A magnetic chitosan for efficient adsorption of vanadium (V) from aqueous solution.

The all-vanadium redox flow battery (VRFB) is becoming a promising technology for large-scale energy storage due to its advantages such as scalability and flexibility. In recent years, the VRFB has been successfully developed and put into use in many countries. It is expected that the abandoned VRFB will generate a large amount of vanadium waste. To our knowledge, there are few reports on the disposal of spent VRFBs. Herein, chitosan-coated nano-zero-valent iron (CS-Fe) is proposed for the first time as adsorbents for the treatment of spent VRFBs. It can provide a new approach to deal with the upcoming large number of spent VRFBs. The calculated maximum adsorption capacity for V(V) of chitosan and CS-Fe reached 209.5 and 511.3 mg/g at 288 K, respectively. CS-Fe showed better adsorption performance than chitosan under different pH conditions and is easy to be separated from the liquid phase. The Freundlich isotherm was suitable for the adsorption process of chitosan, and CS-Fe was more consistent with the Langmuir isotherm. Ionic strength (0.05-0.5 M) had a positive effect on the adsorption capacity of CS-Fe, and the influence of coexisting anions on CS-Fe could be negligible. FTIR and XPS analyses revealed that the primary mechanisms were the electrostatic attraction of chitosan and redox of Fe. The present study confirmed that CS-Fe could be a potential material to efficiently trap V(V) from the VRFB electrolyte.