A Highly Stable Multifunctional Bi-Based MOF for Rapid Visual Detection of S2– and H2S Gas with High Proton Conductivity

Metal organic frameworks (MOFs) constructed with bismuth metal have not been widely reported, especially multifunctional Bi-MOFs. Therefore, developing multifunctional MOFs is of great significance due to the increasing requirements of materials. In this work, a 3D Bi-MOF (Bi-TCPE) with multifunctionality was successfully constructed, demonstrating high thermal stability, water stability, a porous structure, and strong blue fluorescence emission. We evaluated the properties of Bi-TCPE in detecting anions (S^2-, Cr₂O₇^2-, and CrO₄^2-) in aqueous solution, along with the rapid visual detection of H₂S gas and proton conduction. In terms of anion detection, Bi-TCPE achieved the rapid detection of trace S^2- in aqueous solutions, while the K_sv value was 1.224 × 10⁴ M^-1 with a limit of detection (LOD) value of 1.93 μM through titration experiments. Furthermore, Bi-TCPE could sensitively detect Cr₂O₇^2- and CrO₄^2-, with K_sv values of 1.144 × 10⁴ and 1.066 × 10⁴ M^-1, respectively, while LOD reached 2.07 and 2.18 μM. Subsequently, we conducted H₂S gas detection experiments, and the results indicated that Bi-TCPE could selectively detect H₂S gas at extremely low concentrations (2.08 ppm) and with a fast response time (<10 s). We also observed significant color changes under both UV light and sunlight. Therefore, we developed a H₂S detection test paper for the rapid visual detection of H₂S gas. Finally, we evaluated the proton conductivity of Bi-TCPE, and the experimental results showed that the proton conductivity of Bi-TCPE reached 4.77 × 10^-2 S·cm^-1 at 98% RH and 90 °C, achieving an excellent value for unmodified and encapsulated MOFs. In addition, Bi-TCPE showed high stability in proton conduction experiments (it remained stable after 21 consecutive days of testing and 12 cycles of testing), demonstrating relatively high application value. These results indicate that Bi-TCPE is a multifunctional MOF material with great application potential.