Regulation Mechanism Of Hydroxyl Radical Concentration In Heterogeneous UV-Fenton System Catalyzed By Fe₃O₄ Magnetic Nanoparticles

Hydroxyl radical?·OH?is a kind of reactive oxygen species,it has strong oxidazing ability and can be generated in heterogeneous UV-Fenton system.For investigating the degradation mechanism and pathway of organic contaminants,it is of great interest to study the generation and consumption of·OH in heterogeneous UV-Fenton system.In this dissertation,Fe₃O₄ MNPs was used as catalyst,the effects of acetate,malonate,oxalate,citrate and EDTA on the degradation of Orange II in heterogeneous UV-Fenton system were studied,the regulation mechanism of carboxylate ligands on·OH concentration was investigated.Meanwhile,the scavenging efficiencies of alcohols on·OH were compared in heterogeneous and homogeneous UV-Fenton systems by using Fe₃O₄ and free iron ions as catalyst.And the scavengers which suitable for quantitative analysis of·OH were screened out.The main original conclusions of the work are drawn as following parts.1.In heterogeneous UV-Fenton system,it was found that the degradation rate of Orange II was significantly promoted by addition of oxalate and EDTA.The optimum concentrations for both are 0.4 and 0.2 mmol/L,respectively.And when the two were the corresponding concentrations,the time for compelete discoloration was shortened from 60 to 30 min.In oxalate enhanced heterogeneous UV-Fenton system,the optimum conditions for Orange II degradation were:pH=2³,[H₂O₂]₀=10 mmol/L,[Orange II]₀=0.1⁰.2 mmol/L,dosage of Fe₃O₄ MNPs=0.50¹.00 g/L.2.In the heterogeneous UV-Fenton system effected by carboxylate ligands,a possible regulation mechanism of carboxylate ligands on·OH concentration was proposed.When oxalate or EDTA was added in heterogeneous UV-Fenton system,the oxalate or EDTA complex with iron on the surface of catalyst and significantly promoted the leaching of iron in solution.Under UV-light irradiation,the iron redox was accelerated,the·OH generation was promoted.Ultimately,the degradation of Orange II was enhanced.3.The effect of differrent alcohols on the scavenging efficiencies of·OH were compared.The ability of alkanols on scavenging of·OH with the order of tert-butanol>isopropanol>ethanol>n-propanol>n-butanol>methanol.Polyols have enhanced ability to scavenge·OH as the increase of carbon chain length and hydroxyl number.Glycerol is able to scavenge·OH stably and efficiently both in heterogeneous and homogeneous UV-Fenton systems,therefore,it can be used as a high efficient·OH scavenger.