Study Of Degradation Mechanism Of Organic Carbon And Nitrogen Pollutants Induced By Photon Radiation

The highly reactive species hydroxyl radical?·OH?,as well as hydrogen radical?·H?in our ecosystem play crucial roles in various chemical,environmental and biological processes,especially in environmental remediation.However,for many radical reactions,the adsorption,degradation and decomposition in redox processes are very complex.Also the mechanism of decomposition induced by·OH and·H remains unclear until now.In this paper,combined detailed density function calculations with gamma irradiation experiments,we show the reaction mechanisms for representative organic compounds,primidone?PMD?and cyanuric-acid?CYA?.PMD with many organic carbon composed with aromatic ring,heterocyclic ring and alkyl group was selected to elucidate the dominant degradation mechanism induced by·OH.This paper analyzed energy barrier for all possible pathway and the conventional transition state theory was used to analyze the rate constant of the degradation reaction.The reaction rate constants were calculated as follows equation:k=n·?·(k_BT/h)(Q_TS/Q_R)exp(-(E_TS-E_R)/RT).In the first step reaction of PMD with·OH,the most predominant reaction channel is hydrogen atom abstraction and the second dominant channel is radical attacking heterocyclic ring,which overthrow the channel of radical adduct aromatic ring.Moreover,our findings reveal that hydrogen atom abstraction and hydroxylation can increase the C-C bond length,greatly reducing the energy barrier of C-C bond cleavage.The reaction to form HCOOH has the lowest energy barrier of 3.36 kcal/mol,which is different from the conventional views.Corresponding main intermediates obtained from theoretical calculation were detected and confirmed by our multi-techniques,such as HPLC-MS/MS.These results will give a new insight on applicable mechanism of·OH dominated degradation and paves the way toward many other persistent organic compounds.CYA is one of major component of materials&chemicals and also the most important persistent sym-triazine compounds in nature environment,as well as water treatment.The degradation mechanism of CYA is still unclear in varieties of advanced oxidation processes?AOPs?,where·OH is usually regarded as sole dominant radical.Using a combination of density functional theory calculations with experimental observations,we unexpectedly show that sym-triazine ring structure is broken efficiently by the reductive free radicals·H,rather than traditional·OH.The energy barrier of the CYA reacting with·H to form the-NH₂ group and break the sym-triazine ring is only 4.96 kcal/mol,which is clearly lower than that?13.32kcal/mol?of the CYA reacting with·OH.Our theoretical predictions are further confirmed by the experiments of?photon irradiation,which shows when the·H present in reaction,the nitrogen in the CYA?or other nitrogenous compounds including primidone and bezafibrate?is fast degraded into mineral NH₄⁺.In contrast,when the·H is scavenged,CYA is stop to degrade into NH₄⁺.Our results provide a new insight for understanding of the decomposition of nitrogenous materials,and also firstly shed light on the key role of the·H in the organic transformation processes.In a word,study of mechanism of free radical reactions is becoming more and more detailed with the development of multi-technologies and theory methods.These also improve the understanding of properties of radical and molecule.Our paper elucidate the reaction processes of organic carbon as well as organic nitrogen,which will shed light on practical application in environmental remedy,water treatment and direct-drinking water.