Energetics of CO2 and H2O Adsorption on Zinc Oxide

Author(s)

Gouvea, Douglas ^[1] ; Ushakov, Sergey V. ^{[2, 3]} ; Navrotsky, Alexandra ^{[2, 3]}

Affiliation

^[1] Univ Sao Paulo, Dept Met & Mat Engn, Escola Politecn, BR-05508930 Sao Paulo - Brazil

^[2] Univ Calif Davis, NEAT ORU, Davis, CA 95616 - USA

^[3] Univ Calif Davis, Peter A Rock Thermochem Lab, Davis, CA 95616 - USA

• Document type: Journal article
• Source: Langmuir; v. 30, n. 30, p. 9091-9097, AUG 5 2014.
• Web of Science Citations: 23

Abstract

Adsorption of H2O and CO2 on zinc oxide surfaces was studied by gas adsorption calorimetry on nanocrystalline samples prepared by laser evaporation in oxygen to minimize surface impurities and degassed at 450 degrees C. Differential enthalpies of H2O and CO2 chemisorption are in the range -150 +/- 10 kJ/mol and -110 +/- 10 kJ/mol up to a coverage of 2 molecules per nm(2) Integral enthalpy of chemisorption for H2O is -96.8 +/- 2.5 kJ/mol at 5.6 H2O/nm(2) when enthalpy of water condensation is reached, and for CO2 is -96.6 +/- 2.5 kJ/mol at 2.6 CO2/nm(2) when adsorption ceases. These values are consistent with those reported for ZnO prepared by other methods after similar degas conditions. The similar energetics suggests possible competition of CO2 and H2O for binding to ZnO surfaces. Exposure of bulk and nanocrystalline ZnO with preadsorbed CO2 to water vapor results in partial displacement of CO2 by H2O. In contrast, temperature-programmed desorption (TPD) indicates that a small fraction of CO2 is retained on ZnO surfaces up to 800 degrees C, under conditions where all H2O is desorbed, with adsorption energies near -200 kJ/mol. Although molecular mechanisms of adsorption were not studied, the thermodynamic data are consistent with dissociative adsorption of H2O at low coverage and with several different modes of CO2 binding. (AU)

• FAPESP's process: 05/53241-9 - Study of intergranular phenomena in ceramic materials
• Grantee: Reginaldo Muccillo
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 11/02080-6 - CO2 adsorption on ZnO nanoparticles and the relationship with surface enthalpy and size stability
• Grantee: Douglas Gouvêa
• Support Opportunities: Scholarships abroad - Research