Recent progress on water vapor adsorption equilibrium by metal-organic frameworks for heat transformation applications

Adsorption-based heat transformation systems are studied from the twentieth century; however, their performance is low to replace conventional systems. Metal-organic frameworks (MOFs) are providing a new class of micro- and nano-porous organic adsorbents. These have adjustable geometry/topology with a large surface area and pore volume. A comparison of the coefficient of performance (COP) between the MOFs and conventional adsorbents-based cooling systems is made for the years 1975–2020. Conventional adsorbents achieve COP of 0.85, whereas it is improved to 2.00 in the case of MOFs. The main bottleneck in the lower COP level is the low adsorption equilibrium amount. This study is aimed to provide comprehensive detail of water-vapor adsorption equilibrium and physicochemical properties of hydrophilic MOFs. Zn based MOFs are not stable in the presence of water-vapors, whereas MIL series, Zr, Ni, and Cu based MOFs are relatively more stable. Among the studied MOFs, MIL-101(Cr) possesses the highest adsorption uptake of 1.45 kg/kg at 25 °C (saturation condition) and outperformed for heat transformation applications. Its uptake can be increased to 1.60 kg/kg by coating with graphite oxide. For water desalination, MIL-53(Al) exhibits specific daily water production of 25.5 m3/ton.day (maximum) with a specific cooling power of 789.4 W/kg. Both MIL adsorbents are found promising which can be considered for various adsorption applications