Effect Of The Molecular Structure Of Soil Organic Matter On Its Electron Transfer Capacity And Establishment Of An Electron Transfer Space Model

Soil organic matter(SOM)with redox capacity is ubiquitous in terrestrial and aquatic systems.SOM can act as an electron shuttle to transfer electrons between microorganisms and pollutants,which has a crucial effect on the migration and transformation of pollutants in the environment.The pore size of soil micropores limits the direct contact between microorganisms and contaminants diffused into the soil micropores.Recent studies have shown that humic acid can disintegrate low molecular weight fractions(LMWF),but the electron transfer capacity(ETC)of soil organic matter with different molecular weights is poorly understood.Therefore,it is of great significance to study the ETC of soil organic matter in soilmicroporous systems.And to establish a model that can rapidly predict for remediation of soil microporous and groundwater pollution.This study first studied the ETC of humic acid(HA)and soil dissolved organic matter(SDOM)with different total organic matter(TOC)concentration.When the TOC concentration was in the range of 2.5-10 mg C/L,The ETC of HA and SDOM increases rapidly with the increase of TOC concentration,while in the TOC concentration range of 10-50 mg C/L,the ETC increases slowly.Based on the ETC of HA and SDOM,we found that the three-dimensional fluorescence spectra(3DEEM)could only use for qualitative and quantitative analysis of redox functional groups in HA and SDOM when TOC < 10 mg C/L,and it could only analysis qualitatively when TOC = 10-25 mg C/L.HA and SDOM with different molecular weights were obtained by the dialysis method.The ETC of HA and SDOM with different molecular weights was studied by the microbial method.We found that HA and SDOM with different molecular weights could act as electron shuttles and accelerate the electron transfer process.Compared with the high molecular weight fractions,the LMWF HA and SDOM have stronger ETC,about 4-8 times and 3-7 times as much as the high molecular weight fractions.3DEEM showed LMWF HA and SDOM have more quinone fluorophore groups,indicating the strong ETC was closely related to the number of quinone fluorophore groups.The maximum electron hopping distance between two adjacent LMWF HA and SDOM was calculated to be about 100 nanometers based on the above experimental data.Finally,the electron transfer space model of LMWF HA and SDOM was established,including the relationship among TOC concentration,ETC,maximum distance of electron transfer in space,and fluorescence intensity of LMWF HA and SDOM.The model promotes the non-destructive in situ studies of HA,which provides theoretical support for the rapid and accurate prediction of the potential electron transport capacity of organic matter by 3DEEM.