Abstract <p>An innovative approach to providing a sustainable functionalization of biochar via amidation by mechanochemical route in the presence of octadecylamine is presented in this study. The proposed procedure is an attractive, cost-saving, and scalable alternative to the conventional approach meeting environmental sustainability expectations. The material obtained is widely characterized through spectroscopic and morphological techniques, confirming the presence of amide functional groups and ruling out simple amine sorption onto the carbon surface. As the long alkyl chains are introduced onto the biochar, an increase in hydrophobicity is induced, attributed to the exposure of hydrophobic groups and the increase in surface roughness, resulting in a new material for water-repellent coatings on hemp fibers. As a result of dip coating, the coated hemp fiber&#xa0;becomes hydrophobic with an angle contact value of 126° after a single deposition layer of biochar. Moreover, the biochar-coated hemp fibers showed a noticeable capacity (up to 1400%) to absorb several oils (frying, motor, pump, and sunflower) from an emulsion solution.</p> Graphical Abstract <p></p>