Search Results (486)

Titanium dioxide is attractive for energy storage due to its abundance, stability, non-toxicity, low cost, and favorable electronic/optical properties. Colossal permittivity (CP) in co-doped TiO₂ is mainly linked to defect structures rather than intrinsic bulk behavior. This work studies the dielectric properties of TiO₂ co-doped with niobium and magnesium, synthesized by solid-state reaction. Grain size effects were examined by varying ball milling parameters of (½Mg½Nb)_0.05Ti_0.95O₂ and then were correlated with structure, morphology, and dielectric response. X-ray diffraction (XRD), infrared spectroscopy (FTIR), scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS), and impedance spectroscopy (IS) (40 Hz–10⁶ Hz, 150–370 K) were employed for structural, morphological, and electrical characterization. XRD confirmed the rutile phase. For co-doped samples, larger grains yielded higher dielectric constants, reaching high permittivity (ε′ = 429, T = 300 K, f = 10 kHz at 500 rpm for 2 h). Lower loss tangent (tan δ = 0.11, T = 300 K, f = 10 kHz at 200 rpm for 2 h) is linked to Mg segregation at grain boundaries. The most conductive sample showed the highest dielectric constant, suggesting an IBLC polarization mechanism driven by grain boundary effects. XPS confirmed Nb and Mg incorporation, with Ti⁴⁺ dominant and minor Ti³⁺ from oxygen vacancies and surface hydroxylation/defects. Full article

In this work, we investigate advanced photocatalyst Bi₃TiNbO₉ as promising piezophotocatalyst in terms of the effect of synthesis methods on the surface chemistry, structure, and catalytic performance in process of contaminant removal. Samples were prepared via solid-state reaction (BTNO-900) and molten salt synthesis (BTNO-800), leading to distinct morphologies and defect distributions. SEM imaging revealed that BTNO-900 consists of agglomerated, irregular particles, while BTNO-800 exhibits well-faceted, plate-like grains. Nitrogen adsorption analysis showed that the molten-synthesized sample possesses a significantly higher specific surface area (5.9 m²/g vs. 1.4 m²/g) and slightly larger average pore diameter (2.8 nm vs. 2.6 nm). High-resolution XPS revealed systematic shifts in binding energies for Bi 4f, Ti 2p, Nb 3d, and O 1s peaks in BTNO-900, accompanied by a higher content of adsorbed oxygen species (57% vs. 7.2%), indicating an increased concentration of oxygen vacancies and surface hydroxylation due to the solid-state synthesis route. Catalytic testing demonstrated that BTNO exhibits enhanced piezocatalytic efficiency of Methylene Blue degradation (~78% for both samples), whereas BTNO-800 shows significantly reduced photocatalytic activity (45.6%) compared to BTNO-900 (84.1%), suggesting recombination effects dominate in the more defective material. Synergism of light and mechanical stress results in piezophotocatalytic degradation for both samples (92.4% and 93.4%, relatively). These findings confirm that synthesis-controlled defect engineering is a key parameter for optimizing the photocatalytic behavior of Bi₃TiNbO₉-based layered oxides and crucial role of its piezocatalytic activity. Full article

This study employs a multi-technique approach to elucidate how graphene incorporation affects phase formation, microstructure, and thermal behavior in PVA-assisted sol–gel synthesized Ca_2.95Eu_0.05Co₄O_x nanomaterials. XRD confirms the preservation of the primary phases (hexagonal CaCO₃ and cubic CoO) alongside a distinct graphene (002) reflection; a systematic low-angle shift of the calcite (104) peak evidences partial relaxation of residual lattice strain with increasing graphene content, while Scherrer analysis indicates tunable crystallite size. Raman spectroscopy corroborates graphene incorporation through pronounced D (~1300 cm⁻¹) and G (~1580 cm⁻¹) bands and supports the XRD-identified phase coexistence via cobalt-oxide and calcite vibrations in the 200–700 cm⁻¹ region, also indicating increased defect/disorder with graphene loading. SEM shows grain refinement, denser/bridged lamellar textures, and reduced porosity at low–moderate graphene contents (1–3 wt.%), contrasted by agglomeration-driven heterogeneity at higher loadings (5–7 wt.%). EDX reveals increasing carbon with Ca/Co redistribution at accessible surfaces, and TG–DSC corroborates the removal of oxygen-containing groups and oxidative combustion of graphene at mid temperatures. Collectively, Raman–XRD-consistent evidence demonstrates that graphene provides a tunable handle over lattice strain, crystallite size, and grain-boundary architecture, establishing a processing–composition basis for optimizing functional (e.g., electrical/thermoelectric) performance. Full article

