Engineering spherical lead zirconate titanate to explore the essence of piezo-catalysis

doi:10.1016/j.nanoen.2017.08.058

Nano Energy

Volume 40, October 2017, Pages 481-486

https://doi.org/10.1016/j.nanoen.2017.08.058 Get rights and content

Highlights

•
The piezoelectricity of PZT is important than the morphology during piezo-catalysis.
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The free charges in PZT produce oxidized active species on piezoelectric material.
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Active species decompose dye molecules into carbon dioxide and water.

Abstract

Piezo-catalysis induced by piezoelectric polarization has been proven to be a powerful technology for potential applications in the energy and environment. It is generally accepted that piezo-catalysis derived the easily deformation from the piezoelectric materials with one or two dimensions. In this study, piezoelectric materials lead zirconate titanate (PZT) with a spherical morphology was synthesized, which is used to explore whether the widely accepted principle that is one or two-dimensional structure is necessary in the piezo-catalysis process is exclusive. We would like to clarify the relationship between deformation and piezoelectric catalytic performance. In addition, a key fundamental problem that has not yet been fully solved whether the charges of the reaction are from polarized charges or free charges. We investigate the role of polarization charges and free charges in piezoelectric catalysis by doping the piezoelectric material. It is hoped that the study of this work will re-understand and explain the mechanism of piezoelectric catalytic reaction.

Graphical abstract

Introduction

The piezoelectric effect induced by piezoelectric polarization has been widely applied in nanogenerators, piezoelectric field effect transistors and flexible self-powered systems [1], [2], [3], [4], [5]. Recently, the piezoelectric catalysis in environmental purification and hydrogen generation by water splitting has attracted much attention [6], [7], [8], [9], [10], [11]. It is widely accepted that the driving force of piezoelectric catalysis comes from the charge separation caused by the deformation induced by mechanical energy (local vibration) [12], [13], [14].

Currently, the piezoelectric catalytic research is mainly focused on one-dimensional (1D) or two-dimensional (2D) piezoelectric/ferroelectric materials, such as BaTiO₃ rod-like structure, ZnO nanorods, single and few-layers MoS₂ nanoflowers. For instance, Hong et.al reported the piezoelectrochemical water splitting and oxidation of azo dye molecules using BaTiO₃ microdendrites under ultrasonic vibrations [15], [16]. Lv et.al reported the degradation of organic pollutants by using BaTiO₃ coral branches under ultrasonic vibrations and collaboration with Fenton process [7]. Wu et al. reported the piezo-catalyst effect of single and few layers MoS₂ nanoflowers which exhibited an ultra-high degradation activity by introducing the ultrasonic wave in the dark [9]. The general mechanism of the piezoelectric catalytic reaction is that when the 1D or 2D piezoelectric material was mechanically vibrated, the opposite polarity of charges were generated on the spatially opposite sides of the lateral or top/bottom of 1D or 2D piezoelectric materials, thus forming a piezoelectric field [13]. Due to the flexible nature, 1D or 2D nano-materials were tend to bent by mechanical forces. Many of the literatures reported this phenomenon which were recorded by in-situ transmission electron microscopy and atomic force microscopy [17], [18]. This potential can induce the water molecules or dye molecules adsorbed on the piezoelectric material undergoing a redox reaction by electron transfer in the wet chemical environment [15]. The charges induced by the piezoelectric process resulted the water splitting or degradation of the dye molecules which was similar to the direct photocatalytic reaction mechanism [16]. However, polarization charges are different from the free state of the photo-generated electron-hole pairs in the photocatalytic reaction [19], [20]. Its formation is due to the superposition of dipole moment caused by relative displacement of positive and negative charge centers under the action of external forces and it cannot migrate [21], [22]. Therefore, we are interested in how the piezoelectric catalytic reaction process is generated, and whether the enough deformation of low-dimensional piezoelectric materials is necessary for the occurrence of piezoelectric catalytic reaction.

In this article, we designed and prepared a kind of lead zirconate titanate (PbZr_xTi_1−xO₃ (PZT)) material which is a well investigated piezoelectric material and widely used in ultrasonic transducers and piezoelectric resonators [23], [24]. The free charges in the PZT material is obtained by doping narrow band gap semiconductor bismuth ferrite (BFO) via solid reaction process [25]. The samples have a spherical structure without a flexible feature and its elastic deformation is also very small [26], [27]. In order to compare the performance of the PZT samples, the degradation of dye molecules Rhodamine B (RhB) were used as probes to study the piezoelectric catalytic reaction process in solution phase under stirring. The experimental results show that the stirring speed and the doping process have a significant effect on the catalytic reaction. Therefore, it is hoped that our work could understand the readership between the structure and piezoelectric catalytic performance of the sample. Furthermore, we can clear the mechanism of the role of polarization charges and free charges in piezoelectric catalysis.

