Nanopore-filling effect of phenanthrene sorption on modified black carbon

Highlights: • Modification changed the nanoporosity and sorption behavior of black carbon. • The sorption affinity is higher for H₂O₂ oxidation than for other treatments. • Sorption affinity of phenanthrene is positively related to nanoporosity. • Nanopore-filling was the main mechanism for the sorption of phenanthrene. • The molecular sieve effect can affect the nanopore filling volumes. Black carbon was produced by slow pyrolysis under an oxygen-limited condition at 500 °C, and was modified by some chemical methods (oxidation, hydrolysis, activation, and surface recombination). The modified samples were characterized by using elemental analysis, Fourier transformed infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) surface analysis, Boehm titration, cation exchange capacity(CEC)analysis, CO₂ adsorption analysis, and then used to investigate the sorption behavior of phenanthrene. The results showed that the activation of ZnCl₂ gave a maximum nanopore volume of 96.5 μL/g and a specific surface area of 241 m²/g, while the oxidation of NaClO gave a minimum nanopore volume of 63.3 μL/g and a specific surface area of 158 m²/g. The FTIR, XPS, and Boehm titration analysis showed that the new oxygen-containing functional groups were introduced during the oxidation treatments of H₂O₂ and NaClO. The sorption of phenanthrene on all samples was typically nonlinear, and the nonlinear factor (n) was negatively correlated with V_o, especially with V_o at 0–1.1 nm. The sorption parameter (log K_OC) was positively correlated with nanopore volume (V_o) and specific surface area (SSA). Moreover, the model analysis showed that the nanopore filling was the main sorption mechanism, and molecular sieve effect was observed in the sorption of phenanthrene.