Research progress on MOFs/fiber materials for resistive gas sensors

Metal-organic frameworks (MOFs) are a new class of organic–inorganic hybrid materials that show great potential for gas adsorption and storage. However, the powder form of these materials limits the range of their applications. Integration of MOFs on polymer fiber scaffolds to increase the contact area between these frameworks and target molecules and improve the performance of the resulting material is expected to provide new application prospects in gas adsorption, membrane separation, catalysis, and toxic gas sensing. Electrochemical sensors with good flexibility and high sensitivity and selectivity are needed in environmental detection, disease diagnosis, food safety, and other fields. Flexible resistance sensors are sensitive, low cost, and can be produced on a large scale; thus, these sensors have received extensive attention from researchers. Preparing flexible resistance sensors with high sensitivity, high stability, and good wearing comfort is a current and popular area of research. In this paper, we summarized the research and application of MOFs materials combined with metal oxides, textiles and carbon-based conductive fiber materials in the field of resistance gas sensors. Metal oxides act as a conductive material in resistance sensors bearing a metal oxide-and-MOF design. In this design, MOFs play two roles. First, MOFs can wrap precious metals and form nanoparticles encasing these precious metals when calcined. Here, the precious metal functions as a catalyst while the MOF is used as a dispersant to distribute the metal evenly on the surface of the sensing material. Second, the MOFs are combined with the metal oxide by in situ growth or doping on the metal oxide surface. The MOF surface has a large specific surface area and numerous active sites that can bind with the target gas. Resistance sensing is achieved by changing the electronic distribution within the sensing material. When textiles and MOFs are combined, the resulting resistive sensing materials must have a certain electrical conductivity. However, common MOF materials have poor electrical conductivity. Therefore, developing a conductive MOF material in which 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) and 2,3,6,7,10,11-hexaaminotriphenylene (HATP) show strong sensing performance for NO, H₂S, and H₂O is necessary. Carbon nanotube fibers and MOF materials can also be combined to obtain resistive sensor materials. Carbon nanotube materials are characterized by cross contact at the nanoscale and have good mechanical and electrical conductive properties. Thus, they feature certain advantages over other materials when applied to flexible resistive sensors.