1. The repeating unit of the polymer in this scheme is only a simplified model representation showing the three different types of amines present in PEI. The primary and secondary amino group in PEI react with CO2 to form carbamates. In the presence of water these carbamates can react further to form a bicarbonate species. Following our previous study on PEI impregnated on fumed silica and precipitated silica,(30) we present here our work on the preparation, characterization, and preliminary study of the properties of a silica–organic hybrid adsorbent for CO2 capture from air.