Study On Mechanism Of Adsorption And Catalytic Degradation Of Typical Organic Pollutants At Micro-Interfaces Of Goethite

Iron（hydrogen）oxides are abundant in soil and sediments.Due to their large specific surface area,strong electron transport capacity and high surface redox activity,they significantly affect the migration and transformation of a large number of organic pollutants in the environment.Among the iron（hydrogen）oxides,goethite is a type oxide with the most excellent thermal stability,which is widely distributed and environmentally friendly.Therefore,it is of great environmental significance to study the migration and transformation of organic pollutants involved in goethite.In this study,we use a variety of characterization methods and the combination of theory and experimentation to clarify the adsorption,redox process and electron transfer pathways that occur on the surface/interface of iron（hydrogen）oxide at the atomic and molecular-scale,and further reveal its reaction mechanism.The specific contents are as follows:（1）Two kinds of goethite with different contents of exposed{021}facet were successfully synthesized by controlling the drop acceleration rate of alkali solution,and characterized by X-ray powder diffraction（XRD）,transmission electron microscopy（TEM）and high-resolution transmission electron microscopy（HRTEM）.Then the ciprofloxacin（CIP）was chosen as the target pollutant and its adsorption behavior and mechanism on goethite surface was systematically studied by in-situ Attenuated total reflectance Fourier transform infrared（ATR-FTIR）spectroscopy and two-dimensional correlation analysis（2D-COS）.The results show that the goethite with more exposed{021}facet exhibits better adsorption performance,and CIP was found to be adsorbed on{021}and{110}facets by forming a tridentate complex involving the bridge coordination of bidentate ligands,H-bonding,and a bidentate chelate complex.（2）The prepared goethite was used as catalysts for the degradation of tetracycline（TC）by activated persulfate（PS）for studing the effects of different exposed facet on their catalytic performance.It is found that goethite exposed with more{021}facet shows the better catalytic performance,which is attributed to the abundant surface hydroxyl density,stronger electron transfer capacity,faster surface Fe（Ⅱ）/Fe（Ⅲ）cycle and easier generation of active radicals of{021}facet.In the degradation of TC,SO₄^·-and·OH both participate in the surface catalytic oxidation reaction.And goethite still catalyzes the degradation of TC effectively after three cycle experiments,indicating the good stability and availability of catalyst.（3）We constructed a surface catalytic oxidation system with goethite,humic acid（HA）and PS to degrade AO7 and studied the catalytic performance and reaction mechanism of this system.The results show that HA significantly promotes the catalytic performance of goethite for PS and the degradation efficiency of AO7.In this system,HA can reduce the Fe（Ⅲ）of goethite surface to Fe（Ⅱ）through electron transfer,and Fe（Ⅱ）can decompose PS for the generation of abundant SO₄^·-to degrade AO7.Moreover,HA was found to be more conducive to AO7 degradation by goethite exposed with more{021}facet.This may be because{021}facet has a large number of active sites and act with HA through bridging bidentate coordination mode,thereby adsorbing more HA molecule to change its surface properties and giving it stronger reducing ability to coordinate the redox process.