Enhanced VOC adsorption capacity on MOF thin layer with reduced particle size by cryogrinding and microwave method

Metal-organic framework (MOF) thin films are widely used for catalysis, separation, sensors, and electronic devices because of their unique properties such as large surface area, highly ordered crystalline structure, and tunable electrical conductivity. In this research, the sorption behavior of three aromatic hydrocarbons (benzene, toluene, and chlorobenzene) on the MOFs of UTSA-16, HKUST-1, MIL-101, UiO-66, and ZIF-8 was studied. A thin layer of MOF was formed on a gold sensor by solution drop-casting a MOF solution with different compositions. The adsorption capacities were analyzed using a quartz crystal microbalance, and the relative capacities were confirmed using a volumetric method. To investigate the effect of the MOF particle size on the adsorption capacity, a novel cryogrinding method was adopted and the cryoground HKUST-1 showed a 21% (benzene), 23% (toluene), and 20% (chlorobenzene), increase in adsorption capacity over the parent HKUST-1. Similarly, cryoground MIL-101 showed 14% (benzene), 13% (toluene), and 13% (chlorobenzene) increase, while UiO-66 showed 16% (benzene), 19% (toluene), and 16% (chlorobenzene) improvement compared to samples without cryogrinding due to an improved VOC accessibility in small particles. Adsorption capacities for microwave synthesized UTSA-16 were further increased by 12–30% by the cryogrinding process. Morphological properties of the MOFs were investigated using X-ray diffraction, Brunauer–Emmett–Teller analysis, scanning electron microscopy, and thermo-gravimetric analysis.