A sustainable adsorbent for phosphate removal: modifying multi-walled carbon nanotubes with chitosan

Phosphorus, a major culprit for eutrophication of aquatic environments, is dissolved in water primarily in the form of phosphate; hence, it is difficult to remove, and different materials are being investigated, aiming at high removal capabilities. Meanwhile, recovery capability must also be considered, since phosphorus present in wastewater may serve as a potential alternative resource for the mineral phosphorus. Carbon nanotubes are promising for the treatment of phosphate pollution; however, studies about their removal potential are limited. Herein, multi-walled carbon nanotubes were modified with chitosan through simply cross-linking to obtain a novel adsorbent for phosphate removal. Our data show that a maximum adsorption as high as 36.1 ± 0.3 mg P g⁻¹ was achieved in 30 min at pH 3 and 293 K. The adsorption capacity of the composite (chitosan/multi-walled carbon nanotubes) could be maintained at 94–98% even after 5 adsorption–desorption cycles. An exothermic process was obtained, according to the Freundlich isotherm model. Based on the reported performance, the composite has a great advantage compared with other novel adsorbents for phosphate removal, indicating that the composite is a highly potential material to treat phosphorus-induced eutrophication of water bodies.