Effect Of Copper Ion Complexation On Photochemical Activity Of Dissolved Back Carbon And The Mechanism For Micro-pollutants Degradation

Dissolved black carbon（DBC）,which is the water-soluble fraction of black carbon,has been identified as an important constituent of the natural DOM pool.It is important to study the photochemical activity of DBC that play an important role in the photochemical processes of micro contaminants in aquatic environments.China’s important rivers and fishery waters are mainly polluted by copper and cadmium,and lakes and reservoirs are polluted by copper.Cu（II）is a metal ion widely existing in the water environment and an important component in natural water.Environmental micro-pollutants originate from agricultural,industrial,and domestic sewage discharges,enter the water environment,and cause serious impacts on human health and the ecological environment.Therefore,DBC,Cu（II）,and micro-pollutants will have a series of reactions in the water environment.This study simulated the effects of DBC on photodegradation kinetics of widely detected micro-pollutants sulfadiazine（SD）and carbamazepine（CBZ）in water environment with/without Cu（II）.The optical properties of DBC with or with/without Cu（II）complexation under the condition of neutral p H and under soar light were investigated,and the degradation kinetics of SD and CBZ in DBC and DBC-Cu（II）system was studied.（1）In the wheat straw DBC prepared at 200,300,400,500 and 600℃,the p H value of DBC increased from acid to alkali with the increase of pyrolysis temperature,and the TOC value decreased.DBC at each pyrolysis temperature can generate active oxygen radicals DBC*,¹O₂,·OH and O₂^-under solar light.The DBC pyrolyzed at medium and low temperatures has a stronger ability to generate active oxygen radicals than the DBC pyrolyzed at high temperature,It shows that the photochemical activity of DBC decreases with the increase of pyrolysis temperature,among them,DBC prepared at 300℃has strong optical activity.（2）After the concentration of 10 mg C·L^-1DBC solution and 20μM Cu²⁺complexed,there is about 2μM of free Cu²⁺in the solution,it shows that about 18μM Cu²⁺complexes with DBC to form DBC-Cu（II）complex.（3）The chemical probe method and Fourier infrared spectrophotometry were used to compare the optical activity of DBC and DBC-Cu（II）systems with/without Cu（II）complex and the structural changes before and after solar light,combined with Cu²⁺released by sunlight in the DBC-Cu（II）system solution and produced Cu⁺,the results show that DBC and DBC-Cu（II）can produce³DBC^*,¹O₂,·OH,O₂^-under the solar light;In the DBC-Cu（II）system,the original structure of the DBC is changed due to the substitution of-OH and-COOH groups by Cu（II）,In addition,there is a redox cycling between Cu²⁺and Cu⁺in the system solution,therefore,DBC-Cu（II）produced a slight decrease in ¹O₂relative to DBC and more·OH,but significantly reduced ³DBC^*and ¹O₂.through redox cycling between Cu（I）and Cu（II）（4）After studying the effects of DBC and DBC-Cu（II）with/without Cu（II）coordination on the photodegradation kinetics of SD and CBZ,The study found that DBC promotes the photodegradation of SD and CBZ;DBC-Cu（II）will further promote the photodegradation of CBZ,but inhibit of SD.After conducting free radical quenching experiments,it was found that ³DBC^*,¹O₂,O₂^-produced by DBC under solar light are important active species that promote SD photodegradation,The inhibitory effect of DBC-Cu（II）on SD photodegradation is due to the reduction of O₂^-produced in the system;³DBC^*,¹O₂,·OH,and O₂^-produced by DBC and DBC-Cu（II）under light conditions are important active species that promote the photodegradation of CBZ,The further promoting effect of DBC-Cu（II）on the photolysis of CBZ may be that Cu（II）promotes the adsorption between CBZ and DBC.（5）By using free radical quenching method,adding a quencher to the SD/DBC、SD/DBC-Cu（II）,CBZ/DBC,and CBZ/DBC-Cu（II）system quenched respectively the·OH on the surface of the DBC and the solution.It was found that·OH is an important active species that promotes the photolysis of SD and CBZ,The·OH produced in each system under the sunlight is microscopically heterogeneous in the DBC and DBC-Cu（II）surface and solution,and the concentration of·OH on the surface is higher than that in the solution.The complexation of DBC and Cu（II）will promote the photodegradation of contaminants on its surface,especially for positively charged CBZ,copper ions greatly promote the photodegradation of CBZ on the surface of DBC,which in turn accelerates the CBZ photolysis.This study found that the presence of copper ions may affect the adsorption between micro-pollutants and DBC,thereby affecting DBC-mediated pollutant conversion.