An Acid-resistant Magnetic Co/C Nanocomposite for Adsorption and Separation of Organic Contaminants from Water

Magnetic adsorbents have recently been extensively investigated and applied in the field of water purification, because of their magnetic characters which are advantageous for the separation and recycle of these materials. Unfortunately, common magnetic materials are unstable and prone to dissolution in acid environment, thus limiting their practical applications in wide pH range, particularly in acidic condition. Therefore, it is highly imperative to exploit a novel magnetic adsorbent that is acid-resistant, to simplify separation process during the water purification. In present work, an acid-resistant magnetic Co/C nanocomposite was synthesized by using ZIF-67 as both template and precursor. The ZIF-67 was carbonized in an argon atmosphere at 800 degrees C for 1 h, and then treated with acid. Upon calcination at an appropriate temperature in inert atmosphere, the generated Co nanoparticles were uniformly wrapped by graphite layers, due to the graphitization of carbon upon the catalysis effect of Co. The formed graphite layers were able to protect the Co particles from oxidation and acid environment, thus resulting in the generation of an acid-resistant magnetic adsorbent that can be applied in a wide pH range (pH 1-13). Remarkably, the as-synthesized magnetic Co/C nanocomposite demonstrated excellent adsorption performance towards two typical organic dyes (rhodamine B and malachite green) over a wide pH range. The adsorption isotherms of rhodamine B and malachite green on Co/C nanocomposite were well fitted with the Langmuir model. Impressively, the maximum adsorption capacities towards rhodamine B and malachite green were estimated to be 400.0 and 561.8 mg g-(1), respectively, far exceeding many previously reported adsorbents. Moreover, the adsorbent could be easily regenerated by washing with ethylene glycol (EG), suggesting its excellent reusability. Even after 5 cycles of reuse, no obvious capacity degradation was observed. Furthermore, practical application of the magnetic adsorbent was demonstrated by the removal of organic dyes from domestic wastewater with a superior removal efficiency of higher than 97%.