Water adsorption/desorption over metal-organic frameworks with ammonium group for possible application in adsorption heat transformation

Abstract

Typical metal-organic frameworks (MOFs) such as UiO-66 and MIL-125 were modified to introduce –NH2 and –NH3+Cl− groups in order to improve their performances for water adsorption and for possible applications in adsorption heat transformation (AHT). Not only adsorption isotherms but also dynamic water adsorption/desorption (in 10 cycles) results showed that the functionalization, especially loading of the –NH3+Cl− group, was very effective for such purposes. Both the adsorption capacity (especially, at low vapor pressure) and dynamic water uptake (via cyclic adsorption/desorption of water) increased notably with the modification of the MOFs. The positive effect could be explained by hydrogen bonding and electrostatic interactions, which are not possible with the pristine MOFs. Therefore, it could be suggested that loading moieties with charge and ample hydrogen (such as ammonium group) is a very effective means of modifying MOFs for water adsorption or for application in AHT.