Cr(vi) removal by magnetic carbon nanocomposites derived from cellulose at different carbonization temperatures

Magnetic carbon nanoadsorbents fabricated by using cellulose and Fe(NO₃)₃ as the carbon and iron precursors have demonstrated great Cr(vi) removal performance. The magnetic carbon synthesized at a carbonization temperature of 700 °C and a heating rate of 10°C min^-1 (MC7-10) has a greater Cr(vi) removal capacity (22.8 mg g^-1) in neutral solutions due to its larger specific surface area (247.14 m² g^-1). Moreover, the magnetic carbon fabricated at a carbonization temperature of 800°C and a heating rate of 10°C min^-1 (MC8-10) has the highest Cr(vi) removal capacity (278.8 mg g^-1) in acidic solutions, much higher than those of cellulose (12.0 mg g^-1), zero valent iron (ZVI)/chitosan (55.8 mg g^-1) and ZVI doped ordered mesoporous carbon (256.86 mg g^-1). The high removal capacity was attributed to its higher content of ZVI and specific surface area (136.27 m² g^-1) of MC8-10. The reduction of Cr(vi) to Cr(iii) by the oxidation of carbon layer as well as the ZVI in the acidic solution was verified as the main mechanism for Cr(vi) removal. Moreover, the nanoadsorbents could be easily separated from solution by using a permanent magnet after being treated with Cr(vi).