| Layered Double Hydroxides（LDH）is a kind of layered metal hydroxide material with excellent adsorption performance.It is composed of metal main laminate,interlaminar anions and interlaminar water molecules.The type of anion guest and the content of water molecules affect the interlaminar properties of hydrotalcite.Therefore,the determination of interlayer characteristics of hydrotalcite is the basis for the identification of interlayer adsorption/diffusion of organic pollutants,and the regulation of interlayer characteristics is expected to regulate the adsorption/diffusion behavior of organic pollutants in the interlayer.In this paper,the effects of relative humidity,fluorination and different surfactant modification on the interlayer characteristics of Cu Co Fe-LDH and the removal of benzotriazole were studied.The main research results are as follows:（1）Cu Co Fe-LDH was prepared by co-precipitation method.Firstly,the effects of different calcination temperature,initial p H value,solid-liquid ratio,initial concentration and other factors on the removal of benzotriazole by Cu Co Fe-LDH were investigated.XRD,FTIR and TG-DSC characterization analysis showed that calcination at 100℃only removed the interlaminar bound water molecules of Cu Co Fe-LDH,the lamellar structure was complete,and the adsorption effect of benzotriazole was the best.Therefore,the optimal experimental conditions were determined as follows:roasting at 100℃,p H 7,solid-liquid ratio 0.05 g/L,and initial concentration of benzotriazole 10 mg/L.Cu Co Fe-LDH-100 with relative humidity of15%,35%,75%and 90%were prepared.The crystal structures of Cu Co Fe-LDH with different relative humidity were characterized by XRD.The results showed that the base spacing d003did not change significantly with the increase of relative humidity.The changes of hydration degree of Cu Co Fe-LDH with different relative humidity were characterized by FTIR,TG-DSC and Contact Angle,etc.The results showed that the higher the relative humidity,the higher the content of water molecules in the material,the higher the Contact Angle between the material and water decreased from35.3°to 0°,and the higher the hydration degree in the interlayer domain.The effect of Cu Co Fe-LDH with different relative humidity on the removal of benzotriazole from aqueous solution was investigated.The experimental phenomenon showed that the adsorption process of Cu Co Fe-LDH with different relative humidity on benzotriazole was in line with pseudo-second-order kinetic fitting,mainly chemical adsorption,and with the increase of relative humidity,the removal effect of benzotriazole became worse.The 15%-Cu Cu Fe-100 material has the best adsorption effect on benzotriazole,with the removal rate reaching 72.1%,mainly due to the low content of water molecules between 15%-Cu Cu Fe-100 layers,low hydration degree and lower resistance of hydrogen bond network,so it has a better adsorption effect on benzotriazole.（2）Fluoride modification can replace the interlamellar hydroxyl group to further reduce the degree of interlamellar hydration,so the impregnation method was used to synthesize the fluorinated modified material Li F-Cu Co Fe with low water molecular content.The effects of fluorination modification on crystal morphology and hydration characteristics of Cu Co Fe-LDH were analyzed by XRD,SEM,FTIR,TG-DSC,Contact Angle and XPS.XRD analysis showed that the overall crystal structure of Li F-Cu Co Fe was consistent with that of Cu Co Fe-LDH,and the base surface spacing was only reduced by 0.009 nm.Fluorination modification had little effect on the crystal structure of Cu Co Fe-LDH.The changes of hydration characteristics of Li F-Cu Co Fe materials were analyzed by FTIR and TG-DSC,and the results showed that the content of surface water molecules and interlayer bound water of Li F-Cu Co Fe were both reduced.Fluorination modification peeled off a large number of hydroxyl groups in Cu Co Fe-LDH materials,and the degree of hydration was reduced.The edges of the materials with hydroxyl groups peeled were smooth and smooth.The decrease of water content caused the contact Angle between Li F-Cu Co Fe and water to increase from 30.96°to 66.68°,which resulted in the decrease of hydrophilicity.Li F-Cu Co Fe adsorption process of benzotriazole conforms to pseudo second order kinetic fitting,mainly chemisorption.The above results showed that the hydrotalce-like laminate structure of Cu Co Fe-LDH material was not significantly changed by fluorination modification,but the hydration characteristics of Cu Co Fe-LDH material were greatly affected,and the surface water molecular content and interlayer bound water content of Cu Co Fe-LDH material were reduced,the hydration degree was reduced,and the interlayer hydrogen bond network resistance was smaller.Therefore,the adsorption capacity of benzotriazole was improved.（3）Based on the interlayer confining effect of hydrotalce-like materials,in addition to the content of water molecules in the interlayer,the physical and chemical properties of hydrotalce-like materials in the interlayer can be regulated by changing the type and number of organic anions in the interlayer of hydrotalce-like materials.Therefore,Cu Co Fe-LDH was modified by surfactants with different carbon chain lengths（named C3-C12 according to the number of carbon atoms）to investigate the effects of surfactants on the interlayer domain characteristics of Cu Co Fe-LDH and the removal of benzotriazole.The XRD results showed that with the increase of carbon chain length,the interlayer spacing of Cu Co Fe-LDH gradually shifted to the left,but the variation was small.FTIR and TG-DSC analysis results showed that the introduction of surfactants with different carbon chain length caused a great change in the content of carbonate in the interlayer of Cu Co Fe-LDH.This is mainly due to surfactant molecules entering the interlayer and replacing the interlayer carbonates of Cu Co Fe-LDH.The contact Angle analysis showed that the contact Angle between Cu Co Fe-LDH and water increased with the increase of carbon chain,and the maximum Contact Angle between C7-Cu Co Fe and water was 38.38°,and the hydrophobicity was stronger.The absolute value of Zeta potential is higher in neutral environment of C7-Cu Co Fe material,indicating that the repulsive force between molecules of the material is greater than the attraction force,the material has better dispersion in aqueous solution,and the material is not easy to agglomerate.The morphology characteristics of the materials were characterized by SEM.The results showed that the C7-Cu Co Fe material had better dispersion than other surfactant modified materials,and the lamellar agglomeration phenomenon was weakened.The adsorption performance of different surfactant modified Cu Co Fe-LDH on benzotriazole was compared.The adsorption efficiency of the modified Cu Co Fe-LDH was better than that of the original Cu Co Fe-LDH,and the efficiency was C7-Cu Co Fe>C12-Cu Co Fe>C4-Cu Co Fe>C3-Cu Co Fe>Cu Co Fe.The above results show that the hydrophobicity of C7-Cu Co Fe material is relatively large,and the order of the laminates is reduced and the dispersion in water is strong,so the adsorption capacity of benzotriazole organic pollutants is the best.The adsorption mechanism of C7-Cu Co Fe and benzotriazole was investigated by XPS,XRD and FTIR before and after adsorption isotherm and adsorption kinetics.The adsorption isotherm fitting showed that the adsorption process of C7-Cu Co Fe for benzotriazole was more consistent with the Freundlich model,and the adsorption was mainly multi-layer adsorption.The adsorption kinetics was consistent with the pseudo-second-order kinetics,indicating that the adsorption process was mainly chemical adsorption.XPS analysis before and after the reaction showed that the binding energy of Cu2p3/2peak in C7-Cu Co Fe changed from 934.3 e V to 934.8 e V and 932.8 e V,indicating that Cu may be complexed with benzotriazole on the surface of the material to form Cu-BTA.In addition,FTIR analysis results showed that the content of carbonate ions in the interlayer of C7-Cu Co Fe was significantly reduced,indicating that some benzotriazole may bind to C7-Cu Co Fe through ion exchange. |
