Surface charge characterization of metal oxides by potentiometric acid-base titration, revisited theory and experiment

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Abstract

The increased interest in architecting nanocomposites and in clarifying their impact on health and environment necessitates a standardized method of surface characterization, because the behaviour of nanoparticles is governed largely by their surface free energy and interfacial chemistry. Potentiometric acid-base titration has been used for decades to determine surface charge density of oxides, tremendously useful in understanding and modelling oxide/electrolyte interfaces. The method has solid theoretical and experimental foundation. Yet, published values of the point of zero charge (PZC) of chemically identical oxides scatter widely: the deviation of seven units of pH is the rule, rather than an exception. The PZC must reflect the inherent charging behaviour, linked exclusively to the protonation, and determined by the chemistry of the oxides. Assignment of PZC (just like assignment of equilibrium constant of any chemical reaction) requires strict conditions and consistent protocol. We present here such a protocol, and some examples of application. The protocol leads through the basic steps: pH buffer calibration, proton concentration calibration in the background electrolytes, and titrations of oxides. Built-in tests help to eliminate artificial side effects simultaneously from the measurement of pH and from the oxide/electrolyte interfacial equilibria. Although these may seem self-evident, literature survey proves the need to go back to basics in order to obtain precise, reliable and comparable pH-dependent charging of oxides. It is most general that the oxides contain some unrecognized surface impurities and have a strongly pH-dependent dissolution. These distort the results of titrations; their effect increases with decreasing particle size and can become dominant for nanoparticles. The protocol presented here contains the necessary feedback loops to easily recognize and exclude these side effects.

Original languageEnglish
Pages (from-to)302-313
Number of pages12
JournalColloids and Surfaces A: Physicochemical and Engineering Aspects
Volume414
DOIs
Publication statusPublished - Nov 20 2012

Fingerprint

Surface charge
Titration
titration
Oxides
metal oxides
Metals
acids
Acids
oxides
Experiments
Electrolytes
electrolytes
charging
Calibration
chemistry
Nanoparticles
nanoparticles
Protonation
Equilibrium constants
Charge density

Keywords

  • Dissolution
  • Oxide nanoparticles
  • PH measurement
  • PZC
  • Specific ions
  • Surface charge

ASJC Scopus subject areas

  • Colloid and Surface Chemistry

Cite this

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title = "Surface charge characterization of metal oxides by potentiometric acid-base titration, revisited theory and experiment",
abstract = "The increased interest in architecting nanocomposites and in clarifying their impact on health and environment necessitates a standardized method of surface characterization, because the behaviour of nanoparticles is governed largely by their surface free energy and interfacial chemistry. Potentiometric acid-base titration has been used for decades to determine surface charge density of oxides, tremendously useful in understanding and modelling oxide/electrolyte interfaces. The method has solid theoretical and experimental foundation. Yet, published values of the point of zero charge (PZC) of chemically identical oxides scatter widely: the deviation of seven units of pH is the rule, rather than an exception. The PZC must reflect the inherent charging behaviour, linked exclusively to the protonation, and determined by the chemistry of the oxides. Assignment of PZC (just like assignment of equilibrium constant of any chemical reaction) requires strict conditions and consistent protocol. We present here such a protocol, and some examples of application. The protocol leads through the basic steps: pH buffer calibration, proton concentration calibration in the background electrolytes, and titrations of oxides. Built-in tests help to eliminate artificial side effects simultaneously from the measurement of pH and from the oxide/electrolyte interfacial equilibria. Although these may seem self-evident, literature survey proves the need to go back to basics in order to obtain precise, reliable and comparable pH-dependent charging of oxides. It is most general that the oxides contain some unrecognized surface impurities and have a strongly pH-dependent dissolution. These distort the results of titrations; their effect increases with decreasing particle size and can become dominant for nanoparticles. The protocol presented here contains the necessary feedback loops to easily recognize and exclude these side effects.",
keywords = "Dissolution, Oxide nanoparticles, PH measurement, PZC, Specific ions, Surface charge",
author = "M. Szekeres and E. Tomb{\'a}cz",
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AU - Szekeres, M.

AU - Tombácz, E.

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N2 - The increased interest in architecting nanocomposites and in clarifying their impact on health and environment necessitates a standardized method of surface characterization, because the behaviour of nanoparticles is governed largely by their surface free energy and interfacial chemistry. Potentiometric acid-base titration has been used for decades to determine surface charge density of oxides, tremendously useful in understanding and modelling oxide/electrolyte interfaces. The method has solid theoretical and experimental foundation. Yet, published values of the point of zero charge (PZC) of chemically identical oxides scatter widely: the deviation of seven units of pH is the rule, rather than an exception. The PZC must reflect the inherent charging behaviour, linked exclusively to the protonation, and determined by the chemistry of the oxides. Assignment of PZC (just like assignment of equilibrium constant of any chemical reaction) requires strict conditions and consistent protocol. We present here such a protocol, and some examples of application. The protocol leads through the basic steps: pH buffer calibration, proton concentration calibration in the background electrolytes, and titrations of oxides. Built-in tests help to eliminate artificial side effects simultaneously from the measurement of pH and from the oxide/electrolyte interfacial equilibria. Although these may seem self-evident, literature survey proves the need to go back to basics in order to obtain precise, reliable and comparable pH-dependent charging of oxides. It is most general that the oxides contain some unrecognized surface impurities and have a strongly pH-dependent dissolution. These distort the results of titrations; their effect increases with decreasing particle size and can become dominant for nanoparticles. The protocol presented here contains the necessary feedback loops to easily recognize and exclude these side effects.

AB - The increased interest in architecting nanocomposites and in clarifying their impact on health and environment necessitates a standardized method of surface characterization, because the behaviour of nanoparticles is governed largely by their surface free energy and interfacial chemistry. Potentiometric acid-base titration has been used for decades to determine surface charge density of oxides, tremendously useful in understanding and modelling oxide/electrolyte interfaces. The method has solid theoretical and experimental foundation. Yet, published values of the point of zero charge (PZC) of chemically identical oxides scatter widely: the deviation of seven units of pH is the rule, rather than an exception. The PZC must reflect the inherent charging behaviour, linked exclusively to the protonation, and determined by the chemistry of the oxides. Assignment of PZC (just like assignment of equilibrium constant of any chemical reaction) requires strict conditions and consistent protocol. We present here such a protocol, and some examples of application. The protocol leads through the basic steps: pH buffer calibration, proton concentration calibration in the background electrolytes, and titrations of oxides. Built-in tests help to eliminate artificial side effects simultaneously from the measurement of pH and from the oxide/electrolyte interfacial equilibria. Although these may seem self-evident, literature survey proves the need to go back to basics in order to obtain precise, reliable and comparable pH-dependent charging of oxides. It is most general that the oxides contain some unrecognized surface impurities and have a strongly pH-dependent dissolution. These distort the results of titrations; their effect increases with decreasing particle size and can become dominant for nanoparticles. The protocol presented here contains the necessary feedback loops to easily recognize and exclude these side effects.

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