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

Abstract

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.