Surfactant-Templated Mesoporous Silicate Materials as Sorbents for Organic Pollutants in Water

Hexagonal (MCM-41) mesoporous materials were synthesized at 23 °C using hexadecyltrimethylammonium bromide (HDTMA) and tetramethyl-orthosilicate (TMOS) or Na-silicate. Products with (as-synthesized and dried at 23 or 70 °C) HDTMA removed significant amounts of trichlorethylene and tetrachloroethylene from water, similar to the behavior of organic-cation-exchanged smectites. Products without HDTMA (calcined) were weaker sorbents. Structural Al increased the sorption capacity of as-synthesized products but decreased that of calcined products. Structural Al and synthesis using TMOS both increased the stability of as-synthesized materials in 0.005 M CaCl 2 . All as-synthesized materials have apparent Si solubilities between those of quartz and amorphous silica. Si dissolution rates for as-synthesized (using Na-silicate) products at pH ∼7−8 are 2−3 orders of magnitude higher than those of quartz and 1 order of magnitude higher than that of glass. Rates show little ionic strength dependence in up to 0.1 M CaCl 2 at Si concentrations up to three times quartz solubility. HDTMA leaching increased slightly with decreasing ionic strength; however only 1.5% is removed after exchange with 1050 pore volumes of H 2 O. The ease of synthesis, environmental stability, and significant sorption capacity indicate that as-synthesized MCM-41 materials could be used as sorbents for organic pollutants in water and as components of contaminant barriers.