A fundamental study focusing on correlating the local water self-diffusion coefficient to the local free water content in 2-hydroxyethyl methacrylate (HEMA) gels was conducted. HEMA gels were synthesized with different nominal water content (50% to 90%). MRI measurements of local diffusion coefficient distribution and local water content profiles are conducted on a 600 MHz scanner. The local water content is measured via two spin-echo images with sufficiently long repetition time (TR) to eliminate T1-weighting and two values for the echo time (TE) in order to account for T2-weighting. The local diffusion coefficient is determined using a standard pulsed-field gradient spin-echo sequence. The measured local water content and diffusion coefficient data are compared with several single-parameter diffusion models for interstitial diffusion in the hydrogel (Makie-Meares, Stokes-Einstein, Brownian motion around overlapping spheres).

Clathrate hydrates are crystalline inclusion compounds of water and a guest molecule (e.g., methane) that form at temperatures below ambient but above the freezing point of water. There are three known crystalline structures of hydrates (structure I, II, and H) in which cavities within the hydrogen bonded water molecule lattice trap the hydrate-forming species. The clathrate structure excludes dissolved solutes, such as sodium chloride, from the aqueous phase and thereby offers a possible means to produce potable water from seawater or brackish water. The concept of using clathrate hydrates for desalination is not new. However, before clathrate hydrate desalination becomes a viable technology, fundamental issues of controlled hydrate formation, hydrate size and morphology, agglomeration, amount of entrapped salt, and the efficient recovery of hydrates must be understood. This paper will report structural characterization of hydrates formed with several guest molecules over a wide range of conditions in an attempt to further the physicochemical insight needed to address these issues.

Clathrate hydrate formation experiments were performed using a variety of host molecules, including R141b, a commercial refrigerant, C2FCl2H3. Hydrates of R141b were formed at temperatures from 2°C to 6°C and atmospheric pressure from deionized water and 2% - 7% NaCl solutions. Samples of the hydrates were characterized by cold-stage x-ray diffraction and Raman spectroscopy and determined to be structure II. Additional experiments were conducted with a gaseous hydrate former, ethylene, which readily formed hydrates with deionized or saline water at 2°C and several atmospheres of pressure. Experiments with several other hydrate forming molecules were conducted and the results obtained from their structural characterization will be reported. We will also present proof-of-concept experiments demonstrating a novel technique of desalination using these hydrate formers.

Sandia National Laboratories is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin company, for the United States Department of Energy under contract DE-AC04-94AL85000.

To address the concern that a material functionalized to reject dissolved ions may give rise to a highly viscous aqueous interphase within nanometers of its surface, we conducted and interpreted Interfacial Force Microscope measurements of the dissipative forces that resist motion of a tip parallel to a sample, in water. The results are consistent with earlier measurements where the tip approached the sample. They confirm that near hydrophilically functionalized surfaces, interphase viscosities more than a million times that of bulk water can be expected.

Antimicrobial behavior of nitrogen-doped titanium dioxide (TiON) thin films was examined by cell viability assays under visible light illumination, using Escherichia coli as the indicator. The nitrogen doping was found to enable visible-light inactivation of Escherichia coli on titanium oxide films. At a light intensity of 1.6 mW/cm2, TiON films reached a bacterial killing rate of about 50% in half an hour, comparable to those reported for ultraviolet light irradiated TiO2. In the range of nitrogen concentrations from 0.2 to 0.9, the bacterial killing rates showed no clear correlation with the nitrogen concentration for the TiON films.

Mesoporous organosilicates containing an ethylene bridge within the otherwise silicate pore walls and an additional organic functionality extended within the pore showed varying adsorption capacities for mercury and dimethylphenol. Thiol and imidazole functionalized organic-inorganic materials were effective for the adsorption of mercury, whereas the purely siliceous mesoporous MCM-41 was more effective for dimethylphenol adsorption than its organosilicate counterparts.

High flux composite hollow fiber membranes for brackish water desalination based on the interfacial polymerization of a cross-linked polyamide salt rejecting layer onto a semi-permeable hollow fiber support have been developed. These hollow fiber membranes exploit the advantages of using a thin-film composite reverse osmosis membrane (higher flux and salt rejection) with the higher surface area/volume ratio of hollow fiber membrane elements. The composite hollow fiber membranes were prepared by coating a polysulfone hollow fiber with a polyamide salt rejecting layer based on the interfacial polymerization reaction between m-phenylenediamine and trimesoyl chloride/isophthaloyl dichloride. The RO figures-of-merit of these composite polyamide hollow fiber membranes were evaluated for the desalination of a synthetic brackish water feed (2,000 ppm NaCl) at 225 psi over a 60 hour period. After an initial break-in period in which the flux declined 30% due to membrane compaction, the stabilized RO figures-of-merit for these hollow fiber membranes were a water flux of 280 L/m2·day and a salt rejection of 99.1%. Based on the water flux and packing density of the membrane, it is estimated that the stable production of potable water of a hollow fiber membrane element containing these composite membranes will be between 20 and 30% greater than that of a similarly sized spiral wound brackish water membrane element.

The use of natural environmentally benign agents in the treatment of drinking water is rapidly gaining interest due to their inherently renewable character and low toxicity. We show that the common Mexican cactus produces a gum-like substance, cactus mucilage, which shows excellent flocculating abilities and is an economically viable alternative for low-income communities. Cactus mucilage is a neutral mixture of approximately 55 high-molecular weight sugar residues composed basically of arabinose, galactose, rhamnose, xylose, and galacturonic acid. We show how this natural product was characterized for its use as a flocculating agent. Our results show the mucilage efficiency for reducing arsenic and particulates from drinking water as determined by light scattering, Atomic Absorption and Hydride Generation-Atomic Fluorescence Spectroscopy. Flocculation studies proved the mucilage to be a much faster flocculating agent when compared to Al2(SO4)3 with the efficiency increasing with mucilage concentration. Jar tests revealed that lower concentrations of mucilage provided the optimal effectiveness for supernatant clarity, an important factor in determining the potability of water. Initial filter results with the mucilage embedded in a silica matrix prove the feasibility of applying this technology as a method for heavy metal removal. This project provides fundamental, quantitative insights into the necessary and minimum requirements for natural flocculating agents that are innovative, environmentally benign, and cost-effective.

Computational modeling techniques have been used to investigate the interaction of arsenate with the dolomite (211) surface. The suitability of a variety of techniques has been assessed in the context of their applicability to the problem, in order to determine the least computationally expensive method of modeling the mineral-solution interface. To this end, various methods of solvating arsenate have been investigated, and a reliable solvation energy has been determined for the molecule. The adsorption geometry of the primary arsenate ion at the dolomite surface has been determined under vacuum conditions. Additionally, solvation of the dolomite surface has studied using molecular dynamics, and results show that there is some layering 2Å above the surface, and that dissociation of the water molecules occurs in this layer.