Role Of Oxygen Vacancies Research Articles

Insights into the relationship between regulation of oxygen vacancy and singlet oxygen generation in peracetic acid activation

Peracetic acid (PAA) has shown good potential in advanced oxidation techniques, but the mechanism regulating the generation of non-radical species in peracetic acid has not been clarified. Herein, Ov-Co3O4/C-x was prepared by pyrolysis of ZIF-L precursors at different temperatures to achieve the regulation of oxygen vacancy concentration and used for the degradation of sulfamethazine (SMT) by activated PAA. When x = 350 °C, the prepared Ov-Co3O4/C-350 with the highest oxygen vacancy content had the highest SMT removal efficiency and the highest rate constant(kobs), which degraded SMT by 99.6 % within 30 min. The role of oxygen vacancies(OVs) on the surface of Ov-Co3O4/C-350 was investigated using quenching experiments, Electron Paramagnetic Resonance (EPR) and X-ray Photoelectron Spectroscopy (XPS) techniques. The results showed that oxygen vacancy on the metal oxide surface can be converted into more reactive oxygen(O*), and surface OVs of Ov-Co3O4/C-350 enable efficient capture of PAA, thus generating 1O2 and R-O•. The higher the content of oxygen vacancies is, the more 1O2 is produced, while concentration of R-O• was not significantly correlated with oxygen vacancy content. Furthermore, the degradation pathway of SMT was predicted through density functional theory (DFT) calculations and identifications of intermediates, indicating that electron-rich sites such as aromatic rings and S-N bonds in the SMT molecule are more easily oxidized by reactive species. Besides, due to the low biotoxicity of the degradation products of the Ov-Co3O4/C-350/PAA system, the reaction can effectively reduce the biotoxicity and developmental toxicity. This study provides a controllable surface property strategy for a new idea in PAA-based AOP.

State of the Art and Challenges in Complete Benzene Oxidation: A Review.

Increased levels and detrimental effects of volatile organic compounds (VOCs) on air quality and human health have become an important issue in the environmental field. Benzene is classified as one of the most hazardous air pollutants among non-halogenated aromatic hydrocarbons with toxic, carcinogenic, and mutagenic effects. Various technologies have been applied to decrease harmful emissions from various sources such as petrochemistry, steel manufacturing, organic chemical, paint, adhesive, and pharmaceutical production, vehicle exhausts, etc. Catalytic oxidation to CO2 and water is an attractive approach to VOC removal due to high efficiency, low energy consumption, and the absence of secondary pollution. However, catalytic oxidation of the benzene molecule is a great challenge because of the extraordinary stability of its six-membered ring structure. Developing highly efficient catalysts is of primary importance for effective elimination of benzene at low temperatures. This review aims to summarize and discuss some recent advances in catalyst composition and preparation strategies. Advantages and disadvantages of using noble metal-based catalysts and transition metal oxide-based catalysts are addressed. Effects of some crucial factors such as catalyst support nature, metal particle size, electronic state of active metal, redox properties, reactivity of lattice oxygen and surface adsorbed oxygen on benzene removal are explored. Thorough elucidation of reaction mechanisms in benzene oxidation is a prerequisite to develop efficient catalysts. Benzene oxidation mechanisms are analyzed based on in situ catalyst characterization, reaction kinetics, and theoretical simulation calculations. Considering the role of oxygen vacancies in improving catalytic performance, attention is given to oxygen defect engineering. Catalyst deactivation due to coexistence of water vapor and other pollutants, e.g., sulfur compounds, is discussed. Future research directions for rational design of catalysts for complete benzene oxidation are provided.

Role of Oxygen Vacancies and Water in Hydrogen Peroxide Production from Oxygen and Formic Acid Catalyzed by Zirconia-Supported Gold Nanoparticle

Role of Oxygen Vacancies and Water in Hydrogen Peroxide Production from Oxygen and Formic Acid Catalyzed by Zirconia-Supported Gold Nanoparticle

Control of ferroelectricity in Ta-doped HfO2 and its non-zero-crossing current–voltage hysteresis behavior

Hafnium oxide (HfO2)-based ferroelectrics are being explored as potential candidates for ferroelectric memory devices due to their highly compatibility with complementary metal-oxide-semiconductor (CMOS) technology. Enhancing the remanent polarization and investigating the underlying mechanism are crucial tasks. In the present study, tantalum (Ta) was introduced as a dopant to induce ferroelectric properties in HfO2, a large portion of orthorhombic phase was recognized in the as-grown Ta:HfO2 without further thermal treatment. The remanent polarization of Ta:HfO2 thin films can be optimized by adjusting the oxygen flow rates during the sputtering process. The influencing factors for enhanced ferroelectric performance include the control of Ta concentration, its valence state, and the presence of singly ionized oxygen vacancies, which are influenced by oxygen addition. Furthermore, the resistive switching behavior showing non-zero crossing current–voltage (I–V) hysteresis is associated with ferroelectricity and the presence of oxygen vacancies. A model has been proposed to explain the ferroelectric resistive switching with non-zero crossing I–V characteristics by considering the role of oxygen vacancies and polarization effects. This model suggests that the oxygen vacancies at the surface layer, along with ferroelectric polarization, play a crucial role in electron transport.

