Two-Dimensional FePS3 Nanosheets as an Integrative Sonosensitizer/Nanocatalyst for Efficient Nanodynamic Tumor Therapy

As the emerging modalities for tumor therapy, sonodynamic therapy (SDT) and chemodynamic therapy (CDT) can generate reactive oxygen species (ROS), typically inducing tumor cell apoptosis. However, the construction of more efficient sonosensitizers integrated with excellent Fenton/Fenton-like catalytic activity to improve the synergistic therapeutic effect of SDT and CDT is still highly challenging. In this study, 2D semiconductor FePS₃ nanosheets (NSs), as one of the metal phosphorus trichalcogenides for both sonosensitizer and Fenton catalyst, are successfully synthesized via an ultrasonic-assisted liquid phase exfoliation method from bulk FePS₃ and further modified with lipoic acid-polyethylene glycol (LA-PEG) to obtain FePS₃-PEG NSs with desirable biocompatibility. The in vitro and in vivo results demonstrate that the engineered FePS₃-PEG NSs induce the combinatorial SDT/CDT effect attributing to the enhanced ROS generation and significant glutathione depletion, which can conduct highly efficient and safe tumor inhibition and prolong the life span of tumor-bearing mice. This work provides the paradigm of semiconductor FePS₃ NSs as the integrative sonosensitizer/Fenton nanocatalyst for dual nanodynamic tumor therapy, paving the new way for exploring other 2D metal phosphorus trichalcogenides in biomedicine.     

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 Sonodynamic Cancer Therapy through Iron-Doping and Oxygen-Vacancy Engineering of Piezoelectric Bismuth Tungstate Nanosheets

Sonodynamic therapy (SDT) is regarded as a new-rising strategy for cancer treatment with low invasiveness and high tissue penetration, but the scarcity of high-efficiency sonosensitizers has seriously hindered its application. Herein, the iron-doped and oxygen-deficient bismuth tungstate nanosheets (BWO-Fe NSs) with piezotronic effect are synthesized for enhanced SDT. Due to the existence of oxygen defects introduced through Fe doping, the bandgap of BWO-Fe is significantly narrowed so that BWO-Fe can be more easily activated by exogenous ultrasound (US). The oxygen defects acting as the electron traps inhibit the recombination of US-induced electrons and holes. More importantly, the dynamically renewed piezoelectric potential facilitates the migration of electrons and holes to opposite side and causes energy band bending, which further promotes the production of reactive oxygen species. Furthermore, Fe doping endows BWO-Fe with Fenton reactivity, which converts hydrogen peroxide (H₂O₂) in tumor microenvironment into hydroxyl radicals (•OH), thereby amplifying the cellular oxidative damage and enhancing SDT. Both in vitro and in vivo experiments illustrate their high cytotoxicity and tumor suppression rate against refractory breast cancer in mice. This work may provide an alternative strategy to develop oxygen-deficient piezoelectric sonosensitizers for enhanced SDT via doping metal ions.     

压电半导体纳米材料在声动力疗法中的应用进展

随着纳米医学的发展, 利用纳米材料在外源超声波的刺激下催化产生过量的活性氧物种(Reactive Oxygen Species, ROS)以治疗疾病的方法, 被称为声动力疗法(Sonodynamic Therapy, SDT), 已引起人们的广泛关注。目前, 开发可用于SDT的高效声敏剂用于提高ROS产率, 仍然是当前研究和未来临床转化的最大挑战之一。近年来, 得益于压电电子学和压电光电子学的兴起, 基于压电半导体纳米材料的新型声敏剂在SDT中崭露头角, 显示出良好的应用前景。本文从压电半导体的结构出发, 介绍了压电半导体纳米材料应用于SDT的机理研究, 以及利用压电半导体纳米材料作为声敏剂在声动力学癌症治疗及相关抗菌性能方面所取得的研究进展。最后, 本文对该领域存在的问题以及未来的发展趋势进行了展望。     

Theory‐Guided Synthesis of a Metastable Lead‐Free Piezoelectric Polymorph

Many technologically critical materials are metastable under ambient conditions, yet the understanding of how to rationally design and guide the synthesis of these materials is limited. This work presents an integrated approach that targets a metastable lead‐free piezoelectric polymorph of SrHfO₃. First‐principles calculations predict that the previous experimentally unrealized, metastable P4mm phase of SrHfO₃ should exhibit a direct piezoelectric response (d₃₃) of 36.9 pC N^?1 (compared to d₃₃ = 0 for the ground state). Combining computationally optimized substrate selection and synthesis conditions lead to the epitaxial stabilization of the polar P4mm phase of SrHfO₃ on SrTiO₃. The films are structurally consistent with the theory predictions. A ferroelectric‐induced large signal effective converse piezoelectric response of 5.2 pm V^?1 for a 35 nm film is observed, indicating the ability to predict and target multifunctionality. This illustrates a coupled theory‐experimental approach to the discovery and realization of new multifunctional polymorphs.     

