Unlike other porous materials, metal-organic frameworks (MOFs) have special advantages like facile synthesis, which allow the fabrication of MOFs with tunable shapes and pore sizes. Owing to their excellent combination of properties, MOFs have increasingly become a popular material in different applications, including sensing, electrochemical catalysis, drug delivery, and sewage treatment. Nevertheless, the extremely low intrinsic conductivity of most MOFs hinders their application in electronic devices. This insulating property can be attributed to the insulating nature of the organic ligands and the poor overlap between the d orbitals of the metal ions and the π orbitals of organic ligands. To this end, enhancing the conductivity of MOFs has been the focus of the current scientific research.
While numerous strategies for improving the conductivity of MOFs have been proposed, most of them are based on selecting metal ions with high-energy valance electrons. Free pores also provide another way of modulating the electrical properties of nonconductive MOFs. In addition, MOFs are mostly prepared in powder form, which makes it difficult to integrate them with other electronic devices. Therefore, developing simple and effective strategies for preparing high-quality MOF thin films has also become an important research topic.
Among the available MOF materials, Cu3(BTC)2 is deemed suitable for different applications due to its high performance. Although numerous MOF films have been increasingly deposited on different rigid substrates, they fail to meet the requirements of high-performance flexible and smart electronic devices. Previous findings revealed that the conductivity of Cu3(BTC)2 thin films grown from solvents can be improved by enabling the interactions between the interactions with different guest molecules and could be the basis for addressing this inherent problem.
Inspired by the previous findings, a team of researchers from Shaanxi University of Science and Technology: Ms. Chongcai Sun, Professor Weike Wang, Ms. Xueyang Mu, Mr. Yifan Zhang, Mr. Chuang Ma, Mr. Jiankang Zhu and Professor Chengbing Wang proposed a feasible strategy for synthesizing flexible fabric-based Cu3(BTC)2 thin films with enhanced electrical conductivity. In their approach, the insulating polyester fabric was used as a flexible substrate to establish the electrical property of the flexible thin films, and a combination of atom layer deposition and layer-by-layer fabrication techniques were used to synthesize the Cu3(BTC)2 thin film. Most importantly, polypyrrole (PPy) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) redox guest molecules were utilized to improve and regulate the conductivity of the sample MOF thin film. The work is published in the journal, Advanced Materials Interfaces.
The researchers reported an improvement in the conductivity properties of both [email protected]3(BTC)2 and [email protected]3(BTC)2 films by at least four orders of magnitude than the original films. Based on the results of the SEM and XRD analysis of the as-synthesized samples, the authors confirmed that the modified Cu3(BTC)2 thin films retained their original morphology and crystal structure. The strong interaction between the framework and the guest molecules and their important role in improving the electrical conductivity of the films was further illustrated via Raman spectra, FT-IR and XPS. Furthermore, it was worth noting that the films could be fabricated at room temperature.
In summary, the authors reported the successful fabrication of flexible fabric-based Cu3(BTC)2 thin films at room temperature by combining polyester fabric and Cu3(BTC)2 thin films. The fabricated fabric-based Cu3(BTC)2 films exhibited excellent properties, including large-area lightweight, excellent flexibility and uniformity as well as controllable thickness. These properties, in addition to room temperature fabrication possibility, have expanded the application range of MOFs. In a statement to Advances in Engineering, the authors said that the study findings provided a new direction for fabricating highly conductive MOF films with expansive applications in the field of electrical industry, especially wearable and smart electronic devices.
Sun, C., Wang, W., Mu, X., Zhang, Y., Ma, C., Zhu, J., & Wang, C. (2022). Efficiently Regulating the Electrical Properties of Flexible Fabric-Based Cu3(BTC)2 Thin Film by Introducing Various Guest Molecules. Advanced Materials Interfaces, 9, 2101810.