The Role of Oxygen Vacancy on the Carbon Dioxide Photoreduction Using Monoclinic and Tetragonal-phase Zirconium Oxide

The Role of Oxygen Vacancy on the Carbon Dioxide Photoreduction Using Monoclinic and Tetragonal-phase Zirconium Oxide

The catalytic pathways on niobium-cerium loading catalysts for methylene blue elimination in the Fenton-like system: Roles of oxygen vacancies

The oxidation pathways affected by asymmetric and symmetric Ov sites on catalysts in the Fenton-like process should be illustrated in detail. Based on the experimental and theoretical results, it can be revealed that the asymmetric Ov sites favored nonradical species (1O2) formation by triggering H2O2 and DO to produce surface O2·-, and the migration distance between the species and pollutant was shortened due to the excellent adsorption of methylene blue (MB) on the sites. OH species were liable to be generated on the symmetric Ov sites. Calcination and the amount of medium strong acid sites of the support may be important roles in the formation of asymmetric Ovs for the Nb-Ce loading catalyst prepared by impregnation. This work unravels the different catalytc pathways of asymmetric and symmetric Ovs dominated, and also provides a facile strategy to control the oxidation pathway as desirable in the H2O2-Fenton-like system.

Bi Off‐Centering in Centrosymmetric BiOBr Leading to Ultrahigh Bifunctional Piezocatalytic Fuel Generation Efficiencies in Seawater

AbstractPiezocatalytic water‐splitting to simultaneously produce H2 and H2O2 has many potential advantages. However, the necessity to utilize materials having polar structures limits the choice of piezocatalysts. Herein, it is demonstrated that centrosymmetric BiOBr with oxygen defects can simultaneously produce H2 and H2O2 with ultrahigh efficiencies from pure and seawater without needing assistance from noble metals or scavengers. High‐pressure studies confirm that there are no non‐polar‐to‐polar phase transitions in BiOBr, though a novel isostructural phase is discovered. Computational studies reveal that oxygen vacancy distorts the BiOBr structure to induce charge‐localization and polarization. Furthermore, high pressure (i) reduces carrier effective masses and (ii) increases relative O‐2p contribution in the valence band maximum to assist catalysis and improve stability. The role of oxygen vacancy is confirmed by changing its concentration, which proportionally affects H2 evolution. The work paves the way for defect engineering to develop piezocatalysts from a large pool of non‐polar materials.

Insights into the multiple active sites in Bi-Co bimetallic oxide for a deeper understanding of nitrate electroreduction to ammonia

The electrochemical nitrate reduction reaction (NO3RR) is a promising approach for nitrate removal and NH3 production at ambient conditions. The development of various types of efficient electrocatalysts, especially bimetallic oxides with the advantages of superior durability and excellent catalytic activity, have become a research focus. However, the analysis of active sites for bimetallic oxide catalysts either emphasizes the role of bimetallic interactions or focuses on the role of oxygen vacancies (OVs), resulting in a lack of thoroughness. Herein, a Bi-Co bimetallic oxide (BCO) was constructed for NO3RR, illustrating 1.5∼7.8 folds higher NH3 yield rate than those of commercial single metal oxide (Bi2O3, Co3O4). The NO3RR pathway by BCO was explored according to H* capture test, DEMS, and isotope labeling experiment. An in-situ Raman test showed the structure evolution of BCO during NO3RR, and therefore the catalytic sites of BCO were further identified according to physical characteristics before and after NO3RR. Results suggest that Bi0, OVs and amorphous Co oxide as the real active sites play a vital role in nitrate electroreduction. Furthermore, research on 25 articles also indicates the presence of multiple catalytic sites in bimetallic oxides for NO3RR. This study provides a new and comprehensive insight into the active sites identification for the type of bimetallic oxide NO3RR electrocatalysts.

