Extrinsic Oxygen Research Articles

Mitochondrial DNA is a sensitive surrogate and oxidative stress target in oral cancer cells.

Cellular oxidative stress mediated by intrinsic and/or extrinsic reactive oxygen species (ROS) is associated with disease pathogenesis. Oxidative DNA damage can naturally be substituted by mitochondrial DNA (mtDNA), leading to base lesion/strand break formation, copy number changes, and mutations. In this study, we devised a single test for the sensitive quantification of acute mtDNA damage, repair, and copy number changes using supercoiling-sensitive quantitative PCR (ss-qPCR) and examined how oxidative stress-related mtDNA damage responses occur in oral cancer cells. We observed that exogenous hydrogen peroxide (H2O2) induced dynamic mtDNA damage responses, as reflected by early structural DNA damage, followed by DNA repair if damage did not exceed a particular threshold. However, high oxidative stress levels induced persistent mtDNA damage and caused a 5-30-fold depletion in mtDNA copy numbers over late responses. This dramatic depletion was associated with significant growth arrest and apoptosis, suggesting persistent functional consequences. Moreover, oral cancer cells responded differentially to oxidative injury when compared with normal cells, and different ROS species triggered different biological consequences under stress conditions. In conclusion, we developed a new method for the sensitive detection of mtDNA damage and copy number changes, with exogenous H2O2 inducing dynamic mtDNA damage responses associated with functional changes in stressed cancer cells. Finally, our method can help characterize oxidative DNA damage in cancer and other human diseases.

Direct Catalytic Conversion of Carbon Dioxide to Liquid Hydrocarbons over Cobalt Catalyst Supported on Lanthanum(III) Ion‐Doped Cerium(IV) Oxide

AbstractDirect CO2 conversion to liquid hydrocarbons (HCs) in a single process was achieved using cobalt (Co) catalysts supported on lanthanum ion (La3+)‐doped cerium oxide (CeO2) under a gas stream of H2/CO2/N2=3/1/1. The yield of liquid HCs was the highest for 30 mol% of La3+‐doped CeO2, which was because extrinsic oxygen vacancy formed by doping La3+ could act as an effective reaction site for reverse water gas shift reaction. However, the excess La3+ addition afforded surface covering lanthanum carbonates, resulting in depression of the catalytic performance. On the other hand, bare CeO2 lead to an increase in the selectivity of undesirable methane, which arose from reduction of CO2 to CO proceeding by intrinsic oxygen vacancy generated by only Ce3+, and weaker CO2 capture ability of intrinsic oxygen vacancy than extrinsic one, resulting in the proceeding of Sabatier reaction on Co catalyst. The rational design of reaction sites presented in this study will contribute to sustainability.

Normal and Superconducting Properties of La3Ni2O7

Abstract This review provides a comprehensive overview of current research on the structural, electronic, and magnetic characteristics of the recently discovered high-temperature superconductor La3Ni2O7 under high pressures. We present the experimental results for synthesizing and characterizing this material, derived from measurements of transport, thermodynamics, and various spectroscopic techniques, and discuss their physical implications. We also explore theoretical models proposed to describe the electronic structures and superconducting pairing symmetry in La3Ni2O7, highlighting the intricate interplay between electronic correlations and magnetic interactions. Despite these advances, challenges remain in growing high-quality samples free of extrinsic phases and oxygen deficiencies and in developing reliable measurement tools for determining diamagnetism and other physical quantities under high pressures. Further investigations in these areas are essential to deepening our understanding of the physical properties of La3Ni2O7 and unlocking its superconducting pairing mechanism.

