Study on water splitting characteristics of CdS nanosheets driven by the coupling effect between photocatalysis and piezoelectricity

Recent Advances in Piezoelectric Coupled with Photocatalytic Reaction System: Synergistic Mechanism, Enhancement Factors, and Application

The field of photocatalysis has demonstrated numerous advantages in the domains of environmental protection, energy, and materials science. However, conventional modification methods fail to simultaneously enhance carrier separation efficiency, redox capacity, and visible light absorption solely through light activation due to the intrinsic band structure limitations of photocatalysts. In addition to modification methods, the introduction of an external field, such as a piezoelectric field, can effectively address deficiencies in each step of the photocatalytic process and enhance the overall performance. The assistance of a piezoelectric field overcomes the limitations inherent in traditional photocatalytic systems. Hence, this review provides a comprehensive overview of recent advancements in piezoelectric-assisted photocatalysis and thoroughly investigates the interaction between the alternating piezoelectric field and photocatalytic processes. Various ideas for synergistic enhancement of the piezoelectric and photocatalytic properties are also explored. This multifield catalytic system shows remarkable performance in stability, pollutant degradation, and energy conversion, distinguishing it from single catalytic systems. Finally, an in-depth analysis is conducted to address the challenges and prospects associated with piezoelectric photocatalysis technology.

Beyond Conventional Catalysts: Monoelemental Tellurium as a Game Changer for Piezo-Driven Hydrogen Evolution

The increasing demand for clean hydrogen production over fossil fuels necessitates the development of sustainable piezoelectrochemical methods that can overcome the limitations of conventional electrocatalytic and photocatalytic approaches. In this regard, existing piezocatalysts face challenges related to their low piezoelectricity or active site coverage for hydrogen evolution reaction (HER). Driven by global environmental concerns, there is a compelling push to engineer practical materials for highly efficient HER. Herein, monoelemental 2D tellurium (Te) is presented as a class of layered chalcogenide with a non-centrosymmetric crystal structure (P3121 space group). The refined Te nanosheets demonstrate an unprecedented highly efficient H2 production rate ≈9000 µmol g-1 h-1 under ultrasonic mechanical vibration due to built-in piezo-potential in the system. The remarkable piezocatalytic performance of Te nanosheets arises from a synergistic interplay between their semi-metallic nature, favorable free energy landscape, enhanced electrical conductivity and outstanding piezoelectricity. As a proof of concept, the theoretical approach based on Density Functional Theory (DFT) validates the findings due to the gradual exposure of active sites on the Te nanosheets leading to a self-optimized catalytic performance for hydrogen generation. Therefore, mechanically driven Te emerges as a promising piezocatalyst with the potential to revolutionize highly efficient and sustainable technology for futuristic applications.

Dual functionality of the BiN monolayer: unraveling its photocatalytic and piezocatalytic water splitting properties

To achieve scalable and economically viable green hydrogen (H2) production, the photocatalytic and piezocatalytic processes are promising methods. The key to successful overall water splitting (OWS) for H2 production in these processes is using suitable semiconductor catalysts with appropriate band edge potentials, efficient optical absorption, higher mechanical flexibility, and piezoelectric coefficients. Thus, we explore the bismuth nitride (BiN) monolayer using density functional theory simulations, revealing intriguing catalytic properties. The BiN monolayer is a semiconductor with an indirect electronic bandgap (Eg) of 2.08 eV and displays excellent visible light absorption (approximately 105 cm-1). Detailed analyses show that the band edges satisfy the redox potential for photocatalytic OWS via biaxial strain engineering and pH variation. Notably, the solar to hydrogen conversion efficiency (ηSTH) for the BiN monolayer can reach 17.18%, which exceeds the 10% efficiency limit of photocatalysts for economical green H2 production. The obtained in-plane piezoelectric coefficient of e11 = 16.18 Å C m-1 is superior to widely studied 2D materials. Moreover, the generated piezopotential under oscillatory strain stands at 28.34 V, which can initiate the water redox reaction via the piezocatalytic mechanism. This originates from the mechanical flexibility coupled with higher piezoelectric coefficients. The result highlights the BiN monolayer's potential application in photocatalytic, piezocatalytic, and photo-piezo-catalytic OWS.

