Investigation of the Degradation Kinetics of Mellitic Acid,a Marker for Black Carbon,under UV/H2O2 and UV/PDS Systems
The ultimate product of complete oxidation of various carbonaceous materials such as coke,charcoal,and black carbon is mellitic acid,which has attracted significant attention due to its environmental fate and impact.This study focuses on the application of advanced oxidation technologies involving hydroxyl radicals and sulfate radicals.The degradation of mellitic acid under different pH conditions in UV/H2O2 and UV/PDS systems was investigated,and the corresponding second-order reaction rate constants were changed with pH.The range of second-order rate constants for the degradation of the seven forms of Mellitic acid in the UV/H2O2 system was fitted and determined to be(3.2-85.1)× 107 mol-1·L·s-1.Similarly,in the UV/PDS system,the range was determined to be(1.1-30.5)× 107 mol-1·L·s-1.The predictive formulas for the second-order reaction rate constants of Mellitic acid degradation in both systems were established.The models used to simulate the steady-state concentrations of HO and SO4-·in the two systems showed that the steady-state concentrations of both radicals ranged from 10-13 to 10-11 mol·L-1.As the pH increases,[HO·]ss initially increased and then decreased in the UV/H2O2 system,while[SO4·]ss gradually decreased in the UV/PDS system.Additionally,the value of[HO·]ss in acidic conditions is significantly higher than alkaline conditions in the UV/PDS system.Mellitic acid emerges as a significant product following the migration and transformation of black carbon.Establishing a connection between the degradation of mellitic acid and the destiny of black carbon in the environment could offer valuable supplementary insights into the comprehensive investigation and examination of the global carbon cycle.
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