Highly efficient adsorption of aqueous heavy metals by Co-derived metal-organic framework. Synergistic mechanism for enhanced water purification
Rodolfo Peña Rodríguez, Luis Ángel Alfonso Herrera, Jesús Medina Cervantes, Alfredo Morales Tapia, Lidia E. Chiñas, José María Rivera
Abstract
This study opens up exciting possibilities for the application of Co-MOF, a Metal-Organic Framework ([Co(5-NH 2 -bdc)(bpy)0.5(H 2 O)]3·2H 2 O), in the efficient removal of heavy metals (Pb 2+ , Hg 2+ , Cd 2+ , Cu 2+ ) from water. The removal mechanism combines ion exchange and adsorption, influenced by the ionic radius of the metal ions . Langmuir's model determined maximum adsorption capacities (Qm), showing a proportional increase with the ionic radius of heavy metals: 75.47 mg/g (Cu 2+ ), 344.82 mg/g (Cd 2+ ), 485 mg/g (Hg 2+ ), and 526.31 mg/g (Pb 2+ ). Free Gibbs energy , inversely proportional to the metal's ionic radius, was determined as −36.43 kKj/mol (Cu 2+ ), −28.67 Kj/mol (Cd 2+ ), −24.13 Kj/mol (Pb 2+ ), and −21.67 Kj/mol (Hg 2+ ). The pseudo-second-order mechanism explained heavy metal removal , except for Cu 2+ , due to continuous ion exchange. Reutilization experiments showed a decrement in efficacy in the second cycle. Filtration experiments demonstrated a lower removal percentage (close to 60 %) and confirmed the competitive activity of Co-MOF compared to other MOFs, particularly in Cd 2+ removal, with superior rate constants and maximum adsorption capacities.