Infrared study of the adsorption of water and ammonia on calcium carbonate

Abstract

Infrared spectra are reported of calcite as a function of heat treatment temperature in the range 293–583 K and after the adsorption of water, deuterium oxide and ammonia. Isolated and hydrogen-bonded surface hydroxyl groups and associatively adsorbed water were desorbed from the calcite surface at 373 K. Bulk hydroxyl groups in synthetic calcite were destroyed at 583 K. The dissociative adsorption of water leads to isolated hydroxyl groups at Ca²⁺ sites and surface bicarbonate anions. Physisorption of water either involves hydrogen-bonding interactions or occurs at Lewis-acidic Ca²⁺ sites which can also ligate weakly with adsorbed ammonia molecules.