Infrared study of CO2 adsorption on ZnO. Adsorption sites

Abstract

Adsorption of carbon dioxide on a ZnO Kadox-15 powder has been studied by Fourier transform infrared spectroscopy. The following surface species are formed: bidentate carbonates, polydentate carbonates which appear with time or heating, hydrogenocarbonates and linear CO₂ species. Moreover, a band at 1546 cm^–1 could correspond to carboxylates reversibly adsorbed at room temperature. Attention is paid to the effect of CO₂ addition which splits the ν_a(OCO) and δ(CO₂) bands due to linear species and shifts the bidentate carbonates band from 1595 to 1615 cm^–1. Taking account of the band v_a(O¹³CO)(in natural abundance), we deduce that the splitting is due to a coupling between two linear species held by the same Zn²⁺ ion. We propose that such Zn²⁺ ions that are two-fold coordinate are situated on the edges formed by the (0001)(1010) planes.