Mapping the Cu-BTC metal-organic framework (HKUST-1) stability envelope in the presence of water vapour for CO₂ adsorption from flue gases

Cu-BTC metal-organic framework (HKUST-1) was evaluated as the model material for CO₂ capture from flue gas streams. This paper presents an optimised hydrothermal synthesis of HKUST-1 and an analysis of water stability of HKUST-1. Substantial improvements of the hydrothermal synthesis process of HKUST-1 are shown to increase the quantitative yield up to 89.4% at 100°C. Single-component adsorption experiments were carried out under conditions relevant for flue gases adsorption (45-60°C, 0-1barG) to evaluate the performance of HKUST-1 in terms of adsorption capacity, showing that the amount adsorbed of water can reach up to 21.7mmolg^-1, about one order of magnitude higher than CO₂ (1.75mmolg^-1) and almost two orders of magnitude higher than N₂ (0.17mmolg^-1). The hydration process of HKUST-1 framework was investigated using dynamic vapour adsorption under the flue gas emitting conditions. HKUST-1 is sensitive to humid streams and dynamic deformation of its porous structure takes place at 40-50°C and various relative humidity values, leading to the irreversible decomposition of HKUST-1 framework and the consequent deterioration in its adsorption capacity. Under humid conditions, water displaces the organic linkers from the copper centres causing the collapse of HKUST-1 framework. These results provide fundamental knowledge to enable future material design for the modification of the hydrophilic nature of copper sites in HKUST-1 to improve its moisture stability.