Highly piezocatalysis of metal-organic frameworks material ZIF-8 under vibration

Boosting tetracycline degradation of BaTiO3-based piezo-catalysts via modulating phase boundary and band structure

Piezoelectric catalysis, which converts mechanical energy into chemical activity, has important applications in environmental remediation. However, the piezo-catalytic activity of various piezoelectric materials is limited by the weak piezoelectricity as well as the mismatched band-gap, leading to inefficient electron-hole pair generation and difficult carrier migration. Here, a simple strategy combining phase boundary and energy band structure modulation was innovatively proposed to enhance the piezo-catalytic activity of BaTiO3 ferroelectric by Ce ions selecting different doping sites. Thanks to the coexistence of tetragonal (P4mm) and orthorhombic (Amm2) phases effectively flattened the Gibbs free-energy and thus enhanced the piezoelectric activity, as well as suitable energy bandwidth facilitating the carrier migration were realized in the B-sites doped Ba(Ti0.95Ce0.05)O3. The degradation rate constant k of tetracycline (TC) was high to 30.56 × 10-3 min-1, which was 2.03 times higher than that of pure BaTiO3 and superior to most representative lead-free perovskite piezoelectric materials. Theoretical calculations validated that the charge density and high O2 and OH- adsorption energy on the Ba(Ti0.95Ce0.05)O3 surface promoted more efficient •O2- and •OH radicals conversion and bettered response to piezo-catalytic reaction. This work is important to design high-performance piezo-catalysts by synergistic regulation of phase boundary and energy band structure in perovskite materials for long-term antibiotic tetracycline removal.

Ultrasonic controllable synthesis of sulfur-functionalized metal-organic frameworks (S-MOFs) and their application in piezo-photocatalytic rapid reduction of hexavalent chromium (Cr)

The United Nations' Sustainable Development Goals (SDGs) are significant in guiding modern scientific research. In recent years, scholars have paid much attention to MOFs materials as green materials. However, piezo catalysis of MOFs materials has not been widely studied. Piezoelectric materials can convert mechanical energy into electrical energy, while MOFs are effective photocatalysts for removing pollutants. Therefore, it is crucial to design MOFs with piezoelectric properties and photosensitivity. In this study, sulfur-functionalized metal-organic frameworks (S-MOFs) were prepared using organic sulfur-functionalized ligand (H2TDC) ultrasonic synthesis to enhance their piezoelectric properties and visible light absorption. The study demonstrated that the S-MOFs significantly enhanced the reduction of a 10 mg/L solution of hexavalent chromium to 99.4 % within 10 min, using only 15 mg of catalyst. The orbital energy level differences of the elements were analyzed using piezo response force microscopy (PFM) and X-ray photoelectron spectroscopy (XPS). The results showed that MOFs functionalized with sulfur atom ligands have a built-in electric field that facilitates charge separation and migration. This study presents a new approach to enhance the piezoelectric properties of MOFs, which broadens their potential applications in piezo catalysis and piezo-photocatalysis. Additionally, it provides a sustainable method for reducing hexavalent chromium, contributing to the achievement of sustainable development goals, specifically SDG-6, SDG-7, SDG-9, and SDG-12.

Recent advances of piezo-catalysis and photocatalysis for efficient environmental remediation

The efficient degradation of organic pollutants in diverse environmental matrices can be achieved through the synergistic application of piezo-catalysis and photocatalysis. The focus of this study is on understanding the fundamental principles and mechanisms that govern the collaborative action of piezoelectric and photocatalytic materials. Piezoelectric nanomaterials, under mechanical stress, generate piezo-potential, which, when coupled with photocatalysts, enhances the generation and separation of charge carriers. The resulting cascade of redox reactions promotes the degradation of a wide spectrum of organic pollutants. The comprehensive investigation involves a variety of experimental techniques, including advanced spectroscopy and microscopy, to elucidate the intricate interplay between mechanical and photoinduced processes. The influence of key parameters, such as material composition, morphology, and external stimuli on the catalytic performance, is systematically explored. This study contributes to the increasing knowledge of environmental remediation and lays the foundation for the development of advanced technologies using piezo and photocatalysis for sustainable pollutant removal.

