Details
| Originalsprache | Englisch |
|---|---|
| Seiten (von - bis) | 256-264 |
| Seitenumfang | 9 |
| Fachzeitschrift | Applied clay science |
| Jahrgang | 36 |
| Ausgabenummer | 4 |
| Publikationsstatus | Veröffentlicht - Mai 2007 |
Abstract
Chitosan, a natural biopolymeric cation, is a candidate to modify montmorillonite for the adsorption of anions. As an anionic organic pollutant the adsorption of tannic acid was studied. Because of protonation/deprotonation reactions of both chitosan-montmorillonite and tannic acid, the adsorption process is strongly pH-dependent. The objective of this work is to characterize the pH dependency of adsorption in combination with surface charge determinations. Montmorillonite was modified with different amounts of chitosan, corresponding to 20-1000% of the cation exchange capacity (CEC). The deacetylation degree of chitosan was determined by polyelectrolyte titration and was found to be 74%. The uptake of chitosan was determined by the C-content. The interlayer expansion was investigated by X-ray powder diffraction. The adsorption capacity for tannic acid was investigated with the batch technique at pH 3, 4, 5 and 8. As a measure for the adsorption properties, the electrokinetic surface charge was determined with a particle charge detector. The uptake of chitosan by montmorillonite is up to 152% (1.69 molc kg- 1) of the CEC. The resulting anion exchange capacity of chitosan-montmorillonite calculated from C-content is 0.43 molc kg- 1. At low loadings with chitosan (24.7 and 49.5% uptake), a monolayer is formed in montmorillonite. At an uptake of 96.8%, a bilayer structure is observed, which becomes more dominant at higher loadings. On the external surface, a monolayer of chitosan was formed. From pH 4 to 8, the surface charge of all modified montmorillonites is with - 9 to 8 mmolc kg- 1 close to the point of zero charge. The maximal adsorption capacity for tannic acid is found with 240 g kg- 1 (0.14 molc kg- 1) at pH 4. The adsorption process fits in well with the Freundlich isotherm. At lower as well as higher pH values the adsorption capacity decreases up to about 25%. Most probably the exchange sites in the interlayer do not contribute to the adsorption of tannic acid. The observed surface charge is lower than the adsorbed amount of tannin. It is thought that tannin is adsorbed also by van der Waals forces besides ionic forces.
ASJC Scopus Sachgebiete
- Erdkunde und Planetologie (insg.)
- Geologie
- Erdkunde und Planetologie (insg.)
- Geochemie und Petrologie
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in: Applied clay science, Jahrgang 36, Nr. 4, 05.2007, S. 256-264.
Publikation: Beitrag in Fachzeitschrift › Artikel › Forschung › Peer-Review
}
TY - JOUR
T1 - Adsorption of tannic acid on chitosan-montmorillonite as a function of pH and surface charge properties
AU - An, Jong Hyok
AU - Dultz, Stefan
N1 - Funding information: Well-characterized clay samples were obtained from Dr. S. Kaufhold (Federal Institute for Geosciences and Natural Resources, Hannover). This study was supported by the Gottlieb Daimler- and Karl Benz-Foundation through their fellowship program.
PY - 2007/5
Y1 - 2007/5
N2 - Chitosan, a natural biopolymeric cation, is a candidate to modify montmorillonite for the adsorption of anions. As an anionic organic pollutant the adsorption of tannic acid was studied. Because of protonation/deprotonation reactions of both chitosan-montmorillonite and tannic acid, the adsorption process is strongly pH-dependent. The objective of this work is to characterize the pH dependency of adsorption in combination with surface charge determinations. Montmorillonite was modified with different amounts of chitosan, corresponding to 20-1000% of the cation exchange capacity (CEC). The deacetylation degree of chitosan was determined by polyelectrolyte titration and was found to be 74%. The uptake of chitosan was determined by the C-content. The interlayer expansion was investigated by X-ray powder diffraction. The adsorption capacity for tannic acid was investigated with the batch technique at pH 3, 4, 5 and 8. As a measure for the adsorption properties, the electrokinetic surface charge was determined with a particle charge detector. The uptake of chitosan by montmorillonite is up to 152% (1.69 molc kg- 1) of the CEC. The resulting anion exchange capacity of chitosan-montmorillonite calculated from C-content is 0.43 molc kg- 1. At low loadings with chitosan (24.7 and 49.5% uptake), a monolayer is formed in montmorillonite. At an uptake of 96.8%, a bilayer structure is observed, which becomes more dominant at higher loadings. On the external surface, a monolayer of chitosan was formed. From pH 4 to 8, the surface charge of all modified montmorillonites is with - 9 to 8 mmolc kg- 1 close to the point of zero charge. The maximal adsorption capacity for tannic acid is found with 240 g kg- 1 (0.14 molc kg- 1) at pH 4. The adsorption process fits in well with the Freundlich isotherm. At lower as well as higher pH values the adsorption capacity decreases up to about 25%. Most probably the exchange sites in the interlayer do not contribute to the adsorption of tannic acid. The observed surface charge is lower than the adsorbed amount of tannin. It is thought that tannin is adsorbed also by van der Waals forces besides ionic forces.
AB - Chitosan, a natural biopolymeric cation, is a candidate to modify montmorillonite for the adsorption of anions. As an anionic organic pollutant the adsorption of tannic acid was studied. Because of protonation/deprotonation reactions of both chitosan-montmorillonite and tannic acid, the adsorption process is strongly pH-dependent. The objective of this work is to characterize the pH dependency of adsorption in combination with surface charge determinations. Montmorillonite was modified with different amounts of chitosan, corresponding to 20-1000% of the cation exchange capacity (CEC). The deacetylation degree of chitosan was determined by polyelectrolyte titration and was found to be 74%. The uptake of chitosan was determined by the C-content. The interlayer expansion was investigated by X-ray powder diffraction. The adsorption capacity for tannic acid was investigated with the batch technique at pH 3, 4, 5 and 8. As a measure for the adsorption properties, the electrokinetic surface charge was determined with a particle charge detector. The uptake of chitosan by montmorillonite is up to 152% (1.69 molc kg- 1) of the CEC. The resulting anion exchange capacity of chitosan-montmorillonite calculated from C-content is 0.43 molc kg- 1. At low loadings with chitosan (24.7 and 49.5% uptake), a monolayer is formed in montmorillonite. At an uptake of 96.8%, a bilayer structure is observed, which becomes more dominant at higher loadings. On the external surface, a monolayer of chitosan was formed. From pH 4 to 8, the surface charge of all modified montmorillonites is with - 9 to 8 mmolc kg- 1 close to the point of zero charge. The maximal adsorption capacity for tannic acid is found with 240 g kg- 1 (0.14 molc kg- 1) at pH 4. The adsorption process fits in well with the Freundlich isotherm. At lower as well as higher pH values the adsorption capacity decreases up to about 25%. Most probably the exchange sites in the interlayer do not contribute to the adsorption of tannic acid. The observed surface charge is lower than the adsorbed amount of tannin. It is thought that tannin is adsorbed also by van der Waals forces besides ionic forces.
KW - Adsorption isotherms
KW - Chitosan
KW - Montmorillonite
KW - Surface charge
KW - Tannic acid
UR - http://www.scopus.com/inward/record.url?scp=34247215220&partnerID=8YFLogxK
U2 - 10.1016/j.clay.2006.11.001
DO - 10.1016/j.clay.2006.11.001
M3 - Article
AN - SCOPUS:34247215220
VL - 36
SP - 256
EP - 264
JO - Applied clay science
JF - Applied clay science
SN - 0169-1317
IS - 4
ER -