Study On Adsorption Of Hexavalent Chromium By Organic-metal Frameworks

In China,the per capita water resources are small,the regional distribution is uneven,and there are different degrees of pollution.With the acceleration of modernization and the rapid development of industry,heavy metal pollution incidents occur frequently,posing a threat to human health and drinking water safety.Chromium is one of the most commonly used raw materials in industrial production.As an important part of heavy metal pollution,it has attracted extensive attention in recent years.Making more suitable adsorption materials for its efficient removal is one of the research hotspots.Organic-metal Frameworks（MOFs）are organic-inorganic hybrid materials with intramolecular pores formed by the combination of metal ions and organic ligands through coordination bonds.In this paper,three kinds of MOFs were synthesized,and the materials were modified and used to adsorb Cr（Ⅵ）pollutants in water.The factors such as temperature and pH were investigated,and the adsorption models and mechanisms of the three adsorbents were discussed.The main conclusions of the experiment are as follows:（1）Under laboratory conditions,three MOFs were synthesized by hydrothermal solvent method,and the optimal ratio of MOFs synthesis reagents was studied.The optimal synthetic ratio of MIL-101（Fe）is n（organic ligand）:n（Metal Center）=1:2,the optimal synthesis ratio of UiO-66 is n（organic ligand）:n（Metal Center）=1:1,in addition,the optimal synthesis reaction time of UiO-66 is 72 h.（2）MIL-101（Fe）and UiO-66 were subjected to adsorption modification experiment,successfully obtained MIL-101（Fe）-Na₂CO₃ and UiO-66-HCOOH two materials.After the modification of the two adsorbents,the adsorption rate increased by about 28%respectively.（3）The three MOFs systems all conform to the Langmuir adsorption isotherm model,quasi-second-order kinetic model,and thermodynamic model,proving the existence of chemical bond adsorption.The MIL-101（Fe）and UiO-66 MOFs were regenerated and adsorbed,after desorption and re-adsorption for many times,they still have a good adsorption effect,which proves that the recyclability is good.（4）Single factor influence experiments were carried out on MIL-101-Na₂CO₃,UiO-66-HCOOH and TMU-16 adsorbent materials,investigating the effects of reaction time,different pH conditions,reaction temperature and initial pollutant concentration on adsorption experiments.The adsorption capacity of the three MOFs materials are the highest when pH=2 and the reaction temperature is 30℃,and the high concentration of pollutants can promote the adsoption reaction.