Mixed zinc and cobalt hydroxides were synthesized using a precipitation method and tested as adsorbents of hydrogen sulfide from either dry or moist air. The adsorption capacity increased with an increase in the content of cobalt in the structure of mixed hydroxides. The synergistic effect was demonstrated by a fourfold increase in the amount of hydrogen sulfide adsorbed on the surface of the best performing mixed hydroxide in comparison with the hypothetical mixture of the two hydroxides. The initial and exhausted materials were characterized by FTIR, thermal analysis, potentiometric titration, X-ray diffraction, SEM/EDX, and adsorption of nitrogen. The results obtained suggest that an increase in the content of cobalt results in an increase in amorphicity level and in an increase in the number of hydroxyl groups. These groups, besides providing higher basicity thereby increasing the extent of H2S dissociation in the presence of water, are the main active centers reacting with hydrogen sulfide. Defects in the structure and oxygen vacancies result in the oxidation of some H2S to sulfites and sulfates. (C) 2013 Elsevier Inc. All rights reserved.