Experimental investigation of water adsorption in MIL-101 (Cr)-coated microchannels

A novel wash-coating technique was developed to coat a porous layer of MIL-101 (Cr) adsorbent on the inner walls of fused silica microchannels. The optimum adsorbent slurry was prepared using 92.8% ethanol solvent, 1.2% silica binder, and 6% MIL-101 (Cr) and inserted into the channels, which were dried and regenerated. The coatings were characterized using scanning electron microscopy (SEM) and water adsorption performance using adsorption isotherms. Coating thickness as high as 60 μm was achieved, despite the unfavorably smooth surface of fused silica microchannels. Based on gravimetric and volumetric methods, benchtop experimental setups were constructed to measure the vapor uptake in the MIL-101 (Cr) powder and coated channels, respectively. Isotherm experiments were conducted for coated microchannels after wash-coating at three different temperatures. The adsorbent layer demonstrated outstanding adherence and durability after 20 adsorption and desorption cycles. The adsorption isotherms exhibited a type V (DA-like) adsorption isotherm with a reduced magnitude of 88% than the powdered form, which is remarkable for the coated product. The specific surface area (SSA) of the powdered MIL-101 (Cr), which was 1320 m2/g, decreased to 894 m2/g in the coated form, corroborated with the adsorption isotherm results. The uptake and the height of the Type-V curve decreased with increased temperature. Modified Langmuir Adsorption isotherms were fitted for the coated channel adsorption performance, furthering its suitability for use in the mass and energy balance equations using this configuration. These well-characterized coated channels with a high-performance adsorbent can readily scale up adsorption-based heating and cooling systems, improving their performance.