Ferroelectric BaBi4Ti4O15 was prepared using solid-state calcination at 950 °C for four hours. X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy were utilized to understand its microstructure and other structural aspects. Particle size was around < 1.5 µm. This oxide is able to demonstrate piezocatalysis and tribocatalysis as reflected in its dye degradation performance. This oxide showed piezocatalytic activity around 40% in 2 h and tribocatalytic activity around 90% in 12 h. The rate constant for the piezocatalytic reaction is 0.003 min-1 and for tribocatalytic reaction is 0.169 h-1. The rotation speed also affected the tribocatalytic activity of the oxide. Oxide showed 25%, 90%, and 94% tribocatalytic activity at 300, 500, and 700 rpm respectively. This material has demonstrated notable performance of catalysis under different types of mechanical energy sources and under different mechanisms.

Piezocatalysis, a transformative mechanochemical energy conversion technique, has received considerable attention over the past decade for its role in processes such as hydrogen evolution from water. Despite notable progress in the field, challenges remain, particularly in the areas of limited piezocatalysis efficiency and limited availability of materials requiring a non-centrosymmetric structure. Here, a pioneering contribution is presented by elucidating the piezocatalytic properties of hollow CaTiO3 nanocuboids, a centrosymmetric material with a nominally nonpolar state. Remarkably, CaTiO3 nanocuboids exhibit an impressive hydrogen production rate of 3.44 mmol g-1 h-1 under ultrasonic vibrations, surpassing the performance of the well-established piezocatalyst BaTiO3 (2.23 mmol g-1 h-1). In contrast, commercial CaTiO3 nanoparticles do not exhibit piezocatalytic performance. The exceptional performance of hollow CaTiO3 nanocuboids is attributed to the abundance presence of twin boundaries on the {110} facet within its crystal structure, which can impart significant polarization strength to CaTiO3. Extending the investigation to other centrosymmetric materials, such as SrZrO3 and BaZrO3, the experimental results also demonstrate their commendable properties for piezocatalytic hydrogen production from water. This research underscores the significant potential of centrosymmetric materials in piezocatalysis.

In this study, a novel piezoremediation system was developed to remediate an actual soil co-polluted by high contents of per- and polyfluoroalkyl substances (PFAS, 5725 μg/kg soil) and heavy metals (6455 mg/kg soil). Two piezocatalysts, MoS2/ceramsite (MC) and Fe3O4-MoS2/ceramsite (FMC), were synthesized using a facile hydrothermal-coprecipitation method. These two materials were employed to treat the co-contaminated soil in soil slurry environment under sonication. FMC exhibited significantly higher piezoremediation performance than MC, wherein 91.6% of PFAS, 97.8% of Cr6+ ions and 81% of total metals (Cr, Cu, Zn and Ni) were removed from the soil after 50 min of the FMC piezoremediation process. FMC also exhibited the advantages of easy separation from the slurry phase and excellent reusability. In comparison with MC, the Fe3O4-MoS2 heterojunction in FMC can stabilize MoS2 particles on the surface of ceramsite granules, promote the separation of electron/hole pairs, accelerate charge transfer, therefore enhancing piezocatalytic performance. The electron spin resonance analysis and free radical quenching tests show that •OH was the dominant oxidative radical responsible for PFAS degradation. The count of bacteria and the bacterial community structure in the treated soil can be basically restored to the initial states after 30 days of incubation under nutrient stimulation. Overall, this study not only provides a deep insight on soil remediation process, but also offers an efficient and reliable technique for simultaneous decontamination of organic and metal pollutants in soil.

Piezo-photocatalysis combines photocatalysis and piezoelectric effects to enhance catalytic efficiency by creating an internal electric field in the photocatalyst, improving carrier separation and overall performance. This study presents a high-performance piezo-photocatalyst for efficient dye degradation using a synergistic barium titanate (BTO)-MXene composite. The composite was synthesized via a facile method, combining the unique properties of BTO nanoparticles with the high conductivity of MXene. The structural and morphological analysis confirmed the successful formation of the composite, with well-dispersed BTO nanoparticles on the MXene surface. The piezo-photocatalytic activity of the composite was evaluated using a typical dye solution (Rhodamine B: RhB) under ultraviolet irradiation and mechanical agitation. The results revealed a remarkable enhancement in dye degradation (90 % in 15 min for piezo-photocatalysis) compared to individual stimuli (58.2 % for photocatalysis and 95.8 % in 90 min for piezocatalysis), highlighting the synergistic effects between BTO and MXene. The enhanced catalytic performance was attributed to the efficient charge separation and transfer facilitated by the composite\'s structure, leading to increased reactive species generation and dye molecule degradation. Furthermore, the composite exhibited excellent stability and reusability, showcasing its potential for practical applications in wastewater treatment. Overall, this work represents a promising strategy for designing high-performance synergistic catalysts, addressing the pressing need for sustainable solutions in environmental remediation.

