| Sulfate radical-based advanced oxidation technologies and photocatalytic oxidation-based advanced oxidation technologies are particularly effective for the degradation of refractory organic pollutants and have become a research focus in water pollution control area.This dissertation deals with the removal of refractory organic pollutants such as Rhodamine B?RhB?,Methylene Blue?MB?and Malachite Green?MG?in wate by advanced oxidation technologies including the heterogeneous catalyticoxidationsystemsofMnFe2O4/MIL-53?Al?-PMS-RhBaq,Bi2WO6/MIL-53?Al?-RhBaq-oxidantPMS-visiblelightand Bi2WO6/MIL-53?Al?/PVDF-RhBaq-visible light.For the heterogeneous system MnFe2O4/MIL-53?Al?-PMS-RhBaq,the nanocomposite MnFe2O4/MIL-53?Al?was prepared by the sol-gel method using Mn?NO3?2,Fe?NO3?3·9H2O and citric acid as precursors and the metal organic framework material?MOF?MIL-53?Al?as the support,and MnFe2O4 loading,or the mass ratio of MnFe2O4 to MIL-53?Al?is equivalent to 0.5,1 and 2,respectively.Typical MnFe2O4/MIL-53?Al?was characterized by XRD,SEM,XPS and FT-IR techniques and the formation mechanism of MnFe2O4/MIL-53?Al?was proposed.The optimal amount of MnFe2O4 in the MnFe2O4/MIL-53?Al?composite,or the MnFe2O4loading,was experimentally determined.The effects of MnFe2O4/MIL-53?Al?dosage,PMS dosage,initial RhB concentration,initial solution pH as well as reaction temperature on the removal of RhB were investigated.And the reusability of MnFe2O4/MIL-53?Al?was examined by recycling test.The degradation pathway and mechanism of RhB was also proposed.The results showed that the MnFe2O4nanoparticles with size of 50 nm in diameter were decorated on the surface of the bulk crystal MIL-53?Al?,which consisted of bulk microcrystals with an average diameter about 1-2?m,average edge length of about 2-4?m and a thickness about 1?m.The MnFe2O4/MIL-53?Al?prepared at the MnFe2O4 loading of 1:1 showed the highest photocatalytic activity;the degradation efficiency of RhB reached 99.4%in 60 min and no Mn leaching was detected in the treated solutions.In this system,the degradation of RhB followed the first-order kinetic model;the increased catalyst dosage and optimal PMS dosage?0.3 g/L?,the increased reaction temperature,the decreased initial RhB concentration and the unadjusted initial solution pH?5.03?should be responsible for the increased photocatalytic activity.Quenching tests revealed that HO·and SO4-·were both involved in the RhB degradation,and SO4-·was the predominant one.The analysis of XPS spectra suggested that the balance among M?II?/M?III?,O2-/O2 and PMS catalyzed in the water is the principal factor to keep the high catalytic performance.In addition,after regenerating the catalyst by a simple method,the catalyst 1-MFO/MIL still showed high catalytic activity and stability after recycling for 5 times;more than 95.0%of RhB was removed and no Mn leaching was detected.With respect to the heterogeneous system Bi2WO6/MIL-53?Al?-RhBaq-oxidant PMS-visible light,Bi2WO6/MIL-53?Al?was synthesized through hydrothermal method using Bi?NO3?3·5H2O,Na2WO4·2H2O and cetyltrimethylammonium bromide?CTAB?as precursors,and MIL-53?Al?as the support.The composite was characterized by means of XRD,SEM,XPS,FT-IR and UV-vis DRS techniques.The optimum conditions for the preparation of Bi2WO6/MIL-53?Al?were investigated by means of orthogonal design test,and the effect of the single factor Bi2WO6 loading?the molar ratio Bi2WO6 to MIL-53?Al?,equivalent to 0.5,1/1.5,1.25,1.5 and 2,respectively?on the photocatalytic activity and stability of Bi2WO6/MIL-53?Al?was also investigated.In the system Bi2WO6/MIL-53?Al?-RhBaq-visible light,the effects of Bi2WO6/MIL-53?Al?dosage and initial solution pH on the photocatalytic degradation efficiency and degradation rate of RhB was studied.The photocatalytic performance of 1.25-BWO/MIL in the absence and presence of oxidants such as peroxomonosulfate?PMS?,peroxodisulfate?PDS?and hydrogen peroxide?H2O2?has also been investigated in detail.In the Bi2WO6/MIL-53?Al?