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<p>Selenium (Se, IV) poses a severe threat to human health and ecological security; hence, the exploration of high-performance adsorbents for the removal of Se(IV) remains essential. Aiming at Se(IV) adsorption, the open metal sites have shown the potential possibility, especially for the Zr-based MOFs (Zr-MOFs) with excellent stability. Nonetheless, how to effectively build the open metal sites still keep great challenge. In this work, by using the strategy of coordination competition with the competing ligand of HCOOH, a 4-connected Zr-MOF (<b>HNU-88</b>) has been synthesized by the assembling of the zwitterionic ligand 1,3-bis(3,5-dicarboxyphenyl)-1H-imidazole-3-onium chloride (H<sub>4</sub>L<sup>+</sup>Cl<sup>−</sup>) and Zr<sup>4+</sup>. Different from the saturated 12-connetion of the Zr<sub>6</sub> cluster, the remaining binding sites in the <b>HNU-88</b> crystal structure are coordinated by the formic acid and water molecules. Benefiting from the open metal sites in the 4-connected Zr<sub>6</sub> cluster, <b>HNU-88</b> showed good adsorption of Se(IV) with maximum adsorption amounts of 450.56 mg/g. Based on sufficient data of Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS), corroborated by electrostatic potential (ESP) surface and natural population analysis (NPA) calculations, the adsorption site of Se(IV) was confirmed to be on a Zr atom with open metal sites. Interestingly, a metal-organic gel (<b>HNU-G8</b>) with lots of Zr clusters was obtained during the formation of <b>HNU-88</b>, which strikingly reduces the adsorption equilibrium time while maintaining a high adsorption capacity of 284.92 mg/g for SeO<Stack> <sub>3</sub> <sup>2−</sup> </Stack>. The adsorption kinetics of <b>HNU-G8</b> showed that equilibrium was achieved within 3 h, and the trace Se(IV) can be reduced to less than 10 ppb in 30 min, which can be attributed to exposing the more open metal sites of Zr-based clusters. This work provides a new design strategy for the construction of low coordination Zr-MOFs and new materials for the treatment of Se(IV) pollution in the water environment.</p>

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Unlocking open metal sites in Zr-MOF/MOG for efficient and rapid Se(IV) adsorption

  • 期刊论文

  • 发表日期：

    2026年6月22日

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  • Qi Zhou,
  • Guojian Ren,
  • Xiaolong Gong,
  • Nana Ma,
  • Linglong Yi,
  • Qinhe Pan

摘要

Selenium (Se, IV) poses a severe threat to human health and ecological security; hence, the exploration of high-performance adsorbents for the removal of Se(IV) remains essential. Aiming at Se(IV) adsorption, the open metal sites have shown the potential possibility, especially for the Zr-based MOFs (Zr-MOFs) with excellent stability. Nonetheless, how to effectively build the open metal sites still keep great challenge. In this work, by using the strategy of coordination competition with the competing ligand of HCOOH, a 4-connected Zr-MOF (HNU-88) has been synthesized by the assembling of the zwitterionic ligand 1,3-bis(3,5-dicarboxyphenyl)-1H-imidazole-3-onium chloride (H4L+Cl−) and Zr4+. Different from the saturated 12-connetion of the Zr6 cluster, the remaining binding sites in the HNU-88 crystal structure are coordinated by the formic acid and water molecules. Benefiting from the open metal sites in the 4-connected Zr6 cluster, HNU-88 showed good adsorption of Se(IV) with maximum adsorption amounts of 450.56 mg/g. Based on sufficient data of Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS), corroborated by electrostatic potential (ESP) surface and natural population analysis (NPA) calculations, the adsorption site of Se(IV) was confirmed to be on a Zr atom with open metal sites. Interestingly, a metal-organic gel (HNU-G8) with lots of Zr clusters was obtained during the formation of HNU-88, which strikingly reduces the adsorption equilibrium time while maintaining a high adsorption capacity of 284.92 mg/g for SeO 3 2− . The adsorption kinetics of HNU-G8 showed that equilibrium was achieved within 3 h, and the trace Se(IV) can be reduced to less than 10 ppb in 30 min, which can be attributed to exposing the more open metal sites of Zr-based clusters. This work provides a new design strategy for the construction of low coordination Zr-MOFs and new materials for the treatment of Se(IV) pollution in the water environment.