Fourier transform Raman spectroscopy of sorbed HDTMA and the mechanism of chromate sorption to surfactant-modified clinoptilolite
- New Mexico Inst. of Mining and Technology, Socorro, NM (United States)
- Univ. of Georgia, Aiken, SC (United States). Savannah River Ecology Lab.
Surfactant-modified zeolite (SMZ) has potential use as a sorbent for toxic compounds from contaminated waters, in subsurface permeable barriers, or in ex-situ water treatment systems. The authors examined sorption of the cationic surfactant hexadecyltrimethylammonium bromide (HDTMA) to clinoptilolite zeolite and the subsequent sorption of the chromate anion to surfactant-modified zeolite (SMZ). They used Fourier transform (FT) Raman spectroscopy and batch sorption methods to elucidate the structure of sorbed HDTMA and to determine the mechanisms of chromate sorption. At high HDTMA loading levels (above the zeolite`s external cation exchange capacity, ECEC), the Raman spectra indicated that sorbed HDTMA was similar in conformation to solution micelles and, thus, may contain anion exchange sites. Sorbed HDTMA showed less structuring of tail groups and a decrease in head group hydration. At lower loadings, the sorbed HDTMA tail groups tended to have more disorder, similar to solution monomers. When HDTMA loading rates were greater than 100% of the ECEC, chromate sorbed onto SMZ with near-equivalent Br{sup {minus}} counterion exchange. A peak in the Raman spectrum at 902 cm{sup {minus}1} indicated the presence of sorbed Cr{sub 2}O{sub 7}{sup 2{minus}}, although no bulk solution oligomerized chromate species should have been present at a solution pH of 7. A 30 cm{sup {minus}1} shift in the {nu}{sub 1} peak for sorbed versus solution chromate may indicate the surface-enhanced Lewis acid-base interactions were responsible for some chromate sorption in addition to the predominant anion-exchange mechanism.
- Sponsoring Organization:
- Oak Ridge Inst. for Science and Education, TN (United States); USDOE Morgantown Energy Technology Center, WV (United States); Georgia Univ., Athens, GA (United States)
- DOE Contract Number:
- AR21-95MC32108; FC09-96SR18546
- OSTI ID:
- 642239
- Journal Information:
- Environmental Science and Technology, Vol. 32, Issue 13; Other Information: PBD: 1 Jul 1998
- Country of Publication:
- United States
- Language:
- English
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