Efficient removal of cationic malachite green using co-pyrolyzed corn straw biochar-montmorillonite composites

New efficient and sustainable methods for the removal of malachite green (MG) from environmental media are needed. In this study, corn straw was co-pyrolyzed with montmorillonite under a variety of conditions (400, 500, 600, and 700 °C and 10-40 wt% montmorillonite), without any use of toxic chemicals, to produce a series of biochar-clay composites. Characteristics of the composites that make them promising contaminant sorbents include a uniform lamellar-particle micromorphology, enhanced mesoporous structure and surface area (53.0 m² g^-1), and abundant and diverse oxygen/carbon-containing functional groups (i.e., O-H, C-O, C=C, and C-H). The composite produced at 600 °C and 10 wt% montmorillonite had the highest observed MG removal from aqueous solution (6572.1 mg g^-1, 99.6% removal rate). Adsorption of MG by the sorbent was attributed to multiple sorption mechanisms, including physical interaction, cation exchange, and π-π bonding interactions, and was modulated by intra-particle diffusion. This work highlights the potential of corn straw biochar-montmorillonite composites as a favorable adsorbent for environment remediation and water treatment.