Synthesis Of Al-MCM-41 By Coal Fly Ash And Its Adsorption Properties For Cationic Dyes

Water is one of the important and indispensable resources for the survival of human beings and all kinds of organisms.It is also a major requisite for social stability and harmonious development.But with the rapid development of industrialization,water pollution becomes more and more serious.The emission amount of dye wastewater is huge,so how to purify dye wastewater has become an urgent problem.In this study,two kinds of dyestuffs,thiazine methylene blue and triphenymethane crystal violet,selected as the representative cationic dye pollutants.The adsorption properties of Al-MCM-41 synthesized by fly ash are studied.Al-MCM-41 is synthesized by hydrothermal method,using fly ash as the raw material,and characterized by small angle X-ray diffraction(SA-XRD),Fourier transform infrared spectroscopy(FTIR),scanning electron microscopy(SEM),transmission electron microscope(TEM)and static adsorption experiment.The effects of preparation conditions such as Si/Al ratio,pH value,crystallization temperature and crystallization time on the structure and adsorption properties of Al-MCM-41 are studied.Then,the adsorption properties of Al-MCM-41 on methylene blue and crystal violet and its optimal adsorption conditions,including the quality of the adsorbent,initial pH value,temperature and adsorption time,are also studied.Finally,the adsorption mechanism of Al-MCM-41 on methylene blue and crystal violet is studied by analyzing adsorption isotherm and adsorption kinetics.The experimental results show that the optimal conditions for synthesizing Al-MCM-41 are as follows:Si/Al=10,pH=10.50,crystallization temperature=110? and crystallization time=72h.The samples synthesized under these conditions exhibit good degree of order and solidification,and the adsorption performance for methylene blue and crystal violet is the best.The adsorption performance of Al-MCM-41 on the methylene blue and crystal violet is investigated,and the results are as follows:with the increment of Al-MCM-41 dosage,the removal rate of cationic dyes increases and adsorption capacity per gram decreases.Al-MCM-41 has better removal capacity for cationic dyes under alkaline conditions than under acidic conditions.With the same dye concentration,the adsorption rate of Al-MCM-41 on cationic dyes decrease with the increment of adsorption temperature,which indicates that the increment of temperature is not conducive to its adsorption process.From the results of adsorption time,the adsorption process of methylene blue and crystal violet by Al-MCM-41 is divided into the rapid adsorption stage(0?30 min)and slow adsorption stage(30?60 min),culminating in the 60min.The adsorption temperature has a certain influence on the adsorption rate.With increasing reaction temperature,the adsorption equilibrium time of Al-MCM-41 is increases.Investigation of the adsorption mechanism of Al-MCM-41 on methylene blue and crystal violet,obtains the results that:The isotherm model fitting shows that Langmuir model is better than Freundlich model to describe the adsorption process of Al-MCM-41 on those two dyes,so its adsorption form is monomolecular adsorption,which belongs to physical adsorption and exothermic adsorption process.When the temperature is 30 ?,40 ? and 50?,the qmax,fitted on methylene blue is 2049.81,1897.60 and 1589.35mg/g,respectively,and the qmax,exp is 2003.22,1840.35,1579.88mg/g,respectively.Under the same temperature,the qmax,fitted on crystal violet is 443.29,424.19 and 404.70mg/g,respectively,and the qmaxe,exp is 458.33,420.51,383.75mg/g,respectively.The fitting results are in good agreement with the experimental results.The fitting results of pseudo-second-order model are slightly better than the results of pseudo-first-order model,which indicates that the adsorption speed of Al-MCM-41 on cationic dyes is mainly related to the electron-sharing or electron transfer between adsorbate and adsorbent.