Preparation Of Lanthanum-Zirconium Bimetallic Organic Frame Material And Its Performance In Phosphorus Removal

The emission of pesticides,detergents and manure results in serious eutrophication,which mainly due to the excessive amounts of phosphorus.Adsorption has been widely applied for its economy,easy operation,large adsorption capacity and potential selectivity.Metal-organic framework（MOF）,as one sort of novel three-dimensional hybrid material,utilizes the interaction between metal ions and organic ligands to flexibly regulate structures.They have many merits,such as large specific surface area,multi-pore size,adjustable chemical stability and so on.Therefore,the adsorption of phosphate in solution can be achieved through the modification and preparation of polymetallic organic framework.In this paper,phosphate is taken as the research object and lanthanum and zirconium bimetallic composite is used to prepare lanthanum-zirconium bimetallic MOF material,which is used to study the adsorption efficiency of phosphate.Aiming at the difficulty of phosphorus removal from water,in this paper,through screening a number of phosphorus removal adsorbents,the lanthanum and zirconium bimetallic compounds with high affinity for phosphate were finally determined as functional components.The topic synthesized the metal-organic skeleton material composed of lanthanum and zirconium through one simple solvothermal reaction.Furthermore,the key technical advantages of LaZr-MOF for adsorption of phosphate anions were identified.This study proved that LaZr-MOF（2:1）prepared under the temperature of 180℃and heating time of 24 h had the best effect on removing phosphorus.SEM showed that the clump-like LaZr-MOF（2:1）presented the optimal specific surface area as well as pore size.BET indicated that the addition of La and Zr changed the pore volume inversely.XRD presented that the peak strength of LaZr-MOF（2:1）was the weakest,indicating that the lanthanum and zirconium distribution of LaZr-MOF（2:1）is more uniform.FTIR confirmed that Zr and La are successfully coordinated to form LaZr-MOF composite materials.In order to understand the adsorption performance of LaZr-MOF（2:1）for phosphate,several factors,the adsorption isotherm and the adsorption kinetics were studied.The results showed that the applicable p H range of LaZr-MOF（2:1）was wide,and it still maintained 40-65 mg/g as the p H increased from 3 to 10.Although the adsorption capacity of LaZr-MOF（2:1）was the highest when p H=3,the metal leaching was the least when p H=7.The influence of NO₃^-and SO₄^2-on the phosphorus adsorption performance of LaZr-MOF（2:1）was negligible,while the presence of Cl^-promoted the adsorption of phosphorus by LaZr-MOF（2:1）,and the presence of F^-inhibited that.Based on the Langmuir isothermal adsorption model,the maximum phosphorus adsorption capacity of LaZr-MOF（2:1）was 44.5 mg/g.Moreover,the pseudo-second-order kinetic model was more suitable to show the phosphorus absorption of LaZr-MOF（2:1）.Integrating the characterization results of SEM XRD,XPS,FTIR and the adsorption experiment as well as the properties of lanthanum and zirconium into account,the preliminary analysis showed that the dephosphorization mechanism of LaZr-MOF（2:1）may be the joint action of electrostatic attraction and precipitation reaction.The orbital property of LaZr-MOF（2:1）provided the conditions for the formation of high coordination compounds.In acidic environment,the dissolved lanthanum ions and zirconium ions could reacted with phosphate to form insoluble substances.Under the alkaline environment,the dissolved trivalent lanthanum ions and tetravalent zirconium ions hydrolyzed to generate hydroxyl compounds,which provided more sufficient ion exchange sites for the adsorption of phosphate and thus achieved the purpose of phosphorus removal.