Modified mesoporous silicates for metal adsorption.

摘要

Mesoporous silica materials, commonly called Hexagonal Mesoporous Sieves (HMS), are used to adsorb copper, lead, and mercury from aqueous solution. To increase metal adsorption, organic ligands with high metal affinity are grafted to the surface of the HMS materials. Three ligands were used in this research: 3-mercaptopropyltrimethoxysilane (MP), 3-aminopropyltrimethoxysilane (AM), and p-(aminoethylaminomethyl)phenethyltrimethoxysilane (AB). The physical properties of HMS include large surface area and an ordered system of pores. These properties are believed to increase the extraction capabilities of the material by increasing the molar content of the chelating ligand and by making the ligand more accessible. The purpose of this research was to fully characterize HMS and functionalized HMS materials, to determine the adsorption capacity of these materials for the metals of interest, and to ascertain if the increased porosity of HMS improved metal extraction.; All HMS materials were characterized by 29Si Solid State Nuclear Magnetic Resonance (SS-NMR), powder x-ray diffraction (XRD), and surface area analysis. Surface coverage of the grafted ligand was determined by elemental analysis and 29Si SS-NMR. Adsorption isotherms were collected in metal extraction studies and were determined to follow the Langmuir adsorption model. Adsorption capacities were calculated by taking the reciprocal of the y-intercept of the linear Langmuir adsorption isotherm. To test the importance of porosity, silica gel was functionalized using the same ligands. Silica gel has a similar elemental composition as HMS without the pore structure. Adsorption capacity of functionalized silica gel was obtained and compared to the results obtained from HMS.; Extraction experiments showed functionalized HMS to be a superior metal adsorbent compared to silica gel. This greater adsorption capacity was due to increased surface coverage of all three ligands used. In the case of the AM and MP ligands, the higher adsorption capacity is also due to the increased porosity of the HMS material. However, both the SG and HMS materials functionalized with the AB ligand showed the same metal/ligand molar ratio. The large ligand has the effect of decreasing the pore diameter, and therefore making material porosity less important. All functionalized HMS materials were shown to be excellent metal adsorbents.