Bismuth vanadate (BiVO₄) has attracted significant attention as a photoanode material for photoelectrochemical (PEC) water splitting due to its suitable bandgap (~2.4 eV), strong visible light absorption, chemical stability, and cost-effectiveness. Despite these advantages, its practical application remains constrained by intrinsic limitations, including poor charge carrier mobility, short diffusion length, and sluggish oxygen evolution reaction (OER) kinetics. This review critically summarizes recent advancements aimed at enhancing BiVO₄ PEC performance, encompassing synthesis strategies, defect engineering, heterojunction formation, cocatalyst integration, light-harvesting optimization, and stability improvements. Key fabrication methods—such as solution-based, vapor-phase, and electrochemical approaches—along with targeted modifications, including metal/nonmetal doping, surface passivation, and incorporation of electron transport layers, are discussed. Emphasis is placed on strategies to improve light absorption, charge separation efficiency (η_sep), and charge transfer efficiency (η_trans) through bandgap engineering, optical structure design, and catalytic interface optimization. Approaches to enhance stability via protective overlayers and electrolyte tuning are also reviewed, alongside emerging applications of BiVO₄ in tandem PEC systems and selective solar-driven production of value-added chemicals, such as H₂O₂. Finally, critical challenges, including the scale-up of electrode fabrication and the elucidation of fundamental reaction mechanisms, are highlighted, providing perspectives for bridging the gap between laboratory performance and practical implementation. Full article

The activation and dissociation of O₂ molecules play a key role in the oxidation of toxic gas molecules and the oxygen reduction reaction (ORR) in hydrogen–oxygen fuel cells. The interactions between O₂ molecules and the surfaces of Fe-doped γ-graphyne were systematically explored, mainly adopting the combined method of the density functional theory with dispersion correction (DFT-D3) and the climbing image nudged elastic band (CI-NEB) method. The order of the formation energy values of these defective systems is E_f(Fe_C2) < E_f(Fe_C1) < E_f(Fe_D1) < E_f(V_C1) < E_f(V_D1) < E_f(V_C2) < E_f(Fe_D2) < E_f(V_D2), which indicates that the process of Fe dopant atoms substituting single-carbon atoms/double-carbon atoms is relatively easier than the formation of vacancy-like defects. The results of ab initio molecular dynamics (AIMD) simulations confirm that the doped systems can maintain structural stability at room temperature conditions. Fe-doped atoms transfer a certain amount of electrons to the adsorbed O₂ molecules, thereby causing an increase in the O-O bond length of the adsorbed O₂ molecules. The electrons obtained by the anti-bonding 2π* orbitals of the adsorbed O₂ molecules are mainly derived from the 3d orbitals of Fe atoms. There is a competitive relationship between the substrate’s carbon atoms and the adsorbed O₂ molecules for the charges transferred from Fe atoms. In the C1 and C2 systems, O₂ molecules have a greater advantage in electron accepting ability compared to the substrate’s carbon atoms. The elongation of O-O bonds and the amount of charge transfer exhibit a positive relationship. More electrons are transferred from Fe-3d orbitals to adsorbed O₂ molecules, occupying the 2π* orbitals of adsorbed O₂ molecules, further elongating the O-O chemical bond until it breaks. The dissociation process of adsorbed O₂ molecules on the surfaces of GY-Fe systems (C2 and D2 sites) involves very low energy barriers (0.016 eV for C2 and 0.12 eV for D2). Thus, our studies may provide useful insights for designing catalyst materials for oxidation reactions and the oxygen reduction reaction. Full article

