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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 Bi2WO6 (BWO) nanosheets grown vertically on g-C3N4 (CN) coated ZnO nanorods and directly on ZnO. Compared with the photocatalysis, the piezocatalytic efficiency of Rhodamine B (RhB) by BWO/ZnO is significantly increased to 0.121 min−1, which indicated the polarization field promotes band tilt and Z-scheme formation. After introducing the CN interlayer, the piezocatalytic efficiency of BWO/CN/ZnO is further improved (0.217 min−1), which can be attributed to the unique core–shell structure with Z-scheme heterojunctions. This unique structure provides more active sites and excited carrier concentration, the intermediate layer CN also reduces the direct contact and recombination of electrons and holes controlled by polarization potential at the interface between BWO and ZnO. This work deeply analyzes the influence of carrier concentration, separation efficiency and transport process on piezocatalysis, which provides a reference for the design of efficient catalysts.

Developing new techniques that can synthesize one-dimensional piezoelectric materials on a large scale is of great significance for boosting piezocatalytic applications. In this work, we proposed a high-efficiency template hydrothermal method for large-scale synthesis of piezoelectric Na0.5Bi0.5TiO3 (NBT) nanowires. By ion-exchange with Bi3+, Na2Ti3O7 template nanowires can be easily and entirely transformed to NBT. The piezocatalytic activity of the NBT nanowires was thoroughly investigated with respect to their capability to degrade typical organic pollutants, including Rhodamine B, methylene blue, methyl orange, tetracycline hydrochloride, phenol, and bisphenol A. The NBT nanowires exhibited the highest efficiency in piezocatalytic degradation of Rhodamine B, which was completely decomposed within 80 min (rate constant ∼0.0575 min−1). The electron spin resonance spin-trapping technique and active species capture experiments were employed to characterize free radicals. The present work is advantageous for the high yield of NBT nanowires and the excellent piezocatalytic performance. The reported template hydrothermal method can potentially be extended to the synthesis of other perovskite nanowires.

The accurate estimation of photometric redshifts plays a crucial role in accomplishing science objectives of the large survey projects. The template-fitting and machine learning are the two main types of methods applied currently. Based on the training set obtained by cross-correlating the DESI Legacy Imaging Surveys DR9 galaxy catalogue and SDSS DR16 galaxy catalogue, the two kinds of methods are used and optimized, such as EAZY for template-fitting approach and CATBOOST for machine learning. Then the created models are tested by the cross-matched samples of the DESI Legacy Imaging SurveysDR9 galaxy catalogue with LAMOST DR7, GAMA DR3 and WiggleZ galaxy catalogues. Moreover three machine learning methods (CATBOOST, Multi-Layer Perceptron and Random Forest) are compared, CATBOOST shows its superiority for our case. By feature selection and optimization of model parameters, CATBOOST can obtain higher accuracy with optical and infrared photometric information, the best performance ($MSE=0.0032$, $\sigma_{NMAD}=0.0156$ and $O=0.88$ per cent) with $g \le 24.0$, $r \le 23.4$ and $z \le 22.5$ is achieved. But EAZY can provide more accurate photometric redshift estimation for high redshift galaxies, especially beyond the redhisft range of training sample. Finally, we finish the redshift estimation of all DESI DR9 galaxies with CATBOOST and EAZY, which will contribute to the further study of galaxies and their properties., Comment: Accepted for publication in MNRAS. 14 pages, 9 figures, 11 tables

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

Piezocatalysis has emerged as a novel technique to make use of mechanical energy in dealing with organic pollutants in wastewater. In this work, ferroelectric Bi2WO6 (BWO) nanosheets with a characteristic layered crystal structure and in-plane polarization were investigated, with special interest in the influence of their crystal symmetry and oxygen vacancies on the piezocatalytic performance. The nanosheets were synthesized by a hydrothermal process along with thermal annealing at different temperatures and atmospheres. The crystal symmetry, grain size and oxygen vacancies of the crystals were characterized by XRD, SEM, XPS and Raman spectroscopy. The piezocatalytic properties were investigated by degrading Rhodamine B (RhB) solution under ultrasonic vibration. The free radicals generated by ultrasonic treatment were detected and characterized using the electron spin resonance (ESR) method. The essential role of hydroxyl radicals in the dye degradation process was demonstrated by controlled experiments with different scavenger additives. The results show that the crystalline size and oxygen vacancies affect the degree of orthorhombic distortion and formation of defect energy levels, respectively, which will further affect the distribution of piezoelectric potential and piezocatalytic activity. This work will enable us to understand the influence of oxygen vacancies and crystal symmetry on piezocatalysis more intuitively and design more efficient piezocatalysts via a heat treatment control strategy.

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.

Powder-form piezocatalysts suffer from poor recyclability and pose a potential threat of creating serious secondary pollution, which restrict their practical applications. Thin-film piezocatalysts, which not only exhibit good recyclability but also fully contact with solution, are believed to be one of the solutions to address these problems. In this work, the nanostructured BaTiO

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.

A variety of nanostructured Bi

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.

The piezoelectric Bi2WO6 nanosheets with in-plane spontaneous polarization were synthesized by hydrothermal method. The adsorption and piezocatalytic properties of the synthesized Bi2WO6 nanosheets were investigated upon different variants including synthesis conditions, model dye species, and pH of the dye solution. The materials exhibited positive surface charge and selective adsorption ability for the anionic dye methyl orange (MO) in acidic and neutral conditions. The ultrafast removal of MO (kobs = 0.718 ppm s−1) under ultrasonic vibration was mainly controlled by monolayer adsorption, which followed the pseudo-second-order adsorption kinetics and the Langmuir adsorption isotherm. To eliminate the interference of adsorption, the cationic Rhodamine B (RhB) was adopted as the target pollutant for piezocatalytic experiments. The maximum rate constant of RhB removal (3.9 × 10−2 min−1) was obtained in Bi2WO6 sample with the largest specific surface area of 32.8 cm2 g−1. The catalytic nature of the dye degradation phenomenon was confirmed by detection of free radicals and the quenching effect of radical scavengers. The present work demonstrates the potential of Bi2WO6 nanosheets in piezocatalytic applications. Moreover, the synergistic effect of adsorption and piezocatalysis is valuable for in-situ regeneration of the piezoelectric adsorbents.