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The piezocatalytic performance of Sm-doped Pb(Mg1/3Nb2/3)O3-xPbTiO3 solid solutions, which exhibit ultrahigh piezoelectric coefficient with a dependence on PbTiO3 content, was thoroughly investigated. We focused mainly on the influence of piezoelectric property modulation on the piezocatalytic performance of the materials by composition arrangement. The maximal piezocatalytic activity was achieved as the composition approached the morphotropic phase boundary (MPB) at x = 0.29, in which the piezoelectric coefficient also reached the maximum. The linear relationship between the two properties proves that the piezoelectric effect plays a key role in the piezocatalytic performance. As a direct evidence of catalytic reactions, free radicals were detected by electron spin resonance (ESR) technique. Revolution of intermediate products observed by liquid chromatography-mass spectrometry (LC–MS) further confirms the catalytic reactions in the piezoelectricity induced dye degradation process. This work is of great significance for understanding the mechanism of piezocatalytic effect.

It is of great significance to understand the role of carrier in piezocatalysis of composites by studying the separation mode of carriers under dynamic polarization field. Herein, the separation and migration pathways of carriers under piezoelectric field are investigated by synthesizing heterojunctions with Bi

A variety of nanostructured Bi4Ti3O12 materials with diverse morphologies were synthesized by a novel hydrothermal method using layered titanate Na2Ti3O7 as a synthetic precursor. Among these materials, decussated nanoplates exhibit superior piezocatalytic activity compared with other piezocatalysts of the perovskite family. The enhanced piezocatalytic activity is attributed to the large piezoelectric potential difference and the short distance between polar surfaces, which may help enhance the driving force of charge transport. The finite element method (FEM) simulation of piezoelectric response in different Bi4Ti3O12 nanostructures was performed to illustrate the influence of morphological features on the piezocatalytic performance. The catalytic mechanism of Bi4Ti3O12 was investigated by the detection and characterization of free radicals and intermediate products with electron spin resonance (ESR) spin-trapping technique and liquid chromatography-mass spectrometry (LC-MS). This work may push forward the development of piezocatalytic materials, and provide insights into piezocatalysis for environmental applications.

Advanced oxidation processes including piezocatalysis and photocatalysis are considered as promising strategies for environmental remediation. More efforts have been made to clarify the factors that can improve the catalytic efficiency in piezocatalysis. Diphasic Ba1−xCaxTiO3 piezoelectric materials near a solubility limit have been found to exhibit potential for piezoelectric performance far beyond their corresponding single-phasic materials. It is interesting to explore how phase structures (single phase and diphase) will influence the catalytic performance of nanoscale piezoelectric materials. In this study, Ba1−xCaxTiO3 nanowires were used as representative materials to explore the influence of phase structures on catalytic performance. It is found that when x = 0.2 (near the solubility limit), the Ba1−xCaxTiO3 nanowires exhibit better piezocatalytic and photocatalytic performance. This can be ascribed to higher spontaneous polarization induced by the interaction of a ferroelectric tetragonal Ba-rich phase and a normal dielectric orthorhombic Ca-rich phase and band alignment of Ba-rich and Ca-rich phases, which can both effectively enhance charge carrier separation rates. In addition, with the simultaneous assistance of ultrasonic vibration and ultra-violet light, there is a coupling catalytic effect of Ba1−xCaxTiO3 nanowires, with a rate constant kobs of 71% higher than the simple sum-up of the rate constants of piezocatalytic and photocatalytic reactions. The increasing piezo-/photocatalytic degradation efficiency is mainly attributed to increased free charge carrier concentrations (thermally-excited and photo-induced charge carriers) and a strong piezoelectric field induced by the piezoelectric effect, which is beneficial for the separation of free charge carriers. We believe that this work provides mechanistic insights into how phase structures affect catalytic performance and a novel route to furnish environmentally-friendly catalysts that can efficiently utilize multiple energy sources.

A novel catalytic effect of pyroelectric materials induced by a change in temperature, namely pyroelectric catalysis, was found to be attractive due to its ability to utilize waste heat in pollution treatment. In this work, the pyroelectric catalytic properties of BaTiO3 (BTO) nanowires synthesized by a template hydrothermal method have been thoroughly investigated. The nanowires with an elongated polar axis show a superior pyroelectric catalytic performance in comparison with the equiaxial nanoparticles. Our numerical simulation results with a finite element method indicate that the enhanced catalytic efficiency of BTO nanowires can be attributed to the higher pyroelectric potential. On the basis of the pyroelectric effect and our experimental results, a pyroelectric catalytic degradation mechanism has been proposed by taking into account the migration of charge carriers and the formation of reaction radicals. This study for enhancing the pyroelectric catalytic activity by using BTO nanowires may provide a facile, promising, and new reusable strategy for the catalytic degradation of organic dye pollutant by means of temperature variation. It is hoped that the present work gives a clear understanding of the mechanism of pyroelectric catalysis.

