Adsorption of alkylphenols by post-modified UiO-66: Adsorption characteristics and mechanism
This study focuses on the synthesis, characterization, and adsorption performance of a series of UiO-66-based materials for the adsorption of alkylphenols such as bisphenol A (BPA), 4-butylphenol (4-BP), and 4-pentylphenol (PP). The UiO-66 series, including UiO-66-NH 2 –50 %, mesoporous UiO-66 (HCl‑meso-UiO-66), and 4-pentylbenzoic acid-modified 4‑meso-UiO-66, were prepared through a combination of thermal and chemical modifications. Transmission electron microscopy analyses confirmed the successful creation of mesoporous structures, while FT-IR and XPS spectroscopy validated the chemical modifications. The adsorption performance was evaluated through kinetic and isotherm studies, employing pseudo-first-order and pseudo-second-order models as well as Langmuir and Freundlich isotherm models. The results indicated rapid initial adsorption rates, with equilibrium reached within 40 min. The pseudo-second-order model provided the best fit for the kinetic data, while the Freundlich model better described the adsorption behavior for 4-BP and PP, suggesting multilayer adsorption on heterogeneous sites. Thermodynamic studies indicated that 4-BP adsorption is endothermic and non-spontaneous, while BPA and PP adsorption exhibited exothermic and spontaneous characteristics. The study also explored the adsorption mechanisms, highlighting the importance of hydrophobic interactions and size-exclusion effect in the adsorption process. Hydrogen bonding and π-π stacking, although present, was not the primary determinant. The findings underscore the potential of 4‑meso-UiO-66, which exhibited the highest adsorption capacity, particularly for PP, driven by its enhanced pore accessibility, despite a smaller surface area compared to UiO-66-NH 2 –50 %, and hydrophobicity. This work provides valuable insights into the design of efficient adsorbents for alkylphenols enrichment and separation.
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