Valorization of Butia Endocarp via Hydrothermal Liquefaction: A Novel Activated Carbon for Emerging Contaminant Removal

This study investigates the valorization of hydrochar generated from the hydrothermal liquefaction of butia endocarp, an agro-industrial residue, as a precursor for activated carbon (AC) applied to the removal of the emerging contaminants paracetamol and 2,4-D from aqueous solutions. The hydrochar was activated with H₃PO₄ and subjected to pyrolysis, resulting in an AC with a predominantly mesoporous structure, amorphous character, high surface area (S _BET  = 1045 m ²  g⁻ ¹ ), and a total pore volume of 0.139 cm ³  g⁻ ¹ . Kinetic studies indicated rapid adsorption, with the General Order model providing the best fit, revealing distinct adsorption mechanisms for the contaminants. Paracetamol exhibited more complex kinetics (n ≈ 4.8), whereas 2,4-D showed behavior close to first-order kinetics (n ≈ 1). Equilibrium data were well described by the Sips isotherm, resulting in maximum adsorption capacities of 99.5 mg g⁻ ¹ for paracetamol and 116.0 mg g⁻ ¹ for 2,4-D under optimized conditions (pH 2 for paracetamol, natural pH for 2,4-D, adsorbent dosage of 1.5 g L⁻ ¹ , initial concentration of 200 mg L⁻ ¹ , contact time of 3 h, and 55 °C). Thermodynamic analysis demonstrated that adsorption is spontaneous (ΔG° < 0) and endothermic (ΔH° > 0), being favored by increased entropy (ΔS° > 0). The adsorbent exhibited high removal efficiency (> 90%) over a range of concentrations, good reusability, and satisfactory performance in a multicomponent effluent. These results indicate that AC derived from agro-industrial residues represents a sustainable and effective alternative for treating effluents containing emerging contaminants.