Synthesis of zirconium-based metal-organic framework under mild conditions and its application to the removal of cationic and anionic dyes from wastewater

Water resources contaminated by industrial dyes can pose a significant threat to the environment and human health. Herein, we conducted a study on the removal of cationic and anionic dyes, such as methylene blue (MB) and methyl orange (MO), using MIL-140A, a zirconium-based metal-organic framework. MIL-140A is synthesized in a Schlenk flask at 120 °C, whereas its conventional synthesis route involves a teflon-sealed autoclave at 220 °C, highlighting the cost reduction and lower equipment requirements of the low-temperature synthesis. The structure of MIL-140A is characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscope (SEM), and nitrogen adsorption techniques. The optimal pH for the adsorption of two dyes by MIL-140A is pH 5–8 for MB and pH 3 for MO. The adsorption equilibrium can be reached within 60 min at room temperature, and the adsorption of both dyes on MIL-140A follows pseudo-second-order kinetics and Langmuir isotherm, and the maximum adsorption capacity of MO and MB by MIL-140A were 163.6 and 89.2 mg/g, respectively. Thermodynamic studies indicate an entropy-driven spontaneous process. The adsorption mechanism of MO and MB on MIL-140A is investigated using FT-IR and X-ray photoelectron spectroscopy. The adsorption of MO involves coordination between Zr and sulfonate, while MB adsorption occurs via π-π interactions. Additionally, MIL-140A exhibits better removal efficiency for MO from lithium battery wastewater compared to MB, primarily due to stronger coordination interactions than π-π interactions. These findings demonstrate that MIL-140A is a promising adsorbent for effectively removing both anionic and cationic dyes from water resources.