Surface area of ferrihydrite consistently related to primary surface charge, ion pair formation, and specific ion adsorption

Juan C. Mendez*, Tjisse Hiemstra

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

The specific surface area (SSA) of metal oxides is pivotal for scaling of surface phenomena. For ferrihydrite (Fh), the SSA can be assessed by probing the surface with ions that specifically adsorb (e.g. protons or phosphate). In the approach, an appropriate material with a known surface chemical behavior is used as reference, accounting for differences in e.g. surface sites and structure. As Fh is a nanomaterial, the size-dependency of many of its properties requires a consistent implementation for data analysis and modeling. In the present study, the proton adsorption of Fh was measured in NaNO3, NaCl, and NaClO4 solutions using a potentiometric titration methodology that leads to an internally consistent primary data set (H/Fe). For data interpretation, we employed a size-dependent molar mass, mass density, and chemical composition (FeO1.4(OH)0.2·nH2O), as well as a size-dependent surface curvature since the latter increases the value of the Stern layer capacitance. Using well-crystallized goethite as reference, state-of-the-art multisite complexation modeling discloses the underlying SSA of Fh. Similar to goethite, a significant variation in electrolyte affinity constants (logK) is found for Fh. This largely explains the differences in pHPZC reported in literature when using e.g. KNO3 or NaCl rather than NaNO3 as electrolyte solution. Our data collection was done for Fh materials with a known aging history. The same Fh samples were also probed with phosphate ions and the collected primary data (PO4/Fe) were interpreted with the CD model. This methodology yields SSA values that are consistent with those found by probing the surface of Fh with protons. As ion probing with phosphate is rapid and sensitive, it is recommended as a tool to determine the SSA of Fh materials. This enables the development of a consistent thermodynamic database for application of surface complexation modeling in natural systems.

Original languageEnglish
Article number119304
JournalChemical Geology
Volume532
DOIs
Publication statusPublished - 20 Jan 2020

Fingerprint

ferrihydrite
Surface charge
surface area
Ions
adsorption
Adsorption
ion
Specific surface area
Protons
Phosphates
phosphate
Complexation
goethite
complexation
electrolyte
Electrolytes
modeling
Surface phenomena
methodology
Molar mass

Keywords

  • CD model
  • Electrolyte ions
  • Iron nanoparticles
  • Potentiometric titrations
  • Probe ions
  • Surface reactivity

Cite this

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title = "Surface area of ferrihydrite consistently related to primary surface charge, ion pair formation, and specific ion adsorption",
abstract = "The specific surface area (SSA) of metal oxides is pivotal for scaling of surface phenomena. For ferrihydrite (Fh), the SSA can be assessed by probing the surface with ions that specifically adsorb (e.g. protons or phosphate). In the approach, an appropriate material with a known surface chemical behavior is used as reference, accounting for differences in e.g. surface sites and structure. As Fh is a nanomaterial, the size-dependency of many of its properties requires a consistent implementation for data analysis and modeling. In the present study, the proton adsorption of Fh was measured in NaNO3, NaCl, and NaClO4 solutions using a potentiometric titration methodology that leads to an internally consistent primary data set (H/Fe). For data interpretation, we employed a size-dependent molar mass, mass density, and chemical composition (FeO1.4(OH)0.2·nH2O), as well as a size-dependent surface curvature since the latter increases the value of the Stern layer capacitance. Using well-crystallized goethite as reference, state-of-the-art multisite complexation modeling discloses the underlying SSA of Fh. Similar to goethite, a significant variation in electrolyte affinity constants (logK) is found for Fh. This largely explains the differences in pHPZC reported in literature when using e.g. KNO3 or NaCl rather than NaNO3 as electrolyte solution. Our data collection was done for Fh materials with a known aging history. The same Fh samples were also probed with phosphate ions and the collected primary data (PO4/Fe) were interpreted with the CD model. This methodology yields SSA values that are consistent with those found by probing the surface of Fh with protons. As ion probing with phosphate is rapid and sensitive, it is recommended as a tool to determine the SSA of Fh materials. This enables the development of a consistent thermodynamic database for application of surface complexation modeling in natural systems.",
keywords = "CD model, Electrolyte ions, Iron nanoparticles, Potentiometric titrations, Probe ions, Surface reactivity",
author = "Mendez, {Juan C.} and Tjisse Hiemstra",
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day = "20",
doi = "10.1016/j.chemgeo.2019.119304",
language = "English",
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journal = "Chemical Geology",
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}

Surface area of ferrihydrite consistently related to primary surface charge, ion pair formation, and specific ion adsorption. / Mendez, Juan C.; Hiemstra, Tjisse.

