Synthesis of Bi4Ti3O12 decussated nanoplates with enhanced piezocatalytic activity

Ultrathin Ba0.75Sr0.25TiO3 nanosheets with highly exposed {001} polar facets for high-performance piezocatalytic application

The development of piezoelectrics with high catalytic activity to address environmental pollution and energy shortage has long been pursued. In this work, for the first time, a "three-birds-with-one-stone" strategy is proposed to design high-activity piezocatalysts. Interestingly, we achieved ultrathin, highly exposed polar facets and ferroelectric-paraelectric phase transitions in Ba1-xSrxTiO3 nanosheets simultaneously. As expected, Ba0.75Sr0.25TiO3 shows superior piezocatalytic performance for organic pollutant degradation due to its excellent flexibility, highly exposed polar area, and short carrier migration distance. Then, the piezoelectric potential distribution and electron transport ability on the interface of Ba0.75Sr0.25TiO3 were investigated through finite element method (FEM) simulation and density-functional theory (DFT) calculations, which provided a deep insight into the enhanced mechanism. This work thus presents a novel strategy for designing high-performance piezocatalysts and provides new insights for the optimization of the piezocatalytic activity by combining multiple advantages.

Piezo-catalysis in BiFeO3@In2Se3 Heterojunction for High-Efficiency Uranium Removal

Piezo-catalysis emerges as an efficient, safe, and affordable strategy for removing hazardous substances from aquatic environments. Here, the BiFeO3@In2Se3 heterojunction demonstrates remarkable prowess as a piezo-catalyst, enabling the high-efficiency removal of uranium (U) from U(VI)-containing water. A total U(VI) removal efficiency of 94.6% can be achieved under ultrasonic vibration without any sacrificial agents. During the entire catalytic process, piezo-induced electrons, hydroxyl radicals, and superoxide radicals play important roles in U(VI) removal, while the generated H2O2 is responsive to the transformation of soluble U(VI) into insoluble (UO2)O2•2H2O and UO3. Furthermore, auxiliary illumination can accelerate the increase of free charges, enabling the piezo-catalyst to retain more charges. This leads to an improved U(VI) removal efficiency of 98.8% and a significantly increased reaction rate constant. This study offers a comprehensive analysis of the fabrication of high-efficiency piezo-catalysts in the removal or extraction of U(VI) from U(VI)-containing water.

Pioneering Piezoelectric-Driven Atomic Hydrogen for Efficient Dehalogenation of Halogenated Organic Pollutants

The electrocatalytic hydrodehalogenation (EHDH) process mediated by atomic hydrogen (H*) is recognized as an efficient method for degrading halogenated organic pollutants (HOPs). However, a significant challenge is the excessive energy consumption resulting from the recombination of H* to H2 production in the EHDH process. In this study, a promising strategy was proposed to generate piezo-induced atomic H*, without external energy input or chemical consumption, for the degradation and dehalogenation of HOPs. Specifically, sub-5 nm Ni nanoparticles were subtly dotted on an N-doped carbon layer coating on BaTiO3 cube, and the resulted hybrid nanocomposite (Ni-NC@BTO) can effectively break C-X (X = Cl and F) bonds under ultrasonic vibration or mechanical stirring, demonstrating high piezoelectric driven dehalogenation efficiencies toward various HOPs. Mechanistic studies revealed that the dotted Ni nanoparticles can efficiently capture H* to form Ni-H* (Habs) and drive the dehalogenation process to lower the toxicity of intermediates. COMSOL simulations confirmed a "chimney effect" on the interface of Ni nanoparticle, which facilitated the accumulation of H+ and enhanced electron transfer for H* formation by improving the surface charge of the piezocatalyst and strengthening the interfacial electric field. Our work introduces an environmentally friendly dehalogenation method for HOPs using the piezoelectric process independent of the external energy input and chemical consumption.

Multimodal energy harvesting and catalysis of piezoelectric nanosheets for efficient and round-the-clock wastewater treatment

Solar-driven pollutants degradation is an important way for green wastewater treatment, but it is still limited by the intermittent solar flux. Here, we have prepared piezoelectric Bi4Ti3O12 (BTO) nanosheets with abundant physical properties, which can convert extensive solar energy, mechanical energy and temperature variation energy into electrical and chemical energy. It can be used for round-the-clock wastewater treatment by harvesting multi-modal energy. More importantly, the degradation rate of piezoelectric nanosheets can reach 153.4 × 10-3 min-1, and nanosheets can degrade many organic pollutants. In addition, we fabricate porous foam catalysts based on BTO-polydimethylsiloxane (PDMS) composite to prevent secondary contamination. Our results suggest that BTO nanosheets with photoelectric, piezoelectric and pyroelectric catalysis offer a potential approach for round-the-clock wastewater degradation by harvesting solar energy, ambient mechanical energy, and cyclic thermal energy.

Water flow promoted charge separation in piezoelectric Bi4Ti3O12 for the enhanced photocatalytic degradation of antibiotic

Addressing the issue of antibiotic residues in the environment is key to improving the quality of aquatic environments and reducing human health risks. In this study, piezoelectric bismuth titanate (Bi4Ti3O12) nanosheets are synthesized and employed to conduct antibiotic degradation. The piezoelectric potential induced by the water flow shear force is utilized to facilitate charge separation and migration in the photocatalytic process and enhance the catalytic degradation of antibiotic wastewater. As a result, 85% of tetracycline hydrochloride (TC) is degraded within 90 min. The piezo-photocatalytic process exhibits a 2.4 times faster reaction rate and a 15% higher mineralization rate than photocatalysis. Different environmental factors are investigated for their effects on the catalytic activity in piezo-photocatalysis. In situ electrochemical measurement and photoluminescence (PL) spectroscopy under stress demonstrated that the piezoelectric potential shifted the energy band of Bi4Ti3O12 and promoted the charge migration and separation, which produce more active species that favor the efficient catalytic degradation. Finally, the intermediate products of the tetracycline hydrochloride degradation process are analyzed and possible degradation pathways are suggested. This study elucidates the degradation mechanism of Bi4Ti3O12 as a piezo-photocatalyst for antibiotic pollutants, and meticulously investigates the charge transfer mechanism of the catalyst material in response to micro-stress. Hence, it provides an efficient solution for organic wastewater treatment and can potentially provide theoretical support for the development and performance optimization of catalyst materials applied in natural environments.

