Synthesis and characterization of a novel MnOx-loaded biochar and its adsorption properties for Cu2+ in aqueous solution

• A novel engineered sorbent (i.e., MnOx-loaded biochar) was synthesized.
• Layered structures of MnOx were well dispersed on the carbon surface.
• Biochar/MnOx composite has strong sorption capacity to Cu2+.
• MnOx-loaded biochar as a low-cost sorbent may have promising environmental applications.

Biochar/MnOx composite, as a potential adsorbent, was successfully synthesized via KMnO4 modification of corn straw biochar (BC) under high temperature (600 °C). Surface properties and pore structures of the MnOx-loaded BCs were examined by complementary analytical techniques including X-ray photoelectron spectrometer, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, Fourier transform infrared spectrometer, and nitrogen adsorption measurement at 77 K. Layered structures of micro/nano-MnOx were well dispersed on the BC surface heat-treated with 10% KMnO4. Mn exhibited oxidation state between Mn3+ and Mn4+, and the majority of surface oxygen was bonded to Mn in the forms of MnO (63.9%) and MnOH (26.3%). The MnOx-loaded BCs exhibited much higher adsorption capacity to Cu2+ relative to original BC with the maximum adsorption capacity as high as 160 mg/g. The increased adsorption of Cu2+ on the MnOx-loaded BCs was mainly due to the formation of inner-sphere complexes with MnOx and O-containing groups. The stronger binding affinity of Cu2+ with MnOx-loaded BCs was also supported by lower desorption rate relative to original BC. The results suggest that MnOx-loaded BC, as a low-cost adsorbent, may have promising environmental applications.