Preparation Of Organic Modified Magnetic Carbon Composites And Adsorption Of Cr(Ⅲ) In Water

Environmental security issues have become hot topics to be solved urgently in various countries in the 21st century.In recent years,frequent occurrences of heavy metal pollution in various parts of our country have seriously threatened people’s lives.How to strictly monitor the discharge of heavy metal wastewater and efficiently remove heavy metal in water has become extremely urgent.As one of the major pollutants,chromium is widely used in tanning,metallurgy,electroplating,and metal processing.Chromium is divided into Cr(Ⅵ)and Cr(Ⅲ)in water.Cr(Ⅵ)is highly toxic,can cause hereditary genetic defects,cause cancer,and has long-term danger to the environment.The toxicity of Cr(Ⅲ)is only one percent as compared to Cr(Ⅵ),so it is widely used by many industrial enterprises.Because Cr(Ⅲ)is cumulative,most industrial wastewater contains organic complexing agents,dyes,and a large number of other metal substances,which can bind with Cr(Ⅲ)and form stable metal chelates or can covert Cr(Ⅲ)into more toxic form Cr(Ⅵ).In this study,diethylene triamine-modified magnetic carbon-based materials(Fe3O4@C@DETA),chitosan-modified magnetic carbon-based materials(Fe3O4@C@CS),and chrome-printed ethylene diamine tetraacetic acid mesoporous magnetic carbon-based materials(Cr-IIMCE)were prepared.The removal of Cr(Ⅲ)in different complex water environments has been systematically studied.The study includes experimental methods such as contaminant concentration factors,contact time effects,pH variation factors,co-existing cations effect,different complexing agent effects,and reproducibility.At the same time,the structure and surface characteristics of all three composite adsorption materials were systematically analyzed by various characterization methods such as FTIR,Raman,VSM,XRD,XPS,SEM,TEM,Zeta,TGA,and BET,and their adsorption mechanisms were further explored.The main conclusions are as follows:(1)Removal of Cr(Ⅲ)and Cr(Ⅲ)/EDTA in solution by Fe3O4@C@DETAFerrocene was used to prepare magnetic carbon-based materials(Fe3O4@C),and Fe3O4@C@DETA was prepared by diethylene triamine(DETA)modified Fe3O4@C.The different characterization techniques provide the evidence of successful surface modification with DETA,and separated and recovered by applying a magnetic field.At pH=3.0,reaction temperature is 25℃,and the dosage is 0.4 g/L,the adsorption isotherms for Cr(Ⅲ)and Cr(Ⅲ)/EDTA conform to the Langmuir model.The theoretical maximum adsorption amounts are 44.74 mg/g and 47.27 mg/g.The adsorption kinetics conforms to a quasi-second-order kinetic model.Based on the results of adsorption experiments and XPS characterization analysis,Fe3O4@C@DETA mainly removes Cr(Ⅲ)through coordination,used the electrostatic effect and coordination effect of the material surface a in the Cr(Ⅲ)/EDTA water body.After four adsorption and desorption cycles,Fe3O4@C-DETA still has high adsorption efficiency for Cr(Ⅲ)and Cr(III)/EDTA in water.(2)Removal of Cr(Ⅲ)-EDTA in solution by Fe3O4@C@CSCS modified Fe3O4@C composite adsorption material(Fe3O4@C@CS)was prepared using chitosan(CS)as a functional monomer.The combined characterization results show that Fe3O4@C has been successfully functionalized by CS.At pH=4.0,the reaction temperature is 25℃,and the dosage is 0.4 g/L,the adsorption isotherm conforms to the Langmuir model,and the theoretical maximum adsorption amount is 12.63 mg/g,the adsorption kinetics well fit by pseudo-second-order kinetic model,and thermodynamic studies show that the adsorption behavior of Cr(Ⅲ)-EDTA is an endothermic process that occurs spontaneously.Combined with the results of adsorption experiments and XPS characterization analysis,electrostatic adsorption and coordination are the main mechanisms for Fe3O4@C@CS adsorbents to remove Cr(Ⅲ)-EDTA in water.After four adsorption and desorption cycles,Fe3O4@C@CS still has an adsorption efficiency of more than 96.1%for Cr(Ⅲ)-EDTA in water.(3)Selective removal of Cr(Ⅲ)in solution by Cr-IIMCECr-IIMCE composite adsorption material with high selectivity for Cr(Ⅲ)was prepared by ion blotting.Characterization results show that the specific surface area of Cr-IIMCE is as high as 542.10 m2/g,and it has a good mesoporous structure.At pH=3.0,the reaction temperature is 25℃,and the dosage is 0.4 g/L,the adsorption isotherm conforms to the Langmuir model,the theoretical maximum adsorption amount is 21.56 mg/g,and the adsorption kinetics were fitted the pseudo-second-order kinetic model.And the adsorption equilibrium can be reached quickly within 20 min.Thermodynamic studies show that the adsorption behavior of Cr(Ⅲ)is an endothermic process that occurs spontaneously.The adsorption capacity of Cr-IIIMCE to Cr(Ⅲ)is significantly higher than other metal ions,and their relative selectivity factors are all greater than 1 in multi-metal mixed solutions.Combining the results of adsorption experiments and XPS characterization analysis,coordination is the main mechanism of Cr-IIMCE adsorbent removal of Cr(Ⅲ)in water.After four adsorption and desorption cycles,Cr-IIMCE still has an adsorption efficiency of more than 96.88%for Cr(Ⅲ)in water.Fe3O4@C@DETA has high removal efficiency of Cr(Ⅲ)and Cr(Ⅲ)/EDTA in complex heavy metal wastewater.Fe3O4@C@CS can remove the stable Cr(Ⅲ)-EDTA in wastewater.Cr-IIMCE can remove Cr(Ⅲ)with high selectivity under the coexistence environment of multiple heavy metal ions,and can effectively remove the stable complex Cr(Ⅲ).The three composite adsorption materials have excellent magnetic separation characteristics and recyclability.