Laccase-modified cornstalk pith for cleanup of spilled diesel oil

Repurposing corn stalk pith (CSP) from agriculture waste is significant for environmental protection and sustainability. In this work, enzymatic modification of inexpensive and biodegradable CSP was used to prepare two environmentally friendly and efficient oil sorbents by a one-step in situ strategy: (1) cellulose-grafted octadecylamine via the laccase (LAC)-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) system (LCSP) and (2) lignin-grafted octadecyl gallate via the LAC-guaiacol system (GCSP). The oil sorbents were characterized, revealing that they had low density, were hydrophobic (water contact angle (CA) up to 129.7°–144.9°), and had a good diesel sorption capacity in the range of 34–41 g/g, superior to those of most agricultural waste materials reported to date. The sorption kinetic results show that LCSP and GCSP fit a pseudo-second-order model. Sorption equilibrium was simulated by four commonly used isotherm models, and error analysis was performed, confirming that the Freundlich equation best fit the experimental data. Oil sorption was exothermic, with the best oil sorption performance achieved at room temperature. The sorption by the two sorbents of simulated low-concentration dispersed oil was similar, and the sorption by GCSP of high-concentration suspended oil was the best. The effects of solution pH, ion species, salinity, and temperature were also investigated. Overall, the obtained materials demonstrated outstanding environmentally friendly characteristics due to their high availability, agricultural origin and potential for use in remediating light oil spills owing to their fast sorption and high and stable sorption capacity.