『Abstract
This work is aimed at determining phosphate speciation at the
Fe(III)-modified monrmorillonite/aqueous solution interface by
attenuated total reflectance (ATR-FTIR) spectroscopy. IR spectra
are analyzed by second derivative and Fourier self-deconvolution
procedures to reveal the number and positions of overlapped bands
related to phosphate surface complexes. Experiments are conducted
at pH 4.5, 7.0 and 9.0 in order to determine the effects of changing
pH on the surface speciation. The molecular view offered by the
ATR-FTIR measurements is complemented by macroscopic adsorption
data, such as adsorption isotherms and electrophoretic mobilities.
The ATR-FTIR spectral analyses reveal the existence of two inner-sphere
complexes when phosphate adsorbs on modified montmorillonite,
as also suggested from macroscopic adsorption data. The complex
coordination depends on the pH. At pH 4.5, both complexes present
C2V symmetry or lower. on the other hand,
at pH 7.0 and 9.0 one of them is also C2V
or lower while the other one presents C3V
symmetry. Adsorbed phosphate is not associated with montmorillonite
itself but with Fe(III) (hydr)oxides coatings. Therefore, the
clay acts as a carrier or support of the Fe(III)-(hydr)oxides,
and these coatings are responsible for phosphate adsorption.
Keywords: Phosphate; Adsorption; Electrophoretic mobility; ATR-FTIR; Surface complexes; Fe(III)-montmorillonite』
1. Introduction
2. Materials
3. Methods
3.1. Batch phosphate adsorption studies
3.2. Electrophoretic mobility (EM) measurements
3.3. ATR-FTIR experiments
3.3.1. Spectral analysis
4. Results and discussion
4.1. General characterization and adsorption studies
4.2. ATR-FTIR analysis
5. Conclusions
Acknowledgments
Appendix A. Supplementary data
References