The Synthesis Of La-modified Mesoporous Silica For Phosphate Removal

Phosphate is considered to be one of the key nutrient elements for the eutrophication.Efficient removal of phosphate becomes a focus issue in water environment treatment.High efficiency and low cost made adsorption method more popular.The mesoporous material could be modified easily because of its large surface area and the surface,so it becomes a good phosphorus removal material.In this study,two series phosphate adsorbents were produced by sol-gel and grafting methods.All of the adsorbents exhibit high adsorption ability for phosphate.The success preparation of modified mesoporous silica will further enlarge application of the mesoporous material in environment field.This study prepares the La-modified mesoporous silica by sol-gel method and grafting method.The adsorbent was characterized by TEM,BET,XRD,SEM,EDS,VSM and FTIR spectroscopy.The change of the character of La-modified mesoporous silica and unmodified mesoporous silica could be investigated.Various factors such as time,pH,temperature,phosphate concentration and coexist ions which has impact on phosphate adsorption were studied.Mesoporous hybrid film was modified by introducing different amount of La,denoted by MSF-x.The unmodified mesoporous hybrid film and MSF-x were characterized by multiple methods.The result showed that MSF-x's specific surface,pore size and pore volume both have a certain degree of reduced,but it still retain the morphology of mesoporous hybrid film.The content of La in MSF-10 was 18.41%(wt)testing by EDS.The maximum adsorption capacities of MSF-10 were 47.28 mg/g.Optimum pH value for depleting phosphate was 4.0.The Langmuir and Freundlich models were both used to simulate the sorption equilibrium,and the results showed that the Langmuir model fits the experiment data better.For kinetic study,phosphate adsorption fits the pseudo-second-order equation well.The sequence of selectity adsorption coefficient for F-,NO3-,Cland SO42-is F->SO42->NO3->Cl-.After five Recyclability tests,the regeneration efficiency was still higher than 85.78%.Hierarchical porous silica was prepared by sol-gel method,then modified with Fe and La by grafting method.The series of Fe-La-doped hierarchical porous silica were tested by multiple characterization methods,hierarchical porous silica still keeps mesoporous structure,and the highest content of La and Fe in MNTx was 34.27%(MNT-1/10)and 17.24%(MNT-1/2.5)respectively.The unmodified hierarchical porous silica has no absorption efficiency for phosphate,while the series of Fe-La-doped hierarchical porous silica show great absorption efficiency for phosphate.The highest adsorption capacity was 71.99 mg/g.The phosphate adsorption kinetics of MNT-x can be well-fitted by the pseudo-second-order equation.Equilibrium data were modeled by the Langmuir and the Freundlich isotherm,and the results indicate that the Langmuir isotherm model fits better than the Freundlich model.The appropriate pH range is 3.0-6.0.The Fe-La-doped hierarchical porous silica also possess magnetism,so that the absorbent could separate easily under a magnetic field.After five Recyclability tests,the regeneration efficiency was still higher than 90%.