Efficient Removal Of Phosphate In Water By Cerium-based Metal-organic Framework And Its Mechanism Research

With the development of society,phosphorus-containing wastewater has seriously affected the natural environment and even the normal life of human beings.It is urgent to develop new adsorption materials to treat such wastewater.Metal-organic frameworks are a popular class of materials in recent years.Because of their own properties,they have been used for phosphate removal.Cerium itself has a good affinity for phosphate.Based on these two points,cerium-based metal was prepared in the reactor by solvothermal method using cerium chloride heptahydrate as the inorganic metal and terephthalic acid as the organic ligand N'N-dimethylformamide as the solvent.Organic framework?Ce-BDC?and its application to phosphate removal in water.The main conclusion are as follows:?1?The optimal preparation parameters of Ce-BDC are:temperature is 140°C,reaction time is 24 h,and the molar ratio of Ce to terephthalic acid is 1:0.25;SEM and TEM show that Ce-BDC has a rod-shaped structure,and BET results show that the pore structure of the material is mainly mesopores and slit pores;TGA results show that the thermal stability of Ce-BDC is good,mainly in three weightless stages;XRD results show that the synthesized Ce-BDC has a metal-organic framework structure;FTIR results show that Ce and terephthalic acid Coordination was successful,and Ce-OH was present on Ce-BDC.?2?The optimal dosage of Ce-BDC when removing phosphate is 0.5 g?L^-1;when the initial p H of the phosphate solution is between 3-10,the removal rate of phosphate by Ce-BDC can reach more than 99%.It shows that Ce-BDC has a certain tolerance in this p H range,Ce-BDC has a higher zero potential,and its p H_pzc is about 10.7;co-existing anions SO₄^2-,NO₃^-,HCO₃^-,Cl^-at a concentration of 5-100 mg?L^-1,it has almost no effect on the removal of phosphate by Ce-BDC,and CO₃^2-,F^-has almost no effect on the removal of Ce-BDC by phosphorus at low concentrations(10 mg?L^-1),indicating that Ce-BDC has a certain selective adsorption of phosphate;Ce-BDC has certain reusability,and the removal rate can reach more than 90%after 7 times of recycling under low concentration phosphate(10 mg?L^-1),indicating that Ce-BDC has certain practical application value.?3?The process of Ce-BDC adsorption of phosphate is more in line with quasi-first-order kinetics,indicating that the adsorption process is controlled by the surface active sites of the adsorbent,The intraparticle diffusion model shows that Ce-BDC has three control steps for phosphate adsorption,namely external mass transfer process,intra-particle diffusion step and adsorption equilibrium;The Sips adsorption isotherm model and the Redlich-Peterson adsorption isotherm model can more accurately describe the process of phosphate adsorption indicates the heterogeneous characteristics of the surface of Ce-BDC adsorbent,and also shows that the process is multi-molecular layer adsorption and the adsorption is controlled by multiple effects;in addition,the Sips model fitting results show that Ce-BDC has The higher phosphate adsorption capacity is 550.45 mg PO₄^3-?g^-1(183.48 mg P?g^-1)?temperature 298 K?;The results of thermodynamics indicate that the reaction of Ce-BDC to adsorb phosphate can proceed spontaneously,and the increase of temperature is conducive to the progress of the reaction,and the whole reaction proceeds in the direction of entropy increase.?4?The analysis of FTIR,XPS,and Zeta potential tables before and after adsorption showed that the mechanism of Ce-BDC adsorption of phosphate was mainly electrostatic adsorption and phosphoric acid.The exchange of salts with hydroxyl groups on the surface of Ce-BDC and the exchange of a small number of surface carboxyl groups on Ce-BDC and the complexation of Ce and phosphate.