiments show that BOP-24 has a wide range of applications and has a good removal effect on AO7within p H=3.0-9.0.The effect of anions on the degradation of AO7 by BOP-24 is as follows:CO₃^2->SO₄^2->NO₃^->Cl^-.After 4 degradation cycles,the degradation efficiency of BOP-24 on AO7 maintained the initial 81.6%.XRD spectrum analysis found that the crystal structure of BOP-24 remained intact after 4 photodegradation cycles;（3）The measurement results of ultraviolet-visible diffuse reflectance spectroscopy and Mott Schottky curve show that as the load of PBCD-B-D increases,the absorption edge is red-shifted and the band gap gradually narrows.The conduction band potential（ECB）and valence band potential（EVB）of BOB are-0.9 V and 1.87 V（vs.NHE）,respectively,and the ECB and EVB of BOP-24 are-0.35 V and 1.82 V（vs.NHE）,respectively.From the electron paramagnetic resonance spectroscopy experiment and the free radical trapping experiment,it is concluded that superoxide radicals(·O^2-),holes（h⁺）and hydroxyl radicals（·OH）play a role in the BOP system.Transient photocurrent experiments and electrochemical impedance experiments show that BOP-24 has the best charge transfer efficiency and the smallest charge transfer resistance.The mechanism that BOP materials use adsorption and photocatalysis to degrade AO7is due to the introduction of PBCD-B-D.The unique cavity structure results in the enrichment of organic pollutants and shortens the mass transfer distance;the increase in the specific surface area of the material not only provides a large number of reactive adsorption sites and active centers for the system,but also generates oxygen vacancies（OV）To improve charge separation.Finally,this study analyzed the changes in fluorescence by 3D excitation-emission matrix fluorescence spectroscopy.Combined with liquid chromatography-mass spectrometry,the possible degradation pathway of AO7 was determined;（4）The comparative experiments of BOB/PMS,BOP-24/PMS and non-catalyst/PMS systems show that only visible light irradiation without adding photocatalyst cannot activate PMS.Compared with the BOB/PMS system,the k value of BOB-24/PMS is increased by 4.9 times.The introduction of PMS into the BOP-24/visible light system found that,compared with the BOP-24 material,the degradation effect of BOP-24/PMS on AO7 increased from 64.1%to 99.2%within 60 mins.Changing the operating conditions and influencing factors found that the PMS concentration and p H value are positively correlated with the degradation effect of BOP-24/PMS on AO7.Anion effects experiments show that the addition of Cl^-,SO₄^2-and NO₃^-will promote the photodegradation of AO7,while the addition of CO₃^2-will inhibit the photodegradation.PMS,persulfate（PS）and sulfite（Na₂SO₃）were introduced into the system for comparative analysis.The k values of BOP-24/PMS were6.2 and 19.5 times that of BOP-24/PS and BOP-24/Na₂SO₃,respectively.From the results of free radical capture experiments of BOP-24/PMS degradation on AO7,·O^2-,h⁺,·OH and SO₄^·-are all reactive species.In the BOP-24/PMS system,BOP-24 uses adsorption and a unique cavity structure to enrich AO7 near the active site,reducing the path for PMS activation.In addition,PMS can also act as an electron（e^-）acceptor to promote the transfer of part of e^-to PMS,thereby further improving the efficiency of carrier separation.In summary,this thesis has synthesized a new material with adsorption-photocatalytic composite function;It developed a multifunctional coupling water treatment technology of adsorption-photocatalysis-AOP based on SO₄^·-,and clarified the mechanism of synergy.