Enhanced Adsorption Of Mercury Ions And Cationic Dyes By Modified Iron And Magnesium Layered Double Metal Hydroxides

With the development of industry,the exploitation of ores,and the production of dyes inevitably form heavy metals and dye wastewater.Adsorption is considered as one of the most promising wastewater treatment methods,and the development of high-performance adsorption materials is the core of the application of adsorption method.Due to its advantages such as large specific surface area,controllable structure,low production cost and large interlamination capacity,layered bimetallic hydroxides（LDHs）have attracted extensive attention in the field of environmental governance.However,its single active site leads to poor adsorption selectivity and can only deal with a single object.Therefore,it is necessary to develop functional materials based on LDHs with multiple active sites and wide practicability.In this paper,LDHs based adsorbents were specifically designed to treat mercury ions(Hg²⁺)and methylene blue（MB）,and their adsorption behaviors were systematically studied to provide theoretical and technical support for the application of the materials.Based on this,the main contents and results of this paper are as follows:（1）By spontaneous formation of Fe-Mo-S compound,[Mo S₄]^2-chemically solidified between the plates of Fe-Mg layered bimetal hydroxide（Fe Mg-LDH）to obtain sulfur modified Fe Mg-LDH（S/Fe Mg-LDH）.Scanning electron microscopy（SEM）,Fourier transform infrared spectroscopy（FTIR）,X-ray photoelectron spectroscopy（XPS）and X-ray diffraction（XRD）were used to characterize the structure and morphology of the products,which proved the successful preparation of the target products.Based on the theory of soft-soft coordination,S/Fe Mg-LDH was applied to enhancing the adsorption of mercury ions(Hg²⁺).The results showed that the adsorption of Hg²⁺by S/Fe Mg-LDH was basically unaffected by the p H of the solution,and the maximum adsorption capacity reached 550 mg/g.The adsorption process was in accordance with Langmuir isothermal adsorption model and quasi-second-order kinetic model.Adsorption was highly selective and hardly affected by the concentration of Ca²⁺and Mg²⁺.As the sulfur active group was anchored to Fe Mg-LDH by chemical bonds,which avoids its loss in the adsorption process,S/Fe Mg-LDH can be recycled and reused,and the removal rate of Hg²⁺still reaches 91%after four cycles.（2）Based on the recognition and adsorption of the dye molecules containing aromatic ring by the hydrophobic cavities inβ-cyclodextrin（β-CD）,the composite material（S/FM-ECD）containing the hydrophobic cavities and sulfur functional sites was obtained by polymerizingβ-CD in the S/Fe Mg-LDH system with EDTA as the cross-linking agent,and was used to treat the solutions containing Hg²⁺and MB.The characterization results of FTIR,XRD,TG,XPS and SEM indicated the successful preparation of the target material.The adsorption experiment results showed that the adsorption capacity of S/FM-ECD to MB in the two-component system was significantly better than that in the single-component system,while S/FM-ECD had no obvious effect on the adsorption of Hg²⁺in the two systems.The adsorption of Hg²⁺and MB by S/FM-ECD in the two systems conformed to quasi-second order kinetics and Langmur model.（3）Based on the hydrophobic carbon ring on the biochar and the hydrophobic aromatic ring in the dye molecule,the porous biochar was prepared from the shrimp shell.Fe Mg-LDH was synthesized in situ with shrimp shell biochar as the carrier and further modified with sulfur to obtain biochar and S/Fe Mg-LDH composite material（C/FM-S）.The characterization results of FTIR,XRD,TG,XPS and SEM indicated the successful preparation of the target material.Biochar and C/FM-S were used to adsorb Hg²⁺and MB in the single-component system and two-component system respectively.The results showed that the modification of S/Fe Mg-LDH to biochar significantly improved the adsorption of Hg²⁺and MB by biochar.In the two-component system,the adsorption capacity of C/FM-S to Hg²⁺and MB was greater than that of the single-component system,indicating that the adsorption capacity of Hg²⁺and MB on C/FM-S had synergistic effect.In addition,the maximum adsorption capacity of C/FM-S for Hg²⁺and MB in the two-component system were 335and 376 mg/g,which were significantly higher than that of S/FM-ECD for Hg²⁺and MB,which were 224 and 72 mg/g,respectively.This dissertation is based on[Mo S₄]^2-chemically solidified in Fe/Mg layered bimetal hydroxides to prepare composite materials with multiple specific active sites,such as sulfur/hydrophobic cavities or highly aromatized carbon,and specifically treat mercury ions and dye molecules in wastewater,which has a good application prospect.