Removal of diphenols using pine biochar. Kinetics, equilibrium, thermodynamics, and mechanism of uptake

Thermal pyrolysis synthesized activated biochar from the Pinus elliottii sawdust (PS) at 600° C. The obtained activated biochar (PB600) was used for the removal of three diphenols, catechol (CAT), resorcinol (RES), and hydroquinone (HYD), which are utilized mainly in different industries. The PB600 was characterized by several analytical techniques. The BET surface area of 1473 m².g⁻¹ and a total pore volume of 0.707 cm³ g⁻¹ was obtained. The functional groups and amount of acidic and basic groups on the biochar were determined by FTIR and Bohem titration, respectively. From the isotherm studies, it was obtained that the maximum adsorption capacities (Q_max) based on the Liu isotherm model were 419.8 (CAT 45 °C), 263.8 (RES 40 °C), and 500.9 mg g⁻¹ (HYD 25 °C). The values of thermodynamic parameters demonstrated that CAT, RES, and HYD adsorption processes were spontaneous, exothermic, and energetically favorable, and the magnitude of ΔH° was compatible with physisorption. The CAT, RES, and HYD adsorption mechanism onto the biochar is followed by porous filling, π-π interactions, and hydrogen bonds. Subsequently, PB600 biochar was employed as a potential adsorbent for treating simulated industrial effluents in a complex matrix simulating a real industrial effluent, and the overall removal attained up to 95.97 %. In concert with the experimental results, the electronic properties of the developed adsorption systems, including frontier molecular orbitals, charge density difference, and partial density of states, were studied by the density functional theory (DFT) approach to explore the mechanism of adsorption on the activated biochar surface.