Research On Photochemical Activity Of Dissolved Organic Matter And Its Coexistence With Iron

Dissolved Organic Matter?DOM?is widely presented in surface water environment.Under the effect of light,DOM can produce a series of reactive species?RS?,such as singlet oxygen?¹O₂?,hydroxyl radical?·OH?and triplet states of DOM?³DOM*?,which has an important impact on the migration and transformation of organic pollutants.Different sources of DOM have different RS generation ability under different light intensity and environmental conditions,however,the influence of light source,pH and coexisting ions such as Fe???on the ability of DOM to generate RS is still unclear.Therefore,this paper uses Suwannee River humic acid?SRHA?,Suwannee River natural organic matter?SRNOM?and sewage secondary effluent organic matter?EfOM?as the typical DOM,together with furfuryl alcohol?FFA?,4-chlorobenzoic acid?pCBA?and 2,4,6-trimethylphenol?TMP?as molecular probes for ¹O₂,·OH and ³DOM*,to provide a theoretical basis for the study of photochemical conversion of organic pollutants in DOM and its coexistence with Fe.The main conclusions are as follows:?1?DOM from different sources have different abilities producing ¹O₂,·OH and ³DOM*,which are affected by light intensity and solution pH.The ability of DOM to produce RS under mercury lamp is significantly higher than that under xenon lamp.Under the condition of mercury lamp irradiation,SROH's production capacity of ¹O₂,·OH and ³DOM*is greater than that of SRNOM at pH6 and pH7.At pH7,the formation capacity of ¹O₂ and ³DOM*of EfOM was greater than that of SRHA,while the formation capacity of ¹O₂ was less than SRHA and SRNOM;under the condition of Xenon lamp irradiation,the generating capacity of ¹O₂ is SRHA>SRNOM>EfOM,the generating capacity of·OH is SRNOM>SRHA>EfOM,and the generating capacity of ³DOM*is EfOM>SRNOM>SRHA.?2?The presence of Fe???affects the ability of DOM to photoactivate producing RS.In general,Fe???showes an inhibitory effect on the ability of DOM to produce active species,and the inhibitory effect increased with the increase of Fe???concentration.When Fe???concentration is 10?mol·L^-1,the effect of Fe???on the formation of three active substances is promoted or inhibited under different DOM and pH conditions;when Fe???concentration reaches25?mol·L^-1,it has an inhibitory effect on all active substances.When Fe???concentration is up to 50?mol·L^-1,the inhibition rates of Fe???on DOM to produce ¹O₂,·OH and ³DOM*under irradiation conditions of mercury are 11.54%⁴3.03%,26.71%⁷6.08%and 22.99%²9.49%;under the irradiation of xenon lamp,the inhibition rates of Fe???on DOM producing ¹O₂,·OH and ³DOM*were 16.60%³2.10%,13.33%⁴6.12%and 12.97%⁴6.07%,respectively.?3?With the increase of Fe???concentration in DOM solution,the E₂/E₃ value also decreases,indicating that DOM forms a complex with Fe,and the molecular weight increases,resulting in a decrease in RS produced by DOM photosensitization.E₂/E₃ has a positive correlation with the steady state concentration of ¹O₂,·OH and the photodegradation rate constant of TMP with a single DOM.