Study On The Preparation Of Al-MOF Adsorption Material And Its Removal Of Fluoride From Water

Fluorine is one of the essential trace elements for the human body,but long-term drinking of high-fluorine water can cause human fluorosis.The adsorption method is widely used in the removal of fluoride in water due to its simple operation and high economic benefits.Metal Organic Frameworks（MOFs）have attracted much attention in the field of adsorption applications due to their porous and large specific surface area.In this thesis,three kinds of MOFs adsorption materials were prepared by hydrothermal method.The materials were characterized by scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）and other characterization methods.The performance and mechanism of fluoride removal in water were studied.（1）The rice like metal organic framework adsorbent MIL-96（Al）was prepared from aluminum nitrate（Al（NO₃）₃·9H₂O）and 1,3,5-benzenetricarboxylic acid（1,3,5-BTC）by hydrothermal method.The maximum adsorption capacity of MIL-96（Al）for fluoride was 42.19 mg/g at 293 K.The pH has little effect on the fluoride removal performance of MIL-96（Al）.In the range of 3-11,it has a good adsorption effect on fluoride ions in water.The coexisting anions(C1^-,SO₄^2-,NO₃^-,and CO₃^2-)in water have little effect on the fluoride removal effect of MIL-96（Al）,indicating that it has strong anti-interference ability and high selectivity.The adsorption process can be well described by the Langmuir model and the Pseudo second-order kinetic model.The thermodynamic data shows that the process of MIL-96（Al）adsorption of fluoride is spontaneous endothermic.（2）The cluster-shaped metal organic framework adsorbent Al-MOF-5 was prepared from aluminum nitrate（Al（NO₃）₃·9H₂O）and terephthalic acid（H₂BDC）by hydrothermal method.The maximum adsorption capacity for fluoride reached 42.92 mg/g at 293 K.The effect of pH on the fluoride removal performance of Al-MOF-5 was significant,and the removal percentage was slightly increased under acidic and alkaline conditions.The coexisting anions(C1^-,SO₄^2-,NO₃^-,and CO₃^2-)in water have little influence on the defluorination effect of Al-MOF-5,indicating that it has strong anti-interference ability and high selectivity.The adsorption process can be well described by Langmuir model and Pseudo second-order kinetic model.The thermodynamic data show that the adsorption process of fluoride on Al-MOF-5 is spontaneous endothermic.（3）Using MIL-96（Al）and graphene oxide（GO）as raw materials,the MIL-96（Al）/GO composite material was prepared by hydrothermal method,and the best of MIL-96（Al）and GO was selected.The composites were characterized by SEM,TEM,XRD and FTIR.The addition of GO reduces the agglomeration of MIL-96（Al）,and shows more significant adsorption performance and good stability during the adsorption of fluoride.Adsorption is a spontaneous endothermic reaction,conforming to Langmuir model and Pseudo second-order kinetic model.The maximum adsorption capacity increased to63.29 mg/g at 293 K.The pH has almost no effect on the fluoride removal performance of the MIL-96（Al）/GO composite.In the range of 3-11,it has a good adsorption effect on fluoride ions in water.The composite material has strong anti-interference ability and high adsorption selectivity,and the coexisting anions in the water have little effect on the fluoride removal effect of the composite material.The research results in this thesis show that the three prepared fluoride removal adsorption materials all have good fluoride removal performance.The MIL-96（Al）/GO composite has the highest adsorption capacity,and Al-MOF-5 and MIL-96（Al）are equivalent.The fluoride adsorption capacity of the three materials is significantly higher than that of activated alumina.The three kinds of fluoride adsorption materials all have good recycling performance,which can be recycled 5-7 times after regeneration.Under the same experimental conditions,the fluoride removal rate can still reach more than50%.The research results in this thesis can provide certain theoretical and technical support for the preparation and application of MOF-based fluoride adsorption materials.