Preparation Of MOFs Composite Beads And Study On The Adsorption Of Pb²⁺ From Drinks

Lead(Pb²⁺),as one of the typical toxic pollutants in the environment,has the characteristics of high toxicity and wide contact range,and can cause irreversible harm to human.Neither treatment effect nor treatment efficiency of existing methods for the removal of Pb²⁺from drinks can meet the current industrial demand,so the development of an efficient,cheap and convenient method to remove Pb²⁺has become one of the research hotspots.As a kind of crystalline hybrid porous materials,meta-organic frameworks（MOFs）has the excellent characteristics of adjustable,modifiable and high surface area.Compared with traditional adsorbents,the designability and modifiability of MOFs give them a unique advantage in the field of Pb²⁺removal.As one of the classical MOFs,Ui O-66 has excellent chemical stability and high porosity.The adsorption capacity of Pb²⁺can be effectively improved by the modification of Ui O-66 functional group.However,the powdery Ui O-66 is prone to agglomeration and is not conducive to separation,which limit its practical application in solution environment.Sodium alginate（ALG）,as one of the ideal embedding carrier for MOFs,can solve the problem of Ui O-66 aggregation.In this study,amino（-NH₂）and sulfonic（-SO₃H）groups were introduced into degradable ALG to obtain functionalized Ui O-66（NH₂）（U6N）and Ui O-66（SO₃H）（U6S）,and a kind of novel degradable hydrogel-MOFs composite beads were prepared successfully,showing good adsorption performance for Pb²⁺in aqueous solution and drinks.The above research provided theoretical basis and scientific information for the application of functional MOFs and degradable hydrogels in the removal of Pb²⁺from drinks,and exhibited important scientific significance.The main research contents and results are as follows:（1）The functionalized Ui O-66（NH₂）（U6N）and Ui O-66（SO₃H）（U6S）were synthesized by solvothermal synthesis with Zr⁴⁺by introducing-NH₂ and-SO₃H into the carboxyl（-COOH）ortho-position of the organic ligand terylene acid（H₂BDC）.ALG-Ui O-66（A-U6）,ALG-Ui O-66（NH₂）（A-U6N）and ALG-Ui O-66（SO₃H）（A-U6S）composite beads with different functional groups were prepared by solution crosslinking and freeze-drying by dispersing U6,U6N and U6S in ALG solution.A-U6,A-U6N and A-U6S composite beads were investigated by Scanning electron microscope（SEM）,Transmission electron microscope（TEM）,Energy dispersive spectroscopy（EDS）,X-ray diffractometer（XRD）,Fourier transform infrared spectrometer（FTIR）and Thermogravimetric analyser（TGA）to determine corresponding surface morphology,chemical composition,crystal structure,organic functional groups and thermal stability,which showed that U6,U6N,U6S and ALG were successfully combined without obvious structural damage.（2）By exploring the effects of U6 concentration in A-U6 composite beads,substituent types of U6 in ALG-based composite beads,A-U6S composite beads concentration and p H of Pb²⁺solution on Pb²⁺adsorption capacity of composite beads,the optimal adsorption conditions for Pb²⁺of composite beads were obtained.Compared with A-U6 and A-U6N,A-U6S showed the highest adsorption capacity of Pb²⁺,which reached 400.47 mg/g.The results of Langmuir adsorption model and pseudo-second-order kinetic model showed that the adsorption of Pb²⁺by A-U6S composite beads belonged to chemical monolayer adsorption.Thermodynamic studies showed that the adsorption of Pb²⁺by A-U6S was spontaneous and endothermic.When Cu²⁺,Cd²⁺,Zn²⁺,Ca²⁺and Pb²⁺coexisted,A-U6S composite beads showed good adsorption selectivity for Pb²⁺,which can be attributed to the strong electrostatic interaction and electron coupling effect between Pb²⁺and-SO₃H.In addition,after five"adsorption-desorption"cycles,the adsorption capacity of A-U6S on Pb²⁺can still reach 94.18%of the initial adsorption capacity.The ALG in A-U6S can be degraded by 30%H₂O₂ solution,and allowed U6S powder to be recycled.After three“ALG degradation-A-U6S resynthesis”cycles,the adsorption capacity of A-U6S on Pb²⁺reached 91.08%of the initial adsorption capacity.（3）The removal ability of A-U6S composite beads on Pb²⁺from tap water,apple juice drink and milk drink were studied,and further changed A-U6S concentration to make solution with excessive Pb²⁺meet the corresponding national standards.The results showed that the minimum adsorbent concentrations of A-U6S composite beads in tap water,apple juice drink and milk drink were 2250 mg/L,1750 mg/L and 1750 mg/L,respectively.And compared the changes of p H,electrical conductivity,chemical oxygen demand,total nitrogen,total phosphorus,ammonia nitrogen,total dissolved solids and chroma before and after A-U6S composite beads adsorption.After three adsorption-desorption cycles,A-U6S composite beads still had excellent adsorption capacity of Pb²⁺in tap water,apple juice drink and milk drink.In this paper,the adsorption capacity of MOFs composite beads towards Pb²⁺in aqueous solution was explored,and the adsorption capacity and removal of Pb²⁺from tap water,apple juice drink and milk drink were systematically studied.