Biopolymer-Coated Magnetite Nanoparticles and Metal–Organic Framework Ternary Composites for Cooperative Pb(II) Adsorption

The imperfection instability, recyclability, and separation factors of metal–organic frameworks (MOFs) limit their practical applications in the field of catalysis and water purification. Designing MOFs that are benign, flexible, and separable is still a critical challenge. Up to now, most of MOFs have been coated with conventional synthetic polymers, which are undegradable and carcinogenic. However, no studies have reported the stepwise growth of biocompatible polymer-capped Fe3O4 (PFe3O4) nanoparticles (NPs) onto the NH2-MIL-125 (Ti) surface (ternary composite). In this study, a simple stepwise embedding of PFe3O4 NPs onto NH2-MIL-125 (Ti) was successfully employed and used for efficient aquatic scavenging, which can allow synergetic cooperative adsorption with functionality on both the biopolymer and MOF surface. The obtained transmission electron microscopy (TEM) and high-resolution TEM images illustrate that the PFe3O4 NPs were uniformly embedded onto the surface of the MOF. The composite was employed for the quick and significant removal of Pb(II) from aqueous solution. The effects of various parameters like the pH, contact time, initial metal-ion concentration, interfering ions, and temperature on the adsorption capacity of the nanoporous composite were examined. The Langmuir model presented the best fitting with a maximum adsorption capacity of 561.7 mg g–1 at pH 5 and 298 K. Moreover, increasing the PFe3O4 precursor on nanoporous NH2-MIL-125 (Ti) decreased the recovery time (21 s) and enhanced the adsorption process because the same MOF can be recycled six times without obvious loss of the adsorption capacity of Pb(II) in water. Therefore, we can finally conclude that, due to the coating of Fe3O4 with a biopolymer, the composite showed not only highly efficiency in metal-ion adsorption but also high stability for recycling of the material, which is significant for its future practical use in the treatment of industrial waste discharge.