Research On The Properties Of Phosphate Adsorption Removal By Iron-based Metal Organic Frameworks And Their Derivative

With the continuous development of the economy,the degree of urbanization and industrialization is deepening,and a large number of eutrophic components containing nitrogen and phosphorus are discharged into the water environment.The problem of eutrophication of water bodies is more and more serious,and even seriously affects people's normal life.The eutrophication of water has become one of the environmental issues that researchers at home and abroad are paying close attention to.The main determinant factor of eutrophication is the phosphorus content.Therefore,how to remove phosphorus from water has become a key issue.At present,the highest utilization rate in the method of removing phosphorus pollution is the adsorption method,and the adsorption method has attracted much attention because of its simplicity,high efficiency,and environmental protection.And it is particularly important to find a highly efficient and reproducible adsorbent.Metal-organic frameworks?MOFs?are composed of metal ions or metal clusters and multidentate organic ligands,which are a class of porous hybrid nanomaterials.Their inherent large surface area,uniform and tunable cavities,and well tolerated chemistry give them the potential to adsorb and remove phosphorus from water,but related research is scarce until now.Therefore,this paper used solvothermal synthesis to prepare iron-based metal organic frameworks and theirs derivatives for adsorption and removal of phosphate.The full text has four chapters.The main research contents are as follows:Chapter 1:Through the extensive reading and research of the literature on adsorbing phosphate,this chapter introduces the current research progress from these aspects of water eutrophication,the method of removing phosphorus at home and abroad,the type of adsorbent and the analysis of adsorption mechanism.Chapter 2:This chapter introduced the preparation of the amino-functionalized iron-based metal organic framework NH₂-MIL-53?Fe?by a simple one-pot solvothermal method,and studied the adsorption and removal properties of phosphate.The prepared mesoporous NH₂-MIL-53?Fe?adsorbent was characterized by scanning electron microscopy?SEM?,X-ray diffraction?XRD?,Fourier transform infrared spectroscopy?FT-IR?,Zeta potential,thermogravimetric-differential thermal analysis?TG-DTA?,N₂ adsorption-desorption and X-ray photoelectron spectroscopy?XPS?.The phosphate adsorption effect was explored by factors such as contact time,initial phosphate concentration,adsorbent dosage,pH,ionic strength and humic acid concentration.The NH₂ group functionalized MIL-53?Fe?increases the adsorption capacity caused by the electrostatic interaction force.The phosphate adsorption experimental data is in accordance with the pseudo-second-order kinetic model and the Langmuir isotherm model.It is worth noting that NH₂-MIL-53?Fe?exhibits excellent saturated adsorption up to 400 mg/g at 25?,which exceeds the previously reported MOF-based adsorbents and most of adsorbent materials such as activated carbon,iron?hydrogen?oxides.The Dubinin-Radushkevich?D-R?isotherm model demonstrates that phosphate removal is a chemisorption process.The excellent adsorption properties of phosphate are mainly attributed to the synergistic effects of ligand exchange,chelation and electrostatic interaction.Thermodynamic parameters indicate that the adsorption experiments are spontaneous and endothermic.In addition,NH₂-MIL-53?Fe?MOF is also better selective for phosphate than other anions such as chloride,nitrate and sulfate.Finally,the five recyclability of the adsorbent manifests that the obtained NH₂-MIL-53?Fe?is a promising adsorbent for phosphate removal in waste water treatment.Chapter 3:This chapter recommends the synthesis of iron-zirconium bimetallic organic framework MOF?Fe₁-Zr₁?by solvothermal method,and then analyzes the adsorption and removal effect of phosphate.The prepared adsorbent material was characterized by scanning electron microscopy?SEM?,X-ray diffraction?XRD?,Fourier transform infrared spectroscopy?FT-IR?,X-ray photoelectron spectroscopy?XPS?,Zeta potential analysis,and N₂ adsorption-desorption.The experimental results show that the adsorption kinetics data and isotherm data of MOF?Fe₁-Zr₁?are in accordance with the pseudo-second-order kinetic model and the Langmuir isotherm model.By fitting the experimental data of MOF?Fe₁-Zr₁?to the Langmuir isotherm model,the maximum adsorption capacity is 285.7 mg/g.The adsorption kinetics also followed the interparticle diffusion model and the liquid membrane diffusion model.The correlation coefficients R² obtained by fitting the experimental data were 0.9860and 0.9961,respectively,indicating that the rate limitation of the adsorption process was determined by the two diffusion patterns.The Dubinin-Radushkevich?D-R?isotherm model demonstrates that phosphate removal is a chemisorption process,and thermodynamic parameters indicate that the adsorption experiments are spontaneous and endothermic.The process of adsorption of phosphate by MOF?Fe₁-Zr₁?is affected by pH.Under a wide pH range,the adsorption capacity is high especially at neutral pH.The process of adsorbing phosphorus by MOF?Fe₁-Zr₁?is basically not affected by humic acids and anions such as Cl^-,NO₃^-,SO₄^2-.The adsorption-desorption process of phosphate by MOF?Fe₁-Zr₁?reached 10 times,and the removal efficiency remained above 80%,indicating that MOF?Fe₁-Zr₁?is a stable,regenerative and recyclable phosphorus adsorbent.Chapter 4:This chapter introduces magnetic core-shell structure iron-based MOFs nanomaterials based on different solvents?C₂H₅OH,H₂O,DMF?by introducing magnetic ferroferric oxide by solvothermal method,named FMC,FMH,FMD.The adsorption and removal properties of the phosphate were explored.The prepared adsorbent materials were characterized by SEM,TEM,FT-IR,XRD,XPS,Zeta potential,N₂ adsorption-desorption,and SQUID high-precision magnetic measuring instrument techniques to analyze their structure and properties.The experiment was carried out by follows factors according to the reaction time of the adsorbent on the removal of phosphate,the initial phosphate concentration,the amount of adsorbent,the pH value,the salt concentration and the humic acid concentration.Experimental studies have shown that the data of phosphate adsorption by FMC,FMH and FMD are consistent with quasi-secondary kinetics and Langmuir isotherm model,indicating that the adsorption of phosphate process is a single layer of chemical adsorption.The experimental data of FMC was fitted to the Langmuir model to calculate the maximum adsorption capacity of 333.3 mg/g,higher than FMH and FMD.The adsorption removal effect of phosphorus by adsorbent is the best under neutral pH condition.FMC adsorption of phosphate is almost unaffected by salt concentration and humic acid.After 5 cycles of regeneration of FMC,the adsorption removal efficiency can still reach 84.7%.The saturation magnetization of the FMC adsorbent was 11.5 emu/g,indicating that the material is superparamagnetism and can perform magnetic separation well.It can be seen that the iron-based FMC MOF with magnetic core-shell structure is a new type of highly efficient,stable and magnetically separable phosphorus-removing adsorbent.