Enhanced photocatalytic activity of TiO2 anatase nanoparticles modified with malonic acid under reduced power visible light: Synthesis, characterization and degradation of tetracycline and chlorophenol

Charge transfer complexes (CTCs) between nano-TiO2 and chelating ligands are among the most promising alternatives for photocatalytic applications, such as environmental remediation. However, the development of CTCs based on nano-TiO2 modified with malonic acid (MoA) has not yet been investigated in detail.In this study, TiO2-MoA CTCs, synthesized via sol–gel route, were tested for tetracycline (antibiotic) and chlorophenol (pesticide) photocatalytic degradation with, and without, scavengers of reactive oxidizing species, under low-power visible light (26 W). The TiO2-MoA CTCs were thoroughly characterized. TGA-MS and FTIR analyses revealed malonic acid bonded to the TiO2 surface, while the PL and EPR analyses proved the generation of extrinsic oxygen vacancies due to calcination process of the xerogels.CTCs based on nano-TiO2 strongly bonded to malonic acid, and highly sensitive to visible light, have been synthesized by sol–gel method, followed by calcination at 270 °C in air. The as-prepared CTCs showed very high surface areas (between 180.9 and 323.9 m2.g−1), presence of F+ color centers in the calcined CTCs due to extrinsic oxygen vacancies and high photocatalytic activity, degrading approximately 100 % of the tetracycline after 6 h. In addition, it has been proved that the TiO2-MoA CTCs are efficient sources of •O2– radicals.The findings of this research can be generalized to the synthesis, via sol–gel, of other CTCs between TiO2 and bidentate ligands, such as dicarboxylic acids, and explored for air purification and hydrogen production.

Point defects, doping and the path to n-type SnTe

Point defects in SnTe were studied using first-principles modeling. Sn vacancies were found to be spontaneously formed in SnTe and make it intrinsically a p-type semiconductor, in excellent accord with experiments. The calculated electronic structure for Sn vacancy reveals that the Fermi level is shifted down into the valence band and presents p-type behavior. In contrast, the Fermi level shifts near the conduction band minimum (CBM) for Te vacancy and presents an n-type behavior. All the interstitial sites were considered for a comprehensive intrinsic point defect study. The body-centered (tetrahedral) site was found to be a stable interstitial configuration for Sn, whereas the split<111> interstitial was preferred for Te. We found that the electronic structures due to the interstitial configurations were distinct. Sn interstitials defects, Fermi level was shifted inside the conduction band for body interstitial, near to CBM for split 111 interstitial, whereas inside the bandgap for the base and split 110 interstitial defects. Contrary results were obtained for Te interstitial defects; the Fermi level was found inside the valence band for body interstitial, close to VBM for split 111, while the Fermi level was obtained inside the bandgap for base and split 110 interstitial defects. In addition, extrinsic oxygen impurities and other possible dopants that can transform SnTe to n-type were investigated. Interstitial oxygen was found to be stable at the body-interstitial site and is incorporated easily into the material in both Sn- and Te-rich environments, leading the material to p-type. The Fermi level was obtained inside the bandgap for oxygen substituted in Te vacancy and showed no preferred conductivity behavior. Finally, we find that Sb, Bi, and halogens (in Sn-rich conditions) can significantly improve electron concentrations and be promising dopants to transform the material's intrinsic conductivity from p-type to n-type. Notably, the sample should be prevented from incorporating oxygen impurities while doping sample n-type.

A critical review on the stability of natural food pigments and stabilization techniques

This comprehensive review article delves into the complex world of natural edible pigments, with a primary focus on their stability and the factors that influence them. The study primarily explores four classes of pigments: anthocyanins, betalains, chlorophylls and carotenoids by investigating both their intrinsic and extrinsic stability factors. The review examines factors affecting the stability of anthocyanins which act as intrinsic factors like their structure, intermolecular and intramolecular interactions, copigmentation, and self-association as well as extrinsic factors such as temperature, light exposure, metal ions, and enzymatic activities. The scrutiny extends to betalains which are nitrogen-based pigments, and delves into intrinsic factors like chemical composition and glycosylation, as well as extrinsic factors like temperature, light exposure, and oxygen levels affecting for their stability. Carotenoids are analyzed concerning their intrinsic and extrinsic stability factors. The article emphasizes the role of chemical structure, isomerization, and copigmentation as intrinsic factors and discusses how light, temperature, oxygen, and moisture levels influence carotenoid stability. The impacts of food processing methods on carotenoid preservation are explored by offering guidance on maximizing retention and nutritional value. Chlorophyll is examined for its sensitivity to external factors like light, temperature, oxygen exposure, pH, metal ions, enzymatic actions, and the food matrix composition. In conclusion, this review article provides a comprehensive exploration of the stability of natural edible pigments, highlighting the intricate interplay of intrinsic and extrinsic factors. In addition, it is important to note that all the references cited in this review article are within the past five years, ensuring the most up-to-date and relevant sources have been considered in the analysis.

