Preparation of novel magnetic hydrotalcite-based adsorbents and their synergistic adsorption of dye molecules and heavy metal ions: Response surface methodology analysis and adsorption mechanisms investigation

In recent years, the discharge of dyestuff wastewater has caused great pollution to the environment. This study successfully prepared a novel magnetic layered double hydroxide (LDHs)-based adsorbent (Fe₃O₄@LDHs/PCA). This adsorbent was synthesized by intercalating a copolymer (PCA), formed from itaconic acid (IA) and β-cyclodextrin (β-CD), into the interlayers of the LDHs, achieving efficient removal of organic dyes from wastewater. Then, the intercalation structure and abundant functional groups of the adsorbent were analyzed by scanning electron microscopy (SEM), Fourier transmission infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). Subsequently, the adsorption of Fe₃O₄@LDHs/PCA on Congo red (CR) and methylene blue (MB) conformed to the pseudo-second order and Langmuir models, in which the theoretical maximum adsorption capacities were 493.45 ± 24.67 mg/g and 423.87 ± 21.19 mg/g, respectively. Afterwards, the response surface methodology was used to optimize the adsorption process and to obtain a theoretical formula for the maximum adsorption capacity. In addition, the demonstrated feasibility of the adsorbent for industrial applications was confirmed by real water sample experiments, recycle experiments and column adsorption experiments. Moreover, adsorption experiments with the binary systems of CR-Cu²⁺ and MB-Cr₂O₇^2- identified that Fe₃O₄@LDHs/PCA could treat both dyes and heavy metals within a complex environment. Finally, FT-IR and X-ray photoelectron spectroscopy (XPS) were used to analyze the adsorption behavior and adsorption mechanism of Fe₃O₄@LDHs/PCA on dye molecules. In summary, the prepared Fe₃O₄@LDHs/PCA was expected to be an emerging adsorbent for the elimination of mixed dyes from wastewater.