Enhanced piezo-photocatalytic performance in ZnIn2S4/BiFeO3 heterojunction stimulated by solar and mechanical energy for efficient hydrogen evolution

An emerging approach that employs both light and vibration energy on binary photo-/piezoelectric semiconductor materials for efficient hydrogen (H2) evolution has garnered considerable attention. ZnIn2S4 (ZIS) is recognized as a promising visible-light-activated photocatalyst. However, its effectiveness is constraint by the slow separation dynamics of photoexcited carriers. Density functional theory (DFT) predictions have shown that the integration of piezoelectric BiFeO3 (BFO) is conducive to the reduction of the H2 adsorption free energy (ΔGH*) for the photocatalytic H2 evolution reaction, thereby enhancing the reaction kinetics. Informed by theoretical predictions, piezoelectric BFO polyhedron particles were successfully synthesized and incorporated with ZIS nanoflowers to create a ZIS/BFO heterojunction using an ultrasonic-assisted calcination method. When subjected to simultaneous ultrasonic treatment and visible-light irradiation, the optimal ZIS/BFO piezoelectric enhanced (piezo-enhanced) heterojunction exhibited a piezoelectric photocatalytic (piezo-photocatalytic) H2 evolution rate approximately 6.6 times higher than that of pristine ZIS and about 3.0 times greater than the rate achieved under light-only conditions. Moreover, based on theoretical predictions and experimental results, a plausible mechanism and charge transfer route for the enhancement of piezo-photocatalytic performance were studied by the subsequent piezoelectric force microscopy (PFM) measurements and DFT calculations. The findings of this study strongly confirm that both the internal electric field of the step-scheme (S-Scheme) heterojunction and the alternating piezoelectric field generated by the vibration of BFO can enhance the transportation and separation of electron-hole pairs. This study presents a concept for the multipath utilization of light and vibrational energy to harness renewable energy from the environment.

Two-dimensional ternary pentagonal BCX (X = P, As, and Sb): promising photocatalyst semiconductors for water splitting with strong piezoelectricity

Seeking high-performance energy conversion materials is one of the most important issues in designing 2D materials. In the framework of density functional theory, we propose a series of ternary monolayers, penta-BCX (X = P, As, and Sb), and systematically investigate their structural stability, mechanical, piezoelectric, and photocatalytic properties. All three materials are semiconductors with a bandgap ranging from 2.56 eV to 3.24 eV, so they could be promising catalysts for the photolysis of water. Penta-BCX exhibits significant piezoelectric properties attributed to their non-centrosymmetric structure and low in-plane Young's modulus, which are expected to efficiently drive photocatalytic water decomposition. Moreover, the bandgap, band edge position, and light absorption of penta-BCX can be modulated by tensile or compressive strain to enhance their photocatalytic performance in the visible light and ultraviolet regions.

Harnessing ultrasound in photocatalysis: Synthesis and piezo-enhanced effect: A review

The photocatalytic technique has drawn far-ranging interests in addressing the current issues; however, its property suffers from the limited visible light response and rapid recombination of carriers. To address these issues, two specific approaches have been proposed to enhance the photocatalytic activity: (1) ultrasound-assisted synthesis has been utilized to prepare photocatalysts, resulting in refined grain size, increased specific surface area, and reduced photogenerated carrier recombination; (2) sonophotocatalysis and piezoelectric enhanced photocatalysis have been developed to accelerate the reaction, which utilizes the synergism between ultrasound and light. On one side, sonophotocatalysis generates cavitation bubbles which induce more reactive radicals for redox reactions. On the other side, ultrasound induces deformation of the piezoelectric material structure, which changes the internal piezoelectric potential and improves the photocatalytic performance. Currently, intensive efforts have been devoted to related research and great progress has been reached with applications in pollutant degradation, new energy production, and other fields. This work starts by elucidating the fundamental concept of ultrasound-assisted photocatalyst synthesis and photocatalysis. Then, the synergistic behavior between ultrasonic and light in ultrasonic-assisted photocatalysis has been thoroughly discussed, including pollutant degradation, water splitting, and bacterial sterilization. Finally, the challenge and outlook are investigated and proposed.

