Study On The Photo-Activated Molecular Oxygen Mechanism And Biological Toxicity Of Chlorophenol/Anthracene-Derived Environmental Persistent Free Radicals

Environmental Persistent Free Radicals（EPFRs）are emerging pollutants that are formed by electron transfer of aromatic compounds and metal derivatives on the metal surface through heat treatment or light radiation and are stable in the environment,which can adversely affect the health of organisms.Reactive oxygen species（ROS）produced by redox of EPFRs can induce oxidative stress in organisms,which is an important way to cause adverse effects（such as respiratory diseases and cardiovascular diseases）.In particular,EPFRs produce a large amount of ROS under light induction,which accelerates the stress response of organisms.However,there are few reports on the factors affecting the conversion of organic precursors into EPFRs,and the factors affecting the production of ROS induced by EPFRs are not clear,and the biological toxicity of PFRs needs further study.Therefore,in this paper,Al₂O₃and montmorillonite,which are ubiquitous and high in the environment,were selected as carriers,and phenol,chlorinated organic pollutants（p-chlorophenol,2,4-dichlorophenol,2,4,6-trichlorophenol,2,3,4,6-tetrachlorophenol,2,3,5,6-tetrachlorophenol,pentachlorophenol）and anthracene were selected as organic precursors for heat treatment at 300°C and 500°C,respectively.The production,formation mechanism,activation mechanism of molecular oxygen under visible light and biological toxicity of PFRs were studied.The main research contents are as follows:1)The mechanism of chlorophenol and Al₂O₃forming the same PFRs and the transformation mechanism of activating molecular oxygen to generate ROS under visible light and bacterial toxicity;2)The related mechanisms of anthracene and montmorillonite forming different types of PFRs and their properties of photo-activated molecular oxygen,as well as the generation of ROS by different types of PFRs and their biological toxicity.The main research process and conclusions are as follows:（1）Halogen-containing EPFRs can induce ROS production in the environment,but the effect of halogen substituents on EPFRs formation and reactivity is not clear.The effects of chlorine content and position on the formation of PFRs and the activation of molecular oxygen under visible light were systematically studied by using chlorophenols and Al₂O₃-derived PFRs with different chlorine content or chlorine position as models.The results showed that the PFRs formed by Al₂O₃and different chlorophenols after heat treatment at 300°C for 60 min were O-centered persistent free radicals（g=2.0042～2.0047）.The spin concentration of PFRs and their ability to activate molecular oxygen under visible light are closely related to the chlorine content and chlorine position of chlorophenols.With the increase of chlorophenol chlorine content,the concentration of derived PFRs gradually increased,among which pentachlorophenol（PCP）derived PFRs had the strongest signal.Combined with DFT calculation and electrostatic potential diagram,it can be seen that the more chlorine content on the benzene ring,the greater the positive potential of H on the chlorophenol hydroxyl group,so H is easier to leave to form PFRs.With the increase of chlorine content,the ability of PFRs to activate molecular oxygen gradually increased,but the PFRs formed by 2,3,5,6-tetrachlorophenol had the strongest ability to activate molecular oxygen under visible light,because of its special structure,it was easy to be converted into active TCSQ^·-.The biological toxicity of chlorophenol-derived PFRs was investigated using Shewanella oneidensis MR-1 as a model.The results showed that chlorophenol precursors had a significant effect on the toxicity of PFRs.The stronger the activity of PFRs,the stronger the toxicity.This study deepens the understanding of chlorophenol-derived EPFRs and provides new insights into the source control of EPFRs.（2）Different types of PFRs were synthesized by controlling the oxygen content of anthracene and montmorillonite during heat treatment.The pyrolysis conditions were500°C,60 min,and the oxygen content was determined by controlling the time of argon gas.Four PFRs with g factors of g=2.0031,g=2.0034,g=2.0038 and g=2.0042 were synthesized.As the g factor increases,the free radicals centered on C gradually decrease,and the free radical content centered on O gradually increases,and g>2.0040 is all free radicals centered on O.The structure of PFRs was speculated by combining EPR signal and GC-MS detection results.The specific structure of PFRs was verified by Gaussian 09and Spin Fit simulation,and the mechanism of ANT-derived PFRs was speculated.The four PFRs were used to detect the production of ROS in dark,visible light and full light,respectively.The results showed that with the increase of g factor,the rate of ROS production by PFRs gradually accelerated,indicating that the activity of O-centered PFRs was stronger than that of C-centered PFRs,and visible light and full light had obvious induction effects on ROS production,and full light could significantly promote the conversion of H₂O₂to·OH.Through the toxicity detection of porcine intestinal epithelial cells（IPEC-J2）and Shewanella oneidensis MR-1,it was found that with the increase of g factor,the toxicity of PFRs to cells and cells gradually increased,which further proved that the production of ROS was significantly correlated with biological toxicity.