Seebeck coefficient of V2O5-R2O3-TeO2 (R = Sb or Bi) glasses

The thermoelectric power of glasses in the systems V₂O₅-Sb₂O₃-TeO₂ and V₂O₅-Bi₂O₃-TeO₂ was measured at temperatures in the range 373–473 K. The glasses in both systems were found to be n-type semiconductors. The Seebeck coefficient, Q, at 473 K was determined as –192 to –151 VK^–1 for V₂O₅-Sb₂O₃-TeO₂ glasses, and –391 to –202 VK^–1 for V₂O₅-Bi₂O₃-TeO₂ glasses. For these glasses in both systems, Heikes' formula was satisfied adequately for the relationship between Q and In [C _v/(1-C_v)] (C _v = V⁴⁺/V_total, C _v is the ratio of the concentration of reduced vanadium ions), and discussions confirmed small polaron hopping conduction of the glasses in both systems. Mackenzie's formula relating to Q and V⁵⁺/V⁴⁺ was also applicable to the glasses in both systems, and it was concluded that the dominant factor determining Q was C _v.     

Contribution of equilibrium vacancies to vanadium caloric properties

For the first time, data have been obtained on the parameters of the contribution of equilibrium vacancies to the caloric properties of vanadium: the vacancy formation energy, E = 1.22 eV, the vacancy formation entropy, S = 26.8 J/(mole K)⁻¹, and the temperature dependence of the vacancy concentration (at the vanadium melting temperature, T _m = 2220 K, the concentration equals to c = 4.2%). These values are determined on the basis of experimental measurements of the average heat capacity of vanadium. From analysis of the interconnection between the vacancy contribution and the limit temperature of superheating of the beginning of melting, T _sh, we found that the most reliable vacancy-free straight line of the average heat capacity corresponds to (T _sh/T _m) ≈ 1.25 and may serve as a reliability criterion for calculation of the vacancy contribution in metals.     

Piezocatalytic Tumor Therapy by Ultrasound-Triggered and BaTiO3-Mediated Piezoelectricity

Ultrasound theranostics features non-invasiveness, minor energy attenuation, and high tissue-penetrating capability, and is playing ever-important roles in the diagnosis and therapy of diseases in clinics. Herein, ultrasound is employed as a microscopic pressure resource to generate reactive oxygen species (ROS) for piezocatalytic tumor therapy under catalytic mediation by piezoelectric tetragonal BaTiO₃ (T-BTO). Under the ultrasonic vibration, the electrons and holes are unpaired and they are separated by the piezoelectricity, resulting in the establishment of a strong built-in electric field, which subsequently catalyzes the generation of ROS such as toxic hydroxyl (^•OH) and superoxide radicals (^•O₂⁻) in situ for tumor eradication. This modality shows intriguing advantages over typical sonoluminescence-activated sonodynamic therapy, such as more stable sensitizers and dynamical control of redox reaction outcomes. Furthermore, according to the finite element modeling simulation, the built-in electric field is capable of modulating the band alignment to make the toxic ROS generation energetically favorable. Both detailed in vitro cellular level evaluation and in vivo tumor xenograft assessment have demonstrated that an injectable T-BTO-nanoparticles-embedded thermosensitive hydrogel will substantially induce ultrasound irradiation-triggered cytotoxicity and piezocatalytic tumor eradication, accompanied by high therapeutic biosafety in vivo.     

Point‐Defect‐Passivated MoS2 Nanosheet‐Based High Performance Piezoelectric Nanogenerator

In this work, a sulfur (S) vacancy passivated monolayer MoS₂ piezoelectric nanogenerator (PNG) is demonstrated, and its properties before and after S treatment are compared to investigate the effect of passivating S vacancy. The S vacancies are effectively passivated by using the S treatment process on the pristine MoS₂ surface. The S vacancy site has a tendency to covalently bond with S functional groups; therefore, by capturing free electrons, a S atom will form a chemisorbed bond with the S vacancy site of MoS₂. S treatment reduces the charge‐carrier density of the monolayer MoS₂ surface, thus the screening effect of piezoelectric polarization charges by free carrier is significantly prevented. As a result, the output peak current and voltage of the S‐treated monolayer MoS₂ nanosheet PNG are increased by more than 3 times (100 pA) and 2 times (22 mV), respectively. Further, the S treatment increases the maximum power by almost 10 times. The results suggest that S treatment can reduce free‐charge carrier by sulfur S passivation and efficiently prevent the screening effect. Thus, the piezoelectric output peaks of current, voltage, and maximum power are dramatically increased, as compared with the pristine MoS₂.     

