Reactive oxygen species (ROS), including hydroxyl radicals (·OH), superoxide (·O₂⁻), and singlet oxygen (¹O₂), are vital in biological, chemical, and environmental applications. Piezocatalysis, a process where vibrations induce polarization in materials, offers a novel method for ROS generation, especially promising in sonodynamic therapy due to its tissue penetration and ability for in situ ROS generation. However, existing piezoelectric materials like Barium Titanate (BaTiO₃), ZnO, BiFeO₃, and polyvinylidene fluoride (PVDF) suffer from low piezoelectric coefficients or safety/stability issues. Lead zirconate titanate (PZT), while exhibiting a higher coefficient, has environmental and health concerns. This research focuses on poly(tetrafluoroethylene) (PTFE), a chemically inert polymer, known for its piezoelectric properties, but traditionally requiring complex high-voltage polarization. The study hypothesizes that ultrasound can provide a simpler and more effective way to activate PTFE, creating a highly efficient and safe piezocatalyst for ROS generation.

Previous research has explored piezocatalysis using various materials, but limitations exist. While materials like BaTiO₃, ZnO, and BiFeO₃ have been investigated, their low piezoelectric coefficients hinder their efficiency. PZT, although more effective, raises environmental and health concerns due to its lead content. Organic polymers like PVDF show promise, but their piezoelectric coefficients are still relatively low. PTFE, while possessing high potential piezoelectric coefficients, requires complex, high-voltage polarization methods. The existing literature highlights a need for a simple and efficient method to activate PTFE's piezoelectric properties for ROS generation.

The study employed PTFE particles (1–5 µm) and investigated the use of ultrasound irradiation (60 kHz, 10 W) to induce polarization and create piezoelectric electrets. Piezoresponse force microscopy (PFM) was used to analyze the piezoelectric properties of the treated PTFE, comparing it to untreated PTFE and PVDF. Electron spin resonance (ESR) spectroscopy was used to quantify ROS generation (·OH, ·O₂⁻, ¹O₂) under ultrasonic irradiation. The efficiency of the ultrasonically activated PTFE electrets for ROS generation was compared to that of previously reported piezoelectric catalysts. The catalytic activity of the PTFE electrets was tested in different applications, including dye degradation and bacterial inactivation. Experiments included the degradation of various dyes (methylene orange, rhodamine B, 4-chlorophenol) and the inactivation of E. coli bacteria using ultrasonically activated PTFE electrets. The mechanisms of ROS generation were investigated through PFM and ESR, and the potential application of PTFE electrets in water purification and sonodynamic therapy was explored.

Ultrasonic irradiation effectively induced polarization in PTFE particles, creating piezoelectric electrets. PFM measurements showed a significant enhancement in piezoelectric response after ultrasonic treatment, with piezoelectric amplitude up to 23 times higher than that of PVDF. Ultrasonic irradiation of the PTFE electrets resulted in a significantly higher rate of ROS generation compared to previous piezoelectric catalysts. ESR spectroscopy confirmed the generation of ·OH, ·O₂⁻, and ¹O₂. The ultrasonically activated PTFE electrets showed high efficiency in degrading various dyes and inactivating E. coli bacteria. The results indicate that the ROS generation is a result of piezoelectric effects induced by ultrasound, and it does not require oxygen. The study demonstrated a 99.7% inactivation of E. coli bacteria within 15 minutes using a PTFE-coated beaker under ultrasound irradiation. Furthermore, the PTFE-based system successfully inactivated fungi (Candida) and MKN45 human gastric cancer cells. The use of a commercial ultrasound therapy device with PTFE electrets in a model system generated ROS levels comparable to other methods, suggesting potential application in sonodynamic therapy.

The findings address the research question by demonstrating a simple and effective method for activating the piezoelectric properties of PTFE and using it to generate ROS. The high ROS generation rate, coupled with the chemical inertness and biocompatibility of PTFE, makes this a promising approach for various applications. The significantly enhanced piezoelectric response compared to PVDF and other piezoelectric materials indicates a novel and efficient approach to piezocatalysis. The successful application in dye degradation and bacterial inactivation validates the potential of this technology in environmental remediation and water purification. The successful proof-of-concept for sonodynamic therapy suggests a possible alternative to existing sonosensitizers. The observed non-selective nature of ROS generation suggests broader applicability.

This study presents a novel and simple method for generating ROS using ultrasonically activated PTFE electrets. The method leverages the inherent piezoelectric properties of PTFE, which are activated by a mild and convenient ultrasound process. This results in a significant increase in ROS generation rates. The generated ROS showed high efficiency in environmental and biomedical applications, making this technology promising for water purification and sonodynamic therapy. Future research could focus on optimizing the ultrasonic parameters, exploring different PTFE morphologies (e.g., fibers), and conducting in vivo studies to assess the efficacy and safety of PTFE-based sonodynamic therapy.

The study primarily used laboratory-scale experiments. Further research is needed to evaluate the scalability and long-term stability of the PTFE electrets under real-world conditions. The in vivo studies were limited to a proof-of-concept model system, and more comprehensive investigations are needed to fully understand the potential of this method in sonodynamic therapy. The mechanism of PTFE polarization by ultrasound warrants further investigation.