Magnetic mesoporous carbon nanospheres from renewable plant phenol for efficient hexavalent chromium removal

Magnetic mesoporous carbon composites are promising adsorbents for water purification. However, the sustainable synthesis of such mesoporous carbon nanospheres with controllable structures and compositions using renewable biomass as a carbon source is still a great challenge. Herein, mesoporous carbon nanospheres have been successfully synthesized via direct pyrolysis of iron-phenolic coordination polymers. Such coordination polymers are fabricated using plant phenol as a renewable carbon source and iron ions as a metal source. The resultant magnetic mesoporous carbon nanospheres show large pore size (6.7 nm), high specific surface area (512.3 m²/g), excellent performance for Cr(VI) removal with a high adsorption capacity (336.7 mg/g), fast adsorption rate (1.60 × 10⁻³ mg g⁻¹ min⁻¹) and easy magnetic separation property. In the adsorption process, Cr(VI) is first trapped on the surface of magnetic mesoporous carbon nanospheres via electrostatic interaction. Then part of the adsorbed Cr(VI) is reduced to low-toxic Cr(III) by α-Fe/Fe₃C nanoparticles dispersed in carbon nanospheres. This work provides an efficient synthesis strategy for magnetic mesoporous carbon nanospheres using plant polyphenol as a carbon source, which could be used in environmental science, energy storage and catalysis.