An Emerging Family of Piezocatalysts: 2D Piezoelectric Materials

Piezocatalysis is an emerging technique that holds great promise for the conversion of ubiquitous mechanical energy into electrochemical energy through piezoelectric effect. However, mechanical energies in natural environment (such as wind energy, water flow energy, and noise) are typically tiny, scattered, and featured with low frequency and low power. Therefore, a high response to these tiny mechanical energies is critical to achieving high piezocatalytic performance. In comparison to nanoparticles or 1D piezoelectric materials, 2D piezoelectric materials possess characteristics such as high flexibility, easy deformation, large surface area, and rich active sites, showing more promise in future for practical applications. In this review, state-of-the-art research progresses on 2D piezoelectric materials and their applications in piezocatalysis are provided. First, a detailed description of 2D piezoelectric materials are offered. Then a comprehensive summary of the piezocatalysis technique is presented and examines the piezocatalysis applications of 2D piezoelectric materials in various fields, including environmental remediation, small-molecule catalysis, and biomedicine. Finally, the main challenges and prospects of 2D piezoelectric materials and their applications in piezocatalysis are discussed. It is expected that this review can fuel the practical application of 2D piezoelectric materials in piezocatalysis.

Remarkably enhanced catalytic performance in CoOx/Bi4Ti3O12 heterostructures for methyl orange degradation via piezocatalysis and piezo-photocatalysis

A novel heterojunction composite of CoOx/Bi4Ti3O12 was synthesized through a combination of molten salt and photodeposition methods. The optimal sample exhibited superior performance in the piezocatalytic degradation of methyl orange (MO) dye with a degradation rate of 1.09 h-1, which was 2.4 times higher than that of pristine Bi4Ti3O12. Various characterizations were conducted to reveal the fundamental nature accountable for the outstanding piezocatalytic performance of CoOx/Bi4Ti3O12. The investigation of the band structure indicated that the CoOx/Bi4Ti3O12 composite formed a type-I p-n heterojunction structure, with CoOx acting as a hole trapper to effectively separate and transfer piezogenerated carriers. Significantly, the MO degradation rate of the best CoOx/Bi4Ti3O12 sample further increased to 2.96 h-1 under combined ultrasonic vibration and simulated sunlight. The synergy between piezocatalysis and photocatalysis can be ascribed to the following factors. The photoexcitation process ensures the sufficient generation of charge carriers in the CoOx/Bi4Ti3O12, while the piezoelectric field within Bi4Ti3O12 promotes the separation of electron-hole pairs in the bulk phase. Furthermore, the heterojunction structure between Bi4Ti3O12 and CoOx significantly facilitates the surface separation of charge carriers. This increased involvement of free electrons and holes in the reaction leads to a remarkable enhancement in catalytic MO degradation. This work contributes to the understanding of the coupling mechanism between the piezoelectric effect and photocatalysis, and also provides a promising strategy for the development of efficient catalysts for wastewater treatment.

Bi0·5Na0·5TiO3/ZnO Z-scheme heterojunction for piezo-photocatalytic water remediation: Mechanical energy harvesting and energy band configuration

The decaying photocatalytic rate caused by carrier recombination is a thorny problem that has not been properly solved. Improvement of photocatalysis can be achieved through structural innovation, diversification of catalytic modes, or a combination of both. Herein, effective separation of photo-generated carriers in Bi0·5Na0·5TiO3/ZnO composites was achieved by heterojunction construction for energy band regulation and synchronously mechanical energy harvesting from piezoelectric effect. The formation of heterojunctions between Bi0·5Na0·5TiO3 and ZnO was confirmed by electron microscopy and analysis of X-ray photoelectron spectroscopy spectra. The degradation performance of Rhodamine B, a representative industrial dye contaminant, was optimized through the formation of Bi0·5Na0·5TiO3/ZnO heterojunctions and ultrasonic vibration harvesting. Their band structures were described in detail and electrochemical tests were performed to substantiate a novel Z-scheme heterostructure that can explain the carrier separation and transfer processes in catalysis. The piezoelectric polarization field generated by the piezoelectric effect of both Bi0·5Na0·5TiO3 and ZnO coordinates perfectly with the photocatalysis, enabling the piezo-photocatalysis. Our research opens a promising avenue in alleviating charge carrier complexation through heterojunction construction and mechanical strain for future pollutants degradation via catalysis.

Review on Multicatalytic Behavior of Ba0.85Ca0.15Ti0.9Zr0.1O3 Ceramic

Ferroelectric materials are known to possess multicatalytic abilities that are nowadays utilized for removing organic pollutants from water via piezocatalysis, photocatalysis, piezo-photocatalysis, and pyrocatalysis processes. The Ba0.85Ca0.15Ti0.9Zr0.1O3 (BCZTO) ceramic is one such ferroelectric composition that has been extensively studied for electrical and electronic applications. Furthermore, the BCZTO ceramic has also shown remarkable multicatalytic performance in water-cleaning applications. The present review explores the potentiality of BCZTO for water-cleaning and bacterial-killing applications. It also highlights the fundamentals of ferroelectric ceramics, the importance of electric poling, and the principles underlying piezocatalysis, photocatalysis, and pyrocatalysis processes in addition to the multicatalytic capability of ferroelectric BCZTO ceramic.

