Synthesis Of Functionalized Metal-Organic Frameworks With Oxygen Active Sites For Adsorption Of Heavy Metal Ions In Aqueous Solution

With the rapid development of the industrialization and urbanization,more and more heavy metal ions are discharged,which causes serious pollution to the surface water and groundwater.These toxic heavy metal ions are difficult to degrade into eco-friendly products,and can accumulate in organisms through food chain enrichment.Owing to this fact,the removal of heavy metal ions from water is critical in terms of the protection of public health and the environment.New strategies are being developed to efficiently remove these toxic ions.Metal-organic frameworks?MOFs?,constructed by metal ions or metal clusters and organic ligands through coordination bonds,are considered as a favorable platform for the adsorption applications,because of their high surface area,tunable chemical composition,variable pore size distribution and exposed active sites.By ligand modifications or MOF post-functionalization,various functional groups can be purposefully incorporated into the pores of MOFs,giving rise to more active sites for facile adsorption.The functionalized MOFs decorated with various groups were exploited for the removal of heavy metal ions from aqueous solution.Herein,in this thesis,we designed and synthesized a series of functionalized MOFs with oxygen active sites,which acted as adsorbents for removing heavy metal ions from aqueous solutions.This thesis includes the following four parts:1.We take the intrinsic advantages of MOFs and develop a porous Zn?II?-based MOF,{[Zn₃L₃?BPE?_1.5]?4.5DMF}_n?1,H₂L=4,4'-azoxydibenzoic acid,BPE=bis?4-pyridyl?ethylene,DMF=N,N-dimethylformamide?,which decorated with O^-groups for the removal of Pb²⁺.Benefiting from its multiple porosity,sufficient adsorption sites and strong affinity,the activated MOF material exhibits ultrahigh Pb²⁺uptake capacity(616.64 mg g^-1),surpassing all those of reported MOF adsorbents.Moreover,it can selectively capture Pb²⁺with high efficiency?>99.27%?against background ions.Even in the presence of high concentration of competitive ions,such as Ca²⁺or Mg²⁺,effective removal?>99.21%?can also be achieved in a short time.The excellent removal performance demonstrates the strong electrostatic attraction and coordination interaction between the highly accessible O^-groups and Pb²⁺.The possible adsorption mechanism was systematically verified by zeta potential,FT-IR and XPS studies.We first introduce the functional groups with negative charges into the pores of MOFs for removal of heavy metal ions with excellent performance.2.In order to develop efficient material for fast and complete removal of trace Pb²⁺from water,we prepared a novel MOF,{[Cd?ADB?L₂]?1.5DMF?2H₂O}_n?2,H₂ADB=2,2?-azodibenzoicacid,L=?pyridin-3-yl?methyl4-?2-?4-??pyridin-3-yl?methoxy?phenyl?diazenyl?benzoate]?,which decorated with carbomethoxy groups and investigated its removal performance for Pb²⁺as well as the underlying mechanism.A very short equilibrium time?6 min?was achieved,which followed the pseudo-second-order kinetics with a kinetic rate constant k₂ of 0.162 g mg^-1 min^-1.The kinetic rate constant was higher than reported Pb²⁺adsorbents by 1–3orders of magnitude.Importantly,even in a concentration of 0.1 ppm,high removal efficiency?96%?was still obtained and the concentration was reduced to 0.004 ppm.This value is well below the drinking water standard of the World Health Organization?0.01 ppm?.The good removal performance demonstrates a significant affinity between MOF and Pb²⁺,involving the carbomethoxy groups.The possible adsorption mechanism was systematically verified by FT-IR and XPS studies.3.Copper?II?is an essential element in the environment and human body,while exposure to excessive Cu²⁺will potentially cause health issues.It is highly imperative to develop new strategies for the removal of Cu²⁺from aqueous solution.A H-bonded MOF[(Zn₃L₃?H₂O?₆][?Na??NO₃?]?3,H₂L=1,3-benzenedicarboxylic acid?with high stability was elaborately constructed.The uncoordinated carboxylate oxygen atoms in the channels of MOF were designed as active sites to recognize Cu²⁺and further coordinate with it.Without pre-treatment,MOF 3 demonstrated a relative high uptake capacity(379.13 mg g^-1),exceeding most of Cu²⁺adsorbents.Even in the presence of various metal ions and high concentration of interfering ions,highly selective adsorption of Cu²⁺can be achieved.Moreover,the excellent water stability together with the high removal efficiency in the presence of coexisting ions offers MOF 3 the possibility in practical application.The mechanism for Cu²⁺selective adsorption was systematically investigated by UV-vis,FT-IR and fluorescence lifetime techniques,which may originate from the strong interaction between Cu²⁺and the carboxylate oxygen atoms.Our work thus paves a way for developing MOFs as an appealing platform to construct adsorption materials for environmental application.4.Due to the special magnetic and optical properties of rare earth elements?REEs?and no decisive substitutes,the significantly increased consumption of REEs is leading to the global supply risk and the REE shortages,which will hinder the development of industry fields.On the other hand,mining,extraction,and roasting stages for REE production involve high energy consumption and have detrimental environmental impact.REE recovery could help in recycling the valuable resources,relieving their high environmental burden and easing a potential supply crisis.We prepared a novel porous MOF,{[CdL?BPD?]?DMF}_n?4,H₂L=4,4'-azoxydibenzoic acid,BPD=4,4'-bipyridine,DMF=N,N-dimethylformamide?,which decorated with O^-groups and its adsorption performance for RE³⁺were investigated.The activated MOF material exhibited relatively high uptake capacity for RE³⁺(99-211 mg g^-1).Moreover,it can selectively adsorb RE³⁺with high efficiency against the alkaline earth and transition metal ions.These adsorption performances make this MOF one of the most promising materials for adsorbing RE³⁺from aqueous solution.Moreover,the activated MOF can adsorb more than 99.5%RE³⁺after being prepared for column chromatography.