Efficient Removal of Pb(II) and Co(II) Ions from Aqueous Solution with a Chromium-Based Metal–Organic Framework/Activated Carbon Composites

Herein, an efficient adsorbent based on an activated carbon and metal–organic framework was developed for the adsorption of heavy metals from an aqueous solution. The structural and morphological characterizations of the Cr-MOF/AC composite were evaluated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM), exhibiting the formation of crystalline cubic-shaped particles. The Cr-MOF/AC composite showed 3-fold higher specific surface area (2440 m²/g) than AC. The response surface methodology was employed to find the optimum adsorption conditions for the fast and efficient removal of lead and cobalt ions. The study of the kinetics of adsorption showed that the metal ions adsorption followed the pseudo-second-order model. The resultant composite was proved to be an excellent and highly efficient adsorbent with the adsorption capacity as high as 127 and 138 mg/g for lead and cobalt, respectively, under optimal conditions (pH = 5, an adsorption time of 40 min, adsorbent content of 25 mg, and metal ion concentration of 70 ppm). A further investigation on the reusability of adsorbent was also carried out, demonstrating the almost unchanged structure of the Cr-MOF/AC composite after five regeneration cycles. The Cr-MOF/AC composite exhibits a great potential for heavy metal adsorption and wastewater treatment.