Custom-Made Piezoelectric Solid Solution Material for Cancer Therapy

Piezoelectric material-mediated sonodynamic therapy (SDT) has received considerable research interest in cancer therapy. However, the simple applications of conventional piezoelectric materials do not realize the full potential of piezoelectric materials in medicine. Therefore, the energy band structure of a piezoelectric material is modulated in this study to meet the actual requirement for cancer treatment. Herein, an elaborate PEGylated piezoelectric solid solution 0.7BiFeO3 -0.3BaTiO3 nanoparticles (P-BF-BT NPs) is synthesized, and the resultant particles achieve excellent piezoelectric properties and their band structure is tuned via band engineering. The tuned band structure of P-BF-BT NPs is energetically favorable for the synchronous production of superoxide radicals (•O2 - ) and oxygen (O2 ) self-supply via water splitting by the piezoelectric effect. Besides, the P-BF-BT NPs can initiate the Fenton reaction to generate hydroxyl radical (•OH), and thus, chemodynamic therapy (CDT) can be augmented by ultrasound. Detailed in vitro and in vivo research has verified the promising effects of multimodal imaging-guided P-BF-BT NP-mediated synergistic SDT/CDT by the piezo-Fenton process in hypoxic tumor elimination, accompanied by high therapeutic biosafety. The current demonstrates a novel strategy for designing and synthesizing "custom-made" piezoelectric materials for cancer therapy in the future.

Enhanced Piezo-Photocatalytic Performance of Na0.5Bi4.5Ti4O15 by High-Voltage Poling

The internal electric field within a piezoelectric material can effectively inhibit the recombination of photogenerated electron-hole pairs, thus serving as a means to enhance photocatalytic efficiency. Herein, we synthesized a Na_0.5Bi_4.5Ti₄O₁₅ (NBT) catalyst by the hydrothermal method and optimized its catalytic performance by simple high-voltage poling. When applying light and mechanical stirring on a 2 kV mm^-1 poled NBT sample, almost 100% of Rhodamine B solution could be degraded in 120 min, and the reaction rate constant reached as high as 28.36 × 10^-3 min^-1, which was 4.2 times higher than that of the unpoled NBT sample. The enhanced piezo-photocatalytic activity is attributed to the poling-enhanced internal electric field, which facilitates the efficient separation and transfer of photogenerated carriers. Our work provides a new option and idea for the development of piezo-photocatalysts for environmental remediation and pollutant treatment.

Magnetically retrievable Fe3O4@SiO2@ZnO piezo-photocatalyst: Synthesis and multiple catalytic properties

The piezo-/photocatalytic effects of ZnO have been in the limelight because of their great potential in environmental remediation and energy conversion. However, the poor recyclability of the suspended catalysts can cause inevitable secondary pollution, which is one of the major issues that limit the practical application of these materials. To address this problem, a magnetically retrievable Fe₃O₄@SiO₂@ZnO nanocomposite was designed and successfully synthesized by multi-step reactions. The ZnO nanorods were vertically grown on the surface of the magnetic Fe₃O₄@SiO₂ microspheres, while SiO₂ served as an insulator to protect the inner core and to inhibit charge transfer across the core/shell interface. The Fe₃O₄@SiO₂@ZnO nanocomposite can be easily collected and separated by using a magnetic field. Along with the good recyclability, the material also exhibited high efficiencies in piezocatalytic, photocatalytic and piezo-photocatalytic dye degradation processes. The rate constant of piezo-photocatalysis reached 95.9 × 10^-3 min^-1, which was 2.2 and 6.1 times that of the individual piezocatalysis and photocatalysis, respectively. The present result confirmed the existence of a synergetic effect between piezo- and photocatalytic processes. Hereby, we demonstrated that incorporation of a magnetic carrier is a feasible strategy to achieve retrievable and highly efficient piezo-/photocatalyst.

Piezoelectric materials and techniques for environmental pollution remediation

With the rapid development of industrialization and agriculture, a series of critical imminent environmental problems and water pollution have caught wide attention from the public and society. Piezoelectric catalysis technology with piezoelectric materials is a green and environmental method that can efficiently improve the separation of electron-hole pairs, then generating the active substances such as OH, H₂O₂ and O₂^-, which can degrade water pollutants. Therefore, we firstly surveyed the piezoelectric catalysis in piezoelectric materials and systematically concluded and emphasized the relationship between piezoelectric materials and the piezoelectric catalytic mechanism, the goal to elucidate the effect of polarization on piezoelectric catalytic performance and enhance piezoelectric catalytic performance. Subsequently, the applications of piezoelectric materials in water treatment and environmental pollutant remediation were discussed including degradation of organic pollutants, removal of heavy mental ions, radionuclides, bacteria disinfection and water splitting for H₂ generation. Finally, the development prospects and future outlooks of piezoelectric catalysis were presented in detail.

Emerging Advancements in Piezoelectric Nanomaterials for Dynamic Tumor Therapy

Cancer is one of the deadliest diseases, having spurred researchers to explore effective therapeutic strategies for several centuries. Although efficacious, conventional chemotherapy usually introduces various side effects, such as cytotoxicity or multi−drug resistance. In recent decades, nanomaterials, possessing unique physical and chemical properties, have been used for the treatment of a wide range of cancers. Dynamic therapies, which can kill target cells using reactive oxygen species (ROS), are promising for tumor treatment, as they overcome the drawbacks of chemotherapy methods. Piezoelectric nanomaterials, featuring a unique property to convert ultrasound vibration energy into electrical energy, have also attracted increasing attention in biomedical research, as the piezoelectric effect can drive chemical reactions to generate ROS, leading to the newly emerging technique of ultrasound−driven tumor therapy. Piezoelectric materials are expected to bring a better solution for efficient and safe cancer treatment, as well as patient pain relief. In this review article, we highlight the most recent achievements of piezoelectric biomaterials for tumor therapy, including the mechanism of piezoelectric catalysis, conventional piezoelectric materials, modified piezoelectric materials and multifunctional piezoelectric materials for tumor treatment.

