Magnetic Nitrogen-Doped Carbon Composites Decorated with Carbon Nanotubes for Adsorption of Malachite Green

In this work, magnetic nitrogen-doped carbon composites decorated with carbon nanotubes (CNT/Co@N–C) were successfully prepared by carbonizing ZIF-67(Co) and melamine with a ZIF-67(Co)/melamine material synthesized in situ at 525 °C under an inert atmosphere. To improve the malachite green removal performance of the adsorbent, calcination temperatures and mass ratios of the ZIF-67(Co)/melamine-derived CNT/Co@N–C materials were optimized. The malachite green removal performance was evaluated based on various experimental parameters including adsorbent dosage, pH, contact time, and salinity. The results showed that pH and salinity had a small effect on the adsorption process of CNT/Co@N–C materials, thus providing a possibility for practical application in water purification. The adsorption of malachite green onto the CNT/Co@N–C material was consistent with the Langmuir isothermal model and the pseudo-second-order model, and the maximum malachite green adsorption of the material was 3881.30 mg/g. The results also suggested that the adsorption was a monolayer chemisorption process that occurred through electrostatic and π–π stacking interactions. Finally, the recyclability, magnetic properties, high adsorption performance, and high stability of CNT/Co@N–C materials suggest that the materials are a promising adsorbent that can be employed in the removal of malachite green. The present work provides an idea for the synthesis of magnetic carbon nanotubes modified with nitrogen-doped carbon materials derived from metal–organic frameworks (MOFs).