TY - JOUR
T1 - The impact of Mn oxide coatings on Zn distribution
AU - Boonfueng, Thipnakarin
AU - Axe, Lisa
AU - Xu, Ying
AU - Tyson, Trevor A.
N1 - Funding Information: This material is based upon work supported by the National Science Foundation under Grant No. BES 0089903 and the DuPont Young Professor's Grant. The authors thank James A. Dyer and Noel C. Scrivner for their input and support. The authors also thank Kaumudi Pandya for technical support at beamline X11A. Research carried out at NSLS, Brookhaven National Laboratory, was supported in part by the U.S. Department of Energy, Division of Materials Sciences and Division of Chemical Sciences, under Contract No. DE-AC02-98CH10886. In addition, beamline X11 at NSLS is supported by the Office of Naval Research. Finally, the authors thank an anonymous reviewer for the helpful comments.
PY - 2006/6/15
Y1 - 2006/6/15
N2 - Zinc sorption to hydrous manganese oxide (HMO)-coated clay was investigated macroscopically, kinetically, and spectroscopically. Adsorption edges and isotherms revealed that the affinity and capacity of the HMO-coated montmorillonite was greater than that of montmorillonite, and when normalized to the oxide present, the coatings behaved similarly to the discrete Mn oxide. Over two pH conditions, 5 and 6, a linear relationship was observed for the isotherms; further analysis with X-ray absorption spectroscopy (XAS) resulted in one type of sorption configuration as a function of loading and ionic strength at pH 5. However, at a surface loading of 10-3 molZn gHMO - coated clay-1 when the pH increased from 5 to 7, the first shell distance decreased slightly, while the atoms and coordination numbers remained the same; this change may be attributed to an increase in electrostatic interactions. After a contact time of 4 months where an additional 60% of the sites become occupied, the slower sorption process was modeled as intraparticle surface diffusion. Best fit diffusivities ranged from 10-18 to 10-17 cm2 / s, where a slower process was observed for the coated surface as compared to the discrete oxide. Interestingly, the porosity of the Mn oxide coating appears to be influenced by the substrate during its growth, as its increase and shift to a smaller pore size distribution resulted in a diffusivity between that observed for discrete HMO and montmorillonite.
AB - Zinc sorption to hydrous manganese oxide (HMO)-coated clay was investigated macroscopically, kinetically, and spectroscopically. Adsorption edges and isotherms revealed that the affinity and capacity of the HMO-coated montmorillonite was greater than that of montmorillonite, and when normalized to the oxide present, the coatings behaved similarly to the discrete Mn oxide. Over two pH conditions, 5 and 6, a linear relationship was observed for the isotherms; further analysis with X-ray absorption spectroscopy (XAS) resulted in one type of sorption configuration as a function of loading and ionic strength at pH 5. However, at a surface loading of 10-3 molZn gHMO - coated clay-1 when the pH increased from 5 to 7, the first shell distance decreased slightly, while the atoms and coordination numbers remained the same; this change may be attributed to an increase in electrostatic interactions. After a contact time of 4 months where an additional 60% of the sites become occupied, the slower sorption process was modeled as intraparticle surface diffusion. Best fit diffusivities ranged from 10-18 to 10-17 cm2 / s, where a slower process was observed for the coated surface as compared to the discrete oxide. Interestingly, the porosity of the Mn oxide coating appears to be influenced by the substrate during its growth, as its increase and shift to a smaller pore size distribution resulted in a diffusivity between that observed for discrete HMO and montmorillonite.
KW - HMO-coated montmorillonite
KW - Intraparticle surface diffusion
KW - Manganese oxide
KW - Montmorillonite
KW - Sorption
KW - XAS
KW - Zn
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U2 - 10.1016/j.jcis.2006.01.026
DO - 10.1016/j.jcis.2006.01.026
M3 - Article
C2 - 16466736
SN - 0021-9797
VL - 298
SP - 615
EP - 623
JO - Journal of Colloid And Interface Science
JF - Journal of Colloid And Interface Science
IS - 2
ER -