Degradation Of Refractory Organic Pollutant Rhodamine B In Water By Mn₃O₄/ZIF-8-PMS Or Visible-light Driven Photocatalyst CdS/MIL-53?Fe?

Sulfate radical-based advanced oxidation technologies and visible light-based photocatalytic oxidation technologies are particularly effective for the degradation of refractory organic pollutants and have become a research focus in water pollution control area.In this dissertation,the removal of refractory organic dye Rhodamine B?RhB?from aqueous solution is described with the heterogeneous catalytic oxidation system Mn₃O₄/ZIF-8-Rh B_aq-PMS and heterogeneous photocatalytic oxidation system CdS/MIL-53?Fe?-RhB_aq-visible light.As to the heterogeneous catalytic oxidation system Mn₃O₄/ZIF-8-Rh B_aq-PMS,Mn₃O₄/ZIF-8 samples?Mn₃O₄ loading,or the mass ratio of Mn₃O₄ to ZIF-8,is equivalent to 0.15,0.5,1.0 and 1.5,respectively,and solvothermal temperature is set at 90,120,150 and 180°C,respectively?were synthesized by a solvothermal method with ZIF-8 as the support,KMnO₄ as the precursor.The samples synthesized were characterized by X-ray diffraction?XRD?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,X-ray photoelectron spectroscopy?XPS?and Fourier transform infrared?FT-IR?spectra and the formation mechanism of Mn₃O₄/ZIF-8 was proposed.The effects of Mn₃O₄ loading and solvothermal temperature on the performance of the Mn₃O₄/ZIF-8 were investigated.The effects of Mn₃O₄/ZIF-8 dosage,PMS dosage,initial RhB concentration,initial solution pH and reaction temperature on the degradation efficiency and degradation rate of RhB,and the recycling performance of Mn₃O₄/ZIF-8 were also investigated.In addition,the degradation pathway,removal mechanism and degradation by-products of RhB were analyzed.The results showed that Mn₃O₄ sheets with an edge size of 50-150 nm existed on the surface of the hexagonal-structure material ZIF-8 with a particle size of approximately 250 nm.The Mn₃O₄/ZIF-8 sample prepared at the Mn₃O₄ loading of0.5 and solvothermal temperature of 120°C possessed the highest catalytic activity of99.4%RhB degradation in 60 min and negligible Mn leaching.The RhB degradation followed well the first-order kinetics,and the increased 0.5-Mn/ZIF-120 and PMS dosages,decreased initial RhB concentration and increased reaction temperature would accelerate the RhB degradation.The RhB degradation was capable of attaining the maximum of approximately 98%in 40 min at 0.4 g/L 0.5-Mn/ZIF-120 dosage,0.3g/L PMS dosage,10 mg/L initial RhB concentration and 23°C reaction temperature,respectively.Moreover,the quenching tests indicated that HO·was a predominant radical in RhB degradation,but HO·mainly originated from SO₄^-·,hence PMS.Mn₃O₄/ZIF-8 also displayed the good reusability during 5 runs of reuse for the Rh B degradation in the presence of PMS,with the RhB degradation efficiency more than96%and Mn leaching less than 5%for each run.With respect to the heterogeneous CdS/MIL-53?Fe?-RhB_aq-visible light system,a novel composite,CdS/MIL-53?Fe?,was successfully fabricated via a facile solvothermal method with MIL-53?Fe?as the support,Cd?CH₃COO?₂·2H₂O,thioacetamide?TAA?and polyvinylpyrrolidone?PVP?as the precursors.And the resulted samples were characterized by XRD,SEM,TEM,XPS,FT-IR and UV-vis diffuse reflectance spectroscopy.The effect of CdS loading?the mass ratio of CdS to MIL-53?Fe?,equivalent to 0.25,0.5,1.0,1.5 and 2.0,respectively?on RhB photocatalytic oxidation was investigated.The adsorption capacity of RhB onto the CdS/MIL-53?Fe?composite in the dark and the effects of CdS/MIL-53?Fe?dosage,initial RhB concentration and initial solution pH on the photocatalytic degradation of RhB,and the recycling performance of CdS/MIL-53?Fe?were also investigated.Moreover,the degradation pathway and by-products,and degradation mechanism of RhB were analyzed.The results showed that the composite fabrication was able to reduce the CdS particle size to 20-40 nm and result in a good dispersion of CdS nanoparticles onto rod-like MIL-53?Fe?.And the composite prepared at the mass ratio of CdS to MIL-53?Fe?of 1.5:1 displayed the highest RhB photocatalytic degradation efficiency of 86%.The adsorption isotherm of RhB onto CdS/MIL-53?Fe?matched Langmuir model well,with the adsorption capacity of the CdS/MIL-53?Fe?being10.541 mg/g.The RhB photocatalytic degradation followed well the first-order kinetics equation and an approximately 92.5%of photocatalytic degradation of RhB was achieved at 0.5 g/L of 1.5-CdS/MIL dosage,10 mg/L of initial RhB concentration,initial solution pH?4.75?and 23°C of reaction temperature under visible light irradiation.Quenching tests revealed that the predominant free radicals in the CdS/MIL-?53?-RhB_aq-visible light system was O₂^-·;nevertheless,h⁺and HO·also contributed to a certain degree.The recycling test revealed that the 1.5-CdS/MIL composite could be reused for several cycles with 44.2%of RhB degradation in the third run.