PVDF-Based Piezo-Catalytic Membranes-A Net-Zero Emission Approach towards Textile Wastewater Purification

Among the various water purification techniques, advancements in membrane technology, with better fabrication and analysis, are receiving the most research attention. The piezo-catalytic degradation of water pollutants is an emerging area of research in water purification technology. This review article focuses on piezoelectric polyvinylidene difluoride (PVDF) polymer-based membranes and their nanocomposites for textile wastewater remediation. At the beginning of this article, the classification of piezoelectric materials is discussed. Among the various membrane-forming polymers, PVDF is a piezoelectric polymer discussed in detail due to its exceptional piezoelectric properties. Polyvinylidene difluoride can show excellent piezoelectric properties in the beta phase. Therefore, various methods of β-phase enhancement within the PVDF polymer and various factors that have a critical impact on its piezo-catalytic activity are briefly explained. This review article also highlights the major aspects of piezoelectric membranes in the context of dye degradation and a net-zero approach. The β-phase of the PVDF piezoelectric material generates an electron-hole pair through external vibrations. The possibility of piezo-catalytic dye degradation via mechanical vibrations and the subsequent capture of the resulting CO2 and H2 gases open up the possibility of achieving the net-zero goal.

Novel ZIF-8/CNC Nanohybrid with an Interconnected Structure: Toward a Sustainable Adsorbent for Efficient Removal of Cd(II) Ions

Water pollution, especially by heavy metals, continues to pose significant challenges, emphasizing the urgency to develop sustainable processes to remove pollutants while developing sustainable materials derived from renewable sources. In the present research, a nanoscale adsorbent was prepared to remove cadmium (Cd(II)) ions from wastewater by hybridizing zeolitic imidazolate framework-8 (ZIF-8) with a cellulose nanocrystal (CNC). The prepared nanohybrid exhibited an interconnected structure in which the ZIF-8 particles were connected to each other via CNC nanoneedles. The hybridization of ZIF-8 with CNC caused a significant enhancement in the adsorption performance of the fabricated nanohybrid compared to pure ZIF-8, increasing its adsorption capacity by nearly 36%. The adsorption of ZIF/CNC followed the Langmuir isotherm model and pseudo-second-order kinetics models, remarking homogeneous adsorption onto the surface of ZIF/CNC, where chemisorption controlled the rate of adsorption. The thermodynamic study uncovered that the adsorption is spontaneous, endothermic, and entropy-governed as the randomness was increased at the solid-liquid interface. Additionally, the influence of operating variables, such as temperature, adsorbent dosage, pH, and ionic strength, was studied to mimic the adsorption capabilities of the adsorbent in real conditions. Accordingly, the optimum conditions were found to be at 45 °C and pH = 7 with a dosage of 0.4 g/L for the adsorbent. Moreover, the adsorption in a multimetal solution showed that the ZIF/CNC nanohybrid can remove various heavy metals, including Cd(II), Fe(III), Cu(II), and Pb(II) ions simultaneously. Finally, the regeneration study confirmed the great potential of the ZIF/CNC nanohybrid, which retained 94% of its initial adsorption capacity after 5 consecutive adsorption/desorption cycles.

Heterostructured piezocatalytic nanoparticles with enhanced ultrasound response for efficient repair of infectious bone defects