Using the method of laser ablation in liquid, submicron-sized particles of zero-valent amorphous selenium (Se SMPs) were created. A number of composite polymer materials were manufactured based on polyurea and Se SMPs at concentrations ranging 0.1–2.5 wt.%. The manufactured materials showed no significant surface or internal defects at either the macro or micro level. It was found that the Se SMPs were not uniformly distributed inside the polymer, but formed ordered areas with slightly higher and lower concentrations of the particles. It was demonstrated that the manufactured materials did not generate a significant amount of active oxygen species, which could damage biological objects such as protein molecules and DNA, while also exhibiting pronounced bacteriostatic properties without significantly affecting the growth and reproduction of mammalian cells. Materials containing 0.25 and 1% Se SMPs, when added to soil, improved the morphometric parameters of radish plants (Raphanus sativus var. sativus). These polymer composite materials based on polyurea with the addition of Se SMPs are promising functional materials for agriculture due to their antibacterial activity. Full article

Rechargeable aqueous Zn-MnO₂ batteries are positioned as a highly promising candidate for next-generation energy storage, owing to their compelling combination of economic viability, inherent safety, exceptional capacity (with a theoretical value of ≈308 mAh·g⁻¹), and eco-sustainability. However, this system still faces multiple critical challenges that hinder its practical application, primarily including the ambiguous energy storage reaction mechanism (e.g., unresolved debates on core issues such as ion transport pathways and phase transition kinetics), dendrite growth and side reactions (e.g., the hydrogen evolution reaction and corrosion reaction) on the metallic Zn anode, inadequate intrinsic electrical conductivity of MnO₂ cathodes (≈10⁻⁵ S·cm⁻¹), active material dissolution, and structural collapse. This review begins by systematically summarizing the prevailing theoretical models that describe the energy storage reactions in Zn-Mn batteries, categorizing them into the Zn²⁺ insertion/extraction model, the conversion reaction involving MnO_x dissolution–deposition, and the hybrid mechanism of H⁺/Zn²⁺ co-intercalation. Subsequently, we present a comprehensive discussion on Zn anode protection strategies, such as surface protective layer construction, 3D structure design, and electrolyte additive regulation. Furthermore, we focus on analyzing the performance optimization strategies for MnO₂ cathodes, covering key pathways including metal ion doping (e.g., introduction of heteroions such as Al³⁺ and Ni²⁺), defect engineering (oxygen vacancy/cation vacancy regulation), structural topology optimization (layered/tunnel-type structure design), and composite modification with high-conductivity substrates (e.g., carbon nanotubes and graphene). Therefore, this review aims to establish a theoretical foundation and offer practical guidance for advancing both fundamental research and practical engineering of Zn-manganese oxide secondary batteries. Full article

With the aim of reducing catalysts’ cost while maintaining high performance in water splitting, ZnO and RuO₂ were combined into composites with ZnO to RuO₂ mass ratios of 1:1, 2:1, and 10:1. The ZnO/RuO₂ composites were prepared by microwave processing of a suspension containing Zn(OH)₂ in situ precipitated onto RuO₂ powder, and subsequently thermally modified at 600 °C to promote heterojunction formation and alter the defect chemistry. Phase composition, crystal structure, morphology, and optical properties were analyzed in detail employing XRD, TEM/HRTEM, HAADF-STEM with EDS, PL and XPS spectroscopy. The photoelectrocatalytic (PEC) activity of the composites toward the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) was evaluated by linear sweep voltammetry in alkaline electrolyte (0.1 M NaOH, pH 13), before and after one hour of electrochemical system illumination. The analysis focused on surface and bulk oxygen vacancies, which may have a crucial impact in PEC activity, by (1) promoting charge separation and increasing the number of active sites thus enhancing PEC activity, or (2) acting as electron–hole traps and recombination centers, reducing the lifetime of photo-induced charge carriers and thus deteriorating PEC activity. The presented results demonstrate that the combination of ZnO with RuO₂ in a specific mass ratio, along with controlled defect structure, offers a worthwhile route for developing bifunctional, noble-metal-reduced catalysts for green hydrogen and oxygen production. Full article

