A PMS-based Advanced Oxidation Process Was Applied To The Degradation Of Rhodamine B And The Oxidation Of Benzyl Alcohol

Advanced oxidation technology,which has advantages of low pollution and high catalytic activity,has been widely used in water treatment process and fine organic chemical synthesis process.Advanced oxidation processes based on persulfates(SR-AOPS)are getting more and more attentions in terms of environment and energy.Peroxymonosulfate(PMS)is often used as oxidants,and can be activated by heat,alkali,UV,ultrasound and catalyst.Compared to the homogeneous catalytic activation,heterogeneous catalytic activation showed several advantages including the reusability of catalyst,the easy separation of catalyst from the reaction medium and avoiding secondary pollution.PMS can be activated to produce reactive oxygen species(ROS),including sulfate radicals(SO₄^?-),hydroxyl free radical(^·),super oxide free radical(O₂^?-)and singlet oxygen(¹O ₂).While,the application of transition metal-based catalyst in advanced oxidation process often faces the problem of metal leaching,and the catalytic efficiency needs to be further improved.The focus of this thesis is to develop transition metal-based catalysts with high stability and efficiency for the activation of PMS.In the heterogeneous oxidation system,the target substance in solution is completely oxidized or selectively oxidized,which can be divided into two stages.PMS is firstly adsorbed on the catalyst surface,and then activated to produce reactive oxygen species(SO₄^?-?^·?O₂^?-and ¹O ₂).This process occurs on the surface of catalyst and belongs to interfacial reaction process.Secondly,the reactive oxygen species can then react with the target substance in the system to oxidize it.The half-life period of reactive oxygen species is short,and the oxidation of substance by reactive oxygen species is very fast.Therefore,we suppose that the production of reactive oxygen species on the surface of catalyst is the rate control step for the heterogeneous advanced oxidation process.The key steps to improve the reaction rate at the solid-liquid interface are to control the adsorption of the target substance on the catalyst surface,the chemical reaction on the surface of the solid catalyst and desorption of the target product on the catalyst.We selected the selective oxidation of benzyl alcohol(Bz OH)to benzaldehyde(Bz H)and the oxidative degradation of rhodamine B(Rh B)as examples.Starting from these three key steps,we regulated the adsorption,reaction and desorption process to improve the oxidation efficiency.In Chapter 3,the selective oxidation of Bz OH via activated PMS was taken as an example to improve the selectivity of Bz H by regulating desorption of the target product on the catalyst.Bz H is the target product,and accelerating desorption of Bz H is the key to improve the selectivity of Bz OH oxidation process.On the one hand,the interaction between the product and the catalyst was regulated to enhance the desorption of Bz H from the catalyst surface and the Bz H selectivity.On the other hand,the dispersion of catalyst in the system was improved and the conversion rate of Bz OH was improved.The solubility of Bz OH and Bz H in aqueous solution at 25?was significantly different(Bz OH,4.29 g/100 m L;Bz H,0.70 g/100 m L),indicating that the interaction between Bz H and hydroxyl was much lower than that between Bz OH and hydroxyl,and the heterogeneous modification of hydroxyl on the surface of the catalyst was beneficial to the desorption of Bz H on the surface of the catalyst and the dispersion of the catalyst in water.As is known to all,Si O₂ surface is covered by hydroxyl groups,showing good hydrophilicity.A porous V/Si O₂ sphere composite with ordered structure(VOx@Si O₂)was synthesized by sol-gel method.Benefiting from the redox properties of vanadium and hydrophilicity of Si O₂,VOx@Si O₂performed well to activate PMS to selectively oxidize Bz OH into Bz H in aqueous phase and at room temperature.It performed better in water than in various organic solvents.In the VOx@Si O₂/PMS system,the redox cycle of V^V/V^?leaded to the decomposition of PMS.SO₄^?-,¹O ₂ and electron transfer are the main factors for the selective oxidation of Bz OH to Bz H.We also analyze the intrinsic kinetics of the oxidation process and calculate the reaction rate(RA)and reaction order(n=0.33).This study provideed an idea for the development of vanadium-based heterogeneous catalysts to activate PMS and selectively oxidize Bz OH into Bz H.In Chapter 4,we took the selective oxidation of Bz OH into Bz H by supported bimetallic catalyst through PMS activation as an example.The electron transfer between metal species with variable valence states could provide electron for the activation of PMS.We used impregnation method to load vanadium and cobalt on Si O₂,gaining a catalyst with spherical porous structure(Co-V-Si O₂).At room temperature,using water as solvent,Co-V-Si O₂ performed better than VOx@Si O₂ in Chapter 3 to activate PMS for the oxidation of Bz OH into Bz H.A synergistic effect was identified between cobalt and vanadium species.The Co-V-Si O₂ catalyst synthesized in this study has the advantages of low cost,high efficiency and good stability,and has great application potential in the field of organic synthesis.In Chapter 5,we took the degradation of Rh B by activated carbon supported iron catalyst(CA-Fe-C)through PMS activation as an example.The catalyst activity was enhanced by regulating the adsorption of Rh B and the dispersion of Fe species.The stability of the catalyst was improved by regulating the interaction between Fe species and activated carbon carrier.The adsorption of Rh B on the catalyst surface was enhanced due to the high specific surface area of catalyst and the?-?interaction between Rh B and catalyst.Citric acid was used as a ligand to complex Fe species to improve the dispersion of Fe species,After calcination,citric acid decomposed and resulted in the porous structure.The degradation pathway of Rh B in the CA-Fe-C/PMS system was studied by free radical quenching experiment,electron paramagnetic resonance(EPR)experiment and PMS consumption analysis.The main degradation intermediates of Rh B were identified by LC-MS,and the degradation mechanism of Rh B was clarified.In order to study the relationship between Rh B removal and a series of quantitative factors and to find the optimal setting of key control factors,we established a multivariate model of Rh B degradation process using response surface methodology(RSM),and evaluated the reliability of the established Rh B degradation model by ANOVA.In addition,we use the initial rate method to determine the intrinsic reaction rate law.The CA-Fe-C/PMS system can also be used for the degradation of methylene blue(MB),methyl orange(MO)and ofloxacin(OFX).Therefore,the heterogeneous catalyst in this paper has the advantages of excellent performance and low cost,and can efficiently activate PMS for various oxidation processes.In addition,this study demonstrates the idea of regulating the reaction process at the solid-liquid interface.