Scientists from the TPU Research School of Chemistry & Biomedical Engineering, in collaboration with colleagues from China, have developed an innovative technology for creating materials for flexible and durable functional sensors based on metal-organic frameworks (MOFs). This technology involves laser processing of the frameworks, resulting in their transformation into luminescent nanocarbons. The resulting composite demonstrated excellent performance as flexible electrodes for temperature and bending sensors, possessing high mechanical strength.
The creation of multifunctional flexible sensors, such as temperature and pressure sensors, opens up new perspectives for their application in various fields — from transport and energy to medicine. However, traditional sensors often face difficulties in registering changes related to temperature, pressure, or deformation. TPU scientists have discovered that laser processing of MOFs — polymers actively being researched currently — can increase the luminescence signal by up to 70 times. By using the luminescence signal to measure temperature, it is possible to reliably distinguish between temperature changes and sensor deformation.
There are other methods for increasing MOF luminescence, but they usually require significant time investment and complex synthetic processes. The method proposed by TPU scientists for changing the luminescent properties of materials is simple to apply and allows transforming MOFs containing zinc and organic ligands into highly luminescent N-doped nanocarbons. The research was conducted under the guidance of Professor Evgeniya Sheremet from TPU and Professor Ranran Wang from the Shanghai Institute of Ceramics, Chinese Academy of Sciences.
As part of the project, scientists studied a specific type of MOF, called ZIF-8, and the processes occurring as a result of its laser processing. ZIF-8 metal-organic frameworks consist of zinc and organic molecules that self-assemble into crystalline structures. They possess useful properties such as a large surface area, controlled porosity, and a wide range of combinations of metal ions and organic ligands. TPU scientists conducted a series of experiments to determine the effect of continuous laser radiation on photoluminescence properties, applying metal-organic frameworks to various substrates and subjecting them to laser irradiation with varying pulse durations.
The research revealed an interesting effect: when ZIF-8 is irradiated with a laser, it is possible to obtain a material with very intense luminescence regardless of the type of substrate. This was achieved for the first time using a laser. During the study of the material's transformation, it was established that it turns into a nitrogen-doped nanocarbon and zinc oxide nanostructures. Furthermore, when using a flexible polyurethane film printed on a 3D printer, carbon integration into the substrate occurred, making the material electrically conductive and mechanically strong for flexible electronics.
The resulting composite combines the properties of biomechanical compliance, luminescence sensitivity to temperature, and resistance to repeated bending. Scientists also studied the possibility of using the composite for temperature and strain sensors. Luminescence proved to be sensitive to temperature, and electrical resistance to strain. At the same time, the material remains stable for 10 thousand bending cycles, which confirms the durability of the electrodes. This approach can be used to create temperature and bending sensors, where both signals can be measured independently.
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