ABSTRACT:Carbon nanotubes (CNTs) functionalized with magnetic nanoparticles are attractive for environmental remediation applications due to their high specific surface area conducive for adsorption of water con-taminants and the possibility of recovering these nanohybrids after remediation using an external mag-netic field. Most of existing methods for synthesizing magnetic iron oxide/CNTs (MIO–CNTs) composites are carried out in the liquid medium and are tedious, uneconomical, and environmentally unfriendly. Herein, we report a one-pot solid-phase route to synthesize MIO–CNTs composites based on pristine CNTs. MIO–CNTs possess a high specific surface area, good dispersibility, and desirable magnetic proper-ties, making them promising as adsorbents for arsenic removal. The maximum arsenic adsorption capac-ities are 47.41 and 24.05 mg g��1 for As(V) and As(III), respectively. These values are among the highest for carbon-based materials. Oxygen-containing groups on the surface of MIO–CNTs play a crucial role in arsenic adsorption. This work is very important for the practical applications of pristine CNTs containing catalyst nanoparticles without the need of purifications.