Elucidation of amphoteric nature of Pr2O3 using XPS and conductivity measurement in lead-free NKBT host lattice

The study of the piezoelectric response in praseodymium-doped (Na0.41K0.09Bi0.5)TiO3 (NKBT) revealed an unusual behaviour at doping level near 0.5 and 1.0 at%. Although there is a marginal increment in the piezoelectric charge coefficients for samples with praseodymium doping of 0.5–1.0 at% compared to undoped NKBT, importantly, the response drastically diminishes for doping concentrations exceeding 1.0 at%. To comprehend the observed anomaly, X-ray photoelectron spectroscopy (XPS) and temperature dependent conductivity measurement was carried out. These investigations provided critical insights into the role of oxygen vacancy and the behaviour of praseodymium ions in the NKBT matrix. The XPS analysis revealed the presence of core level peak corresponding to O-1s with asymmetric broadening at higher energy side implying the presence of oxygen bound to the perovskite lattice (binding energy: 529.2±0.3 eV) along with oxygen vacancy (binding energy: 531.5±0.4 eV). The XPS study further revealed that the concentration of the oxygen vacancy is lowest around 0.5 at% of praseodymium doping and beyond this the oxygen vacancy increases. The high temperature conductivity measurement supported these findings by showing similar trends in the electrical conductivity. Both the XPS and conductivity measurements further corroborate the conjecture that praseodymium behaves as amphoteric ion. The praseodymium occupies the A-site of perovskite (Na0.41K0.09Bi0.5)TiO3 for lower praseodymium concentration (<1.0 at%), whereas for higher doping concentration (>1.0 at%) it occupies the B-site exhibiting acceptor like behavior that deteriorates the piezoelectric response.

Enhanced antibacterial effect with MgO nanoplates: Role of oxygen vacancy and alkalinity

The rational design of MgO nanomaterials with rich oxygen vacancies has garnered significant attention. However, the influence of oxygen vacancies and alkalinity on the generation and stability of active oxygen, particularly regarding the antibacterial activity of MgO nanomaterials, remains uncertain. In this work, the defective MgO nanoplates with adjustable oxygen vacancy and alkalinity were successfully designed by thermal treatment in different atmospheres (air, vacuum, and N2). MgO nanoplates calcined in N2 atmosphere exhibited superior antibacterial activity against Escherichia coli (ATCC 25922), reducing colony counts from 571.5 to 53.5 CFU/mL at 750 μg/mL compared with MgO nanoplates calcined in air. At a low concentration (100 μg/mL), MgO nanoplates calcined in N2 atmosphere exhibited remarkable antibacterial performance, achieving a colony survival ratio of only 6.8 %. This enhanced performance was correlated with a higher oxygen vacancy (OA) content (51.3 %) in MgO nanoplates calcined in N2 compared to those calcined in air (26.5 %). Advanced characterization techniques and alkalinity measurements revealed that calcination in a N2 atmosphere promoted oxygen vacancy formation on the MgO surface, accelerated MgO surface hydrolysis owing to oxygen vacancies, and increased OH− production. Consequently, this process enhances the participation of adsorbed oxygen in surface reaction, leading to the increased generation and stability of active oxygen in an alkaline environment. These findings provide valuable insights into the design of oxygen vacancies and offer a potential approach for constructing highly antibacterial nanomaterials. Such materials could find applications in personal protection and public health.

Role of oxygen vacancy in controlling the resistive switching mechanism for the development of conducting filaments in response of homo and hetero electrodes: Using DFT approach

In the realm of progression of internet of things, artificial intelligence and cloud services, nonvolatile memory devices such as, resistive random access memory (RRAM) emulated the vision of building internet of everything. In this study, robustness of homo- (Ag–Ag, and Pt–Pt), and hetero- (Ag–Pt) top, and bottom electrodes material without and with incorporated oxygen vacancies (Vos) in Sr4Ti4O12 RS layer were investigated. Presence of conductivity in the absence of external electric field proves the presence of nonvolatile memory behavior. Observed RS behavior (in the range of a few Angstroms) may be used to resolve the scalability issue of the proposed RRAM device system. At the same time, oxygen vacancies (Vos) introduced additional functionalities like: additional reduction sites, and reduction of leakage current by quantizing the conduction within RS material. Diffusion barrier elucidated the diffusion mechanism of oxygen vacancies in the considered heterostructure to understand the energy state and the type of RS conduction mechanism. Potential energy line ups, formation energy and electronic properties identified the Vos as principal sites for reduction of Ag atoms by forming metal oxide (Ag-Vos) complex. It is predicted that ReSET, and hence high resistance state (HRS) is harder to achieve with homo-electrodes. The findings of this study provides the effective solution to scalability, stability, and low power consumption in the realm of Pt–Sr4Ti4O12–Ag (with 2Vos mediated in RS layer) based RRAM devices.