Mechanochemistry constitutes a burgeoning field that investigates the chemical and physicochemical alterations of substances under mechanical force. It enables the synthesis of materials which was challenging to access via conventional thermal, optical, and electrical activation methods. In addition, it diminishes reliance on organic solvents and provides a novel route for green chemistry. Today, as a distinct branch alongside electrochemistry, photochemistry, and thermochemistry, mechanochemistry has emerged as an intersected research field with chemistry and material science. In recent years, the combination of mechanochemistry with controlled radical polymerization has witnessed rapid advancement, providing new sights to polymer science. The mechanochemically controlled radical polymerization (mechano-CRP) not only facilitate the synthesis of polymers with high molecular weight but also enable precise control over polymer chain length and structure. To diminish the side reactions by the strong mechanical force, transitioning from harsh to mild conditions in mechanochemical routes has been recognized as one of the primary advancements. From this perspective, we introduce the progress of mechanochemistry in controlled radical polymerization in recent years, aim to clarify the development trend of this research direction and stimulate senior researchers or newcomers to contemplate the future direction of this field.

Piezocatalysis has emerged as a sustainable alternative for hydrogen peroxide production. However, the current development of efficient piezocatalysts is predominantly focusing on those conventional piezoelectric ceramic oxides with high permittivity and limited catalytic activities. Therefore, innovative approaches to develop novel piezocatalysts in particular from these outstanding paraelectric semiconductors are highly required. In this work, by employing a feasible doping strategy, robust piezoelectric property is created on the Ba2Nb2-xFexO6-δ double perovskite oxides, typically characterized by a stable paraelectric cubic structure. Optimum Fe doping not only intensifies the double perovskite phase but also inspires a phase transition from a centrosymmetric cubic to a piezoelectric tetragonal phase, thereby achieving desirable piezoelectricity and enabling a series of favorable physical properties including redox activity, active sites of anion defects, reduced bandgap, and increased free charge density. All these are important factors to enhance piezocatalytic activity. As a result, Ba2NbFeO6-δ achieved by the optimum Fe doping demonstrated exceptional piezocatalytic H2O2 yield of 512 and 690 µmol g-1 h-1 under atmosphere and oxygen-purging conditions, respectively, without the presence of any sacrificial agents. Mechanistic investigations reveal that both water oxidation and oxygen reduction involve in the H2O2 production, wherein piezopotential plays a critical role not only in facilitating the charge carrier separation and transportation but also in modulating the band structure to enhance the catalyst redox capacity. This study offers a feasible and universal strategy for the design of novel piezocatalysts, expanding the windows for catalyst selection for piezocatalysis.

Untreated wastewater harbors dangerous pathogens, chemicals, and pollutants, posing grave public health threats. Nowadays, there is a rising demand for eco-friendly technologies for wastewater treatment. Recently, piezoelectric materials-based wastewater treatment technology has captured considerable interest among researchers because of its noninvasiveness and rapidity. Herein, a highly efficient piezoelectric composite material is designed with chitosan-incorporated bismuth ferrite (BFO) nanocrystals, to decompose pollutants and ablate bacteria in wastewater. On one hand, piezoelectric BFO has shown exclusive piezo-coefficient for ultrasound-mediated reactive oxygen species (ROS) production. On the other hand, chitosan depicts its biocompatible nature, which not only promotes cellular adhesion but also significantly elevates the ROS production capabilities of BFO under ultrasound. The synergistic effect of these two piezoelectric units in one composite entity shows an improved ROS production, eradicating ∼87.8% of Rhodamine B within 80 min under soft ultrasound treatment (rate constant, k ≈ 0.02866 min-1). After performing the scavenger experiment, it has been found that hydroxyl radicals are the dominating factor in this case. Further, the reusability of the composite piezocatalyst is confirmed through multiple cycles (five times) of the same experiment. The high polarizability of the composite material facilitates the generation of piezoelectric power through finger tapping (∼12.05 V), producing substantial instantaneous piezo-voltage. Moreover, the sample exhibits remarkable antibacterial activity, with nearly 99% bacterial eradication within 30 min. This indicates a significant advancement in utilizing biopolymeric composites incorporated with BFO for fabricating versatile devices with multidimensional applications.

