Here we present a comprehensive experimental and computational study of adsorption of I^- to ZrO₂ particles in water. With batch experiments and a new quantitative spectrophotometric method, the Henry isotherm and the thermodynamic quantities of the Van’t Hoff equation for adsorption of I^- were determined. DFT calculations with periodic models were performed to understand molecular and dissociative water adsorption and I^- adsorption considering adsorbate exchange at the surface to mimic the real system.The DFT calculations show that I^- competes with H₂O and HO^– for the same adsorption sites. I^- is able to displace molecularly adsorbed H₂O, but not the adsorbed HO^– which ultimately provide the bonding environment for I^- at the surface of the oxide. The number of adsorbate binding sites is obtained from the Henry isotherm here used as a limiting case of the Langmuir model. This is possible because, as demonstrated by the DFT data, ΔH_ads is close to constant with increasing coverage of I. The isotherm predicts the formation of a partial overlayer of I-atoms which is also suggested by the DFT data. The ΔH_ads and ΔS_ads determined from experimental data and the Van’t Hoff equation agree with the proposed mechanisms from DFT.