DIVISION OF ENVIRONMENTAL CHEMISTRY
235th ACS National Meeting
New Orleans, LA
April 6-10, 2008
MONDAY MORNING
Advances in Adsorption Processes for Drinking Water Treatment and Sourcewater Protection
Session 3
Cosponsored by WaterCAMPWS, ACS Division of Environmental Chemistry, and AIChE Environmental Division (Group 9)
E. Morgenroth, Organizer
T. H. Nguyen and D. R. U. Knappe, Organizers, Presiding
8:30 — Introductory Remarks.
8:35 —60. Study of hydrophobic water interfaces with phase-sensitive sum-frequency vibrational spectroscopy. C. Tian, Y. R. Shen
8:55 —61. Vibrational spectroscopy on alumina/water interfaces with surface charges. L. Zhang, Y. R. Shen, C. Tian, G. A. Waychunas
9:15 —62. Nitrate and perchlorate removal from water using ion exchange fibers. J. S. Ince, J. L. Langer, J. Economy
ABSTRACTS
ENVR 60
Study of hydrophobic water interfaces with phase-sensitive sum-frequency vibrational spectroscopy
Chuanshan Tian and Y. Ron Shen, Department of Physics, University of California, 366 Le Conte Hall, Berkeley, CA 94720, cstian@berkeley.edu
The self-assembled monolayer of octadecyltrichlorosilane (OTS) on fused silica has been used extensively as a representative hydrophobic surface in the study of water/hydrophobic interfaces. Recent sum-frequency vibrational spectroscopy (SFVS) found that the spectrum in the OH stretch region of the OTS/water interface increases significantly in strength as pH increases from 5.7 to 11, presumably due to surface charging effect, but how it changes the interfacial water structure is not clear. We have carried out a study on OTS/water interface using the newly developed phase-sensitive sum-frequency vibrational spectroscopy (PS-SFVS). It allows measurement of both real and imaginary parts of the surface spectral response with the latter playing a role equivalent to absorption and emission coefficients and provides information on net polar-orientations of various interfacial water species contributing to the different parts of the spectrum. The result shows that at low pH (pH~2), water molecules in both ice-like and liquid-like regions have weak net polar-orientations with H pointing towards the liquid. At high pH (pH~11), they are well aligned with H pointing to the solid substrate. It indicates that OTS/silica is negatively charged at high pH so that the surface field will reorient part of the interfacial water molecules. This seems to suggest that even though the silica surface is covered by the OTS monolayer, deprotonation of the silica surface could still be effective. Alternatively, one may consider that OH- ions could adsorb on the methyl terminals of OTS making the water/OTS interface negatively charged.
This work was supported by a NSF grant through WaterCAMPWS.
ENVR 61
Vibrational spectroscopy on alumina/water interfaces with surface charges
Luning Zhang1, Y. Ron Shen1, Chuanshan Tian1, and Glenn A. Waychunas2. (1) Department of Physics, University of California, Berkeley, Berkeley, CA 94720, Fax: 510-643-8923, zhangln@berkeley.edu, (2) Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720
The charging behavior of α-alumina (0001)/water interfaces at different bulk pH values and salt concentrations has been studied by surface-specific sum-frequency vibrational spectroscopy. The results indicate that the crystalline substrate has a point of zero charge (PZC) around pH 6.0, which is about three pH units lower than powder alumina samples reported before. The different bonding geometry of (Aln)OH (n=1-3) groups at surfaces of crystalline and powder samples is likely responsible for the difference. We have also investigated the net polar orientation of water molecules at alumina/water interfaces with a phase-sensitive detection method. When the pH was changed from above to below the PZC, interfacial water molecules have their net polar orientation flipped following switching of the sign of the surface field. These findings should be relevant to our search of deeper understanding of molecular adsorption processes in water purification when the ionic adsorbents are involved. This work was supported by the NSF Science and Technology Center of Advanced Materials for Purification of Water with Systems (Water CAMPWS; CTS-0120978).
ENVR 62
Nitrate and perchlorate removal from water using ion exchange fibers
Jeffrey S. Ince, James L. Langer, and James Economy, Department of Materials Science & Engineering, University of Illinois at Urbana-Champaign, 1304 W Green St, Urbana, IL 61801, Fax: 217-333-2736, ince@uiuc.edu, jlanger2@uiuc.edu
Nitrate and perchlorate concentrations in many drinking water sources exceed their respective EPA maximum contaminant level of 10 ppm nitrate and reference dose drinking water equivalent level of 24.5 ppb perchlorate. Ion exchange has been found to be an effective means of removing these contaminants from water, but suffers from several drawbacks including leakage and excessive waste brine required for regeneration. We report the performance of ion exchange fibers (IEFs) designed with strong base anion exchange groups for the selective removal of these two anions from water. Selectivity for nitrate removal is shown to be a function of the particular alkyl amine functionality in the fiber. Breakthrough tests show an improvement in removing nitrate in water to levels well below the EPA limit using IEF filters relative to conventional materials. IEFs can be regenerated far more quickly, resulting in a decrease in brine required for regeneration.
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