Synthesis Of Sand/MIL-100(Fe)Composites And Their Adsorptive Properties

As a kind of environmental friendly natural raw material,sand has relatively stable chemical composition,which has attracted extensive attention of researchers in recent years.Owing to its low cost,stable structure and bundent reserves,sand has been widely concerned to prepare various supported catalysts and adsorbents,as well as various high-performance composite materials.Metal organic frameworks(MOFs)are a class of porous materials,composed of metal ions and organic connector,having a large Langmuir surface area and small or medium pores,and they have been widely used in chemical industry.In recent years,because of their excellent chemical stability and rich functional groups,MOFs have gradually become an important materials for the treatment of industrial wastewater pollutants.In this paper,Sand/MIL-100(Fe)composite material was prepared by in-situ synthesis and one-step synthesis from iron nitrate,pyromellitic acid and milled sand obtained from Kubuqi Desert of Inner Mongolia Autonomous Region.All aspects of sand properties were successfully improved by modifying sand MOFs material MIL-100(Fe)with high hydrothermal stability.The adsorption properties of sand before modification and composites on cationic dye methylene blue(MB)and anionic dye Congo red(CR)were studied.The results are as following:1.The Sand/MIL-100(Fe)composites with different proportions were prepared by in-situ synthesis and one-step synthesis methods using ferric nitrate as the Fe(?)source and pyromellitic acid as the organic ligand.The materials were characterized by XRD,BET,TG-DTA,FT-IR and isoelectric point test.The results show that the materials prepared by the two methods are composed of sand and MIL-100(Fe).Compared with the unmodified sand,the specific surface area of the synthesized Sand/MIL-100(Fe)increases significantly.For in-situ synthesis,when the F/S ratio is 2.2,the specific surface area of the composite can reach 412.5m~2/g.For the one-step synthesis method,when the F/S ratio is 0.6,the specific surface area of the composite can reach 866.3m~2/g;and the specific surface area of the prepared pure MIL-100(Fe)can reach1240.8m~2/g.The surface of the prepared composites and the pure MIL-100(Fe)have negative charge under neutral condition.2.The adsorption properties of sand,composite materials prepared by the above two methods and pure MIL-100(Fe)for cationic dye MB were tested.The effects of the amount of adsorbent,pH value of MB solution,adsorption time,initial concentration of MB solution and reaction temperature on the adsorption were investigated.The results showed that under neutral condition,when the initial concentration of MB was 100mg/L,the volume of MB was 20 mL,the amount of adsorbent was 20 mg,and the adsorption time was 60 mins,the composites prepared by the two methods had the best adsorption effect on MB.For in-situ synthesis,when the F/S ratio was 2.2,the highest adsorption rate was 99.1%;for the one-step synthesis method,when the F/S ratio was 0.6,the maximum adsorption rate was 99.0%;the maximum adsorption rate of pure MIL-100(Fe)on MB was 99.4%.The composites synthesized by in-situ method and one-step method exhibited the maximum adsorption capacity of MB of 342.5 mg/g and 355.9 mg/g,respectively,while MIL-100(Fe)alone had the maximum adsorption capacity of 606.0 mg/g.The adsorptions were in accordance with the quasi second-order kinetic model and Langmuir adsorption isotherm model,showing that all of which are monolayer adsorptions.3.The adsorption properties of the above adsorbents on the anionic dye CR were studied,For this we investigated the effects of the amount of adsorbents,pH value of the CR solution,adsorption time,initial concentration of the CR solution and reaction temperature on the adsorption.The results showed that the adsorptions were in accordance with the quasi second-order kinetic model and Langmuir adsorption isotherm model,indicating of the monolayer adsorptions.The maximum adsorption capacity of the composites prepared by in-situ synthesis method and one-step synthesis method were 253.2 mg/g and 404.9 mg/g,respectively;the maximum adsorption capacity of pure MIL-100(Fe)for CR was 423.7 mg/g.