Synthesis and Characterization of Cobalt Metal Organic Frameworks Prepared by Ultrasonic Wave-Assisted Ball Milling for Adsorptive Removal of Congo Red Dye from Aqueous Solutions

The cobalt metal–organic frameworks (Co-MOFs) were efficiently prepared by ultrasonic-assisted ball milling with low cost, utilizing 1, 3, 5-benzenetricarboxylic acid and cobalt (II) acetate tetrahydrate. The structural characteristics were carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetry (TGA), and BET surface areas method. The adsorption of Co-MOFs to Congo Red (CR) was analyzed by Langmuir adsorption isotherm and pseudo-second-order kinetic model. The results showed that the maximum adsorption performance (fitted by Langmuir adsorption isotherm) of the Co-MOFs (with 30 min’s synthesis time and 1:1 molar ratio of the raw material) to CR reached 1.76 × 10 3  mg/g, which is much higher than previous reports. The adsorption experiment reached equilibrium in 30 min. Electrostatic attractions, π–π stacking interactions and pH are considered to play a significant role in the adsorption of Co-MOFs to CR. The adsorption rate of Co-MOFs to CR remains 34% even after it is recycled for the third time. In this paper, the absorption results indicated that Co-MOFs prepared by ultrasonic-assisted ball milling presents a great prospect in the field of CR adsorption.