Xiangdong Feng

Separation of Complexed Mercury from Aqueous Wastes Using Self-Assembled Mercaptan on Mesoporous Silica

Separation of Hg(II) from potassium iodide/sulfate wastes was studied using a novel mesoporous silica material containing self-assembled mercaptan groups. The adsorbent, consisting of self-assembled mercaptan on mesoporous silica (SAMMS) developed at Pacific Northwest National Laboratory (PNNL), was characterized as to its specificity, adsorption capacity, and kinetics for separation of mercury from potassium iodide/sulfate solutions. Aqueous speciation calculations indicated that a major fraction (92–99%) of dissolved mercury in the potassium iodide/sulfate wastes solutions existed as HgI2− 4species. The adsorption data showed that the mercury adsorption capacity of SAMMS material increased with decreasing iodide concentrations. The magnitude of calculated free energy of adsorption indicated that mercury adsorption on this adsorbent is typical of soft acid–soft base interactions. High specificity for anionic complexes of Hg(II) by the SAMMS material was confirmed by distribution coefficient measurements....

MERCURY SEPARATION AND IMMOBILIZATION USING SELF-ASSEMBLED MONOLAYERS ON MESOPOROUS SUPPORTS (SAMMS)

ABSTRACT Mercury (Hg) is one of the most toxic metals found in the environment. The purpose of this study was to investigate the performance of an innovative technology, self-assembled monolayers on mesoporous supports (SAMMS), in separating and immobilizing Hg from aqueous solutions. The high surface area of the mesoporous silica and the covalent binding between the thiol (-SH) group in SAMMS and Hg in solution provide SAMMS with distinctive advantages over existing technologies. The results show that (i) the Hg removal is kinetically quite rapid, (ii) the sorption data follow Langmuir isotherms, (iii) the maximum sorption capacity could be up to 613 mg of Hg per gram of SAMMS, (iv) SAMMS was able to reduce Hg concentrations to below the national pollution discharge emission standard level (12 ppt), (v) the Hg-laden SAMMS was stable in aqueous solution at 70°C, and (vi) the Hg-laden SAMMS was able to pass TCLP (Toxicity Characterization Leaching Procedure) tests of the U.S. Environmental Protection Agenc...

Preparation of composite-crosslinked poly(N-isopropylacrylamide) gel layer and characteristics of reverse hydrophilic–hydrophobic surface

The composite-crosslinked poly(N-isopropylacrylamide) (PNIPAAm) gels were prepared by grafting N-isopropylacrylamide on the surface of glass plates modified by organosilanes. The glass plates as the substrate increase the mechanical strength of composite PNIPAAm gel layers. We investigated the effects of a series of organosilanes and the reaction time of organosilanes on surface characteristics, such as the static contact angle and the layer thickness. We discuss the equilibrium swelling ratio and the water release behavior of the gel layers in terms of the crosslinking density of the composite gels. The composite gels exhibit not only the characteristics of remarkable water release but also the reversed hydrophilic–hydrophobic surface properties. The gel layers are hydrophilic under 25°C and change to hydrophobic above 40°C.

Hybrid Mesoporous Materials with Functionalized Monolayers

Mesoporous materials have great potential for environmental and industrial processes, but many applications require the materials to exhibit specific surface chemistry and binding sites. A new approach has been developed so that organized functional monolayers are covalently bound to mesoporous supports. The functionalized hybrid materials show exceptional selectivity and capacity for removing heavy metals from waste streams. Tailored hybrid materials have also shown potential to selectively bind anions and radionuclides. Rational design of the surface properties of mesoporous materials will lead to more sophisticated functional composites.

Temperature-sensitive switch from composite poly(N-isopropylacrylamide) sponge gels

Thermally sensitive polymers change their properties with a change in environmental temperature in a predictable and pronounced way. These changes can be expected in drug delivery systems, solute separation, enzyme immobilization, energy-transducer processes, and photosensitive materials. We have demonstrated a thermal-sensitive switch module, which is capable of converting thermal into mechanical energy. We employed this module in the control of liquid transfer. The thermally sensitive switch was prepared by cross-linking poly(N-isopropylacrylamide) (PNIPAAm) gel inside the pores of a sponge to generate the composite PNIPAAm/sponge gel. This gel, contained in a polypropylene tube, was inserted into a thermoelectric module equipped with a fine temperature controller. As the water flux through the composite gel changes from 0 to 6.6 x 10{sup 2} L m{sup -2} h, with a temperature change from 23 to 40 degrees C, we can reversibly turn on and off the thermally sensitive switch.

Investigation of the local chemical interactions between Hg and self-assembled monolayers on mesoporous supports.

The synthesis of mesoporous silica has greatly expanded the possibilities for the design of open-pore structures. Because of their large surface area and well-defined pore shape, these materials have great potential in environmental and industrial processes, such as selective extraction of heavy metals from solutions. However, these applications require the materials to have specific attributes such as binding sites and charge density.