| Environmentally persistent free radicals?EPFRs?are novel environmental pollutants with paramagnetic stability,which are generated on the particles surface containing heavy metal oxides exposed to aromatic compounds during thermal process.EPFRs can induce more oxidative stress effects and DNA damage in cells.Therefore,it is necessary to study the characteristics and formation of EPFRs.During the past decade,significant progresses had been made in understanding the formation and nature of EPFRs.However,the current research data on EPFRs is still limited,specially,lacking the study of the characteristics and formation processes of EPFRs formed on unsupported metal oxide particles with full orbit directly reacting with organic precursors and the influence of mixed coexistence of bimetals oxides on EPFRs.Therefore,this manuscript selected znic and lead metal oxides which were main emissions from the particles generated in combustion and the main organic matters including phenol,monochlobenzene and 1,2-dichlorobenzene to study the generation,characteristics and formation mechanism of EPFRs generated on unsupported zinc oxide metal and lead oxide metal and explored the influence of the bimetals on EPFRs.This study focused on the the characteristics and stability of EPFRs formed on the zinc oxide and lead oxide particles with different organic matters and explored the formation processes of EPFRs on metal oxide with full orbit and the influences of bimetal oxides on EPFRs.The main research processes and conclusions were as follows:?1?Characteristics of EPFRs on unsupported zinc oxide particles and their formation mechanism.The zinc oxide particles prepared by mechanical ball milling were reacted with the phenol,monochlorobenzene and 1,2-dichlorobenzene at 230°C to investigate the characteristics of EPFRs and impacts of size on EPFRs.Combined with the experiments,theoretical calculations were conducted to explore the formation mechanism of EPFRs on zinc oxide particles.The results indicated:zinc oxide promoted the formation of EPFRs and the EPFRs on zinc oxide particles exposed to different organic precursors showed different characteristics.The size of zinc oxide particles had few impact on type of EPFRs but had influence on the stability.The spin order of EPFRs on micro zinc oxide particles had a lower spin order of 1016 than the nanozinc oxide particles of 1017.The EPFRs on microznic oxide particles had better stability and longer lifetime;the EPFRs were formed by releasing H atom or Cl atom with partial electron transferring from zinc oxides to the organic matters,which was contrary to the traditional formation mechanism of EPFRs on supported metal oxides particles.These results suggested traditional formation mechanism of EPFRs could not cover the formation of EPFRs on unsupported metal oxides with full orbit,and the surface properties of the particles determined the stability of persistent free radicals.?2?Characteristics of EPFRs on unsupported lead oxide particles and their formation mechanism.The analysis method for EPFRs on zinc oxide was used to investigate the formation,characteristics and formation mechanism of EPFRs on lead oxide.The results showed:lead oxide reacted with precursors of different organic substances;the spin order of EPFRs was 1016,the g value of EPFRs under phenol was 2.0030,and that of the EPFRs of monochlorobenzene was 2.0025,and the EPFRs'g value of 1,2-dichlorobenzene was 2.0020.The half-life of EPFR was1-4 days,the half-life of EPFRs under different organic matters were different,indicating that the interaction between organic matter and lead oxide might be different.EPFRs could be formed on the surface of lead oxide exposed to organic precursors by releasing H or Cl.The difference in adsorption energy on the surface leaded to different half-lives.The different coupling between the organic precursor and lead oxide resulted in different binding of electrons,during the combination process,under phenol and 1,2-dichlorobenzene,partial charge transferred from lead oxide to persistent free radicals,which was different from that under monochlorobenzene.These suggested EPFRs with different stability and characteristics could be generated on lead oxide particles.?3?The synergetic effect of mixed coexistence of zinc oxide and lead oxide double metal oxides on the stability of EPFRs.The effects of bimetallic oxides on EPFRs were studied by using electron paramagnetic and infrared analysis.The results showed that the inclusion of lead oxide and zinc oxide double metal oxides promoted the formation of EPFRs,and the g value was 2.0031.The free radical signal had a line width of 2.6 Gauss.By comparing the EPFRs of the three organic precursors,the spin was within the range of 1014-1015,and the line width was also narrow.The g value under phenol was 2.0030,and the g value under monochlorobenzene was 2.0040.The g value of 1,2-dichlorobenzene was 2.0031.The signal of EPFRs remained unchanged after one month,but the reaction between free radicals made the line width larger,indicating that the bimetallic composite particles had synergistic effect on the stability of EPFRs.?4?The formation of EPFRs on unsupported metal oxides particles with full orbit.The formation of EPFRs on unsupported metal oxide particles mainly formed EPFRs by releasing H or Cl,different from the formation mechanism of conventional EPFRs on transition metal oxide supported on large particulate,the stability and production of EPFRs were affected by the surface properties of the particles include relative dielectric constant and particle size,and so on.The smaller the magnitude of EPFRs formed on the surface of the particles was,the more stability and the longer lasting were.The EPFRs under bimetallic particles were slightly different from the EPFRs on single metals and had a synergistic effect on the stability of EPFRs.The results of study provided a basis for the formation of EPFRs in environmental processes and the assessment of fly ash risk from incineration,providing basic data for studying the potential environmental risks of EPFRs. |
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