The discovery of piezocatalysts opens up a new route to wastewater decontamination. The piezoelectricity of barium titanate nanocrystals induced by ultrasonic vibration was found effective to degrade organic pollutants. In the present work, the products of (Ba,Sr)TiO3 (BST) nanocrystals with different morphologies including nanowires (NWs), nanoparticles (NPs) and their composite were synthesized by a template hydrothermal method. And, the piezocatalytic behavior of them was thoroughly investigated with respect to a possible influence of lowered phase transition temperature on the piezocatalytic behavior. It was found that the elongated BST nanowires were more effective in degrading dye pollutants in comparison with the pure BaTiO3 nanowires and BST nanoparticles, which makes the BST nanowires a better candidate as piezocatalyst. The catalytic nature of the stress induced dye degradation was confirmed by the detection of free radicals and intermediate products during the degradation process. The improveme...

As a new catalytic effect, piezocatalysis has attracted much attention due to its ability to degrade organic pollutants under mechanical vibration. However, improving the efficiency of piezocatalysis still remains a challenge. Here, we report an efficient route to enhance the piezocatalytic performance of BaTiO3 by surface modification with Ag nanoparticles (NPs). The Ag NPs were deposited by a facile in situ photo-reduction method. The piezocatalytic efficiency of the as-prepared samples was investigated by monitoring the degradation of methyl orange (MO) under ultrasonic vibration in the dark. The results indicate that the Ag loaded BaTiO3 particles show greatly enhanced piezocatalytic activity for degradation of MO molecules. A suitable amount of Ag deposition gives the highest piezocatalytic activity, while a higher Ag loading leads to reduced piezocatalytic activity. The degradation of MO and the possible by-products as well as the active radical species generated in the piezocatalytic system were investigated systematically. Based on the experimental results, a mechanism was proposed to explain the enhancement effect of Ag NPs on the piezocatalytic performance of BaTiO3. The strategy presented here provides a promising route towards the development of high-efficiency piezocatalysts for actual applications.

Taking advantage of multiple energy sources is an effective way to enhance the catalytic efficiency of a catalytic system. Here, through rational design, we fabricated CoFe2O4 modified BiOCl hierarchical microspheres (CFO-BiOCl), which not only can make full use of photo, photothermal and mechanical energy but also can be easily recycled from liquid solutions. Photocatalytic activity measurement showed that CFO-BiOCl samples possessed outstanding photocatalytic activity, evident with 99% of rhodamine B decomposed in 5 min and 90% of tetracycline hydrochloride degraded in 10 min under full-spectrum light irradiation. Furthermore, piezo-/photocatalytic degradation rates of tetracycline hydrochloride, bisphenol A and phenol were around 2, 3 and 8 times higher than photocatalytic degradation rates under low-intensity light irradiation. Recycling tests showed that the piezo-/photocatalytic activity of CFO-BiOCl hardly decreased after 5 cycles. The excellent photocatalytic performance of CFO-BiOCl catalysts can be attributed to suitable band alignment of CoFe2O4 and BiOCl and photothermal effect that elevates organic pollutant molecules into a more active state. The generation of piezoelectric field in BiOCl crystals, providing strong driven force for the separation of photo-induced electrons and holes, gives rise to the high piezo-/photocatalytic efficiency. This work may bring a design pattern to fabricate catalysts that can utilize multiple energy sources and give a thorough discussion in the catalytic mechanism.

Nanocrystalline Ba1-xSrxTiO3 (x = 0–0.3) powders were investigated with special interest in their piezocatalytic performance for degradation of organic pollutants. A great improvement of piezocatalytic activity was obtained for the compositions x = 0.2, in which the polarization shows a large change under external stress. Furthermore, with the increase of working environment temperature, the piezocatalytic performance of Ba0.8Sr0.2TiO3 increases firstly and then decreases, giving the best piezocatalytic performance near its Curie temperature . For a better understanding of the piezocatalytic mechanism, the dynamics of charge carriers transfer on solid/liquid interface was discussed with respect to activation energy and overpotential of catalyst. It was suggested that the enhanced piezocatalytic activity of Ba 1-xSrxTiO3 comes from two aspects: (1) the overpotential provided by the piezoelectric effect decreases with the increasing Sr content, (2) the activation energy for the piezocatalytic reaction is greatly reduced at ferro-paraelectric phase transition. Combination of these two aspects gives rise to the nonlinear dependence of piezocatalytic activity on Sr content.

The selective deposition of noble metals on catalysts is an attractive modification method for improving catalytic efficiency. However, it is sometimes hard to achieve when facet energies of nano-catalysts show negligible differences. Here, we reported a piezoelectrochemical method which can realize the selective deposition of Ag nanoparticles on the positively polar end of {001}-enclosed BaTiO3 (BTO) nanocubes/cuboids. Furthermore, BTO nanocubes/cuboids with selectively-deposited Ag nanoparticles show approximately 2 times higher piezocatalytic activity than those with randomly-loaded Ag nanoparticles, and much higher than pure BTO nanocubes/cuboids. The piezocatalytic mechanism revealed that the Ag nanoparticles deposited on positively polar end act as “fast lanes” for electrons to transfer to catalysts/solution interfaces, while those loaded on negatively polar end serve as holes trappers hindering ∙OH formation and pollutant degradation. This work confirms an efficient way to improve piezocatalytic performance and provides an insightful discussion of piezocatalytic mechanism.