In general photocatalytic reactions, the efficiency is often low due to the rapid recombination of photogenerated charge carriers. To address this issue, piezoelectric photocatalysis, which combines the properties of piezoelectricity and photocatalysis, exhibits superior performance in research fields such as water splitting and degradation of organic pollutants. The piezoelectric effect converts mechanical energy (such as wind, tides, water flow, etc.) into chemical energy to drive redox reactions on the surface of piezoelectric catalysts. The piezoelectric potential generated by the piezoelectric effect not only promotes the separation and transfer of charges but also modulates the energy of charge carriers, thereby thermodynamically promoting catalytic reactions.
The specific experimental process of piezoelectric catalysis varies depending on different research directions and types of piezoelectric materials. Here, we take the piezoelectric catalytic water splitting experiment conducted by Professor Manrong Li and Professor Mengye Wang's research group at Sun Yat-sen University as an example:
This experiment consists of three parts: the gas control part, the piezoelectric effect occurrence part, and the product detection part.
First, disperse the synthesized piezoelectric catalyst in a quartz glass reactor containing 30 mL of deionized water. Use a multi-gas atmosphere controller to vacuum and argon purge the quartz glass reactor containing the water suspension approximately 10 times to remove air from the reactor.
Then, place the quartz glass reactor in a 240 W, 68 kHz ultrasonic device, and maintain the reaction temperature at 25°C.
Finally, every 30 minutes, use a syringe to extract 0.4 μL of gas product, and analyze the hydrogen content through gas chromatography. Liquid product H₂O₂ is regularly taken out from the quartz glass reactor in 1 mL solution, centrifuged to remove the piezoelectric catalyst, and quantitatively analyzed using the N,N-diethyl-p-phenylenediamine (DPD)-peroxidase (POD) method.
From this example, it is known that the piezoelectric effect in the experiment is achieved by applying mechanical stress (ultrasound) to the piezoelectric material. Piezoelectric photocatalysis can be achieved by adding a light source to illuminate the sample in this system.
Figure 1: Piezoelectric Photocatalysis Example[2]
According to the experimental results in references [3,4], the catalyst shows significantly enhanced photocatalytic efficiency when mechanical stress (ultrasound) and light are applied simultaneously. The enhancement mechanism is due to the action of mechanical stress (ultrasound), which forms a polarized dipole layer in the piezoelectric photocatalytic material, generating an internal electric field. Under light conditions, photogenerated electrons and holes move in opposite directions under the driving force of the internal electric field, effectively separating and enhancing catalytic performance. The application of ultrasound periodically changes the polarization direction, preventing the piezoelectric polarization charges from recombining with the carriers in the electrolyte, thus providing the driving force to promote charge separation and transfer.
Figure 2: Piezoelectric Photocatalysis Mechanism Schematic[4]
There are many factors that affect the piezoelectric effect, such as piezoelectric material properties, ultrasound power intensity, reaction time, pH value, and design of piezoelectric catalysis reactor. The piezoelectric coefficient of piezoelectric materials has a significant impact on the piezoelectric efficiency. Excellent performance materials can produce a stronger electric field under mechanical stress to promote charge separation and transfer. The mechanical stress induced by ultrasound can induce periodic piezoelectric polarization of the piezoelectric catalyst, which helps to adsorb and desorb charges externally, maintain the driving force of the piezoelectric field, and achieve continuous redox reactions. Among them, the design of the piezoelectric catalysis reactor is particularly important, and reasonable reactor design should meet the following conditions:
Optimize the internal physical conditions of the reactor, such as temperature, pressure, and mass transfer, to improve the activity and selectivity of the catalyst;
Ensure sufficient contact between the catalyst and reactants based on the distribution, shape, and size of the catalyst to increase the reaction rate;
Choose stable and durable materials to ensure long-term reliability, as the reactor may encounter mechanical stress and chemical corrosion during operation;
Consider the scalability of the reactor from laboratory to industrial scale, including reactor size, material cost, and manufacturing process;
Include effective monitoring and control systems to precisely control operating conditions such as temperature, pH, and reactant concentration to ensure the reaction proceeds under optimal conditions.
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In Conclusion:
Piezoelectric phot (piezoelectric) o catalysis as a technology combining piezoelectric effect and photocatalysis, will demonstrate great potential in fields such as energy conversion, environmental governance, and biomedicine by exploring the optimal mechanical stress and piezoelectric photocatalytic materials.
Regarding the interpretation of the literature section, it is only a translation and summary by the author based on the reference literature. If there are any errors, please correct them! This article is for academic sharing only. If there is any infringement, please contact the backstage for deletion.
