Comparative Study On The Photocatalytic Degradation Mechanism Of Lignin And Humic Acid By Copper-based MOF(Cu-BTC)

Animals and plants residues can be transformed to high-polymeric complex organic compound Humic acid（HA）under the degradation of microorganisms.The presence of HA will lead to water color pollution,change the migration and transformation process of heavy metals,and generate carcinogenic disinfection by-products during the disinfection process of drinking water,which seriously threatens human health.Based on the high content of lignin-like components in HA,this paper used the copper-based MOF material（Cu-BTC）,being prepared by the hydrothermal synthesis method,to photo-degrade lignin and HA,and explore their different degradation mechanism under the same photocatalytic degradation conditions by utilizing kinetic fitting,calculation of free radical contribution rate and biodegradability analysis.The results indicated:In each dose photoreaction group,the p H value and TPC in the lignin and HA solution are inversely proportional to the photoreaction time.The maximum changes in p H are 1.02 and 1.97,and the maximum k value of TPC（apparent degradation rate constant）is 1×10^-5 in the 35 mg group and 3.83×10^-5 in the 0 mg group,respectively.k value of each dose group of lignin is lower than that of HA.This demonstrated that the rate of lignin consuming hydroxide and phenolic hydroxyl structure in the photocatalytic process of the material is lower than that of HA,and the TPC effects of the material on lignin and HA are promoting and inhibiting respectively.The mineralization rate of lignin and HA presented negatively correlated with the material dose.The maximum values are98.57%and 88.60%in the 0 mg group,and the mineralization rate of the lignin-added material group is higher than that of HA.This shows that Cu-BTC material can increase the proportion of organic matter in lignin degradation products through the degradation of TPC,which is however difficult to increase the proportion of organic matter in HA.At the same time,the difference in fluorescence intensity and HIX after the photoreaction of lignin and HA indicated that Cu-BTC could reduce the degree of humification of lignin through the depolymerization of the fluorescent structure,and the generation of fluorescent structure to increase the degree of humification of HA.In addition,the changes in the molecular weight of lignin and HA are related to the fluorescence intensity.The decrease in the molecular weight of lignin may be due to the depolymerization of the fluorescence structure,but the increase in molecular weight does not affect the decrease in fluorescence intensity,while the opposite regulation present in HA solution.The difference between the degradation results of lignin and HA may be due to the relatively uniform structure of lignin,and the free radical action of the material can directly depolymerize lignin into small organic molecules.However,The composition of HA is complex,containing antioxidant components such as tannins,which inhibits the catalytic effect of the material.Finally,the free radical contribution rate of each dose group of lignin increases with Cu-BTC dose,the maximum value is 30.00%of 35 mg,while HA only contributes 7.14%and 8.84%in the 10 mg and 20 mg groups respectively.This shows that the free radical catalysis of Cu-BTC material has a greater contribution to lignin,but has a limited effect on HA.Moreover,Cu-BTC material can sharply improve the biodegradability of lignin.There is an optimal B/C change rate of 60.48%in the 20 mg group,but the effect on the biodegradability of HA is not significant.