Electrochemical Analysis And Functional Groups 3DEEM Characterization Of Redox Properties Of Organic Matter Components In Environmental Soil

Soil organic matter(SOM)participating in redox reactions plays a significant role in toxicity,mobility and bioavailability of active pollutants in the soil environment.Recent studies have shown that low molecular weight fraction(LMWF)of humic substances(HS)has large amount of redox-active functional groups and a great reducing capacity.However,little study has reported on electron transfer capacities and distribution and characteristic of redox-active functional groups for such remaining parts of SOM.Remaining opening questions regarding whether LMWF of SOM can present great redox capacity and its mechanism on degradation and transformation of pollutants are still unclear.This study collected different molecular weight fractions from different soils by a dialysis method,and quantified electron transfer capacities of different molecular weight fractions of SOM using an electrochemical method.Results on redox properties of SOM using chemical reduction show that LMWF SOM accounted for only 8%of the TOC content of the stock solution,while 3500-LMWF and 14000-LMWF SOM showed a great reducing capacity with up to 20.1 times and 5.6 times compared to the bulk SOM.Reduced LMWF showed a greater reducing capacity than native LMWF SOM,with 24.3 times for 3500-LMWF and 14.2 times for 14000-LMWF,respectively.However,chemical reduction requires a long time for the reaction,side reactions and catalyst adsorption.These limitations make chemical reduction unsuitable for monitoring and tracking the characteristics and changes of redox properties under different redox conditions.Results on redox properties of SOM using electrochemical reduction show that LMWF SOM accounted for only 8%of TOC content of bulk SOM,while 3500-LMWF and 14000-LMWF SOM showed a great reducing capacity with up to 9.5 times and 14 times compared to the bulk SOM.When Eh increased from-0.49 V to-0.59 V,a significantly increase in the electron accepting capacities of different molecular weight component of SOM and HS was observed,up to double times,while when Eh increased from-0.59 V to-0.69 V,there showed a double-time increase.These results indicate that redox properties of SOM LMWF are related to environmental Eh,and electron functional groups of LMWF SOM were distributed in the Eh range of-0.49 V--0.59 V Electrochemical research method used for the first time can comprehensively explore the soil environment under different redox conditions,and track SOM in the whole groundwater flow process for different sources of SOM or HS participate in the electronic transfer situation.Three-dimensional excitation-emission spectroscopy has been employed to characterize redox-active fluorophores of different molecular weight component of SOM before and after reduction.Quinone-like fluorophores were the main redox-active functional fluorophores in LMWF SOM and it significantly increased after reduction.Structure of quinone-like fluorophores becomes simple after reduction due to the ?-?*transition.This provides a monitoring method to study redox properties and electron flow in redox reaction of SOM,and further provides possibility to better understanding of in-situ soil pollution remediations by means of SOM and HS.