Vacancy Concentration Research Articles

Self-assembled iron (II) phthalocyanine modified oxygen vacancy-rich WO3 nanofibers with unique S-scheme heterojunctions for efficient tetracycline hydrochloride degradation and CO2 reduction

The advancement of efficient photocatalysts is crucial for the conversion of carbon dioxide (CO2) into chemical fuels and wastewater treatment, due to the significant role in promoting energy sustainability and environmental remediation. In this work, we synthesized iron (II) phthalocyanine modified oxygen vacancy-rich (FePc/OVs-rich WO3) photocatalyst with an S-scheme structure through electrospinning-calcination and electrostatic self-assembly. The optimized FePc/WO3–2 nanocomposite demonstrated approximately 3.69-fold enhancement in photoactivity for the conversion of CO2 to CO and CH4, as compared with the OVs-rich WO3 nanofibers. Furthermore, the FePc/WO3–2 catalyst demonstrated outstanding efficacy in activating peroxymonosulfate (PMS) for the degradation of tetracycline hydrochloride (TC), achieving an efficiency of 84.9 % within 60 min and a rate constant of 0.924 h−1. The improved photocatalytic performance is attributed to the prolonged absorption of visible light, enhanced charge separation and the increased density of catalytic reaction sites. The enhancement in charge separation is predominantly linked to the unique S-scheme transfer process, which is characterized by non-overlapping optical absorption, in-situ X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT). This process is further facilitated by the catalytic activity of central Fe2+ in FePc for the degradation of TC. The π-π interaction between FePc and the WO3 nanofibers, which have a high concentration of oxygen vacancies, resulted in a fast electron transfer pathway, allowing efficient transport of photoelectrons. This paper comprehensively examines the advancement of high-performance S-scheme FePc/OVs-rich WO3 photocatalysts for the photocatalytic reduction of CO2 and degradation of tetracycline through the photo-assisted activation of PMS.

Rapidly reversible superwettability on textured metallic surfaces

Reversible superwettability on non-coated metallic surfaces has a broad range of engineering applications, yet achieving a rapid reverse of superwettability is still technically challenging on different metals. Here we show that rapid transition between superhydrophobicity (SHB) /hydrophobicity (HB) and superhydrophilicity (SHL) within tens of minutes can be achieved on femtosecond laser-treated Al surfaces with the assistance of ultraviolet (UV) irradiation and direct-current (DC) sputtering, overcoming traditional challenges posed by Al₂O3 in wettability conversion. The extremely high wettability conversion rate on Al surfaces was found to be related to the formation of textured amorphous metal oxides, whose relative content of oxygen vacancies (OVs) can be more easily changed. In the process of wettability change, there is a linear correlation between the metal surface potential and the cosine value of the contact angle. Our findings provide a versatile approach for designing metal surfaces with rapidly reversible superwettability, enabling various applications such as oil–water separations and the controlled release of hydrophilic drugs.

Oxygen vacancy engineering in Si-doped, HfO2 ferroelectric capacitors using Ti oxygen scavenging layers

In this paper, the ferroelectric properties of TiN/Ti/Si:HfO2/TiN stacks are shown to be modulated by the Ti oxygen scavenging layer, leading to improved remanent polarization and wake-up at low switching fields. Hard x-ray photoelectron spectroscopy is used to measure the oxygen vacancy (VO) concentration in Si-doped HfO2 based capacitors. This VO engineered ferroelectric stack is then assessed at the wafer scale within 16 kbit 1T-1C FeRAM arrays integrated into 130 nm CMOS. The introduction of a Ti oxygen scavenging layer at the top interface of Si:HfO2-based BEOL-integrated metal/ferroelectric/metal capacitors enhances their ferroelectric (FE) behavior (+100% remanent polarization 2.Pr), confirming the positive role of modest concentrations of VO in orthorhombic phase crystallization at low thermal budgets. It is statistically demonstrated at 16 kbit array level that VO-rich FE Si:HfO2 facilitates 2.5 V FeRAM array operation with improved memory window. The field cycling dependence of the memory window is correlated with the VO concentration, and an endurance of 108 cycles is measured at the array level.