Infection of bone defects remains a challenging issue in clinical practice, resulting in various complications. The current clinical treatments include antibiotic therapy and surgical debridement, which can cause drug-resistance and potential postoperative complications. Therefore, there is an urgent need for an efficient treatment to sterilize and promote bone repair in situ. In this work, an ultrasound responsive selenium modified barium titanate nanoparticle (Se@BTO NP) was fabricated, which exhibited significant antibacterial and bone regeneration effects. Selenium nanoparticle (Se NP) was modified on the surface of barium titanate nanoparticle (BTO NP) to form heterostructure, which facilitated the second distribution of piezo-induced carriers under ultrasound (US) irradiation and improved the separation of electron-hole pairs. The Se@BTO NPs exhibited remarkable antibacterial efficiency with an antibacterial rate of 99.23 % against Staphylococcus aureus (S.aureus) and significantly promoted the osteogenic differentiation under ultrasound irradiation. The in vivo experiments exhibited that Se@BTO NPs successfully repaired the femoral condylar bone defects of rats infected by S.aureus, resulting in significant promotion of bone regeneration. Overall, this work provided an innovative strategy for the utilization of US responsive nanomaterials in efficient bacteria elimination and bone regeneration. STATEMENT OF SIGNIFICANCE: Infectious bone defects remain a challenging issue in clinical practice. Current antibiotic therapy and surgical debridement has numerous limitations such as drug-resistance and potential complications. Herein, we designed an innovative ultrasound responsive selenium modified barium titanate nanoparticle (Se@BTO NP) to achieve efficient non-invasive bacteria elimination and bone regeneration. In this work, Se@BTO nanoparticles can enhance the separation of electrons and holes, facilitate the transfer of free carriers due to the cooperative effect of ultrasound induced piezoelectric field and heterojunction construction, and thus exhibit remarkable antibacterial and osteogenesis effect. Overall, our study provided a promising strategy for the utilization of piezocatalytic nanomaterials in efficient antibacterial and bone regeneration.

Enhancing electrochemical properties of a two-dimensional zeolitic imidazole framework by incorporating a conductive polymer for dopamine detection

The zeolitic imidazole framework with a leaf-shaped morphology (ZIF-L) has a wide range of promising applications in gas storage, battery materials, catalytic reactions, and optoelectronic devices due to its planar leaf-like structure and large surface area. However, the low conductivity, weak catalytic activity, and poor stability in the water dielectric medium of ZIF-L limit its further practical application. To solve these problems, we added the conductive polymer heterocyclic poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) to ZIF-L for the sensitive detection of dopamine (DA). The synthesized composite ZIF-L/PEDOT:PSS (ZIF-L/PEDOT) not only retained the surface morphology of ZIF-L but also exhibited excellent electrochemical properties. The higher electrical conductivity of ZIF-L/PEDOT than that of ZIF-L was due to the enhanced electron transfer at the interface between ZIF-L and PEDOT:PSS. As a result, we developed an electrochemical biosensor based on the ZIF-L/PEDOT composite, which has a limit of detection of 7 nM for DA and a wide linear range from 25 nM to 500 μM. Furthermore, the current drop was negligible after 28 days, proving that the biosensor has excellent stability. Based on the above-mentioned outstanding performance, the ZIF-L/PEDOT-based biosensor was successfully used to detect DA in human serum samples. These results demonstrated that ZIF-L/PEDOT is expected to play an essential role in disease detection.

ZIF-8-derived Zn, N-codoped porous carbon as a high-performance piezocatalyst for organic pollutant degradation and hydrogen production

The development of highly efficient piezocatalysts has attracted widespread attention for energy conversion and pollution abatement. This paper reports for the first time exceptional piezocatalytic properties of a Zn- and N-codoped porous carbon piezocatalyst (Zn-N_x-C) derived from the zeolitic imidazolium framework-8 (ZIF-8) for both hydrogen production and degradation of organic dyes. The Zn-N_x-C catalyst has a high specific surface area of 810.6 m²/g and retains the dodecahedron structure of ZIF-8. Under ultrasonic vibration, the hydrogen production rate of Zn-N_x-C has achieved 6.29 mmol/g/h, surpassing most recently reported piezocatalysts. Additionally, the Zn-N_x-C catalyst demonstrates a 94% degradation efficiency for organic rhodamine B (RhB) dye during 180 min of ultrasonic vibration. This work sheds new light on the potential of ZIF-based materials in the field of piezocatalysis and provides a promising avenue for future developments in the area.

