Metal-organic Framework Materials Preparation Based On Carboxylate Ligands And Their Adsorption Capabilities On Organic Dyes

Metal-organic Frameworks（MOFs）materials are composed of metal ions or ionclusters combined with organic ligands to generate a three-dimensional network structure of composite materials.Due to its large surface area,adjustable pore size and porous characteristics,its applications in adsorption,food packaging,drug delivery,catalysis and other aspects have attracted the attention of researchers.The ligands of MOFs are mainly sulfonates,phosphates,azoles,amines,carboxylates,etc.Currently,the ligands of compounds with two,three or four carboxyl groups are used more often,mainly for adsorption,catalysis,drug delivery,magnetic materials,fluorescence,etc.Due to the development of industrial technology,water pollution is becoming more and more serious.Especially organic dyes,which are mostly difficult to degrade and harmful to human health and the environment.Currently,physical,chemical and biological methods are commonly used to remove organic dyes from wastewater.Among them,physical adsorption is the best method to remove organic dyes because it has the least side effects and is simple to operate.However,some MOFs materials are less stable in water,have poor adsorption capacity and are difficult to be separated,thus limiting their practical application,so the need for new MOFs with good stability,good adsorption capacity and easy separation is our future research direction.1.MIL-101（Al）was synthesized using terephthalic acid as the organic ligand and Al Cl₃·6H₂O as the metal source,then MIL-101（Al）was modified with dopamine and used for adsorption of MB in wastewater.The materials were characterized by SEM,XRD,FTIR,BET and TG analysis.We found that the addition of dopamine increased the specific surface area of MIL-101（Al）and also increased the thermal stability of the material.The Langmuir model predicts a maximum adsorption capacity of 252.53mg·g^-1,which is about 50 mg·g^-1 higher than the adsorption capacity of MB for MIL-101（Al）,and the removal of MB remained high after five adsorption resolution cycles.Finally,the mechanism of MB adsorption by PDA-MIL-101（Al）was investigated by selective adsorption experiments and FTIR,it was found that electrostatic adsorption,hydrogen bonding,π-πinteractions and large specific surface area were the main mechanisms.2.Fe₃O₄@Al-MOF nanocomposites with shell-core structure were synthesized by microwave-assisted solvothermal method using 1,3,5-Benzenetricarboxylic acid as the organic ligand,Al Cl₃·6H₂O as the metal source and ferric tetroxide as the carrier.The successful synthesis of Fe₃O₄@Al-MOF with shell-core structure was demonstrated by SEM,TEM,XRD,FTIR and XPS characterization results,and the Fe₃O₄@Al-MOF nanocomposites with superparamagnetic properties,high specific surface area and good thermal stability were demonstrated by VSM,BET and TGA characterization methods.The batch adsorption experiments on CR demonstrated the super high adsorption performance of Fe₃O₄@Al-MOF on anionic azo dyes CR.The adsorption kinetics and isotherm analysis showed that the Langmuir isotherm model and PSO model could accurately predict the data,indicating that chemisorption dominated the monolayer adsorption process with a maximum adsorption capacity of 2446.18 mg·g^-1.In addition,Fe₃O₄@Al-MOF maintained good adsorption performance after five adsorption-desorption cycles and could be regenerated.The adsorption mechanism study showed that the synergistic mechanisms of high porosity,hydrogen bonding interactions,π-πinteractions and electrostatic interactions are the main mechanisms for CR removal by Fe₃O₄@Al-MOF,which has great potential for future wastewater treatment applications.3.Cr-H₄BTC was synthesized by a one-pot method using 1,2,4,5-benzenetetracarboxylic acid as the organic ligand and Cr（NO₃）₃·9H₂O as the metal source to remove CV.Cr-H₄BTC was characterized by SEM,FTIR,XRD,BET and TGA and found to have a small specific surface area and high thermal stability.The adsorption capacity of Cr-H₄BTC for CV was up to 84.67 mg·g^-1,and the adsorption resolution cycling experiments showed that the Cr-H₄BTC material could be cycled at least five times,and the adsorption mechanism was electrostatic adsorption,π-πinteraction and hydrogen bonding synergy.The results of this paper show that the prepared MOFs materials have broad application prospects in the field of industrial wastewater treatment.