Mercury Binding Sites in Thiol-Functionalized Mesostructured Silica

Abstract

Thiol-functionalized mesostructured silica with anhydrous compositions of (SiO(2))(1)(-)(x)()(LSiO(1.5))(x)(), where L is a mercaptopropyl group and x is the fraction of functionalized framework silicon centers, are effective trapping agents for the removal of mercuric(II) ions from water. In the present work, we investigate the mercury-binding mechanism for representative thiol-functionalized mesostructures by atomic pair distribution function (PDF) analysis of synchrotron X-ray powder diffraction data and by Raman spectroscopy. The mesostructures with wormhole framework structures and compositions corresponding to x = 0.30 and 0.50 were prepared by direct assembly methods in the presence of a structure-directing amine porogen. PDF analyses of five mercury-loaded compositions with Hg/S ratios of 0.50-1.30 provided evidence for the bridging of thiolate sulfur atoms to two metal ion centers and the formation of chain structures on the pore surfaces. We find no evidence for Hg-O bonds and can rule out oxygen coordination of the mercury at greater than the 10% level. The relative intensities of the PDF peaks corresponding to Hg-S and Hg-Hg atomic pairs indicate that the mercury centers cluster on the functionalized surfaces by virtue of thiolate bridging, regardless of the overall mercury loading. However, the Raman results indicate that the complexation of mercury centers by thiolate depends on the mercury loading. At low mercury loadings (Hg/S < or = 0.5), the dominant species is an electrically neutral complex in which mercury most likely is tetrahedrally coordinated to bridging thiolate ligands, as in Hg(SBu(t))(2). At higher loadings (Hg/S 1.0-1.3), mercury complex cations predominate, as evidenced by the presence of charge-balancing anions (nitrate) on the surface. This cationic form of bound mercury is assigned a linear coordination to two bridging thiolate ligands.

Mercury nano-trap for effective and efficient removal of mercury(II) from aqueous solution

“…8). This represents an advantage of PAF-1-SH for mercury removal across a wide range of pH, particularly when compared with silica and MOFs based adsorbents [12][13][14][15][16][29][30][31][32][33][34] , which usually suffer from the loss of porosity under such harsh conditions. Mercury adsorption experiments under acid and basic conditions revealed that PAF-1-SH also exhibits high affinities for Hg(II) with K d values of 6.66 Â 10 7 ml g À 1 at pH 1.0 and 2.49 Â 10 7 ml g À 1 at pH 12.8, which render excellent capability of reducing Hg(II) concentrations from 10 p.p.m.…”

“…Conventional adsorbents such as activated carbons 7 , zeolites 8 and clays 9 generally have low capacity and weak binding affinity for mercury. Thiol/thio-functionalized adsorbents, including clays 10 , resins 11 , mesoporous silica [12][13][14][15][16] , activated carbons 17 , mesorporous carbons 18 and chalcogenides 19,20 , are considered very effective sorbents for Hg(II) removal from aqueous solutions due to the soft-soft interaction 21 . Recently, metal-organic frameworks (MOFs) [22][23][24][25][26][27][28] have been explored as a new type of adsorbents for mercury removal [29][30][31][32][33][34] due to their high surface areas, but they usually suffer from instability in water 29,30 or aqueous solutions with a wide pH range 34 and possess low adsorption capacity and weak affinity for Hg(II).…”

Hydrogen-Bonding-Driven Self-Assembly of PEGylated Organosilica Nanoparticles with Poly(acrylic acid) in Aqueous Solutions and in Layer-by-Layer Deposition at Solid Surfaces

“…The Stöber method has often been used for synthesis of organosilica particles through condensation of tetraethoxysilane (TEOS) 6,7 or TEOS co-condensation with other functional silanes, such as 3-aminopropyltriethoxysilane (APTS) [8][9][10] and 3-mercaptopropyltrimethoxysilane (MPTS). [10][11][12] The typical size of organosilica particles synthesized using Stöber conditions is often greater than 500 nm. 6,7,9 The Stöber method was also used to generate mesoporous materials, where homo-or co-condensation of TEOS with other functional silanes was conducted in the presence of low molecular weight or polymeric surfactants as a template.…”

Tuning Single‐Molecule Dynamics in Functionalized Mesoporous Silica

“…These attractive pore systems have been used for numerous applications including molecular and clusterbased catalysis, [2] selective sequestration of contaminants [3] and chromatography, [4] stabilization of conducting nanoscale wires, [5] and as novel drug-delivery systems. [6] For many of these applications, the mesoporous materials are expected to show enhanced properties when their inner channel walls are functionalized with organic moieties to fine-tune hostguest interactions.…”