Synthesis Of Metal-organic Frameworks And Their Adsorption And Separation For Metal Ions

Heavy metal ions are serious poisonous contaminants in wastewater because of their high toxicity,which could induce severe health problems in brain,liver,kidney,and immune system.At the same time,heavy metal ions can also be used as an important metal resource supplement.Therefore,the adsorption separation and recovery of metal ions in wastewater is of great significance.Currently,a variety of treatment technologies have been used to treat heavy metals in water.Compared with other processing technologies such as coagulation,electrolysis and membrane filtration,the adsorption method has low operating cost and high efficiency,and is suitable for ion capture at lower concentrations.Metal-organic framework（MOF）have attracted extensive attention in the field of aqueous adsorption due to their large specific surface area and porosity,good water stability,and controllable adsorption sites.In this paper,the adsorption and separation performance of Ba²⁺,Dy³⁺,Cu²⁺and Ni²⁺in wastewater was studied by constructing functionalized metal-organic framework materials.The specific research contents are as follows:1.The irreversible capture of radioactive ions is of great practical significance.In this study,a novel adsorbent containing sulfonic group,MOF-808-SO₃H,was prepared based on the oxidation of-SH group.Characterizations confirm the successful introduction of-SO₃H,good porosity and stability of the material.The adsorbent exhibits excellent capture ability for Ba²⁺due to strong hard acid-base and electrostatic interactions between the-SO₃H and Ba²⁺,with the adsorption capacity of 152.0 mg g^-1 and the equilibrium adsorption time is 10 min.Synergistic improvement of adsorption capacity and kinetic performance.It was found that the solution at neutral p H was favorable for ion adsorption and temperature cannot affect the adsorption largely.In addition,the capture of Ba²⁺is irreversible,which can effectively avoid secondary pollution caused by ion leakage.Therefore,this work demonstrates that MOF-808-SO₃H can be used as an efficient adsorbent for radioactive Ba²⁺treatment,and proposes a feasible strategy for constructing adsorbents with simultaneous high adsorption capacity and fast kinetics.2.Herein,we constructed a series of defect-containing Ui O-66-（COOH）₂-B using sodium benzoate（BCNa）as a modulator,and the defect levels were determined by thermogravimetric analysis and other characterization methods.Upon the formation of defects,the porosity and surface charge properties of the MOFs were improved,leading to a higher utilization ratio of active groups and higher adsorption capacities for Dy³⁺.Among them,the adsorption capacity of Ui O-66-（COOH）₂-B10 is 150.6 mg g^-1,which is about 2 times that of the unmodified material;Fast adsorption occurred at～5 min,and equilibrium was reached at～60 min.It was found that higher p H and temperature were found to be beneficial for boosting Dy³⁺adsorption.Further,FTIR spectroscopy and XPS investigations indicate that free carboxyl contributes to the capture of Dy³⁺.Thus,this work provides a promising strategy to enhance the utilization ratio of active groups and further adsorption performance.3.A stable Al-based metal-organic framework（MOF-303）was used to selectively capture Cu²⁺from Cu²⁺/Ni²⁺and Cu²⁺/Co²⁺binary systems.MOF-303 possesses classical 1D pore channels,while two adjacent ligands can form a unique 4N bispyrazole adsorption site.The study found that the adsorption site is distributed on the pore wall of the material rather than the pore opening,so the pore blocking effect caused by metal ion adsorption can be greatly reduced.Based on this characteristic,the adsorption capacity of MOF-303 for Cu²⁺can reach 330 mg g^-1,which is almost the same as the theoretical value,realizing the full utilization of the adsorption sites.At the same time,the material exhibits excellent separation selectivity of Cu²⁺/Ni²⁺and Cu²⁺/Co²⁺,a metal ion separation and recovery process in the binary system is constructed.The Cu²⁺selective adsorption mechanism based on the synergistic dualpyrazol sites in MOF-303 was analyzed via a combination of experimental method and theoretical calculation.This work not only proves that MOF-303 is a promising material for selective capture of copper ions,but also clarifies the effective promotion of the adsorption performance by the distribution of adsorption sites in the 1D channel walls.