Facile synthesis of hierarchical CdS nanoflowers for efficient piezocatalytic hydrogen evolution

Piezocatalytic hydrogen evolution has emerged as a promising field for the collection and utilization of mechanical energy, as well as for generating sustainable energy throughout the day. Hexagonal CdS, an established semiconductor photocatalyst, has been widely investigated for its ability to split water into H2. However, its piezocatalytic performance has received less attention, and the relationship between its structure and piezocatalytic activity remains unclear. In this study, we prepared 3D ultrathin CdS nanoflowers with high voltage electrical response and low impedance. In pure water, without the use of any cocatalyst, CdS exhibited a piezoelectric catalytic hydrogen production rate of 1.46 mmol h-1 g-1, which was three times higher than that of CdS nanospheres (0.46 mmol h-1 g-1). Furthermore, the value-added oxidation product H2O2 was produced during the process of piezoelectric catalysis. These findings provide new insights for the design of high-efficiency piezoelectric catalytic hydrogen production.

Recent Advances in Efficient Photocatalysis via Modulation of Electric and Magnetic Fields and Reactive Phase Control

The past several years has witnessed significant progress in enhancing photocatalytic performance via robust electric and magnetic fields' modulation to promote the separation and transfer of photoexcited carriers, and phase control at reactive interface to lower photocatalytic reaction energy barrier and facilitate mass transfer. These three research directions have received soaring attention in photocatalytic field. Herein, recent advances in photocatalysis modulated by electric field (i.e., piezoelectric, pyroelectric, and triboelectric fields, as well as their coupling) with specific examples and mechanisms discussion are first examined. Subsequently, the strategy via magnetic field manipulation for enhancing photocatalytic performance is scrutinized, including the spin polarization, Lorentz force, and magnetoresistance effect. Afterward, materials with tailored structure and composition design enabled by reactive phase control and their applications in photocatalytic hydrogen evolution and carbon dioxide reduction are reviewed. Finally, the challenges and potential opportunities to further boost photocatalytic efficiency are presented, aiming at providing crucial theoretical and experimental guidance for those working in photocatalysis, ferroelectrics, triboelectrics, piezo-/pyro-/tribo-phototronics, and electromagnetics, among other related areas.

Pyro-photocatalytic Coupled Effect in Ferroelectric Bi0.5Na0.5TiO3 Nanoparticles for Enhanced Dye Degradation

Advanced oxidation processes (AOPs), achieved through the continuous attack of reactive oxygen species (ROS), are considered the most efficient way to mineralize organic pollutants. Among them, photocatalysis is the most environmentally friendly strategy for pollution mitigation but is hampered by low conversion efficiency. By exploiting the coupling effect without changing the properties of the semiconductor, the application of pyroelectric fields can significantly improve the catalytic performance. The degradation rate of rhodamine B by Bi_0.5Na_0.5TiO₃ (BNT) nanoparticles under temperature fluctuations and visible light irradiation was up to 98%. The performance was enhanced by 216.54% and 31.48% compared to the pyroelectric catalysis and photocatalysis alone, respectively. The improved performance is due to the introduced pyroelectric potential with the imposition of temperature fluctuations, which can make the domains enhance the polarization of ferroelectrics, thus promoting the charge separation. This method can significantly advance the coupled pyro-photocatalytic reaction of ferroelectric semiconductors and also can enable the synergistic utilization of multiple energy sources such as solar and thermal energy, which is a promising strategy for environmental remediation.