A facile synthesis of highly efficient In2S3 photocatalysts for the removal of cationic dyes with size-dependent photocatalysis

In this study, a 3D thornball-like hierarchical β-In₂S₃, displaying extremely rapid photodegradation of cationic dyes, was synthesized by a facile method. The formation of a uniform thornball-like structure depended on the microwave reaction method and citric acid as the pH regulator. The size of In₂S₃ was easily adjusted by changing the microwave irradiation time from 5 min to 15 min. The morphology, structure, composition, energy level, charge separation, and surface properties of different-sized In₂S₃ were characterized. The results showed that In₂S₃ synthesized in 10 min (In₂S₃-10) displayed optimal interface property for the electron-hole separation, maximum hydrophilia with most surface negative charges for the surface adsorption, contributing to the complete photodegradation of rhodamine B (RhB) in just 25 minutes of visible light illumination. The photodegradation path of RhB was speculated with four possible paths, including the processes of de-ethylation, open-ring of xanthene, and rupture of carbon-carbon bonds up to the decomposition into small molecules. Finally, the reusability of In₂S₃-10 was tested, obtaining nearly 96% photodegradation efficiency after sequential 5 cycles.

Effectively enhanced photocatalytic performance of layered perovskite Bi2NdO4Cl by coupling piezotronic effect

The coupling between piezoelectricity and photoexcitation is an attractive method for improving the photocatalytic efficiency of semiconductors. Herein, a novel layered perovskite photocatalyst Bi₂NdO₄Cl (BNOC) has been successfully prepared via solid-state reaction. PFM results confirm that BNOC has piezoelectricity, and its piezo-photocatalytic degradation performance was evaluated for the first time using tetracycline hydrochloride (TH) as a pollutant model. The results show that the piezo-photocatalytic degradation rate constant is about 1.5 times higher than the sum of the individual photo- and piezo-catalytic components. This synergistic enhancement can be attributed to the band tilting-induced piezoelectric polarization charges and formation of a piezoelectric field, which accelerates the photoinduced charge carrier separation and effectively enhanced the photocatalytic performance. This work may facilitate the development of novel piezoelectric photocatalytic materials that are highly sensitive to the mechanical energy of discrete fluids, and offer ideas for piezo-photocatalysis in environmental applications.

Ferroelectric-assisted charge carrier separation over Bi2MoO6 nanosheets for photocatalytic dye degradation

Low energy conversion efficiency from the absorbed photon to the catalytic species remains a major obstacle for the real application of photocatalysis. In recent years, the introduction of a built-in electric field has proved to be impactful in facilitating the photoinduced charge separation, among which, ferroelectric polarization is highly recommended by getting rid of mechanical stresses. Developing ferroelectrics directly as photoactive semiconductors is promising in view of the synergistic catalytic enhancement. Therefore, Bi₂MoO₆ nanosheets with ultrathin layered structure (<10 nm) and abundant oxygen vacancies were synthesized through the hydrothermal method. The two-dimensional nanostructure created more active sites and a convenient polarization condition. Subsequently, corona poling was applied on the Bi₂MoO₆ nanosheets, which can significantly accelerate the 100% degradation rate of RhB from 50 to 20 min, surpassing that of metal-free photocatalysts. The combined effect of semiconductor, ferroelectric polarization, oxygen vacancies, and nano-layered structure offers new strategies for designing multifield coupling catalysts, providing insights into the regulation of charge carrier dynamics.

Highly Efficient Bi4Ti3O12/g-C3N4/BiOBr Dual Z-Scheme Heterojunction Photocatalysts with Enhanced Visible Light-Responsive Activity for the Degradation of Antibiotics

A novel Bi₄Ti₃O₁₂/g-C₃N₄/BiOBr(BTO/CN/BOB) composite was synthesized by a solvothermal-mechanical mixed thermal method. The composition, structure, and micromorphology of the samples were analyzed. The BTO/CN/BOB composite photocatalyst shows better photocatalytic performance for tetracycline hydrochloride (TC) degradation compared to Bi₄Ti₃O₁₂ and binary composite photocatalysts. The highest degradation rate of TC can reach 89.84% using the BTO/CN/BOB photocatalyst under the optimal conditions, and BTO/CN/BOB still exhibits good photocatalytic properties after recycling. Moreover, it also shows good photodegradation activity for different kinds of antibiotics, implying its wide application prospect. The photocatalytic performance and reuse stability of BTO/CN/BOB were significantly improved, which may be because of the enhanced spectral absorption range and efficient electron transfer capability by the synergistic effect and interaction among Bi₄Ti₃O₁₂, BiOBr, and g-C₃N₄. Finally, the possible degradation pathway and electron transfer mechanism of the dual Z-scheme heterojunction are proposed.

Thin Films (FTO/BaTiO3/AgNPs) for Enhanced Piezo-Photocatalytic Degradation of Methylene Blue and Ciprofloxacin in Wastewater

In this study, we investigate the ability of barium titanate/silver nanoparticles (BaTiO₃/AgNPs) composites deposited on a fluorine-doped tin oxide (FTO) glass using tape-casting method to produce piezoelectric thin film (FTO/BaTiO₃/AgNPs) for piezocatalytic, photocatalytic, and piezo-photocatalytic degradation of methylene blue (MB) and ciprofloxacin (CIP) in wastewater. The prepared piezoelectric materials (BaTiO₃ and BaTiO₃/AgNPs) were characterized using XRD, SEM, TEM, EDS, UV-DRS, TGA, PL, BET, EIS, and chronoamperometry. The UV-DRS showed the surface plasmon resonance (SPR) of Ag nanoparticles on the surface of BaTiO₃ at a wavelength of 505 nm. The TEM images revealed the average Ag nanoparticle size deposited on the surface of BaTiO₃ to be in the range of 10-15 nm. The chronoamperometry showed that the photoreduction of silver nanoparticles (AgNPs) onto BaTiO₃ (BTO) resulted in a piezo-electrochemical current enhancement from 0.24 to 0.38 mA. The composites (FTO/BaTiO₃/AgNPs) achieved a higher degradation of MB and CIP when the photocatalysis and piezocatalysis processes were merged. Under both ultrasonic vibration and UV light exposure, FTO/BTO/AgNPs degraded about 72 and 98% of CIP and MB from wastewater, respectively. These piezoelectric thin films were shown to be efficient and reusable even after five cycles, suggesting that they are highly stable. Furthermore, the reactive oxygen species studies demonstrated that hydroxyl radicals (·OH) were the most effective species during degradation of MB, with minor superoxide radicals (·O₂ ^-) and holes (h⁺). From this study, we were able to show that these materials can be used as multifunctional materials as they were able to degrade both the dye and pharmaceutical pollutants. Moreover, they were more efficient through the piezo-photocatalytic process.

