Synthesis Of Organo-functionalized MCM-41 And Property Studies At Adsorbing Phenol

With the rapid development of chemical industry, a large number of toxic and hazardous chemical substance was discharged into aqueous environment, caused serious pollution to the resources of water, and great damage to the natural environment. Because of lower energy loss and resources could recycled and reused, adsorption was considered to be an efficient and simple method among the industrial wastewater treatments. The synthesis of high property adsorbents which fulfiled the application needs and economical and environmental was the key and the difficulty of adsorption technology studies. Due to high surface area, larger pore size and pore volume, regular pore structure, uniform pore size distribution, tunable pore size and good structural stability, as well as extraordinarily wide possibilities of functionalization, order mesoporous silicas, as a new adsorbent material, caused widespread concerns, and became a research hotspot.In this paper, the synthesis of organo-functionalized mesoporous silicas and their adsorption properties of phenol in aqueous solution were studied. MCM-41 was synthesized by hydrothermal method, using tetraethoxysilane as silica source, cetyltrimethylammonium bromide as surfactant, and under sodium hydroxide alkaline conditions. Adopting grafting method, MCM-41, respectively, reacted with N-(2-aminoethyl)-γ-aminopropyltrimethoxysilane, 3-aminopropyl- triethoxysilane, 3-mercaptotrimethoxysilane and propyltrimethoxysilane and four kinds of organo- functionalized mesoporous silica adsorbents were gained. Via thermogravimetric analysis, X-ray diffraction, infrared spectroscopy and 77K nitrogen adsorption, these samples were characterized. In the investigation of adsorptions of phenol in aqueous solution, the coverage of organic groups, adsorption time, and different organic groups, value of pH, were studied, and adsorption isotherm were drawed, the Freundlich and Langmuir isotherm equation were fitted.The characterizations of samples showed that four organo-functionalized mesoporous silicas absorbents which were N-aminoethyl-γ-aminopropyl- MCM-41, aminopropyl-MCM-41, mercaptopropyl-MCM-41, propyl-MCM-41 were successfully synthesized, and, obtained their parameters, such as specific surface area, pore volume, average pore size.Adsorption studies showed that: adsorption on phenol rate of mesoporous silicas adsorbents which were synthesized was faster, adsorption equilibriums were reached less than 80 min, the introduction of organic groups could significantly increased the adsorption properties of phenol on mesoporous silicas, different organic modified groups, the improvement of adsorption capacity also were different, when the equilibrium concentration of phenol in aqueous solution was 800 mg/L, the saturated adsorption capacity of MCM-41 was only 32.8 mg/g, the capacity of N-aminoethyl-γ-aminopropyl-MCM-41, aminopropyl-MCM-41, mercaptopropyl- MCM-41, propyl-MCM-41 was respectively as 2.5 times, 2.2 times and 1.9 times, 1.7 times as the capacity of MCM-41. The pH of the solution could significantly affect the absorption of organo-functionalized mesoporous silica on phenol, when the pH near 6, all of them had a maximum adsorption capacity, too high pH or too low were both not conducive to its adsorption.The isotherm adsorptions of samples of phenol fitted Freundlich and Langmuir isotherm equation well, and the Freundlich isotherm equation fitted better, with a higher value of R2. The constant a in Freundlich equation which characterized the strength of adsorbent to adsorbate, and the maximum monolayer adsorption capacity qm in Langmuir equation, had same order: N-aminoethyl-γ-aminopropyl-MCM-41>aminopropyl-MCM-41>mercaptopropyl-MCM-41> propyl-MCM-41, which was consistent with adsorption experimental data.