The Research On Mutual Conversion Between Hydroxyl Radical And Common Inorganic Oxyacid Free Radicals

Sulfate radicals,carbonate radicals,nitrate radicals and phosphate radicals are all important intermediates in chemical reactions with oxidizing ability and they exist widely in nature.They have an important impact on the migration of contaminants in both natural and human environments.In this research,the electrode potentials,production methods,detection methods and reaction modes of these radicals with organic compounds were described.By comparison,it is found that these four radicals and hydroxyl radicals react with organic compounds in same manners:electron transfer,hydrogen ion and addition.In addition,a new method for the quantitative determination of sulfate radicals as well as the mutual conversion of these inorganic oxyacid radicals with hydroxyl radicals were also investigated.By comparing the UV-Vis spectra of the products in PMS/TiOSO₄ and H₂O₂/TiOSO₄ systems,and combining with the identification of active substances by free radical scavengers,it was proved that sulfate radicals can be converted into hydroxyl radicals.At the same time,comparing the content of oxidative products in halogen lamp/Na2SO4/H₂O₂ and Na2SO4/H₂O₂,it is speculated that hydroxyl radicals can also be converted into sulfate radicals.On this basis,the effect of sulfate anion content on the degradation efficiency of methyl orange in Fenton system was analyzed.The results showed that the ability of sulfate radical capturing ? electrons from methyl orange was weaker than that of hydroxyl radical.A method for quantitative determination of sulfate radicals by spectrophotometry was developed,using trivalent phosphonium salt as a capture agent.Also,the addition amount of the capture agent,the measurement time,the pH of the reaction system and the influence of common inorganic anions on the determination method were investigated,in order to optimize the measurement conditions.Moreover,the efficiency of activation of persulfate to produce sulfate radicals by different light sources was also analyzed by this method.The results show that the low-pressure mercury lamp with a dominant wavelength of 254 nm has the best effect on persulfate activation.The content of oxidative products in the UV/Na₂CO₃/H₂O₂,UV/H₂O₂/NaH₂PO₄ and UV/H₂O₂/NaH₂PO₄ systems and the corresponding non-illuminated group were compared by double titration.After detection and analysis,percarbonate,perphosphate and peroxynitrate were converted from hydrogen peroxide.It is speculated that hydroxyl radicals can be converted into carbonate radicals,phosphate radicals and nitrate radicals under experimental conditions.Among them,using methyl orange as an indicator,methanol and tert-butanol as a capture agent,the active substances in the UV/Na₂CO₃/H₂O₂ system were studied,and it was further proved that the hydroxyl radicals were converted into carbonate radicals.