Insights into highly efficient piezocatalytic molecule oxygen activation over Bi2Fe4O9: Active sites and mechanism

Environmental remediation is the removal or reduction of environmental contaminants that pose a threat to human health or the environment. This can involve a variety of tasks, such as cleaning up contaminated sites, removing hazardous debris, treating contaminated soil or water, and restoring natural ecosystems. Traditional methods for environmental remediation can have inefficiencies in terms of energy consumption and efficacy. For instance, the capacity of the adsorbent and the availability of the contaminant to be adsorbed can limit adsorption. Photocatalysis, on the other hand, can necessitate UV light sources with high energies and may not be effective for specific types of pollutants. To address these challenges, energy-efficient and low-cost strategies are required.

Piezocatalytic activation of molecular oxygen (O₂) is a promising and energy-efficient strategy for environmental remediation. This method employs a piezocatalyst, which, when subjected to mechanical stress, can activate O₂ and generate reactive oxygen species (ROS) that can degrade pollutants. However, the piezocatalytic activity is not yet adequate, and its activation mechanism is poorly understood, which hinders its further development. Uncertainty regarding the activation mechanism of O₂ by piezocatalysts may contribute to this limitation.  Researchers are attempting to develop a deeper comprehension of the piezocatalytic mechanism and to identify ways to increase the process’s efficacy.

In a new study published in the peer-reviewed Chemical Engineering Journal, Dr. Chuanjian Su, Dr. Chaolin Li and led by Dr. Wenhui Wang from Harbin Institute of Technology along with Dr. Ruhong Li from Zhejiang University identified the active sites and mechanism of piezocatalytic molecular oxygen activation over Bi₂Fe₄O₉ to guide the development of more effective piezocatalysts and piezocatalysis-based advanced oxidation processes.

The authors synthesized novel Bi₂Fe₄O₉ piezocatalyst using a facile hydrothermal process and investigated the piezocatalytic efficacy of molecular oxygen activation over Bi₂Fe₄O₉ piezocatalyst for degradation of a model organic pollutant, sulfamethoxazole, under various conditions. They found that the degradation efficacy of sulfamethoxazole increased with increasing concentrations of Bi₂Fe₄O₉ piezocatalysts and mechanical force. They also overserved that the piezocatalytic degradation system has a reasonable high tolerance towards to the initial pH of the environment. Bi₂Fe₄O₉ piezocatalysts exhibited superior performance in terms of sulfamethoxazole degradation efficiency compared to other reported piezocatalysts. The active species and mechanism of piezocatalytic molecular oxygen activation over Bi₂Fe₄O₉ piezocatalyst were investigated using diverse techniques, including electron paramagnetic resonance spectroscopy, radical scavenger experiments, and density functional theory calculations. And it is found that O•− 2 generated via the molecular oxygen reduction reaction by piezo-electrons and the piezo-holes were confirmed as major active species for organic pollutants degradation. Further theoretical calculations and XPS analyses confirm the Fe²⁺ sites as active centers activate molecular oxygen into O•− 2 via donating the electrons to molecular oxygen and the piezo-electrons reduce Fe³⁺ to Fe²⁺.

The research on piezocatalytic activation of O₂ over Bi₂Fe₄O₉ had tremendous potential for use in environmental purification. In conclusion, Dr. Wenhui Wang and colleagues identified active centers of piezocatalytic O₂ activation at the atomic scale and the corresponding mechanism, which may serve as a guide for the development of more efficient piezocatalysts and piezocatalysis-based advanced oxidation processes. Therefore, this research paves the way for the creation of more energy-efficient and effective environmental remediation strategies.