Manipulation of Charge Transport by Metallic V13O16 Decorated on Bismuth Vanadate Photoelectrochemical Catalyst

Conductive metal oxides represent a new category of functional material with vital importance for many modern applications. The present work introduces a new conductive metal oxide V₁₃O₁₆, which is synthesized via a simplified photoelectrochemical procedure and decorated onto the semiconducting photocatalyst BiVO₄ in controlled mass percentages ranging from 25% to 37%. Owing to its excellent conductivity and good compatibility with oxide materials, the metallic V₁₃O₁₆‐decorated BiVO₄ hybrid catalyst shows a high photocurrent density of 2.2 ± 0.2 mA cm^?2 at 1.23 V versus reversible hydrogen electrode (RHE). Both experimental characterization and density functional theory calculations indicate that the superior photocurrent derives from enhanced charge separation and transfer, resulting from ohmic contact at the interface of mixed phases and superior electrical conductivity from V₁₃O₁₆. A Co–Pi coating on BiVO₄–V₁₃O₁₆ further increases the photocurrent to 5.0 ± 0.5 mA cm^?2 at 1.23 V versus RHE, which is among the highest reported for BiVO₄‐based photoelectrodes. Surface photovoltage and transient photocurrent measurements suggest a charge‐transfer model in which photocurrents are enhanced by improved surface passivation, although the barrier at the Co–Pi/electrolyte interface limits the charge transfer.     

Structural investigations of V<Subscript>2</Subscript>O<Subscript>5</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–CaO glass system by FT-IR and EPR spectroscopies

xV₂O₅·(100 − x)[0.7P₂O₅·0.3CaO] glass system was obtained for 0 ≤ x ≤ 35 mol% V₂O₅. In order to obtain information regarding their structure, several techniques such as X-Ray diffraction, FT-IR, and EPR spectroscopies were used. X-Ray diffraction patterns of investigated samples are characteristic of vitreous solids. FT-IR spectra of 0.7P₂O₅·0.3CaO glass matrix and its deconvolution show the presence in the glass structure of all structural units characteristic to P₂O₅. Their number are increasing for x ≤ 3 mol% V₂O₅ then, for higher content of vanadium ions, the number of phosphate structural units are decreasing leading to a depolymerization of the structure. The structural units characteristic to V₂O₅ were not evidenced but their contribution to the glass structure can be clearly observed. EPR revealed a well resolved hyperfine structure (hfs) typical for vanadyl ions in a C_4v symmetry for x ≤ 3 mol% V₂O₅. For 5 < x < 20 mol% V₂O₅ the spectra show a superposition of two EPR signals one due to a hfs structure and another consisting of a broad line typical for associated V⁴⁺–V⁴⁺ ions. For x ≥ 20 mol% V₂O₅ only the broad line can be observed. The composition dependence of the line-width suggests the presence of dipole–dipole interaction between vanadium ions up to x ≤ 5 mol% V₂O₅ and superexchange interactions between vanadium ions for x > 5 mol% V₂O₅.     

Ultrahigh Piezoelectric Properties in Textured (K,Na)NbO3‐Based Lead‐Free Ceramics

High‐performance lead‐free piezoelectric materials are in great demand for next‐generation electronic devices to meet the requirement of environmentally sustainable society. Here, ultrahigh piezoelectric properties with piezoelectric coefficients (d₃₃ ≈700 pC N^?1, d₃₃* ≈980 pm V^?1) and planar electromechanical coupling factor (k_p ≈76%) are achieved in highly textured (K,Na)NbO₃ (KNN)‐based ceramics. The excellent piezoelectric properties can be explained by the strong anisotropic feature, optimized engineered domain configuration in the textured ceramics, and facilitated polarization rotation induced by the intermediate phase. In addition, the nanodomain structures with decreased domain wall energy and increased domain wall mobility also contribute to the ultrahigh piezoelectric properties. This work not only demonstrates the tremendous potential of KNN‐based ceramics to replace lead‐based piezoelectrics but also provides a good strategy to design high‐performance piezoelectrics by controlling appropriate phase and crystallographic orientation.     

