Enhancement of phenol adsorption on mesoporous carbon monolith modified by NaOH and NH3: equilibrium and kinetic studies

Carbon-coated monoliths (CCMs) were chemically modified by sodium hydroxide (NaOH) and ammonia aqueous solution (NH3) in order to enhance phenol adsorption. The adsorptive performance of phenol onto CCM-NaOH and CCM-NH3 was comparatively evaluated by batch mode. Experiments were carried out by varying pH, contact time, and initial adsorbate concentration. The optimum molarities for modification were 1.5M NaOH and 2M NH3 solutions. The basicity groups of modified CCM were 0.198 and 0.339 mmol g−1 for CCM-NaOH and CCM-NH3 by Boehm titration method, respectively. The presence of basic groups (O–H and NH3) was also confirmed by FT-IR. The studies showed optimum phenol adsorption, at pH 4 for both adsorbents. As compared to unmodified CCM, the CCM-NH3 and CCM-NaOH enhanced phenol uptake by 16.5 and 9.7%, respectively. The maximum equilibrium adsorption capacities were 51.29±0.7 mg g−1 for CCM-NaOH and 54.45±0.7 mg g−1 for CCM-NH3 in the range of concentration 50–350 mg L−1. The equilibrium adsorption data for CCM-NaOH and CCM-NH3 was fitted to both Langmuir and Freundlich models. Kinetic studies of both modified CCMs showed better applicability of pseudo-second-order kinetics model. The regeneration studies showed a 26% drop in adsorption capacity after four cycles for CCM-NH3.