Preparation And Fluorine Removal Performance Of Metal-organic Frame Composite Materials

Many countries around the world suffer from highly fluoridated groundwater,and long-term intake of high levels of fluorine ions can lead to dental fluorosis and bone fluorosis.Therefore,there is an urgent need for practical solutions to remove excess fluorine.Adsorption technology is one of the most widely used technologies,and the central issue is efficient adsorbent materials.Among the already developed materials for fluorine removal,most of them have disadvantages such as low adsorption capacity and weak affinity for fluorine ions.Therefore,it is necessary to develop highly efficient fluorine ion adsorbents with high adsorption efficiency and many active sites.Metal organic frameworks（MOFs）have properties such as large specific surface area,adjustable pore size,convenient introduction of functional groups and easy processing into macroscopic shapes,which make them promising materials for fluorine removal.In order to develop fluorine removal materials with more active centers and better adsorption performance,modification of MOFs materials is a very effective means.In this thesis,we designed and synthesized a series of metal-organic framework composites for efficient fluorine removal,characterized the physicochemical properties of the materials,and investigated their adsorption properties performance and the influencing factors,and broadened the application fields of metal-organic framework composites.The main research contents are as follows:（1）La-UiO-66-（COOH）₂ composites with more active centers for adsorption were obtained by uniform anchoring of lanthanide ions onto the inner and outer surfaces of UiO-66-（COOH）₂ through uncoordinated carboxyl groups.The adsorption process of La-UiO-66-（COOH）₂ on fluorine could be described by pseudo-second-order equation model and the Freundlich isotherm model.It showed good fluorine removal performance in the p H=3～9range.The maximum adsorption capacity of the adsorbent for fluorine ions was 57.23 mg/g at 50°C.The main fluorine removal mechanisms of La-UiO-66-（COOH）₂ were ion exchange and electrostatic interaction.The treated simulated subsurface fluoridated wastewater was able to meet the WHO standards.（2）La-SA/UiO-66-（COOH）₂（La-SA/U）composite coagulation beads with a diameter of about 1 mm were successfully prepared using sodium alginate（SA）as the gel matrix,zirconium-based metal organic framework nanoparticles as the functional filler,and lanthanum ions as the cross-linking agent,which facilitated the solid-liquid separation after fluorine removal.La-SA/U was able to reach the equilibrium of fluorine ion adsorption within 20 min,and the adsorption process of fluorine by this adsorbent conformed to the pseudo-second-order equation model and the Langmuir isotherm model.The maximum adsorption capacity of La-SA/U for fluorine ions was 58.60 mg/g at 50℃.（3）The composite material（PANI@MOF-801）was prepared by modifying polyaniline（PANI）onto a zirconium-based metal organic framework.The adsorption process of PANI@MOF-801 on fluorine was in accordance with the pseudo-second-order equation model and Langmuir isotherm model.The adsorbent showed good fluorine removal performance in the p H=2～11 range.The best fluorine removal performance was achieved when the p H was 7,with an adsorption capacity of 62.70 mg/g.PANI@MOF-801 still showed good fluorine removal performance under the influence of Cl^-,SO₄^2-,NO₃^-and HCO₃^-,indicating that it has good selectivity.