Hong-Xia Liang #; Wei-Hong Zhang #; Guo-Tong Du; Ruijuan Wen; Ya-Nan Ma; Haonan Peng; Dong-Xu Xue * ; Yu Fang. Precis. Chem., 2026, DOI: https://doi.org/10.1021/prechem.6c00085

As a core fundamental feedstock in the petrochemical industry, the C₂ mixed gas obtained from industrial steam cracking contains acetylene and ethane impurities alongside ethylene. Conventional separation processes rely on cryogenic distillation, which incurs high energy consumption. Achieving one-step direct production of polymer‑grade ethylene from the ternary acetylene/ethane/ethylene mixture represents a major challenge in chemical separation. Meanwhile, nerve agents are highly toxic chemical warfare agents that pose severe threats to both public and national security. Developing sensing materials capable of rapid, sensitive, and on‑site real‑time detection of nerve agents is of significant practical importance. Fluorescence sensing, owing to its fast response and portability, is a promising technique for trace‐level toxin screening. To address these issues, this work employs the zigzag dicarboxylate ligand 4,4′‑bipyridine‑4,4′‑dicarboxylic acid (4,4′‑H₂BPyDC) and uses 2‑fluorobenzoic acid as a modulator to construct a series of isostructural rare‑earth metal–organic frameworks with fcu topology under solvothermal conditions.

Gas separation tests show that fcu‑4,4′‑BPyDC‑Yb/Y exhibit significantly higher adsorption capacities for acetylene and ethane than for ethylene, enabling the simultaneous removal of acetylene and ethane from the ternary C₂H₂/C₂H₆/C₂H₄ mixture and thus achieving one‑step ethylene purification. Mixed‑gas breakthrough experiments, ideal adsorbed solution theory (IAST) selectivity calculations, and grand canonical Monte Carlo (GCMC) simulations corroborate the separation performance. The materials feature moderate adsorption enthalpies, allowing regeneration under mild conditions, and retain stable separation efficiency after multiple cycles. In terms of sensing, fcu‑4,4′‑BPyDC‑Eu exhibits a fluorescence turn‑on response toward diethyl chlorophosphate (DCP), a simulant of nerve agents. A gas‑phase sensing film fabricated from this material shows a response time of merely 5 s and a gas‑phase detection limit as low as 3.2 ppb, together with high selectivity and reversible recyclability. Combined characterization by PXRD, FT‑IR, XPS, NMR, and phosphorus spectroscopy on the gadolinium‑based isostructural MOF elucidates the sensing mechanism: DCP induces protonation of the pyridyl nitrogen atoms on the ligand, which modulates the triplet‑state energy level of the ligand, optimizes the energy‑level matching for antenna effect toward Eu³⁺, and suppresses non‑radiative transitions, ultimately producing the fluorescence turn‑on signal.

In summary, this work successfully establishes a platform of fcu‑type rare‑earth MOFs based on a zigzag dicarboxylate ligand, integrating efficient light‑hydrocarbon separation and highly sensitive fluorescent toxin detection within a single isoreticular material platform. This provides new insights into the structural design and application development of multifunctional rare‑earth MOFs.

Figure 1. Structural assembly and pore architecture of fcu‑4,4'-BPyDC-Yb/Y (a) Schematic illustration for the assembly of inorganic Y/Yb cluster nodes and organic 4,4'-BPyDC ligands, (b) Pore sizes of the two types of cages in fcu4,4'-BPyDC-Yb/Y, (c) Sizes of the corresponding triangular windows.

Figure 2. fcu-4,4'-BPyDC-Yb/Y: (a) N₂ sorption isotherms at 77 K; (b) pore size distribution; (c) C₂ gas sorption isotherms at 298 K; (d) Q_st of C₂ gases; (e) IAST selectivity for C₂H₂/C₂H₄ (50/50, v/v) and C₂H₆/C₂H₄ (50/50, 10/90, v/v) at 298 K and 1 bar; and (f) five cyclic breakthrough test curves for C₂H₂/C₂H₆/C₂H₄ (1:1:1) mixture.

Figure 3. (a) Schematic diagram of the sensing system. (b) Sensor response intensities at various DCP concentrations, showing a linear relationship from 0.5 to 1.1 ppm (n = 5). (c) Kinetic response curve of the film to DCP vapor. (d) Selectivity testing experiments of the film for DCP vapors containing 15 interferents were performed. (e) Reproducibility of film for DCP detection.

Figure 4. (a) Proposed mechanism of binding of 4,4'-H₂BPyDC to DCP. (b) ¹H NMR spectra of 4,4'-H₂BPyDC in the absence/presence of DCP. (c) FT-IR spectra of the fcu-4,4’-BPyDC-Eu before and after DCP treatment. (d) N 1s XPS spectrum of fcu-4,4'-BPyDC-Eu before and after DCP treatment. (e) Low-temperature phosphorescence spectrum of fcu-4,4'-BPyDC-Gd before and after DCP treatment. (f) Schematic representation of the energy levels of 4,4'-H₂BPyDC and Eu(Ⅲ).

First Authors: Liang Hongxia and Zhang Weihong, master’s students, Shaanxi Normal University

Correspondence Author: Prof. Xue Dongxu, Shaanxi Normal University

Full Text Link: https://doi.org/10.1021/prechem.6c00085