-RhBaq-oxidant PMS-visible light system,the effects of PMS dosage,initial RhB concentration and initial solution pH on the photocatalytic degradation of RhB were investigated.The degradation pathway and mechanism of RhB as well as the recycling of Bi2WO6/MIL-53?Al?was also investigated.The results showed that the introduction of MIL-53?Al?had a great effect on disagglomeration of nanopowders,and the Bi2WO6 nanoplates with uniform size of 100 nm were decorated on the surface of MIL-53?Al?microcrystals.Based on the analysis procedure of the orthogonal design,the combination of hydrothermal reaction temperature of 120°C,dosage of surfactant CTAB of 0.2g/2 mmol Bi,stirring time of 6 h,nitric acid concentration of 2 mol/L,and the mole ratio of BWO to MIL of 1.25:1 were chosen as a set of op timal preparation conditions.The Bi2WO6/MIL-53?Al?prepared at the molar ratio of Bi2WO6 to MIL-53?Al?of 1.25:1 exhibited the highest photocatalytic activity towards RhB degradation among the various Bi2WO6 loading,and the photocatalytic degradation efficiency of RhB was found to be 97.0%.The catalytic degradation followed well the first-order kinetic model.The photocatalytic degradation rate of RhB increased with the increase of the dosage of catalyst.The photocatalyst reached the highest removal efficiency for RhB at the initial solution pH of 4.75?unadjusted?.Visible-light photocatalyst Bi2WO6/MIL-53?Al?with PMS as an extra oxidant exhibited higher photodegradation efficiency than that with PDS or H2O2;the increased catalyst dosage and optimal PMS dosage,the decreased initial RhB concentration,and the acid initial solution pH?3.0?should be responsible for the increased photocatalytic activity.Reactive oxygen species?O2-·and·OH?and h+generated in the photocatalytic process were identified by radical quenching tests,and it could be deduced that the photoinduced hole,h+,was the most critical species,whereas·O2-and·OH as the secondary active species for the photocatalytic degradation of RhB in the system.The photocatalyst could be regenerated by simple mothed,and the removal efficiency of RhB remained at 80.0%after the fifth cycle.For the heterogeneous Bi2WO6/MIL-53?Al?/PVDF-RhBaq-visible light system,the visible-light photocatalyst Bi2WO6/MIL-53?Al?/PVDF composite film was prepared by the hydrothermal/immersion phase inversion combined method using poly?vinylidene fluoride??PVDF?as the support by blending Bi2WO6/MIL-53?Al?nanocomposites and PVDF casting solution.The composite film was characterized by XRD,SEM,XPS,FT-IR and UV-vis DRS techniques.The effects of different1.25-BWO/MIL loading?the mass ratio of 1.25-BWO/MIL to PVDF casting solution,2%,4%and 6%respectively?on the photocatalytic performance of the composite film were investigated.The effect of reaction variables,such as the photocatalyst6-BWO/MIL/PVDF dosage,initial dye RhB concentration,initial solution pH and dye variable on photocatalytic activity was experimentally investigated.The possibility of other refractory organics?MB and MG?acting as the model pollutants was also explored.The degradation pathway and mechanism of RhB were proposed,and the reusability of Bi2WO6/MIL-53?Al?/PVDF was investigated.The results showed that Bi2WO6/MIL-53?Al?nanoparticles with a diameter of 1-3?m were distributed onto the surface and interior of the composite film,and the size of porous structure increases to 300500 nm with the introduction of Bi2WO6/MIL-53?Al?.And the composite film prepared at the ratio of 6 wt%of 1.25-BWO/MIL?with optimal ratio of Bi2WO6 to MIL-53?Al??to PVDF casting solution showed the highest photocatalytic activity.The photocatalytic degradation of RhB obeyed the first-order kinetic model.The increased photocatalyst dosage,optimal initial RhB concentration and weak acidity?5.03?should be favourable to the increased photocatalytic activity.In addition,Bi2WO6/MIL-53?Al?/PVDF composite film showed degradation capability to other refractory organic pollutants such as MB and MG.The quenching tests revealed that h+was the predominant reactive species,while·O2-and·OH served as the secondary active species for the photocatalytic degradation of RhB in the system.It was found that the photocatalytic activity did not exhibit significant reduction during the recycling process,and the RhB removal of 76.8%could still be achieved even after recycling for 15 times,revealing its potential for practical applications. |
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