Extrinsic Oxygen Vacancies Formation during Crystallization of Al2W3O12 by Calcination in Air

Extrinsic Oxygen Vacancies Formation during Crystallization of Al₂W₃O₁₂ by Calcination in Air

Extrinsic oxygen defects in SnO/SnO2 heterostructure for efficient NO2 gas detection

High selectivity and fast response in the detection of NO2 are key factors in protecting human health in life-threatening environments. The p-n SnO/SnO2 heterostructure is a promising material as a metal oxide for effective chemical reactions with a target gas. It has a synergistic effect on the intrinsic semiconducting properties and the formation of an interfacial electric field in the heterojunction. The extrinsic oxygen vacancies in the SnO/SnO2 structure enhance the chemical reaction in the sensing property. In this study, we developed a defect-SnO/SnO2 heterostructure-based NO2 gas sensor. It shows excellent sensing performances with a high response of 100.86, fast response time of 5.83 s, and superior selectivity (approximately 23 times higher than those of other target gases) in the detection of 50 ppm NO2 at 150 °C. Raman and electron paramagnetic resonance (EPR) results supported the presence of oxygen vacancies in the defect-rich SnO/SnO2 crystal and X-ray photoelectron spectroscopy (XPS) and time-of flight secondary ion mass spectrometry (ToF-SIMS) analyses described the role of SnO/SnO2 heterostructure with oxygen defects as an effective electron donor for the adsorbed oxygen molecules and NO2 target gas. We believe that the direct formation of oxygen vacancies in the SnO/SnO2 heterostructures is a significant reference for the development of high-performance NO2 gas sensors.

Strategic co-doping of ceria for improved oxidation kinetics in solar thermochemical fuel production

La and Yb were incorporated as co-doping elements into Zr-doped ceria to investigate the influence of doping ions by means of ionic radius and valence on the ceria crystal lattice and potentially on thermodynamic and kinetic properties relevant to solar-driven two-step thermochemical CO2 splitting. Both Zr–La and Zr–Yb co-doped ceria clearly exhibited better reduction capability than ceria and partial molar enthalpy and entropy that were in between those of Zr-doped ceria and undoped ceria. In the case of CO2 splitting kinetics, Zr-doped ceria was the slowest in accordance with relevant literature, but La-doped samples were much faster than Yb-doped counterparts suggesting that extrinsic oxygen vacancy formation, even though important, does not primarily determine the CO2 splitting kinetics unlike the hypothesis postulated by previous works. This work elucidates the role of dopant's ionic radius, lattice constant and valence on thermodynamics and CO2 splitting kinetics via experimental demonstration, and provides a new doping strategy not based on the extrinsic oxygen vacancy formation but based on the dopant ionic radius and valence with an insight for the further doped ceria-based redox material discovery.

Constructing extrinsic oxygen vacancy on the surface of photocatalyst as CO2 and electrons reservoirs to improve photocatalytic CO2 reduction activity

Constructing own oxygen vacancies in the photocatalysts is a very promising method to improve their photocatalytic CO2 reduction activity. However, some catalysts have excellent stabilities, making it difficult for them to construct their own oxygen vacancies. To simplify the above difficulty of stable photocatalysts, constructing extrinsic oxygen vacancies on their surface as a novel idea is proposed. Here, a stable TiO2 nanosheet is chosen as a research object, we uniformly deposited BiOCl quantum dots on their surface via a simple adsorption-deposition method. It is found that BiOCl quantum dots are able to simultaneously self-transform into defective BiOCl with many oxygen vacancies when the photocatalyst is performed photocatalytic CO2 reduction. These extrinsic oxygen vacancies can act as “CO2 and photo-generated electrons reservoirs” to improve CO2 capture and accelerate the separation of photogenerated electrons and holes. For the above reasons, the modified TiO2 showed obvious enhancement of photocatalytic CO2 reduction compared to pristine TiO2 and BiOCl. This work may open a new avenue to broaden the use of oxygen vacancies in the process of photocatalytic CO2 reduction.

