Surface complexation modeling of proton and metal sorption onto graphene oxide

Thomas A. Duster; Jennifer E.S. Szymanowski; Chongzheng Na; Allison R. Showalter; Bruce A. Bunker; Jeremy B. Fein

doi:10.1016/j.colsurfa.2014.10.049

Surface complexation modeling of proton and metal sorption onto graphene oxide

Thomas A. Duster, Jennifer E.S. Szymanowski, Chongzheng Na, Allison R. Showalter, Bruce A. Bunker, Jeremy B. Fein

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20 Scopus citations

Abstract

The objective of this investigation was to develop a surface complexation modeling approach to account for proton and metal (Cd, Pb) binding onto many-layered graphene oxide (MLGO) across a range of pH and ionic strength conditions. MLGO particles exhibit large buffering capacities between pH 3 and pH 10 and the buffering behavior is only nominally influenced by ionic strength. In contrast, batch metal sorption experiments illustrate that the striking capacity of MLGO to sorb metals substantially diminishes with increases in ionic strength. X-ray absorption spectroscopy measurements were used to establish reaction stoichiometries and indicate that both Cd and Pb associate with single sites on the MLGO surface. The difference in sorption behaviors for protons and metals is best modeled using a 4-site non-electrostatic surface complexation model that accounts for ionic strength effects as a competition between Na from the background electrolyte and Cd/Pb for available MLGO sorption sites. Using this approach, titration data are used to constrain the site concentrations and pK_a values for MLGO binding sites. The pK_a values (±1σ) are calculated as 4.55 (±0.91), 6.52 (±0.49), 8.48 (±0.21), and 9.98 (±0.21). We then use these parameters and the metal sorption data to determine thermodynamic stability constants for each important Cd- and Pb-MLGO surface complex. The site concentrations and equilibrium constants provided herein are critical for developing and testing remediation strategies for specific water chemistries.

Original language	English
Pages (from-to)	28-39
Number of pages	12
Journal	Colloids and Surfaces A: Physicochemical and Engineering Aspects
Volume	466
DOIs	https://doi.org/10.1016/j.colsurfa.2014.10.049
State	Published - Feb 5 2015
Externally published	Yes

Funding

This research was supported, in part, by a fellowship to T.D. from the Arthur J. Schmitt Foundation . In addition, we performed most experiments and analyses using instrumentation at the Center for Environmental Science and Technology (University of Notre Dame). Dr. Aaron Lussier (Notre Dame) collected the AFM imagery found in the SM. We would also like to thank the staff at MR-CAT for assistance with beamline set-up. MR-CAT is supported by the U.S. Department of Energy and the member institutions . Use of the Advanced Photon Source was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences , under Contract No. DE-AC02-06CH11357 . C.N.’s contribution was supported by the USDOE Office of Nuclear Energy's Nuclear Energy University Programs , the U.S. National Science Foundation's Environmental Engineering Program , the donors of the ACS Petroleum Research Fund , and the University of Notre Dame Sustainable Energy Initiative . This manuscript also benefited greatly from the comments by two anonymous reviewers.

Keywords

Graphene oxide
Metal sorption
Potentiometric titration
Surface complexation modeling

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10.1016/j.colsurfa.2014.10.049

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title = "Surface complexation modeling of proton and metal sorption onto graphene oxide",

abstract = "The objective of this investigation was to develop a surface complexation modeling approach to account for proton and metal (Cd, Pb) binding onto many-layered graphene oxide (MLGO) across a range of pH and ionic strength conditions. MLGO particles exhibit large buffering capacities between pH 3 and pH 10 and the buffering behavior is only nominally influenced by ionic strength. In contrast, batch metal sorption experiments illustrate that the striking capacity of MLGO to sorb metals substantially diminishes with increases in ionic strength. X-ray absorption spectroscopy measurements were used to establish reaction stoichiometries and indicate that both Cd and Pb associate with single sites on the MLGO surface. The difference in sorption behaviors for protons and metals is best modeled using a 4-site non-electrostatic surface complexation model that accounts for ionic strength effects as a competition between Na from the background electrolyte and Cd/Pb for available MLGO sorption sites. Using this approach, titration data are used to constrain the site concentrations and pKa values for MLGO binding sites. The pKa values (±1σ) are calculated as 4.55 (±0.91), 6.52 (±0.49), 8.48 (±0.21), and 9.98 (±0.21). We then use these parameters and the metal sorption data to determine thermodynamic stability constants for each important Cd- and Pb-MLGO surface complex. The site concentrations and equilibrium constants provided herein are critical for developing and testing remediation strategies for specific water chemistries.",