Co-electrolysis of CO₂ and H₂O offers a promising route for efficient and controllable syngas production from greenhouse gases and water. However, the atomic-scale reaction mechanism remains elusive, especially on complex oxide surfaces. In this study, we employ density functional theory (DFT) to investigate the adsorption and activation of CO₂ and H₂O on the FeMoO-terminated (001) surface of Sr₂Fe_1.5Mo_0.5O₆ (SFM), a double perovskite of growing interest for solid oxide electrolysis. Our results show that CO₂ strongly interacts with surface lattice oxygen, adopting a bent configuration with substantial charge transfer. In contrast, H₂O binds more weakly at Mo sites through predominantly electrostatic interactions. Co-adsorption analyses reveal a bidirectional interplay: pre-adsorbed H₂O enhances CO₂ binding by altering its adsorption geometry, whereas pre-adsorbed CO₂ weakens H₂O adsorption due to competitive site occupation. This balance suggests that moderate co-adsorption may facilitate proton–electron coupling, while excessive coverage of either species suppresses activation of the other. Bader charge analysis, charge density differences, and projected density of states highlight the key role of Fe/Mo–O hybridized states near the Fermi level in mediating surface reactivity. These results, obtained for a perfect defect-free surface, provide a theoretical benchmark for disentangling intrinsic molecule–surface and molecule–molecule interactions, and offer guidance for designing high-performance perovskite electrocatalysts for CO₂ + H₂O co-electrolysis. Full article

The sonic-IR method is an innovative approach to defect detection. Ultrasonic waves are input to the inspection object, and the frictional heat generated by friction with the defect interfaces is detected by an infrared camera. A notable advantage of this method is its superior detection ability to detect closure defects that are often missed by other inspection methods. However, the conventional Sonic-IR method of pressing an ultrasonic transducer directly against the inspection object may cause deformation or surface damage, depending on the material and shape of the object. As a method to solve this problem, the immersion Sonic-IR testing, in which ultrasonic waves are input to the inspection object through water, has been proposed. However, this method has a problem in defect detectability because of the small frictional heat at the defects. Large-diameter bubbles in water are difficult to collapse and also cause scattering and attenuation of ultrasonic waves. In contrast, small-diameter bubbles are easily collapsed so that cavitation, which is a source of vibrational energy, is likely to occur. The objective of this study is to investigate the influences of dissolved oxygen and microbubbles on the sound pressure level in the water and heat generation at defects in order to improve the defect detectability of the immersion Sonic-IR testing. Full article

Perovskite nanocrystals (PeNCs) have attracted considerable interest as promising materials for next-generation optoelectronic devices owing to their high photoluminescence quantum yield, narrow emission linewidths, simple composition tunability, and solution processability. However, the practical applicability of these NCs is limited by their compositional, thermal, and environmental instabilities, which compromise their long-term operational performance and reliability. Compositional instability arises from ion migration and phase segregation, leading to spectral shifts and unstable emission. Thermal degradation is driven by volatile organic cations and weak surface bonding, while environmental factors such as moisture, oxygen, and ultraviolet irradiation promote defect formation and material degradation. This review describes the recent advances in improving the photoluminescent stability of PeNCs through compositional engineering (A-/B-site substitution), ligand engineering (X-/L-type modulation), and surface passivation strategies. These approaches effectively suppress degradation pathways while maintaining or improving the optical properties of PeNCs. By performing a comparative analysis of these strategies, this review provides guidelines for the rational design of stable and efficient PeNCs for light-emitting applications. Full article

Reactive oxygen species (ROS) are increasingly recognized as decisive actors in photocatalytic redox chemistry, dictating both the selectivity and efficiency of target reactions, while most photocatalytic systems generate a mixture of ROS under illumination. Recent studies have revealed that tailoring the generation of specific ROS, rather than maximizing the overall ROS yield, holds the key to unlocking high-performance and application-specific catalysis. In this context, the selective production of specific ROS has emerged as a critical requirement for achieving target-oriented and sustainable photocatalytic transformations. Among the various photocatalytic materials, polymeric carbon nitride (PCN) has garnered considerable attention due to its metal-free composition, visible-light response, tunable structure, and chemical robustness. More importantly, the tunable band structure, surface chemistry, and interfacial environment of PCN collectively make it an excellent scaffold for the controlled generation of specific ROS. In recent years, numerous strategies including molecular doping, defect engineering, heterojunction construction, and co-catalyst integration have been developed to precisely tailor the ROS profile derived from PCN-based systems. This review provides a comprehensive overview of ROS regulation in PCN-based photocatalysis, with a focus on type-specific strategies. By classifying the discussion according to the major ROS types, we highlight the mechanisms of their formation and the design principles that govern their selective generation. In addition, we discuss representative applications in which particular ROS play dominant roles and emphasize the potential of PCN systems in achieving tunable and efficient photocatalytic performance. Finally, we outline key challenges and future directions for developing next-generation ROS-regulated PCN photocatalysts, particularly in the context of reaction selectivity, dynamic behavior, and practical implementation. Full article