Ferroelectric bismuth-titanate nanoplatelets and nanowires with a new crystal structure

Two different morphologies of ferroelectric bismuth titanate (Bi₄Ti₃O₁₂) nanoparticles, i.e., nanoplatelets and nanowires, were synthesized by changing the concentration of NaOH during a hydrothermal treatment of precipitated Ti⁴⁺ and Bi³⁺ ions. The nanoparticles' crystal structures were characterized using atomic-resolution imaging with a C_S-probe-corrected scanning-transmission electron microscope in combination with X-ray diffractometry and Raman spectroscopy. The nanoplatelets (10 nm thick and from 50 nm to 200 nm wide) exhibit the Aurivillius-type layered-perovskite crystal structure that is characteristic of Bi₄Ti₃O₁₂, whereas the nanowires (from 15 nm to 35 nm wide and from several hundreds of nm to several μm long) exhibit an entirely new structure with an orthorhombic unit cell (a = 3.804(1) Å, b = 11.816(3) Å, and c = 9.704(1) Å). The nanowire structure is composed of two structural layers alternating along the orthorhombic c-direction: a structural layer composed of two parallel layers of Bi atoms that resembles the (Bi₂O₂)²⁺ layer of the Aurivillius structure, and a structural layer composed of two parallel layers of Ti atoms, where every sixth Ti is replaced with Bi. Observations of the ferroelectric domains with transmission electron and piezo-response force microscopy indicated the ferroelectric nature of both nanostructures. The nanowire structure is a metastable polymorph of the bismuth titanate stabilized at the nanoscale. With annealing at temperatures above 500 °C the nanowire structure topotactically transforms into the Aurivillius structure.

Synergetic Piezo-Photocatalytic Hydrogen Evolution on Cdx Zn1-x S Solid-Solution 1D Nanorods

Conversion of solar and mechanical vibration energies for catalytic water splitting into H₂ has gained substantial attention recently. However, the sluggish charge separation and inefficient energy utilization in photocatalytic and piezocatalytic processes severely restrict the catalytic activity. In this paper, efficient piezo-photocatalytic H₂ evolution from water splitting is realized via simultaneously converting solar and vibration energy over one-dimensional (1D) nanorod-structured Cd_x Zn_1-x S (x = 0, 0.2, 0.4, 0.6, 0.8, 1) solid solutions. Under combined visible light and ultrasound irradiation, Cd_0.4 Zn_0.6 S 1D nanorods deliver a prominently synergetic piezo-photocatalytic H₂ yield rate of 4.45 mmol g^-1  h^-1 , far exceeding that under sole ultrasound or illumination. The consumedly promoted catalytic activity of Cd_0.4 Zn_0.6 S is attributed to strengthened charge separation by piezo-potential as disclosed by light-assisted scanning Kelvin probe force microscopy (SKPFM), increased strain sensitivity, and desirable optimization between piezoelectricity and visible-light response due to the formation of 1D configuration and solid solution. Metal and metal oxide depositions disclose that reduction and oxidation reactions separately occur at the tips and lateral edges of the Cd_0.4 Zn_0.6 S nanorods, in which the spatially separated reactive sites also contribute to super catalytic activity. This work is expected to inspire a new design strategy of coupled catalysis reactions for efficient renewable fuel production.

A review of advances in multifunctional XTiO3 perovskite-type oxides as piezo-photocatalysts for environmental remediation and energy production

Over more than three decades, the field of engineering of photocatalytic materials with unique properties and enhanced performance has received a huge attention. In this regard, different classes of materials were fabricated and used for different photocatalytic applications. Among these materials, recently multifunctional XTiO₃ perovskites have drawn outstanding interest towards environmental remediation and energy conversion thanks to their unique structural, optical, physiochemical, electrical and thermal characteristics. XTiO₃ perovskites are able to initiate different surface catalytic reactions. Under ultrasonic vibration or heating, XTiO₃ perovskites can induce piezo-catalytic reactions due to the titling of their conduction and valence bands, resulting in the formation of separated charge carriers in the medium. In addition, under light irradiation, XTiO₃ perovskites are considered as a new class of photocatalysts for environmental and energy related applications. Herein, we addressed the recent advances on variously synthesized, doped and formulated XTiO₃ perovskite-type oxides showing piezo- and/or photocatalytic exploitation in environmental remediation and energy conversion. The control of structural crystallite size and phase, conductivity, morphology, oxygen vacancy control, doping agents and ratio has a significant role on the photocatalytic and piezocatalytic activities. The different piezo or/and photocatalytic processes mechanistic pathways towards varying applications were discussed. The current challenges facing these materials and future trends were addressed at the end of the review.

