TiO2(101) Anatase Surface Functionalization via Hydroxamate and Carboxylate Anchors


Pratyusha Kalluri with Dr. Robert Hamers and Kacie Louis

UW Department of Chemistry

In conventional dye-sensitized solar cells (DSSC), thin films of TiO2 nano-particles are functionalized via carboxylate anchors.  The efficiency of these cells is highly dependent on the stability of the surface-to-anchor bond.  This study analyzed the stability and suitability of hydroxamate anchors compared with conventional carboxylate anchors for TiO2 surface functionalization.

Electronic properties of both hydroxamate and carboxylate as TiO2 anchors were studied using density functional theory (DFT) and Infrared (IR) spectroscopy.  In the DFT analysis, the Vienna Ab-Inito Simulation Package (VASP/VAMP) was used to run a full geometry optimization and to determine bond enthalpy, employing the PW91 approximation method.  This computational method was used to model and calculate the enthalpy of formation for a 3-Carbon hydroxamate anchor and an 87-atom surface of TiO2(101) anatase before and after functionalization via the hydroxomate anchor.  The same DFT method was also used to model and calculate the enthalpy of formation for a 3-Carbon carboxylate anchor, and an 87-atom surface of TiO2(101) anatase before and after functionalization via the carboxylate anchor.  These calculations were used to estimate the enthalpy of the surface-to-anchor-bond, as an indication of stability.  For experimental analysis, TiO2 nano-particles were synthesized and functionalized with each of the two organic anchors.  The resulting substances were then analyzed using IR spectroscopy.  From these spectrums, the ability of the anchors to easily functionalize TiO2 surfaces was observed.  Both computational and experimental results indicate that hydroxamate anchors are more suitable than carboxylate anchors for TiO2 surface functionalization, due to a more stable anchor-to-surface bond.