Piezoelectric-assisted BiVO₄ Photocatalytic Formaldehyde Degradation And Device Design

Formaldehyde as a typical indoor gas pollutant has the characteristics of low concentration and continuous release,and the widely used air filtration technology is not effective for its degradation.BiVO₄ is considered as an ideal oxide semiconductor photocatalyst due to its excellent light absorption and chemical stability.Nevertheless,its low conduction band position and short photogenerated carrier transmission make photogenerated carrier energetically deficient and photogenerated charge separation inefficient,leading to unfavorable photocatalytic activity and limiting the practical application in formaldehyde degradation.In this work,piezoelectric assisted optoelectronic devices are designed based on piezo-electrostatic field enhanced photocatalytic strategy and applied to formaldehyde degradation in indoor environment.The main contents of the thesis are as follows.（1）Construction and study of piezoelectric-assisted photocatalytic composite structures.The BVO-NWs/PDMS/PZT composite structures were successfully prepared by compounding（010）facet-exposed BiVO₄nanowires with PDMS-insulated piezo-substrate of piezoelectric transducer（PZT）through the template method and spin coating method.The relevant experiments and studies have proved that the PZT piezoelectric substrate generates electrostatic field under a certain stress,and the photocatalytic behavior of BiVO₄ nanowires can be influenced.The CO₂ reduction performance of the photocatalytic layer increased by 5.5 times and the formaldehyde degradation activity increased by 4.2 times under the effect of electrostatic field.It is mainly attributed to the electrostatic field potential gradient driving force for photogenerated carriers separation and transfer,and making the flat-band potential more negative.In addition,it is found that the negative electrostatic field enhances the adsorption energy of polar molecules on the photocatalysis surface,which is also essential for the activity of photocatalytic layer.The piezo-electrostatic field enhanced photocatalytic strategy is significant for improving the separation and transfer kinetics of photogenerated carriers.（2）The piezoelectric-assisted optoelectronic devices design and formaldehyde degradation application.The BVO-NWs/PDMS/PZT is combined with an exhaust fan blade to achieve the excitation of electrostatic field by the environmental force generated from the fan blade rotation.The electrostatic field testing and simulation demonstrate the positive relationship between rotational speed and transient force/deformation.The electrostatic field strength can reach-20 V at the highest rotational speed,and the fan blade rotational speed is the key factor to determine the electrostatic field strength.The formaldehyde degradation performance of the device was tested under actual confined space,and the results showed that the degradation rate of the device could reach 86%in 50 min at the concentration of 1.0 mg/m~3.The apparent quantum efficiency could reach 7.1%,and the purification efficiency was 1.626m~3/（W·h）considered as a high-efficiency purification device according to the national standard.The relevant experiments and DFT calculations have proved that superoxide radicals,hydroxyl radicals and photogenerated holes are the active substances in formaldehyde degradation,and formic acid as an intermediate product would be mineralized into carbon dioxide and water molecules eventually.The electrostatic field enhanced adsorption energy of formaldehyde on the surface of photocatalytic layer and decreased the potential barrier of degradation reaction,which improved the performance of photocatalysis significantly.This study provides a new universal strategy for photocatalytic performance enhancement and photogenerated carrier regulation.And it also provides a reference for the practical application of photocatalytic technology.