Bi4TaO8Cl as a New Class of Layered Perovskite Oxyhalide Materials for Piezopotential Driven Efficient Seawater Splitting

Piezocatalytic water splitting is an emerging approach to generate "green hydrogen" that can address several drawbacks of photocatalytic and electrocatalytic approaches. However, existing piezocatalysts are few and with minimal structural flexibility for engineering properties. Moreover, the scope of utilizing unprocessed water is yet unknown and may widely differ from competing techniques due to the constantly varying nature of surface potential. Herein, we present Bi₄TaO₈Cl as a representative of a class of layered perovskite oxyhalide piezocatalysts with high hydrogen production efficiency and exciting tailorable features including the layer number, multiple cation-anion combination options, etc. In the absence of any cocatalyst and scavenger, an ultrahigh production rate is achievable (1.5 mmol g^-1 h^-1), along with simultaneous generation of value-added H₂O₂. The production rate using seawater is somewhat less yet appreciably superior to photocatalytic H₂ production by most oxides as well as piezocatalysts and has been illustrated using a double-layer model for further development.

Recent Advancements in Photocatalysis Coupling by External Physical Fields

Photocatalysis is one of the most promising green technologies to utilize solar energy for clean energy achievement and environmental governance, such as artificial photosynthesis, water splitting, pollutants degradation, etc. Despite decades of research, the performance of photocatalysis still falls far short of the requirement of 5% solar energy conversion efficiency. Combining photocatalysis with the other physical fields has been proven to be an efficient way around this barrier which can improve the performance of photocatalysis remarkably. This review will focus on the recent advances in photocatalysis coupling by external physical fields, including Thermal-coupled photocatalysis (TCP), Mechanical-coupled photocatalysis (MCP), and Electromagnetism-coupled photocatalysis (ECP). In this paper, coupling mechanisms, materials, and applications of external physical fields are reviewed. Specifically, the promotive effect on photocatalytic activity by the external fields is highlighted. This review will provide a detailed and specific reference for photocatalysis coupling by external physical fields in a deep-going way.

Piezo-photocatalytic flexible PAN/TiO2 composite nanofibers for environmental remediation

Mechanical vibrations and solar energy are ubiquitous in the environment. Hereon, we report the synergic enhancement of the oxidation by simultaneously harvesting solar and mechanical vibrations through flexible piezo and photocatalytic composite nanofiber mats. Surface enriched titanium dioxide nanoparticles incorporated in polyacrylonitrile (PAN/TiO₂) nanofibers were synthesized using a single pot electrospinning process with well-defined fiber diameters with widely tunable loading density. By incorporating photocatalytic TiO₂ in flexible piezoelectric PAN nanofiber support, piezoelectric fields generated under the mechanical deformation promote the separation of the photogenerated electrons and holes to accelerate oxidation of pollutants. Our results demonstrated that the catalytic activity of PAN/TiO₂ nanofibers in photodegradation of Rhodamine B (RhB) can be greatly enhanced by environmental vibration-induced piezoelectricity of PAN nanofibers, with a maximum enhancement factor of ~2.5. The working mechanism for the enhanced photocatalytic activity of PAN/TiO₂ nanofibers by the mechanical vibrations were attributed to the piezoelectric effect of PAN nanofibers, which could efficiently promote the separation of the photogenerated electrons and holes in the TiO₂ nanoparticles. We believe the approach to enhancing the catalytic activity of mat can make full use of the polymer properties and natural energy, and it also can be extended to other composite polymer/semiconductor systems.

Enhanced charge separation in La2NiO4 nanoplates by coupled piezocatalysis and photocatalysis for efficient H2 evolution

