Communications duced to 5 ppb, which is within the acceptable drinking water limits recommended by the US Environmental Protection Agency.
This work has demonstrated, using an example of environmental relevance, the vastly improved access of guest species to the binding sites of adsorbents designed from a mesostructure with well-defined mesopore channels, relative to those prepared from materials with disordered pore networks, such as silica gel. This accessibility principle is relevant to a broad range of materials applications where the availability of reactive sites is a performance-determining factor. Mesoporous molecular sieves thus constitute a unique class of oxides, from which a large number of nanoporous technologies could potentially be engineered based on the advantages of very high surface areas suitable for chemical functionalization and a uniform pore distribution for total access to the active sites.
Experimental
Starting material: HMS was prepared by the hydrolysis of TEOS in a dodecylamine solution following previously reportcd methods [7]. The product was then filtered and allowed to dry at room temperature overnight. The amine template was removed from the precipitated oxide by Soxhlet extraction over ethanol for 4 days.
Adsorbent preparation (MP-HMS): 1 g of HMS was dried under vacuum at 110 "C and refluxed with 1 g of 3-mercaptopropyltrimethoxysilane in 25 mL of dry toluene for 48 h. The functionalized product was then filtered, washed several times with toluene followed by ethanol, and subjected to Soxhlet extraction over ethanol for 18 h in order to remove residual (ungrafted) organosilanc.
Characterization: Powder X-ray diffraction (XRD) patterns for HMS and MP-HMS were recorded on a Rigaku rotaflex diffractometer using Nifiltered CuKn radiation. Proton-decoupled 29Si MAS NMR spectra were recorded on a Varian VRX 400 MHz spectrometer at 79.5 MHz using 7 mm zirconia rotors, a sample spinning frequency of 4 kHz, and a pulse delay of 870 s. Nitrogen adsorption isotherms were measured at 77 K on a Coulter Omnisorp 360CX Sorptometer using standard continuous adsorption procedures. The samples were heated overnight at 110 "C and 10" torr prior to measurement, C, H, N, and S analyzes were performed by the Microanalysis Laboratory at the University of Illinois at Urbana-Champaign.
Hg adsorption studies: 10 mg portions of the functionalized mesostructure (MP-HMS) were stirred for 18 h with 50 mL volumes of mercury(u) nitrate solutions at initial concentrations ranging from 0 to 35 ppm. HgZe concentrations were determined before and after treatment by colorimetric analysis using diphenylthiocarbazone as an indicator [15]. Adsorption isotherms were generated by plotting the amount of Hg adsorbed per gram of MP-HMS as a function of the total (or initial) amount of HgZe per gram of adsorbent. For the packed-bed column experiment, part per billion levels of mercury were measured using cold-vapor atomic adsorption spectroscopy (DLZ Laboratorieg Lansing, Michigan).