Efficient Sequestration of Heavy Metal Cations by [Mo<sub>2</sub>S<sub>12</sub>]<sup>2−</sup> Intercalated Cobalt Aluminum-Layered Double Hydroxide
Heavy metal cations such as Ag<sup>+</sup>, Pb<sup>2+</sup>, and Hg<sup>2+</sup> can accumulate in living organisms, posing severe risks to biological systems, including humans. Therefore, removing heavy metal cations from wastewater is crucial before discharging...
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| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2025-02-01
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| Series: | Inorganics |
| Subjects: | |
| Online Access: | https://www.mdpi.com/2304-6740/13/2/50 |
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| Summary: | Heavy metal cations such as Ag<sup>+</sup>, Pb<sup>2+</sup>, and Hg<sup>2+</sup> can accumulate in living organisms, posing severe risks to biological systems, including humans. Therefore, removing heavy metal cations from wastewater is crucial before discharging them to the environment. However, trace levels and high-capacity removal of the heavy metals remain a critical challenge. This work demonstrates the synthesis and characterization of [Mo<sub>2</sub>S<sub>12</sub>]<sup>2−</sup> intercalated cobalt aluminum-layered double hydroxide, CoAl―Mo<sub>2</sub>S<sub>12</sub>―LDH (CoAl―Mo<sub>2</sub>S<sub>12</sub>), and its remarkable sorption properties for heavy metals. This material shows high efficiency for removing over 99.9% of Ag<sup>+</sup>, Cu<sup>2+</sup>, Hg<sup>2+</sup>, and Pb<sup>2+</sup> from 10 ppm aqueous solutions with a distribution constant, K<i><sub>d</sub></i>, as high as 10<sup>7</sup> mL/g. The selectivity order for removing these ions, determined from the mixed ion state experiment, was Pb<sup>2+</sup> < Cu<sup>2+</sup> ≪ Hg<sup>2+</sup> < Ag<sup>+</sup>. This study also suggests that CoAl―Mo<sub>2</sub>S<sub>12</sub> is not selective for Ni<sup>2+</sup>, Cd<sup>2+</sup>, and Zn<sup>2+</sup> cations. CoAl―Mo<sub>2</sub>S<sub>12</sub> is an efficient sorbent for Ag<sup>+</sup>, Cu<sup>2+</sup>, Hg<sup>2+</sup>, and Pb<sup>2+</sup> ions at pH~12, with the removal performance of both Ag<sup>+</sup> and Hg<sup>2+</sup> cations retaining > 99.7% across the pH range of ~2 to 12. Our study also shows that the CoAl―Mo<sub>2</sub>S<sub>12</sub> is a highly competent silver cation adsorbent exhibiting removal capacity (<i>q</i><sub>m</sub>) as high as ~918 mg/g compared with the reported data. A detailed mechanistic analysis of the post-treated solid samples with Ag<sup>+</sup>, Hg<sup>2+</sup>, and Pb<sup>2+</sup> reveals the formation of Ag<sub>2</sub>S, HgS, and PbMoO<sub>4</sub>, respectively, suggesting the precipitation reaction mechanism. |
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| ISSN: | 2304-6740 |