Modeling of diffusion and oxidation in two dimensions during silicon device processing

A process simulator named “2D-DIFFUSE” has been developed where the coupled diffusion equation of dopant impurity and point defects: interstitials and vacancies, has been solved numerically in two-dimension. The interaction of point defects has been modeled assuming quasi (i.e. local) equilibrium,C ₁ C _v=C ₁*C*_V and constant vacancy,C _v=C _v*, conditions. Indeed, these two assumptions decouple the two point defects diffusion equations. The processes modeled in the present version of the simulator include pre-deposition, diffusion and oxidation. The simulator is quite successful at modeling each process individually as well as integrating various processes and models. The program has also been applied to the simulation of phenomena as the dopant diffusion under various ambients, oxidation enhanced and retarded diffusion, emitter push effect etc. Comparisons between simulation based on point defect parameters from various sources have been made.     

Studies on the formation of V3Ga and V3Si superconducting compounds by a new diffusion process

In the present work, diffusion between vanadium and Cu-20 at.% Ga alloy and that between vanadium and Cu-20 at.% Si alloy were studied. An intermetallic compound, V₃Ga, is formed easily by the selective diffusion of gallium from the Cu-Ga alloy to the vanadium. V₅Si₃ and V₃Si are formed also by the selective diffusion of silicon from the Cu-Si alloy to the vanadium. Copper scarcely dissolves either in V₃Ga, V₅Si₃ or V₃Si. Copper is not effective for enhancing the formation of V₃Si unlike the case of V₃Ga. A large super-conducting critical current density, J _c, is obtained in the V₃Ga formed at temperatures below 700° C while a much smaller J _c is obtained in the V₃Si formed at 800° C. Changes in J _c due to the heat-treatment can be interpreted by the grain growth of the compounds.     

Revealing Nanoscale Chemical Heterogeneities in Polycrystalline Mo‐BiVO4 Thin Films

The activity of polycrystalline thin film photoelectrodes is impacted by local variations of the material properties due to the exposure of different crystal facets and the presence of grain/domain boundaries. Here a multi‐modal approach is applied to correlate nanoscale heterogeneities in chemical composition and electronic structure with nanoscale morphology in polycrystalline Mo‐BiVO₄. By using scanning transmission X‐ray microscopy, the characteristic structure of polycrystalline film is used to disentangle the different X‐ray absorption spectra corresponding to grain centers and grain boundaries. Comparing both spectra reveals phase segregation of V₂O₅ at grain boundaries of Mo‐BiVO₄ thin films, which is further supported by X‐ray photoelectron spectroscopy and many‐body density functional theory calculations. Theoretical calculations also enable to predict the X‐ray absorption spectral fingerprint of polarons in Mo‐BiVO₄. After photo‐electrochemical operation, the degraded Mo‐BiVO₄ films show similar grain center and grain boundary spectra indicating V₂O₅ dissolution in the course of the reaction. Overall, these findings provide valuable insights into the degradation mechanism and the impact of material heterogeneities on the material performance and stability of polycrystalline photoelectrodes.     

EPR and TPR investigation of the redox properties of vanadia based ceria catalysts

Vanadium cerium oxides, with different V/Ce atomic ratios, were prepared using the impregnation method and calcined under air at 500°C. Physicochemical studies have shown that at low vanadium content, polymeric V-O-V chains are stabilized on the ceria surface. Increasing the vanadium content tends to favor the formation of the CeVO₄ and V₂O₅ phases. The redox properties of these oxides have been simultaneously investigated by TPR/TPO and EPR techniques. V-O-V chains and V₂O₅ species are more easily reducible than the CeVO₄ phase. The reduction of V₂O₅ to V₂O₃ proceeds in several steps, the intermediate species being V₆O₁₃, VO₂ and V₅O₉. The reduction of V₂O₅ species interacting with ceria support leads to VO oxide. EPR measurements performed at T = −269°C have permitted to observe progressively different signals of V⁴⁺ in addition to vanadium ions in V²⁺ (3d³) paramagnetic configuration. This attribution is based on an EPR signal at g = 3.956 with eight well resolved hyper fine lines (A = 96 Gauss), which may be attributed to the perpendicular components of one of the fine transitions corresponding to the V²⁺ spectrum. At high reduction temperature, CeVO₄ phase leads in one step to CeVO₃ and a continuous and partial reduction of CeO₂ into Ce₂O₃ is observed. Re-oxidation process shows that polymeric V-O-V chains, easily reducible, are hardly re-oxidized whereas V₂O₅ species, present in the high vanadium loading samples, are easily re-oxidized at low temperatures. However, redox processes seem to be reversible.     

