Studies on the Removal of Phenol and Nitrophenols from Water by Activated Carbon Developed from Demineralized Kraft Lignin

The present investigation deals with the importance of interaction and position of the nitro group in the adsorptive removal of 2-nitrophenol (2-NP), 4-nitrophenol (4-NP) and phenol by demineralized kraft lignin activated carbon (DKLAAC). The adsorption of phenol and NPs on DKLAAC was found to follow the order 2-NP > 4-NP > phenol. In this study, both solubility and donor–acceptor complex mechanism played an important role besides the porosity and surface area of the materials. Accordingly, the NP possessing the least solubility would noticeably exhibit a higher affinity to be adsorbed at the solid–liquid interface. Thus the highly hydrophobic 2-NP was adsorbed to a greater extent followed by 4-NP and phenol. Moreover, the adsorption capacity as affected by contact time, initial phenol concentration, pH, and temperature was also investigated. The experimental adsorption capacity by DKLAAC was 2.09, 2.34, and 2.20 mmol·g⁻¹ for phenol, 2-NP, and 4-NP at 25 °C, respectively, with the maximum amount being adsorbed within 40 min. The experimental data obtained for the removal of phenol and NPs were adequately fitted by the Langmuir adsorption isotherm and pseudo-second order kinetic models. Additionally, the temperature study revealed the adsorption process to be endothermic and spontaneous with high affinity between DKLAAC and phenols.