Piezoelectric catalytic, photocatalytic and adsorption capability and selectivity removal of various dyes and mixed dye wastewater by ZnO nanoparticles

The C-O functional group decorated ZnO nanoparticles with high UV absorption and VIS/NIR reflectance were synthesized by a simple wet chemistry method using various chelating agents. This study attempts to explore the internal mechanism of the piezoelectric catalytic activity, photocatalytic activity and adsorption performance of ZnO nanoparticles. The phase purity, particle size, optical band gap and photocatalytic activity of ZnO nanoparticles showed strong chelating agent - dependent behavior. The ZnO nanoparticles prepared by using EDTA as a chelating agent exhibits smallest particle size, highest photocatalytic activity for the degradation of methyl orange, methylene blue and rhodamine B, high adsorption capacity for the adsorption of Congo red and high vibration-catalytic performance for the vibration degradation of rhodamine B. The synergies mechanism among piezoelectric catalysis, photocatalysis and adsorption capacity of ZnO nanoparticles are discussed on the basis of the experimental results.

Cocatalyst engineering to weaken the charge screening effect over Au–Bi4Ti3O12 for piezocatalytic pure water splitting

The weak driving force and rapid carrier recombination severely restrict the development and utilization of piezocatalysis, but the important reason is the charge screening effect.

Piezoelectric induced reverse photocatalytic performances of carbon nitride with different structures

The piezoelectric properties of graphitic carbon nitride with different structures follow the order PTI > melon > PHI, and the melon and PHI showed reverse activities in the photocatalytic and piezoelectric assisted photocatalytic reactions.

Hydrothermal formation of bismuth-titanate nanoplatelets and nanowires: the role of metastable polymorphs

Understanding the processes involved in the formation of nanoparticles is a prerequisite for the control of their morphology. In this investigation we reveal the processes leading to the formation of...

2D Piezoelectric Bi2 MoO6 Nanoribbons for GSH-Enhanced Sonodynamic Therapy

Reducing the scavenging capacity of reactive oxygen species (ROS) and elevating ROS production are two primary goals of developing novel sonosensitizers for sonodynamic therapy (SDT). Hence, ultrathin 2D Bi2 MoO6 -poly(ethylene glycol) nanoribbons (BMO NRs) are designed as piezoelectric sonosensitizers for glutathione (GSH)-enhanced SDT. In cancer cells, BMO NRs can consume endogenous GSH to disrupt redox homeostasis, and the GSH-activated BMO NRs (GBMO) exhibit an oxygen-deficient structure, which can promote the separation of electron-hole pairs, thereby enhancing the efficiency of ROS production in SDT. The ultrathin GBMO NRs are piezoelectric, in which ultrasonic waves introduce mechanical strain to the nanoribbons, resulting in piezoelectric polarization and band tilting, thus accelerating toxic ROS production. The as-synthesized BMO NRs enable excellent computed tomography imaging of tumors and significant tumor suppression in vitro and in vivo. A piezoelectric Bi2 MoO6 sonosensitizer-mediated two-step enhancement SDT process, which is activated by endogenous GSH and amplified by exogenous ultrasound, is proposed. This process not only provides new options for improving SDT but also broadens the application of 2D piezoelectric materials as sonosensitizers in SDT.

Strain-Induced Ferroelectric Heterostructure Catalysts of Hydrogen Production through Piezophototronic and Piezoelectrocatalytic System

In this work, we discover a piezoelectrocatalytic system composed of a ferroelectric heterostructure of BaTiO₃ (BTO)@MoSe₂ nanosheets, which exhibit piezoelectric potential (piezopotential) coupling with electrocatalyzed effects by a strain-induced piezopotential to provide an internal bias to the catalysts' surface; subsequently, the catalytic properties are substantially altered to enable the formation of activity states. The H₂ production rate of BTO@MoSe₂ for the piezoelectrocatalytic H₂ generation is 4533 μmol h^-1 g^-1, which is 206% that of TiO₂@MoSe₂ for piezophototronic (referred to as piezophotocatalytic process) H₂ generation (∼2195.6 μmol h^-1 g^-1). BTO@MoSe₂ presents a long-term H₂ production rate of 21.2 mmol g^-1 within 8 h, which is the highest recorded value under piezocatalytic conditions. The theoretical and experimental results indicate that the ferroelectric BTO acts as a strain-induced electric field generator while the few-layered MoSe₂ is facilitating piezocatalytic redox reactions on its active sites. This is a promising method for environmental remediation and clean energy development.

Ultrahigh piezocatalytic capability in eco-friendly BaTiO3 nanosheets promoted by 2D morphology engineering

Piezocatalysis, converting mechanical vibration into chemical energy, is an emerging technology to address environmental issues. In this work, we propose an efficient method to significantly improve the piezocatalytic activity by morphology engineering rather than composition design. The catalytic property in BaTiO₃ nanocrystallites with diverse morphologies is investigated by dye degradation and hydrogen production under ultrasonic vibration. The BaTiO₃ nanosheets exhibit an excellent piezocatalytic activity with a degradation rate of 0.1279 min^-1 for Rhodamine B, far beyond those in previous piezocatalytic literature and even comparable to excellent photocatalysts, and also a high hydrogen production rate of 92 μmol g^-1 h^-1. Compared with nanowires and nanoparticles, the 2D morphology greatly enhances the piezocatalytic activity in nanosheets owing to much larger piezoelectric potential. This proves that the piezocatalytic property is dominated by the morphology-dependent piezoelectricity, rather than specific surface area as other catalysis. Dominated by bending vibrating mode, the piezocatalytic activity reaches a maximum at the piezoelectric resonating frequency, and it increases with the ultrasonic power. Moreover, it has good reusability and wide versatility for catalytic degradation. This work gives an in-depth understanding of piezocatalytic mechanism and provides a way to develop high performance and eco-friendly piezocatalysts.

