Preparation Of Kaolinite/Fe₃O₄ Nanocomposites By Solid State Iron-urea Method

With the rapid development of society,environmental problems especially water pollution,have become increasingly prominent.In recent years,the discharge of various printing and dyeing wastewater in China is increasing,which results in the increase of organic matter concentration in water.Therefore,the treatment of printing and dyeing wastewater is very important.At present,adsorption is an economic and feasible method for the treatment of doxycycline,methylene blue,Congo red and other pollutants,and it requires the use of different materials?adsorbents?to remove contaminants?adsorbates?from aqueous solutions.Among various adsorbent materials,natural kaolinite has attracted wide attention as a promising low-cost adsorbent.However,the adsorption performance of natural kaolinite is far lower than that of commonly used adsorbents due to its low activity and specific surface area.Therefore,it is necessary to improve the adsorption performance of kaolinite to make it more suitable for practical application.In this study,a series of CBK/Fe₃O₄ and CK/Fe₃O₄ nanocomposites were prepared by modifying coal-bearing kaolinite?CBK?and commercial kaolinite?CK?by solid phase iron-urea method for the first time,and their adsorption properties for cationic dye methylene blue?MB?and anionic dye Congo red?CR?were studied.The results are summarized as follows:CBK/Fe₃O₄ and CK/Fe₃O₄ nanocomposites were prepared by solid-state reaction from natural coal series kaolin,commercial natural kaolin,urea and iron nitrate.The synthesized samples were characterized by XRD,BET,FT-IR,VSM,DTA-TG and HRTEM.The results show that the nanocomposites are composed of kaolinite and Fe₃O₄nanoparticles dispersed in the framework of the kaolinite.The activation degree of kaolinite is directly proportional to the content of Fe₃O₄ in the composites.When the content of Fe₃O₄ is 30%,the layered structure of kaolinite is completely destroyed and transformed into an amorphous structure.The adsorption properties of above-mentioned two kinds of natural kaolinite and their nanocomposites for MB were studied.For this,the effects of pH value,reaction time,initial concentration of solution,reaction temperature and other factors on the adsorption were investigated.The CBK/Fe₃O₄-5 and CK/Fe₃O₄-7 nanocomposites display the best adsorption performance,and their adsorption efficiencies for MB are 36.9%and 28.5%higher than that of raw kaolinite under the following conditions:solution pH=?7,reaction time=60 min,initial concentration=100 mg/L.The adsorption of MB on CBK and CBK/Fe₃O₄ is in accordance with the quasi second-order kinetic model and Freundlich adsorption isotherm model,indicating the multi molecular layer adsorption.The adsorption of MB on CK and CK/Fe₃O₄ is well described by quasi second-order kinetic model.When the content of Fe₃O₄ is less than 20%,the adsorption of MB fits Langmuir adsorption isotherm model better,showing that the adsorption of MB on CK and CK/Fe₃O₄ is mainly single molecular layer adsorption;however,when the content of Fe₃O₄ is more than 30%,the adsorption of MB is more consistent with Freundlich adsorption isotherm model,indicating that multi molecular layer adsorption is dominant.Above two kinds of natural kaolinite and their nanocomposites were also used for the adsorption of anionic dye CR.The adsorption performance and adsorption mechanism of CR were studied via varying the solution pH value,reaction time,initial concentration of solution,reaction temperature and other factors.When the content of Fe₃O₄ in CBK/Fe₃O₄ and CK/Fe₃O₄ is 5%and 7%,respectively,the both composites exhibit the best adsorption performance under the following conditions:solution pH=?7,reaction time=60 min,initial concentration=100 mg/L.Moreover,the adsorption efficiency of both CBK/Fe₃O₄-5and CK/Fe₃O₄-7 increased by 58.1%and 77.6%when compared to their corresponding raw kaolinite.The adsorption of CR by CBK and CBK/Fe₃O₄ is in accordance with the quasi second-order kinetic model and Freundlich adsorption isotherm model,indicating that the adsorption is mainly multi-molecular layer adsorption.The adsorption of Congo red by CK and CK/Fe₃O₄ is in accordance with the quasi second order kinetic model.When the content of Fe₃O₄ is less than 10%,the adsorption of CR is more consistent with the Langmuir adsorption isotherm model,indicating that the adsorption is mainly single molecular layer;when the content of Fe₃O₄ is more than 20%,the adsorption of CR is more in line with Freundlich adsorption isotherm model,indicating that the adsorption is mainly multi-molecular layer adsorption.