The entropy effect on the structure and microwave dielectric properties of high-entropy Lix(MgZnCoNi)(1-x)/4Al2O4-δ ceramics

In present study, high-entropy Lix(MgZnCoNi)(1-x)/4Al2O4-δ ceramics (x = 0.00–0.45) were synthesized using solid-state reaction route, which formed a single-phase spinel structure with a Fd-3m space group. The reduction in unit cell volume and lattice parameters were attributed to the compression of polyhedral structures. A moderate content of Li+ ions promoted the grain growth and improved the densification of ceramics. The internal connection among the conformational entropy (ΔSconfig), structure, and microwave dielectric properties in high-entropy Lix(MgZnCoNi)(1-x)/4Al2O4-δ ceramics was systematically studied. The dielectric constant (εr) was largely affected by the polarizability, and relatively high conformational entropy helped to increase the phonon vibrational energy and enhance the bond strength, resulting in low εr values. Additionally, the high concentration of oxygen vacancies, high packing fraction, low internal strain/fluctuation and suppressed damping behavior were closely related to relatively low conformational entropy. Notably, the introduction of oxygen vacancy leaded to the Al3+ ions preferentially occupy tetrahedral sites enhancing the covalency. These factors collectively reduced the intrinsic losses and improved the quality factor (Q×f). Moreover, relatively high conformational entropy conduced to the structural stability by improving the M-O (M = Li, Mg, Zn, Co, and Ni) bond strength and valence, which contributes to achieve near-zero temperature coefficient of resonant frequency (τf). As ΔSconfig changes, high-entropy Lix(MgZnCoNi)(1-x)/4Al2O4-δ ceramics presented great microwave dielectric properties: εr values of 5.46 ∼ 8.49, Q×f values of 3,540 GHz (f = 14.84 GHz) ∼ 56,950 GHz (f = 12.99 GHz), and τf values of −58 ppm/°C∼ −14 ppm/°C. Our study demonstrates that the high-entropy strategy effectively enhances microwave dielectric properties. This approach has potential applications across a broad spectrum of microwave dielectrics ceramics.

Influence of catalyst shape on plasma-assisted dry reforming of methane: A comparative study of Ni-CeO2 nano-cubes and nano-octahedra

This study investigated the performance of 10 wt% Ni-CeO2 nano-cubes (NC) and nano-octahedra (NO) shaped catalysts in plasma-assisted dry reforming of methane (DRM) environment to understand the influence of catalyst morphology on catalytic activity and global reaction pathway. The presence of different exposed crystal planes (i.e., (111), (110), and (100)) in the CeO2 shapes led to varied NiOx-CeO2 interactions, with the NO-shaped catalyst exhibiting a higher oxygen vacancy concentration, lattice defects, and moderate basic sites compared to the NC catalyst. This interaction in the plasma DRM environment significantly enhances conversions for both shaped catalysts, with the effect more pronounced in the case of the NO-shaped catalyst. The performance data suggest that running plasma DRM at moderate temperature and higher plasma power is relatively efficient. Increasing temperatures or plasma power diverts the DRM reaction towards more H2 production, reducing CO production for both shaped catalysts. This confirms the crucial role of the catalyst in controlling the global reaction pathway considering plasma power or temperature enhancement. Plasma interactions create additional surface defects during the DRM reaction, and defect concentration is closely linked to catalyst morphology. Carbon deposits on the catalyst surface can be readily removed via CO2 plasma regeneration treatment without affecting catalyst performance. Additionally, prolonged plasma exposure leads to NiO phase separation into concentrated Ni, suggesting a cyclical DRM and regeneration approach rather than a continuous reaction.