Reactive oxygen species (ROS) play a central role in photocatalytic processes relevant to environmental remediation and clean energy. This work focused on the computational investigation of ZnO surface reactivity toward H₂O and O₂ adsorption, as a preliminary step in understanding ROS generation pathways. Surface stability and adsorption energies for isolated and co-adsorbed H₂O and O₂ molecules on different ZnO surfaces (both in their pristine form and with oxygen vacancies) were evaluated using DFT calculations at the PBE-D3 level under various surface coverages. The introduction of vacancies on the pristine (001) and (100) surfaces enhanced O₂ binding, particularly in inclined configurations at the defect sites, with the adsorption energies reaching −2.63 eV and −2.04 eV, respectively. However, the (110) surface showed very strong H₂O binding, but weak O₂ adsorption, which only modestly improved with vacancies. Co-adsorption of H₂O and O₂ exhibited synergistic stabilization, especially on the (001) and (100) surfaces, where ROS were formed through proton transfers either between adsorbed H₂O and O₂ or between H₂O and surface oxygen atoms. These findings provide detailed insight into the mechanistic role of surface defects in ROS generation and support the rational design of ZnO-based photocatalysts. Full article

The development of efficient non-noble metal catalysts is critical for advancing sustainable fuel-cell technologies. This study investigates the effect of carbon support microstructure on the oxygen reduction reaction (ORR) performance of Fe-N-C catalysts. By precisely tuning the pyrolysis temperature of activated carbon (AC) between 600 and 1000 °C, we elucidate the mechanistic influence of the physicochemical characteristics of the carbon support on the ORR activity of the supported catalyst. Increasing the pyrolysis temperature enhanced the electrical conductivity of the carbon support, thereby improving the ORR performance of the catalyst. However, while the defect density and specific surface area of the carbon support initially increased with increasing pyrolysis temperature, they declined when elevated temperatures were used (e.g., 1000 °C), leading to reduced ORR activity. The AC-900 support, pyrolyzed at 900 °C, exhibited an optimal balance of a high surface area, abundant defects, and superior conductivity. An Fe phthalocyanine/AC-900 catalyst synthesized using the AC-900 support exhibited excellent ORR activity (E_1/2: 0.89 V and E_on: 0.95 V vs. reversible hydrogen electrode (RHE)) in 0.1 M KOH. This work highlights the pivotal role of carbon support microstructure in governing the ORR activity of the supported catalyst and provides a rational strategy for designing high-performance non-noble metal electrocatalysts. Full article

Biomass carbon materials exhibit a significant specific surface area, carbon defects, and oxygen-containing functional groups during the electrochemical cathodic oxygen reduction (ORR) process, resulting in an enhanced adsorption–desorption of reaction intermediates (e.g., *OH and *OOH) by the catalyst. In this study, a cost-effective biomass-derived carbon material (HBC-500) was prepared through low-temperature pyrolysis at 500 °C using Spirulina as a precursor for H₂O₂ production. By employing surface engineering modification of the carbon-based material to promote the ORR process’s two-electron selectivity, HBC-500 demonstrated consistent experimental results with the RRDE findings at pH = 5, yielding 238.40 mg·L⁻¹ of hydrogen peroxide within a 90 min duration at a current density of 50 mA·cm⁻². Furthermore, HBC-500 accomplished over 95% degradation within 30 min at pH = 5 and maintained approximately 91.79% electrocatalytic activity after undergoing five consecutive electrocatalytic cycles lasting 300 min. These results establish HBC-500 biomass carbon material as a highly suitable candidate for H₂O₂ production and Fenton degradation of organic wastewater. Full article