Photocatalytic hydrogen evolution is one promising method for solar energy conversion, but the rapid charge recombination limits its efficiency. To this end, in this work, grain size, and hence the charge carrier migration path, is reduced by lowering the synthesis temperature of two-dimensional visible light-responsive La₂NiO₄ perovskite. Interestingly, the hydrogen yield for the piezoelectric response of La₂NiO₄ under only 40 kHz ultrasonic vibration is as high as 680 μmol h^-1 g^-1, which is 80 times that under only 600 mW cm^-2 visible light irradiation. More surprisingly, the hydrogen production rate under both light illumination and ultrasonic vibration is 129 times higher than under visible light irradiation alone. Clearly, a synergistic effect exists between piezocatalysis and photocatalysis. The hydrogen production activity of the samples with water splitting can reach 1097 μmol h^-1 g^-1 without any sacrificial reagent or co-catalyst, when the light intensity reaches about 1000 mW cm^-2, which is a much higher hydrogen evolution rate by piezo-photocatalysis than is achieved by either piezocatalysis or photocatalysis individually. Further analysis indicates that the internal electric field generated by deformation of the La₂NiO₄ edge under piezoelectric action facilitates the directional separation and migration of photogenerated charges, which in turn significantly enhances the efficiency of use of photogenerated charges for hydrogen production. The investigation here provides a novel approach to design a new reaction system for hydrogen production by coupling multiple external physical fields.

Boosting sluggish photocatalytic hydrogen evolution through piezo-stimulated polarization: a critical review

To address the growing energy demand, remarkable progress has been made in transferring the fossil fuel-based economy to hydrogen-based environmentally friendly photocatalytic technology. However, the sluggish production rate due to the quick charge recombination and slow diffusion process needs careful engineering to achieve the benchmark photocatalytic efficiency. Piezoelectric photocatalysis has emerged as a promising field in recent years due to its improved catalytic performance facilitated by a built-in electric field that promotes the effective separation of excitons when subjected to mechanical stimuli. This review discusses the recent progress in piezo-photocatalytic hydrogen evolution while elaborating on the mechanistic pathway, effect of piezo-polarization and various strategies adopted to improve piezo-photocatalytic activity. Moreover, our review systematically emphasizes the fundamentals of piezoelectricity and piezo-phototronics along with the operational mechanism for designing efficient piezoelectric photocatalysts. Finally, the summary and outlooks provide insight into the existing challenges and outline the future prospects and roadmap for the development of next-generation piezo-photocatalysts towards hydrogen evolution.

Piezocatalytic and Photocatalytic Hydrogen Peroxide Evolution of Sulfide Solid Solution Nano-Branches from Pure Water and Air

Hydrogen peroxide (H₂ O₂ ) as a useful chemical has a wide range of applications, and the development of efficient semiconducting materials for H₂ O₂ production is deemed as a promising strategy to realize the energy conversion. In this paper, Cd_x Zn_1-x S (x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1) nano-branches are fabricated and the piezocatalytic and photocatalytic H₂ O₂ evolution performance are studied. Under ultrasound condition, the H₂ O₂ yield of as-synthesized solid solutions is all higher than those of pristine ZnS and CdS, and optimal evolution rate achieves 21.9 µmol g^-1 h^-1 for Cd_0.5 Zn_0.5 S without any sacrificial agent, while it is increased to 151.6 µmol g^-1 h^-1 under visible light irradiation. The piezo/photoelectrochemical tests, piezoresponse force microscopy (PFM), and computational simulation reveal that the nano-branch structure benefits the mechanical energy conversion more, favoring the H₂ O₂ evolution for Cd_0.5 Zn_0.5 S, and a higher concentration of charge carriers is generated in photocatalysis. The active radical trapping and in situ electron spin resonance (ESR) experiments demonstrate that both of the H₂ O₂ generation pathways are originated from oxygen reduction by the sequential two-step single-electron reaction. This work opens a door for promoting the H₂ O₂ production from nanostructure and solid solution design.

Advances in preparation, mechanism and applications of graphene quantum dots/semiconductor composite photocatalysts: A review

Due to the low efficiency of single-component nano materials, there are more and more studies on high-efficiency composites. As zero dimensional (0D) non-metallic semiconductor material, the emergence of graphene quantum dots (GQDs) overcomes the shortcomings of traditional photocatalysts (rapid rate of electron-hole recombination and narrow range of optical response). Their uniqueness is that they can combine the advantages of quantum dots (rich functional groups at edge) and sp² carbon materials (large specific surface area). The inherent inert carbon stabilizes chemical and physical properties, and brings new breakthroughs to the development of benchmark photocatalysts. The photocatalytic efficiency of GQDs composite with semiconductor materials (SCs) can be improved by the following three points: (1) accelerating charge transfer, (2) extending light absorption range, (3) increasing active sites. The methods of preparation (bottom-up and top-down), types of heterojunctions, mechanisms of photocatalysis, and applications of GQDs/SCs (wastewater treatment, energy storage, gas sensing, UV detection, antibiosis and biomedicine) are comprehensively discussed. And it is hoped that this review can provide some guidance for the future research on of GQDs/SCs on photocatalysis.

