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<p>Congo red (CR) is a representative benzidine-based anionic azo dye with high toxicity, carcinogenicity, and poor biodegradability, posing substantial threats to human health and aquatic ecosystems. Therefore, its effective removal from wastewater remains a major environmental challenge. To address this, magnetic Fe<sub>3</sub>O<sub>4</sub>@SiO<sub>2</sub>@PPy-CTAB composite microspheres (PPy: polypyrrole; CTAB: cetyltrimethylammonium bromide) were fabricated using a hydrothermal technique in combination with surface modification and in-situ polymerization. The composite was systematically examined using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), vibrating sample magnetometry (VSM), and X-ray photoelectron spectroscopy (XPS), showing a well-defined core-shell framework, with a specific surface area (SSA) of 52.96 m<sup>2</sup>/g, a saturation magnetization of 42.8 emu·g<sup>− 1</sup>, and a positively charged surface as a result of CTAB modification. Under optimal conditions (pH = 5, Fe<sub>3</sub>O<sub>4</sub>:CTAB mass ratio = 1:1.5), the CR adsorption capacity reached a maximum of 612.68&#xa0;mg/g. Kinetic, isothermal, and thermodynamic analyses indicated that the adsorption process was best described by the pseudo-second-order kinetic model and the Langmuir isotherm model, suggesting a spontaneous, endothermic, and entropy-driven chemisorption process. The adsorption mechanism was primarily governed by electrostatic interactions, synergistic π-π stacking, and hydrogen bonding. After ten desorption-adsorption cycles, the adsorption capacity retained 87.1% of its initial adsorption capacity, demonstrating good reusability. The Fe<sub>3</sub>O<sub>4</sub>@SiO<sub>2</sub>@PPy-CTAB composite demonstrates high CR adsorption capacity (612.68&#xa0;mg/g) and good reusability (87.1% retention after 10 cycles), making it a promising candidate for magnetic separation-based dye wastewater treatment. However, the use of CTAB and organic solvents limits the designation as “green”, and real-world validation is needed before practical application.</p>

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Fabrication of core-shell structured Fe3O4@SiO2@PPy-CTAB magnetic microspheres for the effective adsorption of Congo red

  • 期刊论文

  • 发表日期：

    2026年8月3日

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  • Kai Wang,
  • Aiyuan Li,
  • Xiaoyan Zhou,
  • Shibeike Yu,
  • Bifen Chen,
  • Xiangdong Sun,
  • Chenyang Zhang

摘要

Congo red (CR) is a representative benzidine-based anionic azo dye with high toxicity, carcinogenicity, and poor biodegradability, posing substantial threats to human health and aquatic ecosystems. Therefore, its effective removal from wastewater remains a major environmental challenge. To address this, magnetic Fe3O4@SiO2@PPy-CTAB composite microspheres (PPy: polypyrrole; CTAB: cetyltrimethylammonium bromide) were fabricated using a hydrothermal technique in combination with surface modification and in-situ polymerization. The composite was systematically examined using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), vibrating sample magnetometry (VSM), and X-ray photoelectron spectroscopy (XPS), showing a well-defined core-shell framework, with a specific surface area (SSA) of 52.96 m2/g, a saturation magnetization of 42.8 emu·g− 1, and a positively charged surface as a result of CTAB modification. Under optimal conditions (pH = 5, Fe3O4:CTAB mass ratio = 1:1.5), the CR adsorption capacity reached a maximum of 612.68 mg/g. Kinetic, isothermal, and thermodynamic analyses indicated that the adsorption process was best described by the pseudo-second-order kinetic model and the Langmuir isotherm model, suggesting a spontaneous, endothermic, and entropy-driven chemisorption process. The adsorption mechanism was primarily governed by electrostatic interactions, synergistic π-π stacking, and hydrogen bonding. After ten desorption-adsorption cycles, the adsorption capacity retained 87.1% of its initial adsorption capacity, demonstrating good reusability. The Fe3O4@SiO2@PPy-CTAB composite demonstrates high CR adsorption capacity (612.68 mg/g) and good reusability (87.1% retention after 10 cycles), making it a promising candidate for magnetic separation-based dye wastewater treatment. However, the use of CTAB and organic solvents limits the designation as “green”, and real-world validation is needed before practical application.