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<p>Sulfate is found in industrial and domestic effluents, causing damage to the environment, human health, and industries. This study investigated a new application to the Mg<sub>6</sub>Al<sub>2</sub>(CO<sub>3</sub>)(OH)<sub>16</sub>·4H<sub>2</sub>O layered double hydroxide (LDH) and chitosan composite on sulfate adsorption. Chitosan was synthesized using crustacean waste from southeastern Brazil. The composite was synthesized using the co-precipitation method with pH variation. The chitosan deacetylation degree (<i>DD%</i>) was 54.47%. We characterized the synthesized materials before and after the sulfate adsorption experiments using X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray (SEM–EDS) spectrometry, and Fourier transform infrared spectroscopy (FTIR). Based on the literature, the Mg<sub>6</sub>Al<sub>2</sub>(CO<sub>3</sub>)(OH)<sub>16</sub>·4H<sub>2</sub>O LDH and chitosan presented typical morphology and structure. The pH<sub>ZCP</sub> for the composite was 8.07, indicating that anion adsorption is favored at pH values lower than this point. The adsorption equilibrium is reached after 180&#xa0;min, with a maximum sulfate loading of 234.5&#xa0;mg&#xa0;L<sup>−1</sup>. Experimental data are fitted to pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Elovich models. Pseudo-first-order (<i>R</i><sup>2</sup> = 0.93) and pseudo-second-order (<i>R</i><sup>2</sup> = 0.91) models best described the adsorption kinetics. This suggests the possibility of a mixed mechanism of sulfate adsorption on the Mg<sub>6</sub>Al<sub>2</sub>(CO<sub>3</sub>)(OH)<sub>16</sub>·4H<sub>2</sub>O LDH and chitosan composite involving both physical and chemical adsorption. The Langmuir, Freundlich, Redlich–Peterson, and Toth isotherm models are used to understand the adsorption process. The Redlich–Peterson model (<i>R</i><sup>2</sup> = 0.96) presented the best result. In the Redlich–Peterson model, the parameter <i>β</i> was 0.84. Since it is close to 1, we can conclude that adsorption occurs in a monolayer, similar to the Langmuir model. Both LDH and chitosan, when used separately for sulfate adsorption, showed low levels of anion adsorption. However, when combined in a composite structure, we observed a synergistic effect, indicating the efficiency of the composite as an adsorbent for sulfate ions in this novel application.</p>

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Efficient adsorption of sulfate on a Mg6Al2(CO3)(OH)16·4H2O layered double hydroxide and chitosan composite synthesized from crustacean waste

  • 期刊论文

  • 发表日期：

    2025年2月13日

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  • Maria Luiza Gomes Soares Pessanha,
  • Otávio Barreto Pessanha,
  • Maria Luiza Monteiro Serafim,
  • Pedro Henrique Fonseca Rabelo,
  • Nathália Isidoro Ribeiro,
  • Damaris Guimarães

摘要

Sulfate is found in industrial and domestic effluents, causing damage to the environment, human health, and industries. This study investigated a new application to the Mg6Al2(CO3)(OH)16·4H2O layered double hydroxide (LDH) and chitosan composite on sulfate adsorption. Chitosan was synthesized using crustacean waste from southeastern Brazil. The composite was synthesized using the co-precipitation method with pH variation. The chitosan deacetylation degree (DD%) was 54.47%. We characterized the synthesized materials before and after the sulfate adsorption experiments using X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray (SEM–EDS) spectrometry, and Fourier transform infrared spectroscopy (FTIR). Based on the literature, the Mg6Al2(CO3)(OH)16·4H2O LDH and chitosan presented typical morphology and structure. The pHZCP for the composite was 8.07, indicating that anion adsorption is favored at pH values lower than this point. The adsorption equilibrium is reached after 180 min, with a maximum sulfate loading of 234.5 mg L−1. Experimental data are fitted to pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Elovich models. Pseudo-first-order (R2 = 0.93) and pseudo-second-order (R2 = 0.91) models best described the adsorption kinetics. This suggests the possibility of a mixed mechanism of sulfate adsorption on the Mg6Al2(CO3)(OH)16·4H2O LDH and chitosan composite involving both physical and chemical adsorption. The Langmuir, Freundlich, Redlich–Peterson, and Toth isotherm models are used to understand the adsorption process. The Redlich–Peterson model (R2 = 0.96) presented the best result. In the Redlich–Peterson model, the parameter β was 0.84. Since it is close to 1, we can conclude that adsorption occurs in a monolayer, similar to the Langmuir model. Both LDH and chitosan, when used separately for sulfate adsorption, showed low levels of anion adsorption. However, when combined in a composite structure, we observed a synergistic effect, indicating the efficiency of the composite as an adsorbent for sulfate ions in this novel application.