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.

Piezoelectric effect enhanced photocatalysis in environmental remediation: State-of-the-art techniques and future scenarios

Photocatalysis has been widely used as an advanced oxidation process to control pollutants effectively. However, environmental photocatalysis' decontamination efficiency is restricted to the photogenerated electron-hole pairs' rapid recombination. Recently, emerging investigations have been directed to generate internal electric field by piezoelectric effect to enhance the separation efficiency of photogenerated charge carriers for better photocatalytic performance; however, there are still huge knowledge gaps on the rational application of piezo-photocatalysis in environmental remediation and disinfection. Thus, we have conducted a comprehensive review to better understand the physicochemical properties of piezoelectric materials (non-centrosymmetric crystal structures, piezoelectric coefficient, Young's modulus, and etc.) and current study states. We also elucidated the strategy of piezo-photo catalysis system constructions (mono-component, core-shell structure, and etc.) and underlying mechanisms of enhanced remediation performance. Addressing the current challenges and future scenarios (degradation of organic pollutants, disinfection, and etc.), the present review would shed light on the advanced wastewater treatment development towards sustainable control of emerging containments.

Synergetic degradation of organic dyes and Cr(vi) by the piezocatalytic BZT-xBCT

Recently, piezo-catalysts have gained considerable attention owing to their unique ability to degrade pollutants by harvesting trivial mechanical energy from the surrounding environment.

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.

Piezo-phototronic effect on photocatalysis, solar cells, photodetectors and light-emitting diodes

The piezo-phototronic effect (a coupling effect of piezoelectric, photoexcitation and semiconducting properties, coined in 2010) has been demonstrated to be an ingenious and robust strategy to manipulate optoelectronic processes by tuning the energy band structure and photoinduced carrier behavior. The piezo-phototronic effect exhibits great potential in improving the quantum yield efficiencies of optoelectronic materials and devices and thus could help increase the energy conversion efficiency, thus alleviating the energy shortage crisis. In this review, the fundamental principles and challenges of representative optoelectronic materials and devices are presented, including photocatalysts (converting solar energy into chemical energy), solar cells (generating electricity directly under light illumination), photodetectors (converting light into electrical signals) and light-emitting diodes (LEDs, converting electric current into emitted light signals). Importantly, the mechanisms of how the piezo-phototronic effect controls the optoelectronic processes and the recent progress and applications in the above-mentioned materials and devices are highlighted and summarized. Only photocatalysts, solar cells, photodetectors, and LEDs that display piezo-phototronic behavior are reviewed. Material and structural design, property characterization, theoretical simulation calculations, and mechanism analysis are then examined as strategies to further enhance the quantum yield efficiency of optoelectronic devices via the piezo-phototronic effect. This comprehensive overview will guide future fundamental and applied studies that capitalize on the piezo-phototronic effect for energy conversion and storage.

High piezocatalytic capability in CuS/MoS2 nanocomposites using mechanical energy for degrading pollutants

Piezocatalysis, driven by mechanical energy and piezoelectric effect, is of great potential in addressing the environmental issues. In this work, a piezoelectric catalyst was fabricated by growing few-layer MoS₂ nanosheets onto CuS, for the piezocatalytic degradation of Rhodamine B (RhB), methylene blue (MB) and hexavalent chromium (Cr (VI)). The excellent removal efficiency of Cr (VI) and RhB can be reached 100% within 180 s, through the piezocatalysis of CuS/MoS₂-0.6 driven by mechanical stirring in the dark. Impressively, the piezoelectric current of CuS/MoS₂-0.6 is 48 and 35.7 times higher than that of pure CuS and MoS₂, respectively. The significantly enhanced piezocatalytic performance can be ascribed to the formation of CuS/MoS₂ heterojunction and the piezoelectric field generated by MoS₂ nanosheets, which promotes the efficient separation of electrons and holes. This study provides insights into strategies to improve catalytic performance through utilizing mechanical energy and opens a new horizon for environmental remediation.

