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Kₓ[Bi₄–ₓMnₓS₆], Design of a Highly Selective Ion Exchange Material and Direct Gap 2D Semiconductor
- Wang, Ruiqi, Chen, Haijie, Xiao, Yi, Hadar, Ido, Bu, Kejun, Zhang, Xian, Pan, Jie, Gu, Yuhao, Guo, Zhongnan, Huang, Fuqiang, Kanatzidis, Mercouri G.
- Journal of the American Chemical Society 2019 v.141 no.42 pp. 16903-16914
- adsorbents, adsorption, cadmium, cations, cesium, chromium, heavy metals, ion exchange, lead, manganese, metal ions, pH, potassium, remediation, rubidium, semiconductors, slabs, spectroscopy, strontium, sulfides, temperature, wastewater, water purification, zinc
- Layered sulfides with high selectivity for binding heavy metal ions and radionuclide ions are promising materials in effluent treatment and water purification. Here we present a rationally designed layered sulfide Kₓ[Bi₄–ₓMnₓS₆] (x = 1.28) deriving from the Bi₂Se₃-structure type by targeted substitution to generate quintuple [Bi₄–ₓMnₓS₆]ˣ⁻ layers and K⁺ cations between them. The material has dual functionality: it is an attractive semiconductor with a bandgap of 1.40 eV and also an environmental remediation ion-exchange material. The compound is paramagnetic, and optical adsorption spectroscopy and DFT electronic structure calculations reveal that it possesses a direct band gap and a work function of 5.26 eV. The K⁺ ions exchange readily with alkali or alkaline-earth ions (Rb⁺, Cs⁺, and Sr²⁺) or soft ions (Pb²⁺, Cd²⁺, Cr³⁺, and Zn²⁺). Furthermore, when the K⁺ ions are depleted the Mn²⁺ ions in the Bi₂Se₃-type slabs can also be replaced by soft ions, achieving large adsorption capacities. The ion exchange reactions of Kₓ[Bi₄–ₓMnₓS₆] can be used to create new materials of the type Mₓ[Bi₄–ₓMnₓS₆] in a low temperature kinetically controlled manner with significantly different electronic structures. The Kₓ[Bi₄–ₓMnₓS₆] (x = 1.28) exhibits efficient capture of Cd²⁺ and Pb²⁺ ions with high distribution coefficient, Kd (10⁷ mL/g), and exchange capacities of 221.2 and 342.4 mg/g, respectively. The material exhibits excellent capacities even in high concentration of competitive ions and over a broad pH range (2.5–11.0). The results highlight the promise of the Kₓ[Bi₄–ₓMnₓS₆] (x = 1.28) phase to serve not only as a highly selective adsorbent for industrial and nuclear wastewater but also as a magnetic 2D semiconductor for optoelectronic applications.