Boosting Piezo/Photo-Induced Charge Transfer of CNT/Bi4O5I2 Catalyst for Efficient Ultrasound-Assisted Degradation of Rhodamine B

Strain-induced internal electric fields present a significant path to boosting the separation of photoinduced electrons and holes. In addition, piezo-induced positive/negative pairs could be released smoothly, taking advantage of the excellent electroconductibility of some conductors. Herein, the hybrid piezo-photocatalysis is constructed by combining debut piezoelectric nanosheets (Bi4O5I2) and typical conductor multiwalled carbon nanotubes (CNT). The photocatalytic degradation efficiency that the hybrid CNT/Bi4O5I2 exhibits was remarkably increased by more than 2.3 times under ultrasonic vibration, due to the piezo-generated internal electric field. In addition, the transient photocurrent spectroscopy and electrochemical impedance measurement reveal that the CNT coating on Bi4O5I2 enhances the piezo-induced positive/negative migration. Therefore, the piezocatalytic activity of CNT/Bi4O5I2 could be improved by three times, compared with pure Bi4O5I2 nanosheets. Our results may offer promising approaches to sketching efficient piezo-photocatalysis for the full utilization of solar energy or mechanical vibration.

A new strategy for large-scale synthesis of Na0.5Bi0.5TiO3 nanowires and their application in piezocatalytic degradation

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.

Synergistic catalysis of BiOIO3 catalyst for elimination of organic pollutants under simultaneous photo-irradiation and ultrasound-vibration treatment

Development of efficiently catalytic strategy for oxidative purification of organic pollutants is of great significance. Photocatalysis has become one of the most important technologies in the past half a century, but the inefficiency of photocatalysts drastically suppresses its practical application. This work proposes a synergistic photopiezocatalysis of BiOIO₃ under simultaneous photo-irradiation and ultrasound-vibration treatment to degrade various organic pollutants. Different from the high recombination of photo-excited charges in photocatalysis, the ultrasound-induced stress deforms the pyroelectric BiOIO₃ to form a piezoelectric potential that drives photo-/thermo-generated free electrons and holes in catalyst to diffuse along opposite directions. In comparison with the single photocatalysis and piezocatalysis, the photopiezocatalysis possesses a synergistic effect, presenting evidently enhanced catalytic performance for decomposing a variety of organic dyes and a persistent organic pollutant 2,4-DCP. No apparent decrease in activity during successive five runs demonstrates that the photopiezocatalysis of BiOIO₃ has a high stability and reusability. Finally, a plausible photopiezocatalysis mechanism is proposed based on the determination of active species produced on catalyst and intermediates during pollutant degradation. Our findings provide a new insight to promote charge separation and meanwhile develop an efficient synergistic photopiezocatalysis for environment remediation.

Cocatalyst Engineering in Piezocatalysis: A Promising Strategy for Boosting Hydrogen Evolution

Piezoelectric semiconductor-based piezocatalysis has emerged as a promising approach for converting mechanical energy into chemical energy for renewable hydrogen generation and wastewater treatment under the action of mechanical vibration. Similar to photocatalysis, piezocatalysis is triggered by the separation, transfer, and consumption of piezo-generated electrons and holes. Inspired by this, herein, we report that the cocatalyst, which is widely used in photocatalysis, can also improve the semiconductor-based piezocatalytic properties. In the proof-of-concept design, well-defined Pd as a model cocatalyst has been deposited on the surface of piezoelectric BiFeO₃ nanosheets, which not only facilitates the separation of charge carriers by accepting the piezoelectrons from BiFeO₃ but also lowers the activation energy/overpotential through supplying highly active sites for the proton reduction reaction. Consequently, the as-obtained hybrid piezocatalyst delivers a high H₂ evolution rate of 11.4 μmol h^-1 (10 mg of catalyst), 19.0 times as high as that of bare BiFeO₃. The band tilting induced by the piezoelectric potential is proposed to lower or eliminate the Schottky barrier and smooth the electron transfer from BiFeO₃ to Pd, while the exposed facet, domain size, and loading amount of Pd cocatalyst are proved to be the key parameters determining the ultimate piezocatalytic activity. Our work provides some enlightenment on advancing the design and fabrication of more efficient piezocatalysts for H₂ evolution based on rational engineering on the cocatalyst.

Enhanced Piezocatalytic Activity of Sr0.5Ba0.5Nb2O6 Nanostructures by Engineering Surface Oxygen Vacancies and Self-Generated Heterojunctions

Piezocatalysis provides a promising strategy for directly converting weak mechanical energy into chemical energy. In this work, we report a simple one-step hydrogen reduction route for the simultaneous generation of surface defects and heterojunctions in Sr_0.5Ba_0.5Nb₂O₆ nanorods fabricated by a molten salt synthesis method. The as-fabricated Sr_0.5Ba_0.5Nb₂O₆/Sr₂Nb₂O₇ nanocomposites with controllable oxygen vacancies exhibited excellent piezocatalytic activity under ultrasonic vibration, with an about 7 times enhancement of the rate constant (k = 0.0395 min^-1) for rhodamine B degradation and an about 10 times enhancement of the water-splitting efficiency for hydrogen generation (109.4 μmol g^-1 h^-1) for the optimized sample (H₂ annealed at 500 °C) compared to pristine Sr_0.5Ba_0.5Nb₂O₆ nanorods. This work demonstrates the essential role of a well-modulated oxygen vacancy concentration in the piezocatalytic activity and provides an inspiring guide for designing self-generated heterojunction piezocatalysts.

Remarkable Piezophoto Coupling Catalysis Behavior of BiOX/BaTiO3 (X = Cl, Br, Cl0.166 Br0.834 ) Piezoelectric Composites

Polarization field engineering of piezoelectric materials is considered as an advisable strategy in fine-tuning photocatalytic performance which has drawn much attention recently. However, the efficient charge separation that determines the photocatalytic reactivities of these materials is quite restricted. Herein, a judicious combination of piezoelectric and photocatalytic performances of BiOX/BaTiO₃ (X = Cl, Br, Cl_0.166 Br_0.834 ) to enable a high piezophotocatalytic activity is demonstrated. Under the synergic advantages of chemical potential difference and piezoelectric potential difference in BiOX/BaTiO₃ composites, the photoinduced carriers recombination is largely halted, which directly contributes to the significantly promoted piezophotocatalytic activity of piezoelectric composites. Inspiringly, the BiOBr/BaTiO₃ composites under light irradiation with auxiliary ultrasonic activation result in an ultrahigh and stable photocatalytic performance, which is much higher than the total of those by isolated photocatalysis and piezocatalysis, and can rival current excellent photocatalytic system. In fact, the theoretical piezoelectric potential difference of BiOBr/BaTiO₃ composites reaches 100 mV, which far exceeds the pure BaTiO₃ of 31.21 mV and BiOBr of 30 mV, respectively. First, fabrication of BiOX/BaTiO₃ piezoelectric composites and its remarkable piezophoto coupling catalysis behavior lays new ground for developing high-efficiency piezoelectric photocatalysts in purifying wastewater, killing bacteria, and other piezophototronic processes.