keywords = "Graphene oxide, Metal sorption, Potentiometric titration, Surface complexation modeling",

author = "Duster, \{Thomas A.\} and Szymanowski, \{Jennifer E.S.\} and Chongzheng Na and Showalter, \{Allison R.\} and Bunker, \{Bruce A.\} and Fein, \{Jeremy B.\}",

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AU - Duster, Thomas A.

AU - Szymanowski, Jennifer E.S.

AU - Na, Chongzheng

AU - Showalter, Allison R.

AU - Bunker, Bruce A.

AU - Fein, Jeremy B.

PY - 2015/2/5

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N2 - The objective of this investigation was to develop a surface complexation modeling approach to account for proton and metal (Cd, Pb) binding onto many-layered graphene oxide (MLGO) across a range of pH and ionic strength conditions. MLGO particles exhibit large buffering capacities between pH 3 and pH 10 and the buffering behavior is only nominally influenced by ionic strength. In contrast, batch metal sorption experiments illustrate that the striking capacity of MLGO to sorb metals substantially diminishes with increases in ionic strength. X-ray absorption spectroscopy measurements were used to establish reaction stoichiometries and indicate that both Cd and Pb associate with single sites on the MLGO surface. The difference in sorption behaviors for protons and metals is best modeled using a 4-site non-electrostatic surface complexation model that accounts for ionic strength effects as a competition between Na from the background electrolyte and Cd/Pb for available MLGO sorption sites. Using this approach, titration data are used to constrain the site concentrations and pKa values for MLGO binding sites. The pKa values (±1σ) are calculated as 4.55 (±0.91), 6.52 (±0.49), 8.48 (±0.21), and 9.98 (±0.21). We then use these parameters and the metal sorption data to determine thermodynamic stability constants for each important Cd- and Pb-MLGO surface complex. The site concentrations and equilibrium constants provided herein are critical for developing and testing remediation strategies for specific water chemistries.

AB - The objective of this investigation was to develop a surface complexation modeling approach to account for proton and metal (Cd, Pb) binding onto many-layered graphene oxide (MLGO) across a range of pH and ionic strength conditions. MLGO particles exhibit large buffering capacities between pH 3 and pH 10 and the buffering behavior is only nominally influenced by ionic strength. In contrast, batch metal sorption experiments illustrate that the striking capacity of MLGO to sorb metals substantially diminishes with increases in ionic strength. X-ray absorption spectroscopy measurements were used to establish reaction stoichiometries and indicate that both Cd and Pb associate with single sites on the MLGO surface. The difference in sorption behaviors for protons and metals is best modeled using a 4-site non-electrostatic surface complexation model that accounts for ionic strength effects as a competition between Na from the background electrolyte and Cd/Pb for available MLGO sorption sites. Using this approach, titration data are used to constrain the site concentrations and pKa values for MLGO binding sites. The pKa values (±1σ) are calculated as 4.55 (±0.91), 6.52 (±0.49), 8.48 (±0.21), and 9.98 (±0.21). We then use these parameters and the metal sorption data to determine thermodynamic stability constants for each important Cd- and Pb-MLGO surface complex. The site concentrations and equilibrium constants provided herein are critical for developing and testing remediation strategies for specific water chemistries.

KW - Graphene oxide

KW - Metal sorption

KW - Potentiometric titration

KW - Surface complexation modeling

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ER -

Surface complexation modeling of proton and metal sorption onto graphene oxide

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