Preparation Of Copper-Based Metal Organic Frameworks Compositegel Beads And Their Application In Seawater Desalination

Desalination and wastewater reuse are important ways to address global water scarcity.Traditional urban wastewater advanced treatment technology and seawater desalination technology such as reverse osmosis（RO）have the problems such as high energy consumption and serious membrane pollution due to external pressure drive.Among various water treatment technologies,adsorption methods have some advantages such as simple process,easy operation,and high efficiency.So,adsorption methods are widely used in the removal of pollutants in water,including heavy metals,organic pollutants,and dyes.However,there are few reports on the separation of soluble salts such as NaCl in water by adsorption for desalination process.In recent years,the combination of adsorbent materials such as sodium alginate and metal-organic frameworks（MOFs）can not only obtain formable composite adsorbents,but also significantly improve stability and adsorption capacity,which showing great potential for water purification.In this study,sodium alginate was used as the matrix,polyvinyl alcohol（PVA）or sodium carboxymethylcellulose（CMC）was introduced to form an interpenetrating network structure,and then the composite gel beads adsorption materials embedded with copper-based metal-organic framework（Cu-MOF）were synthesized in situ by solvothermal method,and their adsorption performance on soluble salts（NaCl）in water was systematically investigated and the adsorption mechanism was studied,and the main research contents and results were as follows:（1）Preparation and characterization of alginate/polyvinyl alcohol composite gel ball coated with Cu-MOF（Alg/PVA@Cu-MOF）and its adsorption performance and mechanism on soluble salt（NaCl）in water:Alg/PVA@Cu-MOF was obtained by using sodium alginate（SA）as the main raw material,PVA was penetrated into the copper alginate gel network by interpenetrating network technology,and then Cu-MOF was formed in situ in the gel network by solvothermal method.A series of Alg/PVA@Cu-MOF with different chemical structures were prepared by changing the temperature of the solvothermal reaction,and the prepared Alg/PVA@Cu-MOF adsorbent was characterized by a variety of technical methods,including SEM,FTIR,XRD,and XPS,and its adsorption properties and related mechanisms for soluble salts（NaCl）in water were systematically studied.The results show that the Alg/PVA@Cu-MOF prepared under the reaction condition of 120°C has a good removal rate of NaCl in water,the best adsorption effect at p H=7,the highest adsorption capacity could reach 24.14mg·g^-1.The adsorption equilibrium time is about 500 min,and it also has a good adsorption effect on other common ions in seawater.The Pseudo-second-order model can better fit the results of adsorption kinetics,indicating that the adsorption process of Alg/PVA@Cu-MOF on NaCl in water is dominated by chemical adsorption,The Langmuir model can better fit the experimental results,indicating that the adsorption process is monolayer homogeneous adsorption,and the theoretical maximum adsorption capacity of the Langmuir model is 41.80mg·g^-1.Combined with the characterization results and adsorption data,the adsorption mechanism of Alg/PVA@Cu-MOF on NaCl in water includes ion exchange reaction,electrostatic action and adsorption precipitation.（2）Preparation and characterization of alginate/carboxymethylcellulose composite gel ball coated with Cu-MOF（Alg/CMC@Cu-MOF）and its adsorption performance and mechanism on soluble salt（NaCl）in water.In order to further improve the adsorption capacity and stability of Cu-MOF-based composite gel balls,Alg/CMC@Cu-MOF was prepared by blending alginate with sodium carboxymethylcellulose（CMC）.CMC is similar in molecular structure to SA,containing a large number of functional groups such as carboxyl groups（-COOH）and hydroxyl groups（-OH）,which can act as coordination and reaction sites.It is not only conducive to the introduction of more Cu-MOF,but also can enhance the mechanical strength and stability of the gel network through hydrogen bonding with Alg.A series of Alg/CMC@Cu-MOF with different chemical structures were prepared by changing the temperature of the solvothermal reaction,and the prepared Alg/CMC@Cu-MOF was characterized by a variety of technical means including SEM,FTIR,XRD,and XPS.Its adsorption properties and related mechanisms for soluble salts（NaCl）in water were systematically studied.The results show that the highest adsorption capacity of Alg/CMC@Cu-MOF can reach 56.54mg·g^-1 at p H=7,and the equilibrium adsorption time of the adsorbent is about 20 min,showing a relatively fast adsorption efficiency.Pseudo-second-order kinetics can better fit the kinetic data,indicating that the adsorption process is dominated by chemical adsorption.The Langmuir model can better fit the experimental data of the adsorption isotherm,indicating that the adsorption process is a single-layer homogeneous adsorption,and the theory of the Langmuir model maximum adsorption capacity reached 241.60mg·g^-1.Alg/CMC@Cu-MOF also shows good adsorption effect on other common ions in seawater,and has good practical application potential.The adsorption mechanism of Alg/CMC@Cu-MOF on NaCl in water includes ion exchange reaction,electrostatic interaction and adsorption precipitation.