Adsorptive removal of Congo red from aqueous solution using zeolitic imidazolate framework-67

In the present paper, the Congo red dye (CGR) adsorption onto zeolitic imidazolate framework-67 (ZIF-67) is demonstrated. ZIF-67 was synthesized using the microwave method. The obtained ZIF-67 was characterized by means of X-ray diffraction (XRD), scanning electron microscope (SEM), thermal gravity analysis (TG), and X-ray photoelectron spectroscopy (XPS). ZIF-67 was employed to adsorb CGR from aqueous solutions. The first-order and second-order kinetic model, and Weber's intra-particle-diffusion and Boyd's film-diffusion model were utilized to study the adsorption kinetics. The equilibrium adsorption data at different temperatures were interpreted using the Langmuir and Freundlich models. The thermodynamics from 301 K to 331 K was also addressed. ZIF-67 exhibited excellent adsorption in terms of favourable thermodynamics, ultra-high adsorption and superb fast kinetics. The adsorption capacity of ZIF-67 for CGR could be as high as 714.3 mg g-1 at 301 K, which could be improved at higher temperatures. In addition, ZIF-67 also exhibited very high adsorption for some other dyes such as rhodamine B and methylene blue. ZIF-67 was stable and could also be conveniently reused for several times. These peculiarities facilitate ZIF-67 to become one of the most promising adsorbents to remove dyes from water.