Mechanistic Study of Porosity Formation in Liquid-Assisted Mechanochemical Synthesis of Metal-Organic Framework Cu3(BTC)2 for Adsorption-Based Applications

The mechanochemical synthesis of metal-organic framework Cu-3(BTC)(2) was conducted with various amounts of water-ethanol liquid added prior to grinding. Using the XRD, SEM and N-2 sorption results, an attempt was made to explain the mechanisms by which liquid may affect the formation of Cu-3(BTC)(2) and its porosity in the grinding process. The experimental results show that microporosity is controlled by the degree of crystallinity of Cu-3(BTC)(2) structures. Within the range of liquid-assisted grinding (LAG), it is found that an increase in the amount of liquid in grinding leads to a larger microporosity in Cu-3(BTC)(2). The formation of mesoporosity and macroporosity is determined by two competing events in LAG: particle breakage and its agglomeration. When the addition of liquid leads to particle breakage over its agglomeration as the dominant event in LAG, it results in smaller Cu-3(BTC)(2) particles, and the network space of these particles constitutes mesoporosity and macroporosity. When the addition of liquid gives rise to particle agglomeration as the dominant event, however, most of this network space collapses so that mesoporosity and macroporosity in the Cu-3(BTC)(2) samples diminish significantly.