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Pore size and surface charge control in mesoporous TiO(2) using post-grafted SAMs
Dereje Hailu Taffa1, Murugavel Kathiresan, Lorenz Walder
1Institute of Chemistry, University of Osnabrück, Barbarastrasse. 7, D-49069 Osnabrück, Germany.
Physical Chemistry Chemical Physics : PCCP
|February 4, 2010
Summary
This study modified titanium dioxide (TiO2) mesoporous scaffolds with phosphonic acids to control pore charge and diameter. The modified materials show tunable charge transport, with potential applications in ion-exchange voltammetry.
Area of Science:
- Electrochemistry
- Materials Science
- Surface Chemistry
Background:
- Mesoporous titanium dioxide (TiO2) scaffolds are crucial for various applications.
- Controlling surface charge and pore size is key to tuning their functionality.
- Grafting phosphonic acids offers a versatile method for surface modification.
Purpose of the Study:
- To investigate the effect of pore size and surface modification on charge transport in mesoporous TiO2.
- To explore the relationship between pore characteristics, surface charge, and ion permeability.
- To evaluate the potential of modified TiO2 for applications like ion-exchange voltammetry.
Main Methods:
- Preparation of two types of TiO2 scaffolds: sintered (s-TiO2) and self-assembled (t-TiO2) with different pore sizes.
- Post-grafting of TiO2 pore walls with phosphonic acids containing pyridinium or sulfonate head groups.
- Characterization using FTIR spectroscopy.
- Investigation of charge transport via cyclic voltammetry with various electroactive and non-electroactive tracer ions.
Main Results:
- Surface modification successfully tuned pore diameter and surface charge.
- Faradaic current was controlled by surface charge, tracer ion charge, and pore diameter.
- High preconcentration of ions was observed, with partitioning coefficients up to 7 x 10^3 for [Fe(CN)6](4-/3-).
- Phenomena like electrostatic closure, charge inversion, and charge propagation modes were identified.
- s-TiO2 demonstrated superior electrostatic barrier formation compared to t-TiO2, attributed to its narrow pore bottlenecks.
Conclusions:
- Surface-grafted phosphonic acids provide effective control over charge transport in mesoporous TiO2.
- The interplay between pore size, surface charge, and ion properties dictates ion permeability.
- Modified TiO2, particularly s-TiO2, shows promise for electrochemical applications such as ion-exchange voltammetry due to enhanced ion preconcentration and electrostatic effects.
