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Preparation of Functional Silica Using a Bioinspired Method
Published on: August 1, 2018
Interaction of silicic acid with goethite
Tjisse Hiemstra1, Mark O Barnett, Willem H van Riemsdijk
1Department for Soil Quality, Wageningen University, P.O. Box 8005, NL 6700 EC Wageningen, The Netherlands. tjisse.hiemstra@wur.nl
Journal of Colloid and Interface Science
|February 20, 2007
Summary
Silicon adsorption on goethite (alpha-FeOOH) peaks at pH 9, influenced by proton co-adsorption and surface complexation. At high concentrations, Si polymerization occurs, affecting particle charge and point of zero charge.
Area of Science:
- Geochemistry
- Environmental Science
- Colloid and Surface Science
Background:
- Silicon (Si) is an abundant element in natural waters, influencing water quality and mineral interactions.
- Goethite (alpha-FeOOH) is a common iron oxyhydroxide mineral in soils and sediments, acting as a significant sorbent.
- Understanding Si adsorption on goethite is crucial for predicting element mobility and geochemical processes.
Purpose of the Study:
- To investigate the adsorption behavior of silicic acid on goethite across environmentally relevant Si concentrations.
- To quantify Si adsorption using advanced surface complexation models and theoretical calculations.
- To elucidate the mechanisms of Si adsorption, including surface complex formation and polymerization.
Main Methods:
- Batch adsorption experiments covering natural Si concentration ranges.
- Interpretation using the charge distribution (CD) and multi-site surface complexation (MUSIC) model with an extended Stern (ES) layer option.
- Modeling of Si adsorption as bidentate surface complex formation, with CD values derived from MO/DFT calculations.
- Consideration of Si polymerization at high Si loadings.
Main Results:
- Si adsorption on goethite exhibits a pH-dependent behavior, with maximum adsorption around pH 9.
- The extended Stern (ES) model successfully described adsorption, accounting for interfacial water ordering.
- A bidentate surface complex model, validated by theoretical CD values, accurately represented adsorption data.
- Si polymerization was proposed to explain adsorption at high Si concentrations (>10(-4) M).
- Adsorbed Si polymers were found to hydrolyze at high pH, releasing protons and altering surface charge.
Conclusions:
- The study provides a robust thermodynamic and mechanistic understanding of Si adsorption on goethite.
- The application of a theoretically derived CD value reduced model complexity and improved predictive power.
- The findings highlight the importance of considering Si polymerization and its acid-base properties in geochemical modeling.
- The model accurately predicts changes in particle charge and the point of zero charge (IEP) due to Si adsorption and proton release.
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