Extrinsic Point Defects in TiO2–Acetylacetone Charge-Transfer Complex and Their Effects on Optical and Photochemical Properties

TiO2-based visible-light-sensitive nanomaterials are widely studied for photocatalytic applications under UV-Vis radiation. Among the mechanisms of visible-light sensitization, extrinsic oxygen vacancies have been introduced into TiO2 and charge-transfer complexes (CTCs) have been formed between chelating ligands, such as acetylacetone, and nanocrystalline TiO2 (TiO2-ACAC). However, the influence of extrinsic oxygen vacancies on the photocatalytic performance of TiO2-based CTCs is unknown. In this work, surface/bulk extrinsic oxygen vacancies were introduced into TiO2-ACAC through calcination at 270 °C under static air, argon, and hydrogen atmospheres. TiO2-ACAC CTCs were characterized by X-ray powder diffraction, thermogravimetric analysis, diffuse-reflectance spectroscopy, photoluminescence, electron paramagnetic resonance (EPR), and X-ray photoelectron spectroscopy techniques. The correlation between EPR-spin trapping and tetracycline (TC) photodegradation, using scavengers, highlighted the key role of the superoxide radical in TC degradation by TiO2-ACAC CTCs under low-power visible-light radiation. The increased extrinsic oxygen vacancies concentration was not beneficial for the photocatalytic performance of TiO2 CTCs, since bulk extrinsic oxygen vacancies additionally act as recombination centers. In fact, the TiO2-ACAC CTC with the lowest extrinsic oxygen vacancies concentration exhibited the highest photocatalytic performance for TC degradation due to an adequate distribution of extrinsic bulk oxygen vacancies, which led to the trapped electrons undergoing repeated hopping, reducing the recombination rates and improving the efficiency in superoxide radicals production. Our findings indicated that TiO2-ACAC CTCs are able to degrade pollutants via interactions with electronic holes and principally superoxide radicals and also, provided fundamental information about the influence of surface/bulk extrinsic oxygen vacancies on the photocatalytic performance, lattice parameters, and optical and photochemical properties of TiO2-based CTCs.

Effect of Intrinsic and Extrinsic Oxygen Vacancies on the Conductivity of Gd-Doped CeO2 Synthesized by a Sonochemical Route

Effect of Intrinsic and Extrinsic Oxygen Vacancies on the Conductivity of Gd-Doped CeO₂ Synthesized by a Sonochemical Route

Oxygen vacancies and their role on the magnetic character of polycrystalline CeO2

The structural, electronic and magnetic properties of high purity nanostructured CeO2 powders were investigated under various reducing atmospheres. By performing in situ experiments, it was demonstrated that the appearance of oxygen vacancies promotes a paramagnetic behaviour in an initially diamagnetic oxide. This conclusion is inferred through a careful and detailed correlation between the magnetic measurements and the analysis of the electronic properties, obtained by X-ray absorption experiments under different atmospheres. After exposing the CeO2 powders to a reducing atmosphere, a residual state is obtained and the samples continue to exhibit a paramagnetic behaviour characterized by lower susceptibility values than those obtained during the in situ experiments. The results of ex situ Electronic Paramagnetic Resonance (EPR) measurements at room temperature further support the finding of paramagnetic behaviour in all the samples. EPR was used to characterize the electronic defects ascribed to intrinsic oxygen vacancies already present in the “as prepared” samples and extrinsic oxygen vacancies originated during the reducing treatments. The quasi-linear dependence observed between the intensity of the EPR signal characteristic of annealed samples and the duration of the corresponding reducing treatment suggests that there is a direct correlation between the paramagnetic residual state and the creation of extrinsic oxygen vacancies that occurs at high temperature under reducing atmosphere.

Extrinsic Point Defects in Low-Positive Thermal Expansion Al2W3O12 and Their Effects on Thermal and Optical Properties.

