Pine Cone biomass as an efficient precursor for the synthesis of activated biocarbon for adsorption of anionic dye from aqueous solution: Isotherm, kinetic, thermodynamic and regeneration studies

This study describes the synthesis of activated biocarbon from Pinus kesiya cone by ZnCl₂ activation and it's efficacy in the removal of Alizarin Red S (ARS) dye. The prepared biocarbon was characterized using Elemental analysis, Scanning Electron Microscopy (SEM), FT-IR spectroscopy, Brunauer-Emmett-Teller (BET) surface area analysis and zero point charge. BET surface area and total pore volume of the synthesized carbon was found to be 878.07 m² g⁻¹ and 0.412 cm³ g⁻¹ respectively. The impact of process parameters like adsorbent dosage, pH, initial concentration, and contact time were determined using batch experiments and an increase in adsorption capacity was observed with increase in the initial dye concentration, adsorbent dosage and contact time. The adsorption isotherm was well defined by Langmuir model with a maximum adsorption capacity of 118.06 mg g⁻¹. Pseudo-second order kinetics gave the best correlation value (R² > 0.99) reflecting the chemical nature of the adsorption process. Thermodynamic studies showed that adsorption was spontaneous (negative ∆G°) and endothermic in nature (positive ∆H°). Regeneration of spent carbon was also evaluated in order to assess the reusability which shows that the regenerated carbon can be used till the third cycle.