Sulfate Free Radicals And The Reaction Of The Pcb

Polychlorinated biphenyls(PCBs) in the environment pose long-term risk to public health.However,biphenyl(BP) as the parent molecule of PCBs,which can be generated by the dechlorination of PCBs,will still be discharged by variety of industries.So we must pay attention to its pollution.High aqueous solubility,high stability,relatively low cost and benign end products make persulfate(S2O82-) oxidation a promising choice among the advanced oxidation processes (AOPs) for remediation of the environment.And with the high oxidation efficiencies of the free radicals,more steady and with a longer half life than hydroxyl radicals,Sulfate radicals(SO4·-) have make sulfate radical-based processes very effective for the degradation of recalcitrant organic compounds.In this paper S2O82-was UV-activated to generate SO4·-free radicals to degradating BP and showed a good result.The effect of initial concentration of K2S2O8,illumination intensity,illumination time,pH and NO3-on BP degradation was discussed.The reaction products were analyzed and discussed.Obtained results are as follows:1. Operating at K2S2O8initial concentration of0.02mol·L-1,illumination distance of4cm,pH=5.0and reaction time of50min by313nm UV rays,about96.5%of BP was degradated. Process of BP degradation follows first order reaction kinetics.2. The increasing of K2S2O8initial concentration will significantly enhance the degradation rate.The reaction rate of the low concentration section isn’t proportional to the initial concentration because in the higher concentration only part of S2O82-decomposited to SO4·-free radicals.But at the high concentration section of S2O82-,as the initial concentration of K2S2O8is between0.04-0.06mol·L-1,the degradation rate of BP will nearly be proportional to the concentration.3. Increasing in illumination intensity can promote the degradation of BP,especially at a lower K2S2O8initial concentration.4. Alkaline environment is conducive to increasing the degradation rate of BP,which can be attributed to the pathway to form the free radicals,and the downward trend of pH in the process.5. The adding of NO3-will lead to the inhibition of BP degradation.However,the K2S2O8concentration plays a much more important role in the reaction than NaNO3. 6.The reaction between SO4·-radical and BP transformed to Hydroxybiphenyl. And the reaction was influenced by pH.The adding of NO3-lead to Hydroxybiphenyl and Hydroxy-nitrobiphenyl.And it shows those products can be further degraded.The topic of this article is of good academic significance and practical value.The result provides theoretical support for degradation of BP and PCBs in the environment. And also provides support for application of sulfate radical anion in the pollution control of BP in the water.