| Environmental persistent free radicals?PFRs?as a new type of environmental risk substances widely exist in different environmental media or materials,including atmospheric particulate matter,soil minerals,natural organic matter,and carbonaceous materials.Carbonaceous materials?including biochar,soot,coke,etc.?produced by incomplete combustion are distributed in the natural environment such as the atmosphere,soil,sediment,and water bodies.The source of black carbon is different,its physical and chemical properties and structural characteristics are different,and the characteristics carried by PFRs also have obvious differences.In particular,the types,stability and reactivity of PFRs directly affect their potential environmental behavior and ecological risks.Therefore,this paper takes life source black carbon?such as soot?and industrial source black carbon?such as coke and biochar?as the research objects,combining electronic paramagnetic resonance spectrometer,fourier transform infrared spectroscopy,scanning electron microscope and other spectroscopy means.Based on the differences in the abundance of PFRs and active oxygen radicals on black carbon particles from different sources,the formation process,reactivity and stability of PFRs on black carbon were studied,and the relationship between the stability and activity of PFRs on black carbon was found and provided valuable information for evaluating the environmental behavior of PFRs in carbonaceous materials.The main conclusions are as follows:?1?The concentrations and types of PFRs on black carbon particles from different sources are different.The abundance of PFRs on the soot particles produced by different raw materials are different.The abundance of soot produced by wood as raw material is greater than that produced by coal.The concentration of PFRs reaches 1017 spins/g,and the main type of PFRs are carbon-centered free radicals with oxygen-containing functional groups.The concentration of PFRs on coke reached 1018 spins/g,and the main type of PFRs was carbon-centered free radicals.The concentration of PFRs on biochar prepared with lignin as raw material reaches 1018 spins/g.The types of biochar PFRs prepared at different temperatures are different,but in general,all three types of free radicals of biochar exist,namely carbon-centered free radicals,oxygen-centered free radicals and carbon-centered free radicals with oxygen-containing functional groups.The main reasons for the different concentrations and types of black carbon PFRs are:pyrolysis conditions?especially temperature?,types of oxygen-containing functional groups?such as phenolic hydroxyl groups?,and types of pyrolysis raw materials.?2?Different types of black carbon particles induce different types and abundances of reactive oxygen species?ROS?.The types of soot ROS produced by rural households are mainlyˇOH and 1O2;coke has only a very low concentration ofˇOH;biochar is mainlyˇOH and O2?-.The formation of ROS on black carbon is mainly caused by the electron transfer?redox?reaction between the active substances?PFRs?and small environmental substances?O2 and H2O?,but the generation of ROS on different media are different.The generation of ROS on the surface of biochar is mainly caused by the unstable PFRs in carbonaceous materials.The concentration of ROS is positively correlated with the concentration of PFRs.That is,the PFRs with higher reactivity can easily induce the formation of ROS,and at the same time,the phenolic hydroxyl groups on biochar participate in the formation of ROS.?3?The stability of various PFRs and ROS on carbonaceous particles are different.PFRs of different materials are weak in light and water,easily react and stable in soil.Through the analysis of the stability of various free radicals on biochar,it can be found that the oxygen-centered PFRs are the most stable and the attenuation rate is the smallest,and the carbon-centered PFRs have a larger attenuation rate.The stability of ROS on carbonaceous particles depends on the conversion ability of unstable PFRs.?4?The unstable PFRs on carbonaceous particles are the main contributors to the production ofˇOH to promote the degradation of adsorbed polycyclic aromatic hydrocarbons on the surface of biochar.Unstable PFRs as an electron donor to transfer electrons to the activator to generate ROS,and even produceˇOH to conversion of organic pollutants without adding an activator.By studying the PFRs of black carbon and reactivity from different sources,this article clarifies the generation path and attenuation characteristics of PFRs in black carbon media,which provides a solid scientific basis for understanding the environmental chemical behavior of PFRs on black carbon particles,and provides effective theoretical support for the stabilization,transformation and degradation of PFRs in black carbon and other ecological environmental behavior and effects. |
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