A combined experimental and theoretical investigation of the adsorption of 4-Nitrophenol on activated biocarbon using DFT method

Porous activated biocarbon from Ravenna grass was utilized as an adsorbent for the removal of 4-Nitrophenol from aqueous solution. Chemical activation process using potassium hydroxide was adopted for the activated biocarbon preparation. The essential features of the prepared adsorbent represented by BET surface area, pore volume and pH_ZPC were 919 m²g⁻¹, 0.324 cm³g⁻¹ and 8.1 respectively. SEM, FTIR, XRD and TGA analysis revealed the microcrystallite and porous structure of the synthesized biocarbon with abundant functional groups and high thermal stability. Batch adsorption tests were conducted for 4-Nitrophenol adsorption, and the optimum adsorbent dose, pH, initial 4-Nitrophenol concentration and contact time were found to be 0.5 g, 7, 400 mgL⁻¹ and 40 minutes, respectively. The equilibrium isotherm study revealed the suitability of the Langmuir isotherm with a maximum adsorption capacity of 50.89 mg/g. The pseudo-second-order kinetic model well represented the adsorption kinetics data, while thermodynamics study indicated the spontaneity (ΔG<0) and endothermic nature (ΔH>0) of the adsorption of 4-Nitrophenol. Density functional theory (DFT) calculations performed at the B3LYP level indicated that the interaction of 4-Nitrophenol with pristine and functionalized activated biocarbon is favorable.