Preparation Of Modified MCM-48 Mesoporous Material And Its Adsorption Of Pollutants In Water

At present,the problem of water pollution is becoming more and more serious,and the sewage containing organic pollutants and inorganic pollutants has seriously affected the water source,soil and human health of rivers and lakes.As mesoporous silica nanoparticles,MCM-48（Mobil Composition of Matter No.48）has uniform pore size,large specific surface area and pore volume,and unique double helix pore structure.In recent years,it has been widely used in the field of pollutant adsorption in water.After physical or chemical modification,it is used as a specific adsorbent for various pollutants.However,the adsorption effect of unmodified MCM-48 material on pollutants in water is average,but after modification,functional groups are successfully grafted on its surface and pore channels,increasing the adsorption active sites and improving the adsorption performance of adsorbent materials on target pollutants.In this paper,two kinds of modified MCM-48 materials,MCM-48-NH₂ and MCM-48-SH,were prepared by amino group modification and sulfhydryl group modification respectively.MCM-48-NH₂ is used to adsorb and remove humic acid（HA）from agricultural wastewater.Through a series of characterization of MCM-48-NH₂ adsorption materials,the material characteristics were studied in order to achieve the expected effect of adsorbing HA in agricultural wastewater.In this study,the effects of p H,salinity,concentration,temperature and adsorption time of MCM-48-NH₂ on the adsorption effect of HA in wastewater were explored,and the adsorption performance of MCM-48-NH₂ on HA in wastewater was analyzed,and its practical application effect was verified in farmland wastewater samples.The results showed that MCM-48-NH₂ material not only retained the basic structure of MCM-48,but also successfully grafted the functional group-NH₂.Both p H and salinity of solution have effects on adsorption.When p H is 4～9,the adsorption effect is good,and when p H is 6,the adsor ption effect is the best.Salinity also has a certain influence on adsorption,and low concentration of ionic strength is beneficial to adsorption.The temperature has little effect on the adsorption capacity,but the adsorption rate increases with the increase of temperature.The adsorption of HA on MCM-48-NH₂follows the Freundlich isotherm model,and the kinetic adsorption can fit the pseudo-second-order kinetic model.The maximum adsorption capacity of HA is 322.21 mg/g,and the removal rate can reach 94.33%.MCM-48-SH is used to remove Cr（Ⅵ）from wastewater by adsorption.In this study,the mature preparation conditions of MCM-48-SH were explored,and an ideal mesoporous material was synthesized through a series of material characterization to achieve t he expected effect of adsorbing Cr（Ⅵ）in water.In this paper,a series of experiments were designed to adsorb Cr（Ⅵ）in aqueous solution,and the effects of initial concentration,adsorption time,solution p H,competitive ions and other factors on the adsorption effect were explored,and the adsorption performance of MCM-48-SH for Cr（Ⅵ）in wastewater was analyzed.The characterization results show that MCM-48-SH material not only retains the pore structure and specific surface area of MCM-48,but also successfully grafted with functional group-SH.The adsorption of Cr（Ⅵ）on MCM-48-SH follows Langmuir isotherm model,and the adsorption is controlled by chemical adsorption.Kinetic adsorption can be fitted by pseudo-second-order kinetic model.The maximum adsorption capacity of chromium is 18.388 mg/g,and the removal rate can reach 93.45%.The adsorption of Cr（Ⅵ）by MCM-48-SH was affected by the concentration of Cr（Ⅵ）within 3 d,and the adsorption capacity reached the maximum when the concentration of Cr（Ⅵ）was 80 mgl-1.Under these conditions,the adsorption effect of MCM-48-SH on Cr（Ⅵ）is better than that of unmodified MCM-48 and amino-modified MCM-48.The p H of the solution and the existence of other coexisting ions such as Cl^-,PO₄^3-and SO₄^2-will also affect the adsorption effect,and the adsorption effect is the most obvious when p H=2.Other competitive ions in the solution have effects on the adsorption of Cr（Ⅵ）by MCM-48-SH,among which anions have a great influence.In the comparative adsorption experiment,the adsorption effect of MCM-48-SH on Cr（Ⅵ）is obviously better than that of other two common adsorbents:coconut shell activated carbon and bentonite.To sum up,two kinds of mesoporous silica materials prepared in this study:amino-modified MCM-48-NH₂ and sulfhydryl-modified MCM-48-SH can both produce good adsorption effects on target pollutants.Among them,MCM-48-NH₂ has obvious adsorption effect on HA,low requirements for adsorption environment and short adsorption time,so it is a good adsor bent for removing HA.The adsorption of Cr（Ⅵ）by MCM-48-SH is mainly controlled by chemical adsorption,mainly the adsorption of Cr₂O₇²-,which has a good adsorption effect under acidic conditions.In practical production,Cr（Ⅵ）can be effectively removed by adjusting the p H of the wastewater to be treated.