Design And Synthesis Of Metal-organic Frameworks For Water Purification

Metal-organic frameworks(MOFs),emerging as a new class of crystalline nanoporous materials,have arised a great deal of interest due to their high surface area and adjustable pore size as well as facile functionalization.In recent years,the prospect of MOFs for water purification starts to emerge correspongding to the development of highly water-stable MOFs.Considering the unique advantage of MOFs compared with other porous materials,it is of great importance to design and synthesize high-performance MOF-based adsorbents for water purification.From the design perspective of pore size and its chemical environment,in this work a series of task-specific MOF-based high-performance adsorbents were designed and synthesized according to different pollutants in industrial wastewater.Besides,the adsorption mechanism was also explored.The main works are as follows:1.In view of the capture of radioactive barium ions in nuclear wastewater,we propose a concept of barium ion trap based on MOFs.That is,the adsorption performance of MOFs towards Ba2+ could be greatly improved by introducing a strong barium-chelating group(sulfate or sulfonate groups)into the pore structures of MOFs.Herein,as a proof of concept,MOF-808-SO4 and MIL-101-SO3H(Cr)for Ba2+capture were systematically investigated.The results showed that MOF-808-SO4 exhibits a high Ba2+ uptake capacity of 131.1 mg g-1 at room temperature,which surpasses most of the reported adsorbents and can selectively capture barium from water,whereas MIL-101-SO3H(Cr)shows ultrafast kinetics with a kinetic rate constant k2 of 27.77 g mg-1 min-1 Both of the two MOF-based ion traps possess high water stability and can capture barium irreversibly.2.In view of Hg2+ removal in wastewater,highly water-stable MOF-808 was selected as host material to demonstrate this.Two new MOFs,namely MOF-808-TGA and MOF-808-AA-EDT,were designed and synthesized by grafting thioglycolic acid and ethanedithiol onto the metal clusters of MOF-808 respectively via direct substitution and tandem post-modification.The results show that both two modified MOF materials exhibit excellent Hg2+ removal performance.The removal efficiency of MOF-808-TGA and MOF-808-AA-EDT are>99%with Hg2+concentration of 10 mg L-1.It should be noting that the saturated adsorption capacity of MOF-808-AA-EDT towards Hg2+is 1077 mg g-1,which surpasses all the MOF materials reported in previous literatures.The mechanism study shows that the excellent adsorption performance of MOF-808-AA-EDT towards Hg2+can be traced to the strong affinity between sulfur in MOF material and mercury ions.3.Current technologies for removing heavy metal ions are typically metal ion specific.Herein,we report the development of a broad-spectrum heavy metal ion trap by incorporation of ethylenediaminetetraacetic acid(EDTA)into a robust metal-organic framework.EDTA in MOF material shows strong chelation with various heavy metal ions,which can be ascribed that EDTA has both hard and relative softer sites together as well as high coordination number.The capture experiments for a total of 22 heavy metal ions,covering hard,soft,and borderline Lewis metal ions,show that MOF-808-EDTA is very effective,with removal efficiencies of>99%for all cases.Breakthrough experiments of MOF-808-EDTA show that the terminal concentration of 19 tested heavy metal ions was reduced from 5 mg L-1 to 0.01-1.9 ?g L-1,which are much lower than the acceptable limits in drinking water standards of WHO.On the other hand,due to the strong chelation of MOF-808-EDTA with various metal ions,this material could serve as a host to prepare well-dispersed single or multiple metal catalysts.The amounts and types of loading metal ions as well as uptake ratio can be selected and tuned according to practical needs.4.In view of dimetridazole(DMZ)antibiotics capture in wastewater,MIL-53(Al)was used as an example to demonstrate this.We propose a strategy of using highly flexible metal-organic framework for DMZ capture and excellent performance was achieved.Over 90%of DMZ can be removed within 10 min and the adsorption kinetics will reach equilibrium after 60 min of contact.Besides,MIL-53(Al)exhibits an excellent saturated adsorption capacity of 467.3 mg g-1,surpassing all previous reported MOF-based adsorbents and various adsorbent materials.The mechanism study reveals that the structure of MIL-53(Al)endure a switch from narrow pore(NP)to large pore(LP)form with the increase of DMZ concentration,which allows to feature high uptake capacity and high removal effiency at low DMZ concentration.