Investigation on optical and electrical properties of multilayer ITO/AZO/ITO transparent conductive oxides

This paper examines how varying the thickness of the indium tin oxide (ITO) seed layer, ranging from 8 to 20 nm, impacts the optical, electrical, and structural properties of triple-layer transparent conductive oxide ITO/aluminum doped zinc oxide (AZO)/ITO. ITO and AZO films were deposited by DC and RF magnetron sputtering, respectively. The thickness and density of each layer were measured by X-ray reflectometry (XRR). X-ray diffraction showed that as the thickness of the ITO seed layer increased, both the average size of the crystallites and the volume of the crystalline phase in the AZO film also increased. Measurements of the electrical characteristics indicated a decrease in resistivity as the thickness of the ITO seed layer increased. This reduction is attributed to enhanced charge mobility, resulting from improved crystallinity. It has been shown that a 20-nm-thick ITO seed layer is sufficient to achieve a charge mobility comparable to that of pure ITO films. The photoluminescence spectra have shown a decrease in the concentration of the oxygen vacancies with the introduction of both the cover and seed layers of ITO. The figure of merits (FOM) of the triple-layer coatings and the optical constants of the AZO and ITO films were calculated. The results of this paper indicate that the ITO20/AZO48/ITO12 triple-layer coating possesses optimal characteristics for use in high-efficiency silicon solar cells.

Micro-regulating defect-charge delocalization in Cr-doped SrTiO3 for boosting visible-light-driven overall water splitting

Difficulties in developing efficient visible-light-response photocatalysts have led to a lack of optimism in the utilization of large-scale solar energy. This article enhances the understanding of the Cr-SrTiO3 catalyst for photocatalytic overall water splitting from the perspective of micro-regulation of Ti3+ defects and oxygen vacancy concentration. The advanced characterization techniques including XPS and EPR confirm these analyses. Compared to pure Cr-SrTiO3, the Na, Cr-SrTiO3 achieve a H2 production of 40.09 μmol∙h−1, indicating that adjusting the defect state can have a major impact on carrier migration. In addition, DFT calculations show that the phenomenon of charge localization varies with the introduction of Na+/K+/Cs+, and compared to pure SrTiO3 and Cr-SrTiO3, the additional introduction of Na+ causes the best delocalization properties cooperating with Cr3+, indicating a significant transition from deep traps centered on Ti3+ to shallow defects, which is the key to improving photocatalytic activity.

Extremely low loss and high electrical resistivity in CaBi2Nb2O9 high-temperature piezoelectric ceramic by adding WO3

An appropriate amount of WO3 was added into CaBi2Nb2O9 high-temperature piezoelectric ceramics to improve the dense microstructure and enhance the electrical properties. A portion of W ions can be incorporated into the lattice, resulting in an increase in the lattice distortion and spontaneous polarization. As a result, the ferroelectric and piezoelectric properties of the ceramics are promoted. Additionally, reducing the concentration of oxygen vacancies can increase the resistivity of ceramics and significantly reduce the dielectric loss. The CBNO-0.375 wt% WO3 sample shows a large piezoelectric coefficient of 17.1 pC/N, a high remnant polarization of 12.60 µC/cm2, a high TC of 951°C and a large electrical resistivity of 1.86 × 106 Ω·cm at 600 °C. Moreover, the dielectric loss at 600 °C maintains a low value of 0.0076, which is one to two orders of magnitude lower than that of CBNO-based ceramics. Therefore, the method of adding WO3 to construct a CBNO ceramic provides a new strategy for high-temperature piezoelectric applications.

Spinel-structured catalyst formed by Fe, Cu, and Co composites for efficient toluene oxidation

Due to its distinctive structure and properties, MFe2O4 has been extensively investigated in catalytic oxidation. In this study, we synthesized a ternary metal composite Fe-based spinel catalyst using the sol-gel method for toluene oxidation. The catalytic performance assessments showed that the catalytic performance of Cu0.7Co0.3Fe2O4 (T90 = 262 °C, 100,000 mL·g−1·h−1) was superior to that of CuFe2O4 (T90 = 270 °C) and CoFe2O4 (T90 = 310 °C), compared to binary metal spinel catalysts. The characterization results indicate that the strong interactions among Cu, Co, and Fe in the ternary metal composite structure increased the content of oxygen vacancy at lower temperatures, thereby increasing the content of surface reactive oxygen species and improving catalytic performance. This study highlights the potential application of Fe-based spinel structures to develop more efficient spinel catalysts.

