Nanoporous carbon adsorbents for water purification from phenol compounds

The purpose of the work is to compare the adsorption of phenol (P) and 4-chlorophenol (CP) by activated carbons (ACs) from coals and coking semi-products (CSPs). The ACs with specific surface SDFT = 1009–1547 m2/g were prepared by alkaline activation at a KOH/substrate ratio of 1 g/g (800 °С, 1 h). The characteristics of ACs porosity were calculated by nitrogen adsorption – desorption isotherms (–196 °С). The adsorption capacities for P (АP) and CP (АCP) were measured at 25 °C, АC dosage – 1 g/l and concentration 5 mmol/l. The specific adsorption capacities (АP(S), АCP(S)) and the initial adsorption rates of P (VP) and CP (VCP) for the first 5 minutes of adsorption were also determined. The coal and CSP type were established to determine the porosity and adsorption activity of ACs. Adsorption kinetics obeys the pseudo-second order model (R2 ≤ 0.996). The maximum capacities are AP(m) = 1.52–3.11 mmol/g and ACP(m) = 1.63–3.87 mmol/g. Initial rates are VP = 0.096–0.258 mmol/g·min and VCP = 0.107–0.607 mmol/g·min. With an SDFT increase, the values of AP(m) and ACP(m) increase linearly. It was found that the specific capacities, which are proportional to the surface concentration of adsorption centers (AdCs), decrease linearly with the SDFT growth for ACs from coals. The opposite trend was found for ACs from CSPs. All samples adsorb CP better than phenol in proportion of АCP(S) = 1.455·АP(S)–0.456 (R2 = 0.944). The AdCs concentration increase was found to increase the CP specific adsorption rate. The opposite effect is observed for phenol – an AdCs concentration increase decreases the rate probably due to decreasing the energy of the interaction of P with AdCs. The ACs from low-rank coals were shown to be the most active adsorbents. The SPCs also improve adsorption properties, which makes promising their use for ACs preparation.