(465c) Sulfur-Based Surface Functionalization of Amorphous Silica Particles for Metals Removal

Surface functionalization of amorphous silica particles (also known as ?silanization? or ?silylation?) occurs by hydrolysis and then condensation of the surface silanol (SiOH) groups with the Si center of a silane compound. Silanes which contain sulfur functional groups, such as thiols and disulfide bonds, are used to functionalized silica particles for the efficient removal of mercury from aqueous and vapor streams. Amorphous silica particles (of various pore volumes and particle diameters) have been functionalized using 3-mercaptopropyl trimethoxy silane (MPTMS) and bis[3-(triethoxysilyl) propyl]-tetrasulfide (?S4?). It is well-known that Hg2+ is efficiently removed using thiol functional groups, but Hg0 is removed using disulfide bonds, which form a sulfur-based polymer network on the silica particle surface. Various methods of forming this network, including the oxidation of thiol functional groups once on the surface, are discussed, and resulting morphologies are characterized using differential scanning calorimetry (DSC), N2 sorption and surface area experiments, and high-resolution transmission electron microscopy (HRTEM). Quantification of silanol groups and the extent of the silanization reaction are determined using various techniques, such as infrared spectrometry (IR), diffuse reflectance infrared Fourier-transform spectrometry (DRIFTS), thermogravimetric analysis (TGA), and Ag+ titration with the thiol functional groups. Some applications requires high capacity in short residence times, and this ?dynamic? capacity is related to parameters such as microporous and mesoporous surface area, extent of functionalization, and surface morphology.