Oxygen vacancy-suppression strengthened the internal electric field in ZnIn2S4/BiVO4 S-scheme heterojunction to boost photocatalytic removal of aqueous pollutants

The impact of internal electric field intensity (IEF) within step-scheme (S-scheme) heterojunctions is profound on photocatalytic performance. Furthermore, the presence of oxygen vacancies in the photocatalysts has a significant influence on their photocatalytic characteristics. Thus, a ZnIn2S4/BiVO4 S-scheme heterojunction was strategically engineered for photocatalytic degradation. The modulation of oxygen vacancy levels in the oxidation photocatalyst (OP) was utilized to adjust the IEF within the S-scheme heterojunctions. BiVO4 with controlled oxygen vacancies was synthesized using a simple approach, and the impact of oxygen vacancies on the charge transfer across the heterojunction was thoroughly examined. Subsequently, various characterization results, verified that the IEF in the heterojunction with suppressed oxygen vacancy levels (10 %BV-600) was stronger, while those with elevated vacancy levels (10 %BV-400) showed weaker IEFs. Comprehensive results confirmed that the S-scheme heterojunction is formed between ZnIn2S4 and BiVO4. Under visible irradiation, the 10 %BV-600 sample demonstrated remarkable photocatalytic activity, achieving a 96.4 % degradation of methyl orange within 60 min. Intriguingly, the rate constants for methyl orange removal for the 10 %BV-600 sample were approximately 3 and 27 times greater than those of the individual ZnIn2S4 and BiVO4, respectively. Moreover, the photocatalytic performance of the 10 %BV-400 sample, which had a lower IEF, was inferior to that of the 10 %BV-600 sample. These results underscore the superior photocatalytic capabilities of heterojunctions with a strengthened IEF due to suppressing oxygen vacancy. This work provides insights into the role of oxygen vacancy in regulating IEF intensity in heterojunctions.

The role of oxygen vacancies in enhancement of photocatalysis and ferromagnetism of (Mn, Co) co-doped ZnO nanoparticles

(Mn, Co) co-doped ZnO nanoparticles (NPs) were synthesized using the sol-gel method. Rietveld refined XRD patterns indicated that the NPs exhibited hexagonal wurtzite structures. Co and Mn ions were successfully introduced into the ZnO NPs at different concentrations. Moreover, Raman peak at 520 cm−1 was related to the defects induced by doping with Mn and Co ions. Fitting the O 1s XPS spectra of the NPs showed that more oxygen vacancies formed with increasing Co and Mn doping. Because there were more oxygen vacancies, photocatalytic dye degradation of rhodamine B enhanced at higher Co and Mn concentrations. Photoluminescence spectra showed that the NPs containing more Mn and Co had more single charged oxygen vacancies. The experimental and theoretical results showed that the exchange interactions between the Mn2+-Co2+ ions mediated by singly charged oxygen vacancies was responsible for room temperature ferromagnetism in the (Mn, Co) co-doped ZnO NPs.

Unraveling the influence of oxygen vacancies in MoOx catalysts on CO2 hydrogenation

Oxygen vacancies in oxides are core parameters determining the catalytic performance in various reactions. This study investigated the influence of oxygen vacancies of MoOx catalysts on the reverse water gas shift (RWGS) reaction to gain a deep insight into the structure–function relationship. A distinct volcano-shaped trend was observed among MoOx catalysts with different amounts of oxygen vacancies. Through comprehensive characterizations and steady-state kinetic analysis, an optimal concentration of oxygen vacancies was identified to not only facilitate the adsorption and activation of CO2 but also restrain the formation of by-product CH4. In-situ characterizations combined with DFT calculations uncovered a formate-involved reaction pathway over the oxygen vacancies structured MoOx catalyst, with the hydrogenation of formate identified as the rate-determining step. These findings not only showcase the potential of Mo-based oxides in CO2 hydrogenation reactions but also provide fundamental insights into the role of oxygen vacancies in shaping catalytic behavior.

Enhancing reductive conversion of levulinic acid and levulinates to γ-valerolactone: Role of oxygen vacancy in MnOx catalysts

Oxygen vacancies (Ov) in metal oxides play a crucial role in modifying the electronic and acidic properties of catalysts, thereby influencing their catalytic activity. This study explores the impact of Ov in MnOx catalysts on their acidic and catalytic properties for the Meerwein–Ponndorf–Verley reduction of levulinic acid (LA) and levulinate to γ-valerolactone (GVL). Various characterization techniques demonstrate that surface Ov significantly modulate the acidic properties of MnOx catalysts, positively correlating with Lewis/Brønsted acid ratio and GVL yield. In situ DRIFTS and DFT calculations further unveil the reaction mechanism, revealing that Ov facilitate the activation and dehydrogenation of isopropanol and subsequent hydrogen transfer and hydrogenation of LA, leading to enhanced GVL production. These insights underscore the pivotal role of Ov in MnOx catalysts for the efficient conversion of LA to GVL, highlighting their importance in improving catalytic performance.

