The nature of the surface acidity of anodised titanium: an XPS study using 1,2-diaminoethane

The nature of the surface acidity of freshly anodised and thermally annealed anodised titanium was investigated using X-ray photoelectron spectroscopy. 1,2-Diaminoethane (ethylenediamine) was used as a basic nitrogenous probe capable of producing both Lewis and Brønsted interactions with acidic surface sites. Comparison with wet polished copper indicated that both Lewis and Brønsted acid sites were present within the anodised titanium surface region. Thermal annealing under vacuum appeared to have little effect on the number of available Lewis sites, but substantially reduced the number of Brønsted sites. This was related to dehydroxylation of the surfaces, and indicated that strongly Brønsted acidic hydroxyl groups are present on anodised titanium surfaces.