Piezoelectric materials for ultrasound-driven dissociation of Alzheimer's β-amyloid aggregate structure

Piezoelectric materials can evoke electrochemical reactions by transferring charge carriers to reactants upon receiving mechanical stimuli. We report a newly discovered function of piezoelectric bismuth oxychloride (BiOCl) nanosheets for dissociating Alzheimer's β-amyloid (Aβ) aggregates through ultrasound-induced redox reactions. The accumulation of Aβ aggregates (e.g., Aβ fibrils, plaques) in the central nervous system is a major pathological hallmark of Alzheimer's disease (AD). Thus, clearing Aβ aggregates is considered a key for treating AD, but the dissociation of Aβ aggregates is challenging due to their extremely robust structure consisting of β-sheets. BiOCl nanosheets are a biocompatible piezoelectric material with piezocatalytic activity in response to ultrasound. Our analyses using multiple spectroscopic and microscopic tools have revealed that BiOCl nanosheets effectively disassemble Aβ fibrils under ultrasound stimulation. Sono-activated BiOCl nanosheets produce piezo-induced oxidative stress, which effectively destabilizes the β-sheets in Aβ fibrils. In vitro evolution has also shown that sono-activated BiOCl nanosheets can effectively alleviate the neuro-toxicity of Aβ fibrils. Furthermore, ex vivo evolution demonstrated that amount of Aβ plaques in AD mouse's brain slices was drastically reduced by treatment with sono-activated BiOCl nanosheets.

Constructing a novel and high-performance liquid nanoparticle additive from a Ga-based liquid metal

The development of a high-performance nanoparticle (NP) additive for lubricating oil is a research hotspot for the tribology and engineering areas. In this study, the concept of a novel liquid nano-additive has been proposed based on the emergence of Ga-based liquid metals (GLMs), which display excellent extreme-pressure and high-temperature lubricity. Herein, the liquid NPs (designated as GLM-NP/C12) were prepared from a GLM droplet through the ultrasonic method, modified with 1-dodecanethiol, and are mainly distributed at 286 ± 21 nm. They have a core-shell structure with liquid-state GLM on the inside, and gallium oxide and a self-assembled alkylthiolate monolayer on the outside. In terms of the tribological performance, GLM-NP/C12s have a wonderful dispersion-stability in PAO10 oil, and provide excellent anti-adhesion, friction-reducing, and wear-resistance properties. When the additive concentration was 0.17 wt% in PAO10, the friction coefficient was reduced by 39% and the wear rate was reduced by 93% compared to those lubricated by the neat PAO10. This kind of liquid nano-additive has the advantages of easy preparation, internal composition regulation and recyclability, compared to conventional solid NPs. In addition, the liquid NPs were readily introduced into the frictional interfaces. More generally, the optimal additive concentration of the liquid NPs was much lower than that of the solid NPs. This observation has important implications for understanding the differences of the lubrication mechanisms between the solid and liquid nano-additives, and may provide a new design method and strategy of nano-additives for lubricating oil.

Synthesizing BaTiO3 Nanostructures to Explore Morphological Influence, Kinetics, and Mechanism of Piezocatalytic Dye Degradation

Piezocatalysts have attracted much attention due to their excellent degradation ability for organics. In this work, three types of BaTiO₃ (BTO) nanostructures, including hydrothermally synthesized nanocubes (NCs), sol-gel calcined nanoparticles (NPs), and electrospun nanofibers (NFs), are prepared for catalyzing the dye degradation. Compared with the NCs and NPs, the NFs exhibit a higher piezocatalytic degradation performance due to the large specific surface area, fine crystal size, and easy deformation structure. Moreover, the kinetic factors, including initial dye concentration, ionic strength, ultrasonic power, and applied action, influencing the degradation performance of the BTO NFs are analyzed deeply. A high degradation rate constant of 0.0736 min^-1 is achieved for rhodamine B, which is superior compared with the previous reports. The excellent stability of BTO NFs is demonstrated by the cycling tests, where a high degradation efficiency of 97.6% within 110 min is still obtained after the third cycle. Furthermore, the mechanism of piezocatalysis revealed that the hydroxyl and superoxide radicals are the main reactive species in the degradation process. This work is of importance for the development of high-performance piezocatalysts and highlights the potential of piezocatalysis for water remediation.

BaTiO3 Nanosheets and Caps Grown on TiO2 Nanorod Arrays as Thin-Film Catalysts for Piezocatalytic Applications

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 BaTiO₃ (BTO) thin films were fabricated by a facile hydrothermal method for their potential applications in piezocatalysis. The vertically standing BTO nanosheets grown on the top of TiO₂ nanorod arrays exhibited superior piezocatalytic performance as well as piezo-electrochemical property. Given the different strain states between thin-film piezocatalyst and powder-form piezocatalyst, both the impact force of water and isostatic pressure are taken into consideration in finite element method (FEM) simulation. The FEM simulation shows that a stronger piezoelectric filed can be built in BTO nanosheets because of their easier deformation, and thus can lead to a higher piezocatalytic degradation efficiency. Our work presented here is expected to provide a potential route for the nanoengineering of thin-film piezocatalysts and clarify the catalytic mechanism for substrate-fixed piezocatalysts.