Potassium Iodide/biochar/UV Process For Efficient Photocatalytic Degradation Of Perfluorooctanoic Acid(PFOA) And Perfluorooctane Sulfonate(PFOS)

At present,Perfluorooctanoic acid（PFOA）and perfluorooctane sulfonic acid（PFOS）are widely distributed in the water environment.The environmental pollution caused by PFOA and PFOS has caused widespread concern around the world.Due to their stability,persistence,PFOA and PFOS are difficult to be completely degraded by conventional methods.Photodegradation technology has shown great potential and excellent application prospects in effectively removing PFOA and PFOS in aqueous solutions.Although photodegradation technology can efficiently degrade PFOA and PFOS,most photodegradation technologies are based on strong oxidants or reducing agents,which are difficult to achieve in the environment.Therefore,the development of durable,safe and easy-to-operate photodegradation technologies for PFOA and PFOS has become a research focus in the environmental field.In this study,we took PFOA and PFOS as the research object,mercury lamp as the light source,constructed UV system and UV/Na₂SO₃system.On the basis of these system,we took KI as photosensitizer,biochar as hydrophobic interface provider,built UV/KI/biochar system to improve the degradation efficiency of PFOA and PFOS.The specific experiment results are as follows:Under UV radiation,PFOA at the concentration of 40μmol·L^-1was completely degraded within 8 h.Under the same condition,the degradation rate of PFOS within 1 h was30%,and the degradation rate of PFOS did not increase after continuous illumination for 8 h.This result was consistent with the literature report,indicating that PFOS is difficult to degrade in the UV direct photodegradation system.By adding the reducing agent Na₂SO₃to construct a UV/Na₂SO₃photocatalytic degradation system,the degradation rate of PFOA and PFOS were greatly improved.PFOA and PFOS are tested.In the presence of 20mmol·L^-1Na₂SO₃（p H 10）,both PFOA and PFOS were completely degraded with 1 h,which proved that the photodegradation efficiency of PFOA and PFOS could be effectively improved under the action of a certain catalyst.Furthermore,glucose was used as raw material to prepare biochar material rich in-OH and-COOH by hydrothermal synthesis.Relying on the hydrophobic interface of the biochar material and using potassium iodide as the photosensitizer,a potassium iodide/biochar/UV photocatalytic potassium iodide/biochar/UV system was constructed.Compared with the biochar/UV system（the degradation rate of PFOS was less than 70%in 4 hours）and the potassium iodide/UV photocatalytic system（the degradation rate of PFOS was less than 30%in 4 hours）,the potassium iodide/biochar composite system accelerated the photocatalytic degradation rate,and the degradation rate of PFOA and PFOS reached 100%in 0.5 h and 1.5 h,respectively.XPS results showed that C=O might be the main factor for the efficient degradation of PFOA and PFOS in the potassium iodide/biochar/UV photocatalytic system.Potassium iodide/biochar/UV system has high availability in natural environment,long-term stability,and high application value.