Construction Of Layered Double Hydroxide Carbon-based Composites And Study Of Their Fluorine Removal Performanc

Fluoride was the main contaminant in natural water worldwide.The upper limit of fluoride（F^-）content in drinking water was defined by the World Health Organization（WHO）as 1.5 mg·L^-1.Highly fluoride water has a wide distribution in China,and the proportion of the population drinking highly fluoride water was high.The adsorption met effectively removed F^-from water,showing owed simple operation,high efficiency,low cost,and no secondary pollution.Layered double hydroxides（LDHs）,as typical anionic layered compounds,have unique advantages in the adsorption treatment of anions because of their exchangeable guest anions.LDHs materials as adsorbents mainly remove F^-by ion exchange,and the ion exchange capacity needed to be improved;the stacked growth of LDHs two-dimensional nanosheets limited the diffusion and adsorption of F^-;the solid-liquid separation in the form of sodium-meter powder was difficult,and the recycling problem needed to be solved.For the above problems,this paper achieved the optimization of F^-adsorption performance through the strategies of main plate layer cation modulation,material structure design construction,and carbon material immobilization modification.（1）By modulating the ratio of M²⁺and M³⁺in the main plate layer of LDHs,the laminate charge density is regulated to improve the anion exchange efficiency.（2）Selecting cheap and non-polluting expanded graphite（EG）as the carbon skeleton for the controlled dispersion growth of LDHs along the graphite nanolayer to achieve the immobilization of LDHs.（3）Constructing three-dimensional EG/LDHs composites,increasing the layer spacing of LDHs,improving the utilization of LDHs,and optimizing the fluoride removal performance.With the above strategies,a synergistic regulatory mechanism for the fluoride removal efficiency of EG/LDHs composites was established.We obtained EG/LDHs adsorbents with high efficiency in removing F^-from water bodies.The main research of this thesis is as follows:（1）The EG/MgAl-LDHs interlayer composites（EG/MA）were constructed by vacuum-assisted and hydrothermal methods,using EG as the carbon skeleton and selecting the Mg²⁺/Al³⁺molar ratio of the main sheet cation with optimal adsorption performance.The dispersive growth of MgAl-LDHs on the graphite lamellae was controlled by regulating the amount of EG.The spatial effect of EG/MA facilitated the diffusion and adsorption of F^-within the material,which improved the ion exchange efficiency of LDHs.The synergistic effect of EG and MgAl-LDHs optimized the adsorption efficiency of EG/MA.It was shown that the adsorption of F^-in solution by EG/MA composites was achieved mainly through the main layer cation coordination and interlayer anion exchange.The Q_eof F^-adsorption by EG/MA composites reached50.4 mg·g^-1,which was monomolecular layer adsorption,and the adsorption process was spontaneous and heat-absorbing and belonged to chemisorption related to ion exchange.EG/MA was subjected to common interference in practical aqueous applications anions were not significantly affected and the selectivity was good.Immobilization of the adsorbent for recovery was achieved by immobilization on the EG backbone.Adsorbent regeneration was achieved by high-temperature calcination and structural reconstruction.（2）The EG/CoMgAl-LDHs interlayer composites（EG/CMA）were constructed by the vacuum-assisted and hydrothermal methods.The Co²⁺was introduced into the MgAl-LDHs motherboard layer,and the(Co²⁺+Mg²⁺)/Al³⁺molar ratio with the optimal adsorption performance was selected.The relative molar ratio between Co²⁺and Mg²⁺was adjusted to optimize the number of CoMgAl-LDHs interlayer anions.The spatial structure of EG/CMA was regulated by controlling the amount of EG.The introduction of Co²⁺increased its coordination with F^-,which in turn improved the adsorption of F^-by the EG/CMA composites.It was shown that the Q_ereached 53.7mg·g^-1,and the adsorption process conformed to the proposed primary adsorption kinetic equation for physical and chemical adsorption;satisfied the Sip model for mixed adsorption;and the adsorption process was spontaneous heat absorption.EG/CMA showed high interference resistance and good selectivity in practical applications.The recovery of adsorbent was achieved by immobilization on the EG backbone.Adsorbent regeneration was achieved by high-temperature calcination and structural reconstruction.