Alkyl chain length of quaternized SBA-15 and solution conditions determine hydrophobic and electrostatic interactions for carbamazepine adsorption

• Published in: Scientific reports 2023-03, Vol.13 (1), p.5170-5170, Article 5170
• Main Authors: Kang, Jin-Kyu, Lee, Hyebin, Kim, Song-Bae, Bae, Hyokwan
• Format: Article
• Language: English
• Subjects: 704/172/169/895; 704/172/169/896; Adsorption; Ammonium; Carbamazepine; Electrostatic properties; Humanities and Social Sciences; Hydrophobicity; Ionic strength; Ions; multidisciplinary; pH effects; Science; Science (multidisciplinary); Silica; Water treatment
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-023-32108-3

Santa Barbara Amorphous-15 (SBA) is a stable and mesoporous silica material. Quaternized SBA-15 with alkyl chains (Q SBA ) exhibits electrostatic attraction for anionic molecules via the N + moiety of the ammonium group, whereas its alkyl chain length determines its hydrophobic interactions. In this study, Q SBA with different alkyl chain lengths were synthesized using the trimethyl, dimethyloctyl, and dimethyoctadecyl groups (C1Q SBA , C8Q SBA , and C18Q SBA , respectively). Carbamazepine (CBZ) is a widely prescribed pharmaceutical compound, but is difficult to remove using conventional water treatments. The CBZ adsorption characteristics of Q SBA were examined to determine its adsorption mechanism by changing the alkyl chain length and solution conditions (pH and ionic strength). A longer alkyl chain resulted in slower adsorption (up to 120 min), while the amount of CBZ adsorbed was higher for longer alkyl chains per unit mass of Q SBA at equilibrium. The maximum adsorption capacities of C1Q SBA , C8Q SBA , and C18Q SBA , were 3.14, 6.56, and 24.5 mg/g, respectively, as obtained using the Langmuir model. For the tested initial CBZ concentrations (2–100 mg/L), the adsorption capacity increased with increasing alkyl chain length. Because CBZ does not dissociate readily (pK a  = 13.9), stable hydrophobic adsorption was observed despite the changes in pH (0.41–0.92, 1.70–2.24, and 7.56–9.10 mg/g for C1Q SBA , C8Q SBA , and C18Q SBA , respectively); the exception was pH 2. Increasing the ionic strength from 0.1 to 100 mM enhanced the adsorption capacity of C18Q SBA from 9.27 ± 0.42 to 14.94 ± 0.17 mg/g because the hydrophobic interactions were increased while the electrostatic attraction of the N + was reduced. Thus, the ionic strength was a stronger control factor determining hydrophobic adsorption of CBZ than the solution pH. Based on the changes in hydrophobicity, which depends on the alkyl chain length, it was possible to enhance CBZ adsorption and investigate the adsorption mechanism in detail. Thus, this study aids the development of adsorbents suitable for pharmaceuticals with controlling molecular structure of QSBA and solution conditions.