Sodium dodecyl sulfate intercalated and acrylamide anchored layered double hydroxides: A multifunctional adsorbent for highly efficient removal of Congo red

Abstract

In this study, a novel adsorbent was designed and synthesized via intercalation of sodium dodecyl sulfate (SDS) in the interlayer, and subsequent grafting of acrylamide (AM) on the layer of layered double hydroxides (LDH) (named as AM/SDS-LDH), and applied for congo red (CR) removal. The morphological structure, wettability and physicochemical properties of the adsorbents were thoroughly characterized using SEM, EDS, N₂-adsorption/desorption isotherm, static contact angle, XRD and FTIR. Results elucidated that SDS and AM were successfully introduced into the interlayer and onto the layer of LDH, respectively. Adsorption experimental results suggested that the maximum adsorption capacities of CR on SDS-LDH and AM/SDS-LDH at pH 5.0 and 293 K were 714.29 and 1118.78 mg/g, respectively, which were much higher than that of CR on LDH (588.24 mg/g). Based on the BET, XRD and FTIR analysis, the higher adsorption capacity of AM/SDS-LDH was mainly attributed to high surface area, large basal spacing as well as the abundant NH₂ groups. The experimental data can be well fitted by pseudo-second-order kinetic and Langmuir isotherm models. Thermodynamic parameters indicated the adsorption process was favorable under the higher temperature condition. The synergistic effect existed during the adsorption process of CR onto AM/SDS-LDH, including the electrostatic interactions, anion exchange and hydrophobic-hydrophobic interactions. Overall, this study provided a strategy for design and fabrication of highly efficient adsorbents.

Keywords: Acrylamide; Congo red adsorption; Interaction mechanism; Layered double hydroxides; Sodium dodecyl sulfate.