Section snippets

Synthesis of PZT materials

The Zr-rich PZT doped with Bismuth ferric (BF) was prepared by a conventional solid-state reaction method [25]. Raw chemicals including ethanol, Pb₃O₄, ZrO₂, TiO₂, Bi₂O₃, Fe₂O₃ (AR) were purchased from Sinoreagent and used without further purification. The powders of Pb₃O₄, ZrO₂, TiO₂, Bi₂O₃ and Fe₂O₃ (molar rate of Pb: Zr: Ti: Bi: Fe = 100: 97: 3: 10: 10) were mixed and grinding with a planetary ball mill for 6 h with the presence of ethanol. The mixtures were pressed into a cylinder with a few

Results and discussion

The XRD patterns of PZT catalysts show strong characteristic diffraction peaks ascribing to rhombohedral phase of PZT (JCPDS, No. 89-8012) (Fig. 1a). There is no obvious diffraction peak of BFO in PZT-1 sample which is mainly due to the low doping content and high dispersion of Bi and Fe elements. In comparison with the diffraction peaks of PZT-1 and PZT-2, the doping of Bi and Fe elements has no effect on the crystal structure of the PZT crystal phase. Meanwhile, it can be seen that the PZT-3

Conclusions

In summary, three types of ferroelectric PZT were prepared and their catalytic degradation activity were investigate to explore the process of piezo-catalysis. The sample of PZT-1 can achieve deep mineralization of organic dyes by water flow. The degradation efficiency of RhB gradually increased from 10% (200 rpm) to 37% (900 rpm) with the increase of the stirring rate within 30 min. Furthermore, the spherical structure of the PZT-1 can produce piezoelectric catalytic activity which indicates that

Acknowledgements

This work is supported by National Natural Science Foundation of China (Grant nos. 21237003, 21407106, 21522703, 21377088), Shanghai Government (14ZR1430800, 13SG44, 15520711300), International Joint Laboratory on Resource Chemistry (IJLRC), and Ministry of Education of China (PCSIRT_IRT_16R49). Research is also supported by The Program for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning and Shuguang Research Program of Shanghai Education Committee.

Yawei Feng received his B.S. degree in Chemical Engineering and Technology from Henan University of Science and Technology in 2014, and he is currently pursuing a M.S. degree in Shanghai Normal University. His research interests are focused on the coupling of piezotronics/piezo-phototronics and catalysis.

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LiLi Ling received her B.S. degree in pharmaceutical engineering from Henan University of Science and Technology in 2015, and she is currently pursuing a M.S. degree in Shanghai Normal University. Her research interests are mainly focused on the synthesis and application of nanomaterials.

Yanxu Wang received her master degree in applied chemistry in 2017 from Shanghai Normal University, China. Her research interests are mainly focused on the design and synthesis of multiferroic materials for energy conversion and storage.

Zhenmin Xu is currently studying for the doctor degree in Shanghai Normal University, China. His research interests are mainly focused on the design and synthesis of nanomaterials for photocatalysis.

Fenglei Cao received his master degree in physical chemistry in 2015 from Shanghai Normal University, China. Her research interests are mainly focused on the design and synthesis of photocatalysts for environment and energy applications.

Prof. Hexing Li got doctor degree from Fudan University. Now, he is working as a vice-director of Chinese National Photocatalysis Committee and an Associated Editor of Appl. Catal. B Environ. He is also working as editorial board members of ACS Appl. Mater. Interface, Catal. Commun. and Current Green Chem. etc. His research interest in environmental catalysis including photocatalysis for removing pollutants and thermocatalysis for green chemistry. More than 200 papers and 2 monographs have been published.

Prof. Zhenfeng Bian received his Ph.D. in Environmental chemistry from the Shanghai Normal University in 2010. He has been a JSPS Postdoctoral Fellow in the lab of Professor Tetsuro Majima during 2010–2013. He became a Professor in the Department of Chemistry at Shanghai Normal University in 2013. He research interests are focused on the design and synthesis of TiO2-based nanomaterials for environmental and energy photocatalysis.

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Full paperEngineering spherical lead zirconate titanate to explore the essence of piezo-catalysis

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Synthesis of PZT materials

Results and discussion

Conclusions

Acknowledgements

Science

ACS Nano

RSC Adv.

Nano Energy

Nano Energy

Nano Energy

J. Chem. Technol. Biotechnol.

Phys. Chem. Chem. Phys.

Adv. Mater.

Sci. Rep.

Adv. Mater.

Angew. Chem. Int. Ed.

Appl. Phys. Lett.

Sensors

J. Phys. Chem. Lett.

J. Phys. Chem. C

J. Mater. Chem.

Science

Nano Energy

Chem. Soc. Rev.

Adv. Mater.

Full paper
Engineering spherical lead zirconate titanate to explore the essence of piezo-catalysis