Alginate beads impregnated with sulfonate containing calix[4]arene-intercalated layered double hydroxides: In situ preparation, characterization and methylene blue adsorption studies

Abstract

The present research describes the in situ preparation of novel alginate nanocomposite beads impregnated with unmodified MgAl-NO₃ layered double hydroxide (LDH) and a sulfonate containing calix[4]arene-intercalated LDH (SuLDH). The effect of intercalation of LDH on the methylene blue adsorption efficiency of Alg/SuLDH beads was investigated and compared with Alg/LDH and pure alginate beads (Alg). The prepared beads were characterized by FTIR, XRD, TGA, SEM, BET, and swelling ratio analysis. Among samples, the Alg/SuLDH beads showed the highest thermal stability, crystallinity, water swelling ratio, and specific surface area. In addition, based on the batch adsorption studies, Alg/SuLDH beads exhibited higher adsorption efficiency compared to Alg/LDH and Alg beads. The obtained equilibrium adsorption data were modeled by the Langmuir and Freundlich adsorption isotherm models. Regarding the Langmuir model, the maximum adsorption capacity of Alg beads, Alg/LDH, and Alg/SuLDH nanocomposite beads was obtained 540.54, 598.80, and 653.59.36 mg/g, respectively. The kinetic adsorption studies also demonstrated that the adsorption of MB by all samples well obey the pseudo-second-order kinetic model. This study proposes the Alg/SuLDH beads as a highly developed adsorbent for removal of MB from wastewaters. The reusability experiments showed that the Alg/SuLDH beads retained 72.55% of initial activity after 5 cycles.

Keywords: Alginate beads; Calix[4]arenes; Intercalation; Layered double hydroxides; Methylene blue.