Experimental Studies On The Adsorption, Separation And Detection Of Heavy Metal Ions From Aqueous Solution By Metal-Organic Frameworks

A variety of toxic and harmful substances existe in waste water. Among them, tansition metal ions have done great harm to human and ecosystem. So, the separation of metal ions has been regarded as one of hot spots. As a new class of nanoporous materials with special pore structure and high specific surface area and porosity, metal-organic frameworks ?MOFs? have been explored in areas of adsorption and separation of both gas and liquid phases, catalysis, biological medicine, fluorescence, magnetic, electrochemical and so on. However, the related works on the adsorption and separation of heavy metal ions are very limited in MOFs. As an example, we adopted several stable MOFs to selectively capture Cu²⁺ over Ni²⁺ from aqueous solutions in this study. And on the basis of water stable MOFs and water-soluble quantum dots, we also studied the preparation of fluorescent probes of heavy metal ions. The main contents are as follows:1. We studied the effects of both pore size and functional groups of MOFs on the adsorption and separation of Cu²⁺/Ni²⁺. In order to systematicly study, we prepared 9 water stable isoreticular MOFs by solvothermal method: UiO-66?Zr?, UiO-66?Zr?-Br, UiO-66?Zr?-NH₂, UiO-66?Zr?-NH-?CH₂?₂-SO₃H, UiO-66?Zr?-COOH, UiO-66?Zr?-2COOH, Zr-FUM, Zr-2,6 NDC, UiO-67. The nine MOFs were characterized by PXRD, N₂ adsorption and desorption isotherms at 77 K and TGA.2. By inductively coupled plasma ?ICP?, the tests showed that the pore size of MOFs had little effect on the adsorption. On the contrary, the functional groups showed significant effect in the adsorption and the best MOF is UiO-66?Zr?-2COOH. Due to the unique chelation effect of two carboxyl groups on the adjacent organic ligands as well as the Jahn-Teller effect, in aqueous solution UiO-66?Zr?-2COOH exhibited the highest selectivity ?26.96? for Cu²⁺/Ni²⁺ among the reported adsorbents. And the process was fast with less than 60 min for equilibration and conformed to the pseudo-second-order. The regenerated MOFs still kept the good selectivity and stability. The above results show that UiO-66?Zr?-2COOH can be used as a recyclable adsorbent for the separation of heavy metal ions.3. By the method of water dissolve, the composite materials of qua ntum dots and the water stabile MOFs such as ZIF-8, UiO-66?Zr?, UiO-66?Zr?-2COOH were successfully synthesized. The application of QDs/ZI F-8 was studied, and the detection of Hg²⁺ was obvious. These results may be helphul for the study of the composite materials of quantum do ts and MOFs.