Study On Preparation And Adsorption Of Layered Double Hydroxide And Their Resource Reutilization

With the rapid development of industry,the problem of water pollution has been widely concerned.One of the main pollutants comes from organic dyes.High toxicity of dyes of can cause serious harm to people's health.sewage treatment methods mainly include physical methods?adsorption methods?,chemical methods and biodegradation methods.However,among these treatment technologies,the adsorption method is widely used in the dye wastewater treatment process due to its high efficiency,economical and environmental friendliness.At present,the widely used adsorbent materials mainly include activated carbon,LDH,zeolite molecular sieves and some inorganic materials.Among them,LDH is capable can rapidly adsorb anionic dyes from water bodies due to its unique interlayer structure,such as congo Red?CR?.In this study,a series of LDH functional materials were successfully prepared and applied to the removal of dyes in water.The main results are as follows:?1?A series of CaMgAl-layered double hydroxide?LDH?materials with different Mg/Ca ratios were prepared by a co-precipitation method using CaCl₂·2H₂O,Mg?NO₃?₂·6H₂O and Al?NO₃?₃·9H₂O as raw materials.The properties of as-prepared CaMgAl-LDH samples were characterized.The results indicate that the anion of NO₃^-can preferentially enter the layered structure in the solutions of coexisted NO₃^-and Cl^?,and the intercalation of NO₃^-leads to an increase in interlayer spacing.The as-formed CaMgAl-LDH has a superior thermal stability.The adsorption performance of CaMgAl-LDH onto Congo red?CR?was also investigated.The adsorption kinetic of CR onto CaMgAl-LDH follows the pseudo second order kinetic model and the Langmuir equation.Based on the calculated adsorption thermodynamic parameters such as the Gibbs free energy??G⁰?,entropy??S⁰?and enthalpy??H⁰?,the adsorptions are spontaneous and endothermic reactions.The CaMgAl-LDH has a good adsorption performance on CR,and Ca₈Mg₂Al₅-LDH exhibits the optimum adsorption capacity of 115.5 mg/g for CR.These results indicate that CaMgAl-LDH obtained has a promising potential application as an efficient absorbent for water purification.?2?The hierarchical hollow Mg-Al layered double hydroxide microspheres?HHMs?were successfully synthesized by hydrothermal method in the presence of carbon dots?CDs?.The morphology and structure of the as-prepared samples were characterized by XRD,SEM,TEM,FT-IR and TG-DTG techniques.The growth process of HHMs was investigated in detail,and the Ostwald ripening mechanism was suggested for the hierarchical formation of HHMs.Adsorption isotherms and adsorption kinetics of HHMs for conge red?CR?were investigated.The results showed that the Langmuir model had the best agreement and the maximum adsorption capacity of CR was 209.62 mg/g.The adsorption kinetic data followed the pseudo-second-order kinetic model.Moreover,the thermodynamic parameters?G^o,?H^o and?S^o showed that the CR adsorption process by HHMs was endothermic and spontaneous.The as-prepared HHMs could be a potential adsorbent for the wastewater treatment containing anion dyes.?3?By recycling the MgAl-LDH adsorbed by the anionic dye CR,it was used as a new type of cationic dye adsorption material to explore the removal of cationic dye MB in water.Studies have shown that the resulting material has good adsorption properties for MB.The material adsorbed by MB is dried and recovered,and the CR in the water body can be repeatedly adsorbed and has good adsorption effect.In addition,we have investigated the cyclic adsorption performance of the material on CR and MB.The results show that the prepared material still has good adsorption performance after 4 batch adsorption cycles,and the dye removal rate can still reach more than 80%.?4?A series of carbon materials were synthesized by using LDH as a pore-forming agent,and applied to the adsorption of the organic dye methylene blue?MB?in water.Studies have shown that LDH not only increases the pore size of carbon materials,but also increases its activity specific surface area,with a specific surface area of about 1342.93 m²/g.The experiment investigated the effect of materials prepared under different preparation conditions on the adsorption properties of MB.The results show that the LDH addition amount is 1.5 mmol and the Mg/Al ratio is 2 in the calcination environment of inert atmosphere.When the calcination temperature is 800 ^oC,the prepared material has the best adsorption performance for MB.Moreover,the amount of LDH added and the calcination temperature are directly proportional to the adsorption performance of the material on MB.