The current study is aimed at comparison of adsorption behaviors of silica-supported Cu nanoparticles (Si-N-Cu) and micrometric copper powder (Mi-Cu) for uptake of iodine vapor. The Si-N-Cu was synthesized by the decomposition of aqueous Cu(NO3)(2) Solution at supercritical condition, followed by reduction of the sample by H-2-N-2 mixture. The Si-N-Cu sample with 29.4 nm Cu particles adsorbed 95% of I-2 at partial pressure 10(-5) bar in 1h, while the 1 mu m Mi-Cu adsorbed 51% of iodine in 6 h, indicating higher yield and faster kinetics of the nanometric sample. Theoretical analysis revealed the existence of a strong thermodynamic size effect in the Cu-I-2 reaction system, so that molar vertical bar Delta G vertical bar for 2 nm Cu particles was 2.5 times larger than vertical bar Delta G vertical bar for 1 mu m particles. For the Mi-Cu, kinetics obeyed a three-dimensional diffusion model, While in the case of Si-N-Cu, diffusion did not play any role in the kinetics. Apparently, no passivation mechanism was operative in the iodination.