Piezoelectric Metal-Organic Frameworks Based Sonosensitizer for Enhanced Nanozyme Catalytic and Sonodynamic Therapies

The regulation of electrostatic electric fields through electrical stimulation is an efficient method to increase the catalytic activity of nanozymes and improve the therapeutic effect of nanozyme catalytic therapy. Piezoelectric materials, which are capable of generating a built-in electric field under ultrasound (US), not only improve the activity of nanozymes but also enable piezoelectric sonodynamic therapy (SDT). In this study, a sonosensitizer based on a Hf-based metal-organic framework (UIO-66) and Au nanoparticles (NPs) was produced. Under US irradiation, UIO-66 can generate a built-in electric field inside the materials, which promotes electron-hole separation and produces reactive oxygen species (ROS). The introduction of Au NPs facilitated the electron transfer, which inhibited the recombination of the electron-hole pairs and improved the piezoelectric properties of UIO-66. The value of the piezoelectric constant (d₃₃) increased from 71 to 122 pmV^-1 after the deposition of Au NPs. In addition, the intrinsic catalase and peroxidase activities of the Au NPs were increased 2-fold after the stimulation from the built-in electric field induced through US exposure. In vivo and in vitro experiments revealed that the proposed sonosensitizer can kill cancer cells and inhibit tumor growth in mice through the enhanced piezoelectric SDT and nanozyme catalytic therapy. The piezoelectric sensitizer proposed in this work proved to be an efficient candidate that can be used for multiple therapeutic modalities in tumor therapy.

Effect of Strontium Substitution on the Tribocatalytic Performance of Barium Titanate

This study investigates the impact of Sr doping on the tribocatalytic performance of BaTiO₃ in degrading organic pollutants. Ba_1-xSr_xTiO₃ (x = 0-0.3) nanopowders are synthesized and their tribocatalytic performance evaluated. By doping Sr into BaTiO₃, the tribocatalytic performance was enhanced, resulting in an approximately 35% improvement in the degradation efficiency of Rhodamine B using Ba_0.8Sr_0.2TiO₃. Factors such as the friction contact area, stirring speed, and materials of the friction pairs also influenced the dye degradation. Electrochemical impedance spectroscopy revealed that Sr doping improved BaTiO₃'s charge transfer efficiency, thereby boosting its tribocatalytic performance. These findings indicate potential applications for Ba_1-xSr_xTiO₃ in dye degradation processes.

Piezoelectrically enhanced photocatalysis of KxNa1-xNbO3 (KNN) microstructures for efficient water purification

As a kind of excellent multifunctional metal oxide semiconductor, K_xNa_1-xNbO₃ (KNN) has been widely applied in a variety of fields such as photocatalysis and energy harvesting due to its excellent piezoelectric, dielectric and photovoltaic properties in recent decades. In this report, octahedron-shaped K_0.4Na_0.6NbO₃ (KNN-6) microstructures assembled by cubic nanoparticles with {010} exposed facets were synthesized via a one-pot hydrothermal reaction. Due to the accumulation of electrons on the exposed facets, which was conducive to the separation of photo-generated electron-hole pairs, the microstructures could achieve a highly efficient photocatalytic performance for wastewater degradation. In addition, owing to the piezoelectric effect of KNN crystals, the degradation efficiency could be further enhanced by introducing ultrasonic vibration. Using methylene blue (MB) as the organic dye to evaluate their wastewater degradation efficiency, the KNN microstructures achieved their best catalytic performance when the atomic ratio of KOH to NaOH in the reactant was set at 4 : 6 (KNN-6). Under the synergistic effect of light irradiation and ultrasonic vibration, MB could almost be completely (99%) degraded within 40 minutes by KNN-6 microstructures, which was several times more efficient than that of pure NaNbO₃ or KNbO₃ in previous reports. This work demonstrated that the K_0.4Na_0.6NbO₃ (KNN-6) microstructure could be a prominent candidate for wastewater purification. The formation mechanism of KNN crystals and the role of the piezoelectric effect in the photocatalytic process were also discussed.