Piezocatalytic Effect Induced Hydrogen Production from Water over Non-noble Metal Ni Deposited Ultralong GaN Nanowires

Piezoelectric material-based catalysis that relies on an external stress-induced piezopotential has been demonstrated to be an effective strategy toward various chemical reactions. In this work, non-noble metal Ni-decorated ultralong monocrystal GaN nanowires (NWs) were prepared through a chemical vapor deposition (CVD) technique, followed by a photodeposition method. The piezocatalytic activity of the GaN NWs was enhanced by ∼9 times after depositing the Ni cocatalyst, generating hydrogen gas of ∼88.3 μmol·g^-1·h^-1 under ultrasonic vibration (110 W and 40 kHz), which is comparable to that of Pt-loaded GaN NWs. Moreover, Ni/GaN NWs with smaller diameters (∼100 nm) demonstrated superior piezocatalytic efficiency, which can be attributed to the large piezoelectric potential evidenced by both finite-element analysis and piezoresponse force microscopy measurements. These results demonstrate the promising application potential of non-noble metal loaded GaN nanostructures in hydrogen generation driven by weak mechanical energy from the surrounding environment.

Photocatalysis Enhanced by External Fields

The efficient conversion of solar energy by means of photocatalysis shows huge potential to relieve the ongoing energy crisis and increasing environmental pollution. However, unsatisfactory conversion efficiency still hinders its practical application. The introduction of external fields can remarkably enhance the photocatalytic performance of semiconductors from the inside out. This review focuses on recent advances in the application of diverse external fields, including microwaves, mechanical stress, temperature gradient, electric field, magnetic field, and coupled fields, to boost photocatalytic reactions, for applications in, for example, contaminant degradation, water splitting, CO₂ reduction, and bacterial inactivation. The relevant reinforcement mechanisms of photoabsorption, the transport and separation of photoinduced charges, and adsorption of reagents by the external fields are highlighted. Finally, the challenges and outlook for the development of external-field-enhanced photocatalysis are presented.

Direct Z-scheme CdS–NiPc heterojunctions as noble metal-free photocatalysts for enhanced photocatalytic hydrogen evolution

A direct Z-scheme CdS-NiPc heterojunction was successfully synthesized by a one-step hydrothermal method. The optimal photocatalytic H2 production rate could reach 17.74 mmol h−1 g−1, which was 19.1 times higher than that of the pure CdS sample.

A cathodic photocorrosion-assisted strategy to construct a CdS/Pt heterojunction photocatalyst for enhanced photocatalytic hydrogen evolution

A novel strategy based on the cathodic photocorrosion effect of CdS was developed to fabricate a CdS/Pt heterojunction photocatalyst, achieving a remarkable enhancement for H₂ evolution.

Sustainable Internal Electric Field for Enhanced Photocatalysis: From Material Design to Energy Utilization

The intrinsic internal electric field in a ferroelectric photocatalyst is beneficial for improving the photocatalytic properties because of its positive effect on the separation and migration of photogenerated carriers. However, this kind of internal electric field is static and easily saturated by inner and outer shielding effects, seriously restricting its potential in photocatalysis. To overcome this problem, a sustainable internal electric field was introduced into photocatalysis based on piezoelectric and pyroelectric effect, which exhibits good capability in consistently boosting photocatalytic activity, thus becoming a hot research topic. In this Perspective we summarize the recent significant progress in the construction of sustainable internal electric fields for facilitating photocatalysis from material design to energy utilization. Moreover, the fascinating influence of sustainable internal electric fields on carrier behavior is also discussed. Finally, a summary and outlook for building a sustainable internal electric field to further enhance photocatalytic performance are provided.