Dissolution of arsenic bearing minerals in groundwater (used as drinking water) can lead to concentrations of >0.05 mg/L of arsenite in many countries, causing serious health effects. Several existing technologies rely on coagulation and adsorption to remove the less toxic form of arsenate (As (V)) (easier to remove from solution than As (III) due to its anionic charge) and the use of harsh oxidants (e.g. ozone). In this work nanocrystalline titanium dioxide (TiO₂) has been used as a photocatalytic oxidant (PCO) to oxidise As (III) which also functions as an adsorbent with a high surface area to remove the As (V) from solution. Most previous research has monitored only As (III) removal from solution and the mechanism of PCO is a controversial topic.  The main aim of this work was to use X-ray Photoelectron Spectroscopy (XPS) to study the adsorption and speciation of arsenic adsorbed on TiO₂ following PCO.  Aims also included finding a suitable commercial TiO₂, characterisation of adsorption of As (V), PCO reactions under different conditions, speciation of arsenic adsorbed by XPS and preliminary studies of the mechanism of PCO and the binding of arsenic species to the surface.