Role of oxygen vacancies on Li-doped Ni:ZnO thin films for enhanced NO2 gas sensing applications

Role of oxygen vacancies on Li-doped Ni:ZnO thin films for enhanced NO2 gas sensing applications

Role of oxygen vacancy in high-entropy Cu1Zn1Al0.5Ce5Zr0.5Ox for CO2 hydrogenation reaction

High-entropy oxides (HEOs) have garnered significant attention in catalysis due to their excellent redox properties and superior stability. In this study, we prepared and investigated a high-entropy oxide, Cu1Zn1Al0.5Ce5Zr0.5Ox, to elucidate the impact of oxygen vacancy density on the CO2 hydrogenation reaction. Comparisons were made with binary or ternary solid solutions composed of the same cations present in this HEO, and possessing the same phase structure. The HEO exhibits a higher surface oxygen vacancy density as evidenced by Raman spectroscopy and XPS. The increased number of oxygen vacancies significantly increases the active sites and enhances the strength for CO2 adsorption. Combined with kinetic analysis, it is suggested that the enhanced CO2 adsorption leads to improved CO2 conversion on the HEO. Moreover, the formation of oxygen vacancies facilitates H2 dissociation and supply, which is pivotal for methanol formation on the HEO. The stability of the HEO Cu1Zn1Al0.5Ce5Zr0.5Ox surpasses that of the medium entropy oxide, showing no significant deactivation after 100 hours of reaction.

The Role of Oxygen Vacancy and Hydrogen on the PBTI Reliability of ALD IGZO Transistors and Process Optimization

The Role of Oxygen Vacancy and Hydrogen on the PBTI Reliability of ALD IGZO Transistors and Process Optimization

Reduction mechanism and energy transfer between Eu3+ and Eu2+ in Eu-doped materials synthesized in air atmosphere

Abstract This article critically examines the reduction mechanisms and energy transfer processes between trivalent europium ions (Eu3+) and divalent europium ions (Eu2+) in materials synthesized in an air atmosphere. It also encompasses various materials and conditions, including a critical analysis of the reduction mechanism and energy transfer between Eu3+ and Eu2+ in Eu-doped materials. Specific investigations include exploring the reduction process in BaMgSiO4:Eu, focusing on factors influencing the reaction. The article also covers low-temperature self-reduction, addressing conditions and mechanisms such as the charge compensation model and laser-induced reduction. Additionally, it explores the influence of charge compensation on luminescent properties, emphasizing enhancements in red emission. Investigations into the role of oxygen vacancies in the reduction of Eu3+ and their implications on material properties are presented. This article further digs into abnormal reduction processes and the formation of defect centers in Eu3+-doped pollucite, proposing a substitution defect model for the self-reduction of europium ions in silicate Ba(Eu)MgSiO4 phosphors. Unusual reduction phenomena, such as reduction via boiling water in Yb2Si2O7:Eu3+ phosphors, and reductions in various glass systems, including porous glass, ZnO–B2O3–P2O5 glasses, aluminoborosilicate glasses, europium-doped Li2B4O7 glass, and aluminosilicate oxyfluoride glass (AOG), are also thoroughly examined.

Role of oxygen vacancy on rapid densification and giant dielectric properties of flash sintered Ca2+ and Ta5+ co-doped TiO2 ceramics

(Ca, Ta) co-doped TiO2 ceramics were successfully prepared using flash sintering technology, and the effects of oxygen vacancies on the rapid densification and giant dielectric properties were studied. The results suggest that the maximum volume fraction of oxygen vacancies in flash-sintered samples is approximately 10%. Oxygen vacancies decrease the barrier energy level of atomic diffusion and provide convenient diffusion channels, resulting in rapid densification of the sample within 24 min at 1100 °C. All flash-sintered samples exhibit high relative density, exceeding 95%. Oxygen vacancies promote the electron-pinning defect dipole effect at low temperatures. As the temperature increases, carriers such as oxygen vacancies move to the grain boundary, forming an internal barrier layer capacitance effect. The optical dielectric constant reaches 7.25 × 104, and the dielectric loss drops to 0.09. Oxygen vacancy play an important role in both flash sintering technology and the giant dielectric properties of co-doped TiO2 ceramics.