High-temperature heat capacity of the oxide compounds in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–V<Subscript>2</Subscript>O<Subscript>5</Subscript> system

The compounds BiVO₄, Bi₄V₂O₁₁, and Bi₁₂V₂O₂₃ have been prepared by solid-state synthesis using stoichiometric mixtures of Bi₂O₃ and V₂O₅. The effect of temperature on the heat capacity of the synthesized bismuth vanadates has been studied by differential scanning calorimetry in the range 350–950 K. The C _p (T) curves have extrema at 531.7 K for BiVO₄ and at 725.2 and 852.8 K for Bi₄V₂O₁₁, which are due to polymorphic transformations of these compounds.     

Effect of nanocrystallization on the structural and electrical conductivity enhancement of vanadium-based glasses

A new glass–ceramic nanocomposites material was prepared by a thermal nanocrystallization of V₂O₅–Bi₂O₃–P₂O₅ system with different V₂O₅ content. The amorphous state of glassy materials is confirmed by X-ray diffraction. It was shown by XRD and SEM studies that by suitable heat-treatment glasses can be turned into glass–ceramic nanocomposites consisting of crystallites smaller than 80 nm inserted in the glassy matrix. Also, it was shown that thermal nanocrystallization of as-prepared glassy samples leads to creation of nanocrystalline grains of V₂O₅, Bi₂O₃, and BiVO₄ phases. The glass–ceramic nanocomposites obtained show giant enhancement of electrical conductivity than the as-prepared glasses. The conductivity enhancement was recognized to interfacial regions adjacent crystalline grains. The conduction of the present glasses and their glass–ceramic nanocomposites was confirmed to be due to primarily non-adiabatic hopping of small polaron between vanadium ions.     

Piezoelectric and Nonlinear Optical Properties of PbGe4O9 Crystals

The piezoelectric coefficients and second-order nonlinear optical responses of different PbGe₄O₉ polymorphs were measured as a function of temperature. The PbGe₄O₉ crystals were found to possess attractive piezoelectric and nonlinear optical properties. The room-temperature piezoelectric charge coefficient d ₁₁ of -PbGe₄O₉ crystals exceeds that of quartz by a factor of 8.6. -PbGe₄O₉ exhibits 90° phase matching for the fundamental frequency and second harmonic of Nd:YAG lasers.     

Facile integration of brown TiO2−x with Bi4V2O11 and BiVO4: Double S-scheme mechanism for exceptional visible-light photocatalytic performance in degradation of pollutants

Heterogeneous photocatalysis has been denoted as a promising approach to dealing with environmental and energy crises. Herein, quantum dots (QDs) of TiO_2?x/Bi₄V₂O₁₁/BiVO₄ (T_OVBBV) heterojunction photocatalysts were successfully synthesized through a facile one-pot hydrothermal process with varying amounts of integrated Bi₄V₂O₁₁ and BiVO₄ semiconductors. The resultant photocatalysts were characterized by XPS, FT-IR, EDX, XRD, PL, EIS, SEM, TEM, HRTEM, BET, and UV–vis DRS techniques, and their photocatalytic efficiencies were examined via removing tetracycline (TC), azithromycin (AZi), and rhodamine B (RhB) under visible-light illumination. The results showed exceptionally promoted photocatalytic degradation efficiencies of the studied pollutants using the ternary T_OVBBV-2 nanocomposite. The T_OVBBV-2 nanocomposite was 45.4, 11.6, and 19.8-times more effective than TiO₂, 7.24, 5.85 and 2.34-folds better than TiO_2?x, and 9.81, 9.23, and 1.61-times more effective than Bi₄V₂O₁₁/BiVO₄ for photooxidation of TC, AZi, and RhB, respectively. The significant enhancement in the photocatalytic efficacy of the T_OVBBV-2 nanocomposite originated from the defective oxygen sites in the titanium dioxide structure, which subsequently facilitated the transfer of photo-induced charge carriers through the formed tandem n-n heterojunctions amongst TiO_2?x, Bi₄V₂O₁₁, and BiVO₄ components. In addition to high photocatalytic activities, the T_OVBBV-2 photocatalyst demonstrated good photostability and durability after concurrent applications. This work recommends the T_OVBBV photocatalyst for facile photocatalytic treatment of pollutants owing to its simple preparation route, high degradation outcomes, and robust structure for practical applications.