With the growing population, industrialization, and agriculture, water contamination not only affects people but entire ecosystems. Metal–organic frameworks (MOFs), because of their large surface area and porosity, show great potential as adsorbents for removing pollutants, such as heavy metals, from contaminated water. The current research aims at examining copper (II) benzene-1,3,5-tricarboxylate (Cu-BTC) MOFs and understanding the mechanism for their adsorption of Pb(II) from aqueous solution. The Cu-BTC samples were characterized using FTIR and XRD, and their surface area and porosity were determined based on N2 adsorption isotherms. The concentration of Pb(II) in the solutions was measured using atomic absorption spectroscopy (AAS). Both kinetic and equilibrium adsorption data were collected and then analyzed using numerical models. The analyses led to the findings that the limiting steps in the adsorption of Pb(II) on Cu-BTC are (a) pore diffusion of Pb(II) and (b) the availability of the active sites on Cu-BTC MOFs. It was further revealed that the former step is more dominant in the adsorption of Pb(II) when the lead concentration is low. The latter step, which is directly proportional to the surface areas of the MOFs, affects the adsorption to a greater extent when the lead concentration is high. The results also show that adsorption of Pb(II) ions on Cu-BTC is mainly a multi-layer heterogeneous process.

The mechanochemical synthesis of metal-organic framework Cu3(BTC)2 was conducted with various amounts of water–ethanol liquid added prior to grinding. Using the XRD, SEM and N2 sorption results, an attempt was made to explain the mechanisms by which liquid may affect the formation of Cu3(BTC)2 and its porosity in the grinding process. The experimental results show that microporosity is controlled by the degree of crystallinity of Cu3(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 Cu3(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 Cu3(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 Cu3(BTC)2 samples diminish significantly.