Adsorption irreversibility of Zn(II) on TiO2 at various temperatures was studied using a combination of classical macroscopic methods and extended X-ray absorption fine structure (EXAFS) spectroscopy. When the temperature was increased from 5 to 40 degrees C, the Zn(II) adsorption capacity increased by 130%, and adsorbed Zn(II) became more reversible. The standard Gibbs free energy change (AGO) of the adsorption reaction at 5, 20, and 40 degrees C was determined to be -19.58 +/- 0.30, -22.28 +/- 0.10, and -25.14 +/- 0.21 kJ mol(-1), respectively. And the standard enthalpy (Delta H-0) and entropy (Delta S-0) were 24.55 +/-2.91 kJ mol(-1) and 159.13 +/- 0.53 J mol(-1) K-1 respectively. EXAFS spectra results showed that the hydrated Zn(II) was adsorbed through fourfold coordination with an average Zn-O bond distance of 1.98 +/-0.01 angstrom. Two Zn-Ti atomic distances of 3.25 +/- 0.02 and 3.69 +/-0.03 angstrom were observed, which corresponded to an edge-sharing linkage mode (strong adsorption) and a corner-sharing linkage mode (weak adsorption), respectively. As the temperature increased from 5 to 40 degrees C, the number of strong adsorption sites (N-1) remained relatively constant while the number for the weak adsorption sites (N-2) increased by 31%. These results indicate that the net gain in adsorption capacity and the decreased adsorption irreversibility at elevated temperatures were due to the increase in available weak adsorption sites (N-2) or the decrease in the ratio of N-1/N-2. Both the macroscopic sorption/desorption equilibrium data and the molecular level evidence of this study suggest that in a given environmental system (e.g., soils or natural waters) zinc and other similar heavy metals are likely more mobile at higher temperatures. (C) 2007 Elsevier Inc. All rights reserved.