B-site Doping Boosts the OER and ORR Performance of Double Perovskite Oxide as Air Cathode for Zinc-Air Batteries.

Double perovskite oxides are key players as electrocatalytic oxygen catalysts in alkaline media. In this study, we synthesized B-site doped NdBaCoaFe2-aO5+δ (a= 1.0, 1.4, 1.6, 1.8) electrocatalysts, systematically to probe their bifunctionality and assess their performance in zinc-air batteries as air cathodes. X-ray photoelectron spectroscopy analysis reveals a correlation between iron reduction and increased oxygen vacancy content, influencing electrocatalyst bifunctionality by lowering the work function. The electrocatalyst with highest cobalt content, NdBaCo1.8Fe0.2O5+δ exhibited a bifunctional index of 0.95 V, outperforming other synthesized electrocatalysts. Remarkably, NdBaCo1.8Fe0.2O5+δ, demonstrated facilitated charge transfer rate in oxygen evolution reaction with four-electron oxygen reduction reaction process. As an air cathode in a zinc-air battery, NdBaCo1.8Fe0.2O5+δ demonstrated superior performance characteristics, including maximum capacity of 428.27 mA h at 10 mA cm-2 discharge current density, highest peak power density of 64 mW cm-2, with an outstanding durability and stability. It exhibits lowest voltage gap change between charge and discharge even after 350 hours of cyclic operation with a rate capability of 87.14%.

Crystal phase-driven performance of MnO2 in aqueous phase low-temperature thermal catalysis: Synergistic interactions between Mn3+ and surface lattice oxygen

Catalytic oxidation at mild conditions is crucial for mitigating the high pressure and high temperature challenges associated with current catalytic wet air oxidation (CWAO) technologies in wastewater treatment. Among potential materials for catalytic oxidation reactions, polycrystalline MnO2 existed in natural minerals holds considerable promise. However, the relationships between different crystal phases of MnO2 and their catalytic activity sources in aqueous phase remain uncertain and subject to debate. In this research, we synthesized various MnO2 crystal phases, comprising α-, β-, δ-, γ-, ε-, and λ-MnO2, and assessed their catalytic oxidation efficiency during low-temperature heating for treatment of organic pollutants. Our findings demonstrate that λ-MnO2 exhibits the highest catalytic activity, followed by δ-MnO2, γ-MnO2, α-MnO2, ε-MnO2, and β-MnO2. The variations in catalytic activity among different MnO2 are attributed to variances in their oxygen vacancy abundance and redox activity. Furthermore, we identified the primary active species, which include Mn3+ and superoxide radicals (•O2–) generated by surface lattice oxygen of MnO2. This research highlights the critical role of crystal phases in influencing oxygen vacancy content, redox activity, and overall catalytic performance, providing valuable insights for the rational design of MnO2 catalysts tailored for effective organic pollutant degradation in CWAO applications.

Tuning Stark effect by defect engineering on black titanium dioxide mesoporous spheres for enhanced hydrogen evolution

Defects can strongly affect the lattice, strain, and electronic structures of nanomaterials photocatalysts, like a double-edged sword of both positive significance and negative influence on photocatalytic performances. To date, most studies into defects only partially elucidated their beneficial or detrimental roles in photocatalysis. However, a quantitative understanding of the photocatalytic performances modulated by defect concentration still needs to be discovered. Here, a series of TiO2−X mesoporous spheres (MS) with different oxygen vacancy concentrations for photocatalytic applications were prepared by high-temperature chemical reduction. The link between oxygen vacancy concentration and photocatalytic performance was successfully established. The localization of carriers dominated by the Stark effect is first enhanced and then weakened with increasing oxygen vacancy concentration, which is a crucial factor in explaining the double-edged sword role of defect concentration in photocatalysis. As the reduction temperature rises to 300 °C, carrier localization dominated by the quantum-confined Stark effect maximizes the separation ability of photo generated electron hole pairs, thus exhibiting the best catalytic performance for photocatalytic hydrogen production and the degradation of organic pollutants, as demonstrated by a hydrogen evolution rate of 523.7 µmol g-1 h-1 and a ninefold higher RhB photodegradation rate compared to TiO2 MS. The work offers excellent flexibility for precisely constructing high-performance photocatalysts by understanding vacancy engineering.

