Two Dual-Function Zr/Hf-MOFs as High-Performance Proton Conductors and Amines Impedance Sensors

Abstract

In the field of sensing, finding high-performance amine molecular sensors has always been a challenging topic. Here, two highly stable 3D MOFs DUT-67(Hf) and DUT-67(Zr) with large specific surface areas and hierarchical pore structures were conveniently synthesized by solvothermal reaction of ZrCl 4 /HfCl 4 with a simple organic ligand, 2,5-thiophene dicarboxylic acid (H 2 TDC) according to literature approach. By analyzing TGA data, it was found that the two MOFs have defects (unsaturated metal sites) that can interact with substrates (H 2 O and volatile amine gas), which is conducive to proton transfer and amine compound identification. Further experiments showed that at 100 °C and 98% relative humidity (RH), the optimized proton conductivities of DUT-67(Zr) and DUT-67(Hf) can reach the high values of 2.98 × 10 −3 and 3.86 × 10 −3 S cm −1 , respectively. Moreover, the room temperature sensing characteristics of MOFs' to amine gases were evaluated at 68, 85 and 98% RHs, respectively. Impressively, the prepared MOFs-based sensors have the desired stability and higher sensitivity to amines. Under 68% RH, the detection limits of DUT-67(Zr) or DUT-67(Hf) for volatile amine gases were 0.5 (methylamine), 0.5 (dimethylamine) and 1 ppm (trimethylamine), and 0.5 (methylamine), 0.5 (dimethylamine) and 0.5 ppm (trimethylamine), respectively. As far as we know, this is the best performance of ammonia room temperature sensors in the past proton-conductive MOF sensors.

Syntheses and High Proton Conductivities of Two 3D Zr(IV)/Hf(IV)-MOFs from Furandicarboxylic Acid

“…We compared the proton conductivity of Zr and Hf-based organic frameworks of recent years (Table ). The performance of the obtained MOFs material is not as good as some MOFs reported in recent years, − but this MOF material is better than most other reported MOFs, ,,,,,− and the fact that it can reach 10 –3 order of magnitude without modification also indicates the great potential of this material. Moreover, there is also a phenomenon that Hf outperforms Zr in homogeneous MOFs in the table, which further confirms our speculation.…”

Design, Preparation, and High Intrinsic Proton Conductivity of Two Highly Stable Hydrazone-Linked Covalent Organic Frameworks

“…This also explains the complexity of the proton-conducting mechanism in crystalline solids. 3,59 Note that the σ of TpBth is moderately high compared to the intrinsic proton conductivity of the reported COFs (Table 1) 65−70 and has potential for application. We think that the most important point is that the number of COFs with intrinsic proton conduction in the literature is very limited, and it is necessary to develop COFs with high performance for future convenient applications.…”

“…The potential applications of crystalline porous materials such as metal–organic frameworks (MOFs), − hydrogen-bonded organic frameworks (HOFs), and covalent organic frameworks (COFs) − in the field of proton conductivity have drawn the extensive attention of researchers owing to their explicit structures and designability. The crystalline nature of these porous materials offers the possibility to explore the pathways and mechanisms of proton conduction compared to Nafion, an amorphous polymer that has been successfully applied commercially today.…”

Defect-containing metal–organic framework materials for sensor applications

“…Crystal sizes mildly influence response speed but profoundly affect it. Similarly, under the guidance of defect engineering, Kang and their colleagues 97 successfully synthesized highly stable 3D MOFs, namely DUT-67(Hf) and DUT-67(Zr), through a solvothermal reaction. These defect-rich MOFs demonstrated excellent proton conductivities and were employed as highly sensitive room temperature sensors for detecting ammonia.…”