Synthesis, Characterization and computational study of Ni-based Metal-organic framework for water treatment

Abstract

Metal-organic frameworks (MOFs) are an emerging class of crystallized porous polymeric materials, consisting of organic linkers with metal ions. Due to their rich porosity, larger surface chemistries and tune-able pore size MOF have been greatly used for catalysis, drug delivery, gas adsorption, and storage over the past two decades. However, there is a need to address the crucial environmental challenge i.e; water treatment, which needs the researcher’s attention. To address the challenge both computational and experimental study were performed with aim to use NiBDC MOF as adsorbent for removal of Cd, Pb, and Hg dissolved in water. The detailed computational studies were performed for large scale screening and prediction of MOFs efficiency as adsorbent. Cluster and fragment models of Ni-BDC MOF were designed to predict its crystal structure, thermodynamic stability, reactivity, electronic properties and adsorption kinetics using the Grand Canonical Monte Carl, Molecular Mechanics, Molecular Dynamics and Quantum mechanics. The use of the quantum mechanical method provided an insight into in-depth structural analysis on the discrete level for evaluation of Cd, Pb, and Hg binding propensity with Ni-BDC MOF. On the basis of computationally predicted structure; MOF consisting of Ni linked together by organic bridging ligands i.e; benzene-tri-carboxylic acid was synthesized via hydrothermal process. The Ni-BDC has shown efficient and enhanced properties. Synthesis of Ni-BDC was followed by spectroscopic Batch experiments for analysis of removal of Cd, Pb, and Hg. Computational cluster and fragment model results revealed that Ni-BDC has provided sufficient surface area for the adsorption of toxic metals from contaminated water. This study mainly focused on the removal of heavy metal ions (Cd, Pb, Hg). However; Experimentally; Pb was found to have the highest adsorption affinity with Ni-BDC by adsorption energy (-59963 KJ/mol), adsorption constant (1.33x1010), and Gibbs Free Energy (-53090.0 J/mole). Whereas the parallel results of higher removal of Pb by Ni-BDC were also calculated by experimental study through Langmuir adsorption constant (0.0762 g/l) and Gibbs Free energy (-30434.2 J/mole). The computational and experimental study both coincided with and confirmed the adsorption of metal chlorides on porous surface of Ni-BDC following the order Pb> Hg> Cdfrom water. A combined experimental and computational study offers a unique insight into the nature of Ni-BDC interactions at the molecular and atomistic levels.