In situ Ion Pumping Anodization to Confine Single‐Atom Fe onto TiO2 Nanotubes for Enhanced Noble‐Metal‐Free Photocatalytic Hydrogen Generation

AbstractAchieving a high dispersity of deposited transition metal is crucial in the anodization preparation of noble‐metal‐free composites for photocatalytic hydrogen generation. Herein, for the first time, an in situ ion pumping anodization method is proposed to confine single‐atom Fe within the spatially ordered structure of anodized TiO2 nanotubes (TNT), assisted by ferric sodium salt of ethylenediaminetetraacetic acid (EDTA) as an “ion pump” to deliver Fe3+ toward anodes. Both experimental and theoretical calculations confirm that highly dispersed single‐atom Fe can interact with single‐electron‐trapped oxygen vacancies (SETOV), effectively reducing the oxygen vacancy concentration in TiO2 nanotubes. This reduction promotes efficient charge carrier separation through the Fe(III)/Fe(II) pathway and enhances hydrogen desorption, ultimately boosting the photocatalytic hydrogen evolution performance.

Exploring Heterointerface Characteristics and Charge-Storage Dynamics in ALD-Developed Ultra-Thin TiO2-In2O3/Au Heterojunctions

Directional ionic migration in ultra-thin metal-oxide semiconductors under applied electric fields is a key mechanism for developing various electronic nanodevices. However, understanding charge transfer dynamics is challenging due to rapid ionic migration and uncontrolled charge transfer, which can reduce the functionality of microelectronic devices. This research investigates the supercapacitive-coupled memristive characteristics of ultra-thin heterostructured metal-oxide semiconductor films at TiO2-In2O3/Au Schottky junctions. Using atomic layer deposition (ALD), we nano-engineered In2O3/Au-based metal/semiconductor heterointerfaces. TEM studies followed by XPS elemental analysis revealed the chemical and structural characteristics of the heterointerfaces. Subsequent AFM studies of the hybrid heterointerfaces demonstrated supercapacitor-like behavior in nanometer-thick TiO2-In2O3/Au junctions, resembling ultra-thin supercapacitors, pseudocapacitors, and nanobatteries. The highest specific capacitance of 2.6 × 104 F.g−1 was measured in the TiO2-In2O3/Au junctions with an amorphous In2O3 electron gate. Additionally, we examined the impact of crystallization, finding that thermal annealing led to the formation of crystalline In2O3 films with higher oxygen vacancy content at TiO2-In2O3 heterointerfaces. This crystallization process resulted in the evolution of non-zero I-V hysteresis loops into zero I-V hysteresis loops with supercapacitive-coupled memristive characteristics. This research provides a platform for understanding and designing adjustable ultra-thin Schottky junctions with versatile electronic properties.

Numerical characterization of thermal transport in hexagonal tungsten disulfide (WS2) nanoribbons