The fabrication of an S-scheme heterojunction demonstrates as an efficient strategy for achieving efficient charge separation and enhancing catalytic activity of piezocatalysts. In this study, a new S-scheme heterojunction was fabricated on the PbBiO2Br surface through the photo-deposition of NiO nanoparticles. It was then employed in the piezoelectric catalytic degradation of Rhodamine B (RhB). The results demonstrate that the NiO/PbBiO2Br composite exhibits efficient performance in piezocatalytic RhB degradation. The optimal sample is the NiO/PbBiO2Br synthesized after 2 h of irradiation, achieving a RhB degradation rate of 3.11 h-1, which is 12.4 times higher than that of pure PbBiO2Br. Simultaneous exposure to visible light and ultrasound further increases in the RhB degradation rate, reaching 4.60 h-1, highlighting the synergistic effect of light and piezoelectricity in the NiO/PbBiO2Br composite. A comprehensive exploration of the charge migration mechanism at the NiO/PbBiO2Br heterojunction was undertaken through electrochemical analyses, theoretical calculations, and in-situ X-ray photoelectron spectroscopy analysis. The outcomes reveal that p-type semiconductor NiO and n-type semiconductor PbBiO2Br possess matching band structures, establishing an S-scheme heterojunction structure at their interface. Under the combined effects of band bending, interface electric fields, and Coulomb attraction, electrons and holes migrate and accumulate on the conduction band of PbBiO2Br and valence band of NiO, respectively, thereby achieving effective spatial separation of charge carriers. The catalyst\'s synergistic photo-piezoelectric catalysis effect can be ascribed to its role in promoting the generation and separation of charge carriers under both light irradiation and the piezoelectric field. The results of this investigation offer valuable insights into the development and production of catalytic materials that exhibit outstanding performance through the synergy of piezocatalysis and photocatalysis.

Molybdenum disulfide (MoS2)-based materials for piezocatalysis are unsatisfactory due to their low actual piezoelectric coefficient and poor electrical conductivity. Herein, 1T/3R phase MoS2 grown in situ on multiwalled carbon nanotubes (MWCNTs) was proposed. MoS2@MWCNTs exhibited the interwoven morphology of thin nanoflowers and tubes, and the piezoelectric response of MoS2@MWCNTs was 4.07 times higher than that of MoS2 via piezoresponse force microscopy (PFM) characterization. MoS2@MWCNTs exhibited superior activity with a 91% degradation rate of norfloxacin (NOR) after actually working 24 min (as for rhodamine B, reached 100% within 18 min) by pulse-mode ultrasonic vibration-triggered piezocatalysis. It was found that piezocatalysis for removing pollutants was attributed to the synergistic effect of free radicals (•OH and O2•-) and nonfree radical (1O2, key role) pathways, together with the innergenerated-H2O2 promoting the degradation rate. 1O2 can be generated by electron transfer and energy transfer pathways. The presence of oxygen vacancies (OVs) induced the transformation of O2 to 1O2 by triplet energy transfer. The fast charge transfer in MoS2@MWCNTs heterostructure and the coexistence of sulfur vacancies and OVs enhanced charge carrier separation resulting in a prominent piezoelectric effect. This work opens up new avenues for the development of efficient piezocatalysts that can be utilized for environmental purification.

Piezocatalysis-induced dye degradation has garnered significant attention as an effective method for addressing wastewater treatment challenges. In our study, we employed a room-temperature sonochemical method to synthesize piezoelectric barium titanate nanoparticles (BaTiO3: BTO) with varying levels of Li doping. This approach not only streamlined the sample preparation process but also significantly reduced the overall time required for synthesis, making it a highly efficient and practical method. One of the key findings was the exceptional performance of the Li-doped BTO nanoparticles. With 20 mg of Li additive, we achieved 90 % removal of Rhodamine B (RhB) dye within a relatively short timeframe of 150 minutes, all while subjecting the sample to ultrasonic vibration. This rapid and efficient dye degradation was further evidenced by the calculated kinetic rate constant, which indicated seven times faster degradation rate compared to pure BTO. The enhanced piezoelectric performance observed in the Li-doped BTO nanoparticles can be attributed to the strategic substitution of Li atoms, which facilitated a more efficient transfer of charge charges at the interface. Overall, our study underscores the potential of piezocatalysis coupled with advanced materials like Li-doped BTO nanoparticles as a viable and promising solution for wastewater treatment, offering both efficiency and environmental sustainability.