Oxidized biochar obtained from pine needles as a novel adsorbent to remove caffeine from aqueous solutions

In this work, pine needles were used as a precursor to produced oxidized biochar (PNCO) in order to explore its adsorptive capability for caffeine (CAF) from aqueous media. The adsorption equilibrium was achieved in 150 min and the adsorption followed the pseudo-second order kinetic model. The increase of temperature from 298 K to 313 K enhanced the adsorption whereas with further raise of temperature up to 323 K, a decrease was noticed. Both Langmuir and Freundlich isotherm models fitted well the experimental adsorption data. The maximum monolayer adsorption capacity evaluated applying the Langmuir adsorption model was 5.35 mg/g, 6.54 mg/g and 6.26 mg/g, at 298, 313 and 323 K, respectively. The thermodynamic studies showed that the adsorption was endothermic and entropy-driven with increasing randomness in the solid/solution interface. Based on FTIR and ionic strength studies the adsorption of CAF by PNCO is mainly based on electrostatic interactions and the formation of outer-sphere complexes. Application of PNCO to real wastewater sample containing CAF, showed that the PNCO is capable to adsorb CAF with a removal capacity of 1.41 mg/g. (C) 2020 Elsevier B.V. All rights reserved.