In this study, we have investigated the thermal transport characteristics of single-layer tungsten disulfide, WS2 nanoribbons (SLTDSNRs) using equilibrium molecular dynamics simulations with the help of Green-Kubo formulation. Using Stillinger-Weber (SW) inter-atomic potential, the calculated room temperature thermal conductivities of 15 nm × 4 nm pristine zigzag and armchair SLTDSNRs are 126 ± 10 W m−1K−1 and 110 ± 6 W m−1K−1, respectively. We have explored the dependency of thermal conductivity on temperature, width, and length of the nanoribbon. The study shows that the thermal conductivity of the nanoribbon decreases with the increase in temperature, whereas the thermal conductivity increases with an increase in either the width or length of the ribbon. The thermal conductivity does not increase uniformly as the size of the ribbon changes. We have also observed that the thermal conductivity of SLTDSNRs depends on edge orientations; the zigzag nanoribbon has greater thermal conductivity than the armchair nanoribbon, regardless of temperature or dimension variations. Our study additionally delves into the tunable thermal properties of SLTDSNRs by incorporating defects, namely vacancies such as point vacancy, edge vacancy, and bi-vacancy. The thermal conductivities of nanoribbons with defects have been found to be considerably lower than their pristine counterparts, which aid in enhanced values for the thermoelectric figure of merit (zT). We have varied the vacancy concentration within a range of 0.1% to 0.9% and found that a point vacancy concentration of 0.1% leads to a 64% reduction in the thermal conductivity of SLTDSNRs. To elucidate these phenomena, we have calculated the phonon density of states for WS2 under different aspects. The findings of our work provide important understandings of the prospective applications of WS2 in nanoelectronic and thermoelectric devices by tailoring the thermal transport properties of WS2 nanoribbons.

Low-Temperature Decomposition and Oxidation of the Nerve Agent Simulant on Mesoporous Nickel Oxide and Cu-Doped Nickel Oxide.

In an effort to develop the next frontier filtration material for chemical warfare agent (CWA) decomposition, we synthesized mesoporous NiO and CuxNi1-xO (x = 0.10 and 0.20) and studied the decomposition of CWA simulant diisopropyl fluorophosphate (DIFP) on their surfaces. Mesoporous NiO and CuxNi1-xO were fully characterized and found to be a solid solution with no phase separation up to 20% copper dopant. The synthesized materials were successfully templated producing ordered mesoporous metal oxides with high surface areas (67.89- 94.38 m2/g). Through Raman spectroscopy, we showed that pure NiO contained a high concentration of Ni2+ vacancies, while Cu2+ reduced these defects. Through in situ infrared spectroscopy, we determined the surface species formed, potential pathways, and driving factors for decomposition. Upon exposure of DIFP, all materials produced similar decomposition products CO, CO2, carbonyls, and carbonates. However, decomposition reactions were sustained longer on mesoporous NiO, facilitated by the higher Ni2+ vacancy concentration. NiO was further studied with DIFP, first at low dosing temperatures (-50 °C), which still resulted in the production of CO and carbonates, and then, second, with a higher pretreatment temperature, which showed the importance of terminal hydroxyls/water to fully oxidize decomposition products to CO2. Mesoporous NiO demonstrated high decomposition and oxidation capabilities at temperatures below room temperature, all without any external excitation or noble metals, making it a promising frontier filtration material for CWA decomposition.

In-situ investigation of helium effect on diverse precipitate/matrix interface areas in irradiated 5052 aluminum alloy

Due to its low neutron cross-section and high irradiation swelling resistance, 5052 aluminum alloy is extensively utilized in the core structure and irradiation shielding of research nuclear reactors. Indeed, irradiation-induced defects may accumulate preferentially in the precipitates of aluminum alloys during service, leading to prior impairment of these precipitates, thereby inducing the degradation of mechanical properties. The interaction between irradiation defects and precipitates under irradiation, however, remains inadequately understood. In this work, the microstructure of 5052 aluminum alloy irradiated in-situ with He+ at different temperatures and subsequent annealing was investigated by transmission electron microscopy. After 1.0 dpa irradiation at different temperatures, the evolution of He bubbles within the precipitate was greater than in the matrix, and manifested a pronounced growth threshold between 373 K and 473 K. During post-irradiation annealing, compared to the matrix, also the dynamic evolution of bubbles was observed on the inner side of the precipitate interface, where bubbles coalesced and rapidly dissolved. The dynamic behavior of He bubbles within different precipitates manifested a certain discrepancy, and sink strength of two typical Al-containing precipitates was estimated. The difference in bubble evolution can be attributed to the different sink efficiency and vacancy concentration gradient around the precipitate.

