Enhanced Removal of Acetylsalicylic Acid Using Surfactant-Modified Natural Zeolites

Widely consumed because of its analgesic properties, acetylsalicylic acid and its metabolites are considered as emerging contaminants identified in several regional water sources. Although sophisticated removal techniques such as microbial-degradation and electrochemical-membrane approaches are explored, the search for simpler adsorbent technologies remains popular. In this study, surfactant-modified natural zeolites were developed, characterized, and investigated for its adsorption performance for acetylsalicylic acid. Surfactant-modification using Hexadecyltrimethylammonium-bromide (HDTMA-Br) and Dioctadecyldimethylammonium-bromide (DODA-Br) at 100 and 200 % of the External Cation Exchange Capacity were employed. Zeolite samples were characterized for their thermal, crystallographic, morphological, and physicochemical properties. EDX data, FTIR spectra, and Zeta Potential data confirmed surfactant modification on the surface of the zeolite. XRD showed that modifications did not alter the crystallinity of the zeolites after modification. Batch adsorption experiments were carried out to examine adsorption isotherms in aqueous solutions at pH ≈ 7.5. The linearity observed in Freundlich isotherm across all adsorbents suggests heterogenous surface adsorption sites of the base material. Bilayer-DODA-modified zeolites showed significantly promising sorption capacity for acetylsalicylic acid among all adsorbents due to anion exchange, electrostatic interaction, and hydrophobic interaction. This suggests the role of the bilayer and longer carbon chains in influencing adsorbent’s affinity towards acetylsalicylic acid. HIGHLIGHTS Successful Surfactant modification of Philippine Natural Zeolites. Enhanced sorption of Acetylsalicylic Acid. Exploration of One-tailed and Two-tailed cationic surfactants for monolayer and bilayer modification. GRAPHICAL ABSTRACT