Remarkable Pyro-Catalysis of g-C3N4 Nanosheets for Dye Decoloration under Room-Temperature Cold-Hot Cycle Excitation

Pyroelectric materials have the ability to convert the environmental cold-hot thermal energy such as day-night temperature alternation into electrical energy. The novel pyro-catalysis technology can be designed and realized on the basis of the product coupling between pyroelectric and electrochemical redox effects, which is helpful for the actual dye decomposition. The organic two-dimensional (2D) graphic carbon nitride (g-C₃N₄), as an analogue of graphite, has attracted considerable interest in the field of material science; however, its pyroelectric effect has rarely been reported. In this work, the remarkable pyro-catalytic performance was achieved in the 2D organic g-C₃N₄ nanosheet catalyst materials under the continuous room-temperature cold-hot thermal cycling excitation from 25 °C to 60 °C. The pyro-catalytic RhB dye decoloration efficiency of the 2D organic g-C₃N₄ can reach ~92.6%. Active species such as the superoxide radicals and hydroxyl radicals are observed as the intermediate products in the pyro-catalysis process of the 2D organic g-C₃N₄ nanosheets. The pyro-catalysis of the 2D organic g-C₃N₄ nanosheets provides efficient technology for wastewater treatment applications, utilizing the ambient cold-hot alternation temperature variations in future.

Piezocatalytic Techniques in Environmental Remediation

As a consequence of rapid industrialization throughout the world, various environmental pollutants have begun to accumulate in water, air, and soil. This endangers the ecological environment of the earth, and environmental remediation has become an immediate priority. Among various environmental remediation techniques, piezocatalytic techniques, which uniquely take advantage of the piezoelectric effect, have attracted much attention. Piezoelectric effects allow pollutant degradation directly, while also enhancing photocatalysis by reducing the recombination of photogenerated carriers. In this Review, we provide a comprehensive summary of recent developments in piezocatalytic techniques for environmental remediation. The origin of the piezoelectric effect as well as classification of piezoelectric materials and their application in environmental remediation are systematically summarized. We also analyze the potential underlying mechanisms. Finally, urgent problems and the future development of piezocatalytic techniques are discussed.

Strong Tribocatalytic Nitrogen Fixation of Graphite Carbon Nitride g-C3N4 through Harvesting Friction Energy

Mechanical energy derived from friction is a kind of clean energy which is ubiquitous in nature. In this research, two-dimensional graphite carbon nitride (g-C₃N₄) is successfully applied to the conversion of nitrogen (N₂) fixation through collecting the mechanical energy generated from the friction between a g-C₃N₄ catalyst and a stirring rod. At the stirring speed of 1000 r/min, the tribocatalytic ammonia radical (NH₄⁺) generation rate of g-C₃N₄ can achieve 100.56 μmol·L⁻¹·g⁻¹·h⁻¹ using methanol as a positive charge scavenger, which is 3.91 times higher than that without any scavengers. Meanwhile, ammonia is not generated without a catalyst or contact between the g-C₃N₄ catalyst and the stirring rod. The tribocatalytic effect originates from the friction between the g-C₃N₄ catalyst and the stirring rod which results in the charges transfer crossing the contact interface, then the positive and negative charges remain on the catalyst and the stirring rod respectively, which can further react with the substance dissolved in the reaction solution to achieve the conversion of N₂ to ammonia. The effects of number and stirring speed of the rods on the performance of g-C₃N₄ tribocatalytic N₂ fixation are further investigated. This excellent and efficient tribocatalysis can provide a potential avenue towards harvesting the mechanical energy in a natural environment.

In Situ Construction of ZIF-67-Derived Hybrid Tricobalt Tetraoxide@Carbon for Supercapacitor

The Co3O4 electrode is a very promising material owing to its ultrahigh capacitance. Nevertheless, the electrochemical performance of Co3O4-based supercapacitors is practically confined by the limited active sites and poor conductivity of Co3O4. Herein, we provide a facile synthetic strategy of tightly anchoring Co3O4 nanosheets to a carbon fiber conductive cloth (Co3O4@C) using the zeolitic imidazolate framework-67 (ZIF-67) sacrificial template via in situ impregnation and the pyrolysis method. Benefiting from the enhancement of conductivity and the increase in active sites, the binder-free porous Co3O4@C supercapacitor electrodes possess typical pseudocapacitance characteristics, with an acceptable specific capacitance of ~251 F/g at 1 A/g and long-term cycling stability (90% after cycling 5000 times at 3 A/g). Moreover, the asymmetric and flexible supercapacitor composed of Co3O4@C and activated carbon is further assembled, and it can drive the red LED for 6 min.

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.