Tailoring oxygen vacancies by synergy of dual metal cations in LaCo0.8M0.2O3 (M = Cu, Ni, Fe, Mn) towards catalytic oxidation of toluene

Enhancing the catalytic performance of transition metal oxide catalysts is prerequisite for the efficient catalytic oxidation of VOCs. Here the B-site partially substituted LaCoO3 (LaCo0.8M0.2O3, M = Cu, Ni, Fe and Mn) catalysts was synthesized for the catalytic oxidation of toluene. Among these catalysts, LaCo0.8Ni0.2O3 catalyst exhibits remarkable catalytic performance for toluene with T50 = 226 °C and T90 = 239 °C at an initial toluene concentration of 1000 ppm, whose T50 (and T90) reduced by 13 °C (and 34 °C) compared with that of LaCoO3. Confirmed by BET, XPS, and EPR characterizations, Ni substitution improves the specific surface area, Co3+/Co2+ ratio, Oads/Olatt ratio, and oxygen vacancies concentration. This improvement indicates the improvement of adsorption and activation of reactant, mobility of oxygen species, thereby contributing to the superior catalytic performance in toluene oxidation. The B-site of LaCoO3 occupied by dual cations caused the lattice distortion and formation of oxygen vacancies due to the ionic radii difference between Co and Ni cations. Moreover, the apparent activation energy of LaCo0.8Ni0.2O3, as the determining factor for the catalytic oxidation rate, was remarkably reduced. Our findings confirmed the synergy effect of Co and Ni cations at B-site on the enhancement of catalytic activity, which provides a promising strategy for oxygen vacancy engineering.

Local charge regulation via selenium vacancies engineering in dielectric cobalt diselenide with enhanced microwave absorption

The weak electromagnetic loss capability of the single semiconductor material is difficult to meet the complicated electromagnetic environment nowadays, so vacancy engineering is employed to optimize the dielectric loss capability of CoSe2. Selenium vacancies are introduced into CoSe2 by re-annealing treatment, and the test results show that the selenium vacancies concentration enlarged with annealing temperature. The formation of selenium vacancies introduces a localized state in CoSe2, which enhances the capability of CoSe2 to trap charge carriers, and the increased conductivity contributes to the enhancement of the dielectric loss capability. Density Functional Theory (DFT) calculations demonstrate that the selenium vacancies disrupt the original charge equilibrium distribution of the CoSe2, and the non-recombined positive and negative charge centers induce a strong electric dipole polarization loss. Benefiting from the optimization of CoSe2 dielectric loss by the selenium vacancies engineering, RLmin of CoSe2-600 reaches −30.73 dB and the effective absorption bandwidth reaches 4.00 GHz at 1.8 mm. This study provides a simple and effective solution to optimize the microwave absorption performance of single-component microwave absorption materials.

Highly efficient aerobic epoxidation of styrene using mesoporous Co-Ni catalysts

This work reports the synthesis and characterization of mesoporous cobalt-nickel mixed metal oxide catalysts with varying Co:Ni ratios using an inverse micelle template self-assembly method. Their structural and morphological properties and catalytic performance in styrene epoxidation were evaluated. Among them, the 73CoNi-250 catalyst (Co: Ni70:30 mol/mol%, calcined 250°C) exhibited a unique flower-like morphology and the highest surface area, which XPS analysis linked to a higher concentration of oxygen vacancies. Notably,73CoNi-250 demonstrated exceptional catalytic activity for styrene epoxidation, achieving near-complete styrene conversion (>99 %) and high selectivity (94 %) for styrene epoxide under mild reaction conditions without the need for oxidants such as peroxides. Furthermore, the catalyst exhibited excellent reusability (≥ 4 cycles) without significant activity loss or changes in mesoporosity. Kinetic studies revealed a first-order reaction profile and a significantly enhanced rate constant compared to the best-reported values (fivefold) in the literature, further underlining the catalyst's efficiency, and emphasizing the environmentally friendly approaches in chemical synthesis.