Removal of Congo Red dye by a New Metal–Organic Framework (MOF): Multivariate Optimization and Adsorption Characterization

Congo red (CR), an anionic diazo dye, is known as a human carcinogen, which is very difficult to remove because of optical, physico-chemical, and thermal stability due to its aromatic structure. Metal-organic frameworks (MOFs) are a new class of nanoporous materials and consist of two main components, bridging organic ligands and metal ions or clusters of metal ions. In among methods of the synthesis of MOFs, sonochemical method is an effective and fast approach for the synthesis of smaller size MOFs. In this study, the new metal-organic framework of [Ni2(F)2(bipy)2(H2O)2](VO3)2.10H2O was prepared using sonochemically method to obtain a new adsorbent for removal of Congo red from aqueous solution. The elemental analysis (C, H, and N), FT-IR spectroscopy, field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray (EDX), and thermogravimetric analysis (TGA) were explored to identify of adsorbent structure. The Box-Behnken design (BBD) was employed to obtain the optimal conditions of CR removal (sorbent dosage = 0.0107 g, CR concentration = 50 mg/L, and temperature = 45 ℃). The isotherm and kinetics studies of the adsorption process showed that Langmuir isotherm, with qmax = 242.1 mg/g, and pseudo-second-order model describe the experimental data well. According to the results of thermodynamic investigate, the adsorption process of CR is endothermic and spontaneous.