In: Chemical Geology, Vol. 532, 119304, 20.01.2020.

Research output: Contribution to journalArticleAcademicpeer-review

TY - JOUR

T1 - Surface area of ferrihydrite consistently related to primary surface charge, ion pair formation, and specific ion adsorption

AU - Mendez, Juan C.

AU - Hiemstra, Tjisse

PY - 2020/1/20

Y1 - 2020/1/20

N2 - The specific surface area (SSA) of metal oxides is pivotal for scaling of surface phenomena. For ferrihydrite (Fh), the SSA can be assessed by probing the surface with ions that specifically adsorb (e.g. protons or phosphate). In the approach, an appropriate material with a known surface chemical behavior is used as reference, accounting for differences in e.g. surface sites and structure. As Fh is a nanomaterial, the size-dependency of many of its properties requires a consistent implementation for data analysis and modeling. In the present study, the proton adsorption of Fh was measured in NaNO3, NaCl, and NaClO4 solutions using a potentiometric titration methodology that leads to an internally consistent primary data set (H/Fe). For data interpretation, we employed a size-dependent molar mass, mass density, and chemical composition (FeO1.4(OH)0.2·nH2O), as well as a size-dependent surface curvature since the latter increases the value of the Stern layer capacitance. Using well-crystallized goethite as reference, state-of-the-art multisite complexation modeling discloses the underlying SSA of Fh. Similar to goethite, a significant variation in electrolyte affinity constants (logK) is found for Fh. This largely explains the differences in pHPZC reported in literature when using e.g. KNO3 or NaCl rather than NaNO3 as electrolyte solution. Our data collection was done for Fh materials with a known aging history. The same Fh samples were also probed with phosphate ions and the collected primary data (PO4/Fe) were interpreted with the CD model. This methodology yields SSA values that are consistent with those found by probing the surface of Fh with protons. As ion probing with phosphate is rapid and sensitive, it is recommended as a tool to determine the SSA of Fh materials. This enables the development of a consistent thermodynamic database for application of surface complexation modeling in natural systems.

AB - The specific surface area (SSA) of metal oxides is pivotal for scaling of surface phenomena. For ferrihydrite (Fh), the SSA can be assessed by probing the surface with ions that specifically adsorb (e.g. protons or phosphate). In the approach, an appropriate material with a known surface chemical behavior is used as reference, accounting for differences in e.g. surface sites and structure. As Fh is a nanomaterial, the size-dependency of many of its properties requires a consistent implementation for data analysis and modeling. In the present study, the proton adsorption of Fh was measured in NaNO3, NaCl, and NaClO4 solutions using a potentiometric titration methodology that leads to an internally consistent primary data set (H/Fe). For data interpretation, we employed a size-dependent molar mass, mass density, and chemical composition (FeO1.4(OH)0.2·nH2O), as well as a size-dependent surface curvature since the latter increases the value of the Stern layer capacitance. Using well-crystallized goethite as reference, state-of-the-art multisite complexation modeling discloses the underlying SSA of Fh. Similar to goethite, a significant variation in electrolyte affinity constants (logK) is found for Fh. This largely explains the differences in pHPZC reported in literature when using e.g. KNO3 or NaCl rather than NaNO3 as electrolyte solution. Our data collection was done for Fh materials with a known aging history. The same Fh samples were also probed with phosphate ions and the collected primary data (PO4/Fe) were interpreted with the CD model. This methodology yields SSA values that are consistent with those found by probing the surface of Fh with protons. As ion probing with phosphate is rapid and sensitive, it is recommended as a tool to determine the SSA of Fh materials. This enables the development of a consistent thermodynamic database for application of surface complexation modeling in natural systems.

KW - CD model

KW - Electrolyte ions

KW - Iron nanoparticles

KW - Potentiometric titrations

KW - Probe ions

KW - Surface reactivity

U2 - 10.1016/j.chemgeo.2019.119304

DO - 10.1016/j.chemgeo.2019.119304

M3 - Article

VL - 532

JO - Chemical Geology

JF - Chemical Geology

SN - 0009-2541

M1 - 119304

ER -