Study On Adsorption Properties And Mechanism Of Layered Double Hydroxide/Carbon Composite Aerogels For Heavy Metals In Water

Layered double hydroxides（LDHs）are a type of metal hydroxides composed of two or more metal components,which have promising application prospects in the field of heavy metal adsorption due to its low cost,non-polluting,easy to synthesize and other characteristics.However,how to systematically construct LDHs composites with excellent performance and cost-effectiveness,improve the utilization efficiency of LDHs,and evaluate their heavy metal adsorption properties still needs to be investigated from multiple dimensions such as experiments and models.Herein,based on the synthesis of a large amount of literature at home and abroad,this paper combines the difficulties faced by LDHs in practical applications,uses the synergistic effect between different functional carbon materials and LDHs to construct LDHs composites with unique nanostructures,in order to improve the adsorption performance of LDHs for heavy metals.The adsorption performance of LDHs composites was systematically studied in single heavy metal cation pollutant systems,single heavy metal oxyanion pollutant systems,and heavy metal cation and oxyanion composite pollutant systems.Machine learning regression algorithms were integrated to establish an adsorption prediction algorithm model using adsorption data as research parameters,providing a theoretical basis for further optimization design of complex water treatment systems,improvement of operational control level,and promotion of engineering practice applications.The main research content and results are as follows:（1）Mg Al-LDHs were synthesized in situ on the surface of biochar（BC）using a hydrothermal method,and the BC-supported Mg Al-LDHs were combined with calcium alginate（CA）to prepare a aerogel composite material BC@LDHs/CA（LBCA）.The results showed that the LBCA composite material could improve the aggregation phenomenon of LDHs,and its specific surface area increased from 5.75 m²/g to 45.5 m²/g.The maximum adsorption capacities of LBCA for Cu（Ⅱ）and Cd（Ⅱ）were 51.25 mg/g and48.99 mg/g,respectively.In addition,the removal rates of Cu（Ⅱ）and Cd（Ⅱ）by the same amount of LBCA were 96%and 86%,respectively,which were higher than those of LDHs by 51%and 22%,respectively.Mechanism studies found that Sur-OH-and Sur-O-complexation occurred mainly during the adsorption process of LBCA,as well as heavy metal carbonate precipitation and isomorphic substitution.Furthermore,the adsorption cycle test results showed that LBCA could be reused at least five times with good cyclic performance.（2）Nitrogen-doped carbon spheres（CS）were synthesized using glucose as the carbon source and urea as the nitrogen source via a hydrothermal method.The activated carbon spheres（ACS）were obtained by potassium hydroxide activation,and then Mg Al-LDHs were loaded on the surface of ACS to prepare an aerogel material ACS@LDHs/CNFs（ALDC）by combining with nanocellulose fibers（CNFs）.The adsorption performance of ALDC for C（Ⅵ）was studied.The results showed that ALDC exhibited excellent adsorption performance,with a removal rate of 90%for 100 mg/L C（Ⅵ）under a solid-liquid ratio of 1 g/L,and the theoretical adsorption capacity could reach 44.88 mg/g.Meanwhile,the aerogel material encapsulated with nanocellulose fibers can effectively reduce secondary pollution.Mechanism studies found that the interaction between ALDC and C（Ⅵ）mainly involved complexation/chelation with surface functional groups,electrostatic interactions,and ion exchange.（3）LDHs were grown in situ on the surface of graphene oxide（GO）using a hydrothermal method,and then added to nanocellulose fibers（CNFs）to prepare an aerogel composite material GO@LDHs/CNFs（LDGC）.It was found that LDGC had poor adsorption rates for solutions containing only Cu（Ⅱ）or C（Ⅵ）（single system）at a solid-liquid ratio of 1 g/L.However,when Cu（Ⅱ）and C（Ⅵ）coexisted in the solution（binary system）,the co-adsorption of Cu（Ⅱ）and C（Ⅵ）by LDGC was increased by 12%and57.7%,respectively,compared to the single system,and the theoretical adsorption capacity for Cu（Ⅱ）and C（Ⅵ）reached 97.46 mg/g and 106.88 mg/g,respectively.In contrast,experiments showed that the adsorption performance of single LDHs in binary systems was worse than that in single systems due to strong antagonistic effects.Mechanism studies showed that LDGC exhibited excellent synergistic effects due to charge compensation between-COOH groups and epoxy groups（ring-opening reactions occurred in binary systems）,which was verified by coexisting other metal ion experiments.Similarly,LDGC had good cyclic reuse performance and maintained good adsorption effects during four consecutive cycles of adsorption-regeneration.（4）Prediction model was established with environmental impact factors as parameters using random forest（RF）as the main algorithm model to accurately predict the adsorption capacity of LDHs composite materials for Cu（Ⅱ）and C（Ⅵ）.The fitting coefficients R² of each model for predicting the adsorption capacity of LDHs composite materials were ranked as follows based on training/validation using adsorption data:RF(R_Cu²=0.927,R_Cr²=0.947)>RBF(R_Cu²=0.927,R_Cr²=0.926)>SVR(R_Cu²=0.898,R_Cr²=0.901).The prediction model combined with machine learning can effectively predict the adsorption behavior of ions in the removal solution of nanocomposites.At the same time,the importance ratio of various environmental factors affecting the adsorption effect was analyzed,among which for Cu（Ⅱ）,adsorption time and pollutant composition were its main limiting factors,while for C（Ⅵ）,pH and pollutant composition were key conditions...