A2M3O12-type ceramics are potentially useful in a variety of applications due to their peculiar thermal and mechanical properties. In addition, their intrinsic coefficients of thermal expansion can be finely tuned through different mechanisms. Despite the great influence of extrinsic point defects on physical properties, only a few reports have dealt with their relationship to thermal expansion and thermal conductivity. Extrinsic oxygen vacancies in orthorhombic Al2W3O12, in different concentrations, were formed through heat treatments in argon or hydrogen atmospheres. X-ray powder diffraction, diffuse reflectance spectroscopy, and Raman and electron paramagnetic resonance spectroscopies were used to study the as-formed vacancies, and X-ray photoelectron spectroscopy was employed to propose a charge compensation mechanism. It was found that the intrinsic coefficient of thermal expansion of orthorhombic Al2W3O12 was severely affected by extrinsic oxygen vacancies. Thermal expansion was decreased up to 40% (from 25 to 400 °C) with respect to the extrinsic-point-defect-free counterpart. Unit-cell volumes of defective orthorhombic Al2W3O12 were larger, while their W-O bonds were weaker, likely leading to higher lattice flexibility and enhanced low-energy transverse acoustic modes. Extrinsic oxygen vacancies could be an additional mechanism for fine-tuning the intrinsic coefficients of thermal expansion in A2M3O12-type ceramics and in other framework structures built through two or threefold linkages.

Oxidation kinetics of La and Yb incorporated Zr-doped ceria for solar thermochemical fuel production in the context of dopant ionic radius and valence

The influence of ionic radii and valence of dopants in Ce0.9LaxYbyZr0.1−x−yO2−δ (x = 0, 0.05, 0.1, y = 0, 0.05, 0.1) on the oxidation kinetics were investigated by thermogravimetric analysis in synthetic air and were compared to undoped ceria. Samples co-doped with Zr–La and Zr–Yb exhibited moderate oxidation kinetics that were slower than undoped ceria, but much faster than 10mol% Zr-doped ceria. The extrinsic oxygen vacancy induced by the trivalent dopants improves the kinetics at oxidation temperatures below 700 °C, where the diffusion, and not the surface exchange reaction is the limiting factor. A smaller ionic radius of the substituent (i.e. r(Yb3+) < r(La3+)) in the co-doped ceria tends to facilitate lower activation energy resulting in slightly faster oxidation kinetics at temperatures below 700 °C. In contrast, additional extrinsic vacancies are rather obstructive at high temperatures (i.e. T> 700 °C) due to a change of rate limiting mechanism from bulk oxygen diffusion to surface exchange reaction. Overall, the valence of the dopant rather than the ionic radius seems to determine the oxidation kinetics primarily, and additional La or Yb doping on Zr-doped ceria is appealing especially when the applications are focused on low temperature reactions.

Evaluation of Er Doped CeO2-δ as Oxygen Transport Membrane.

Ceria based materials are robust candidates for a range of applications involving redox reactions and high oxygen activity. The substitution of erbium in the ceria lattice introduces extrinsic oxygen vacancies. Further addition of Co introduces electronic carriers. We have studied the structural and redox behavior of Ce1−xErxO2-δ (x = 0.1 and 0.2) and the influence of adding 2 mol% of Co in the electrochemical properties. A limitation in the solubility of Er cation is found. Diffusion and surface exchange coefficients have been obtained by electrical conductivity relaxation and the DC-conductivity and O2 permeation measurements show the importance of the electronic component in the transport properties, obtaining an oxygen permeation flux of 0.07 mL·min−1·cm−2 at 1000 °C, for a 769 μm thick membrane.

Microstructure and Electrical Properties of Lanthanides-doped CaBi2Nb2O9 Ceramics

Calcium bismuth niobate (CaBi2Nb2O9, CBN) is a promising candidate for high-temperature applications in aerospace, shipping, and nuclear industries, owing to its ultra-high Curie temperature (TC∼x223C 940 °C). Lanthanide ions modified CBN based ceramics were prepared by a conventional solid-state sintering route. The crystal structure, microstructure, and high-temperature electrical properties of CBN ceramics doped by different lanthanide dopants (La, Ce, Nd, Sm, Dy, Er, Yb) were studied and the underlying mechanism was also discussed. Among these doping ions, Ce3+/Ce4+ doping CBN ceramics exhibits anomalous electrical properties. Impedance analysis was introduced to clarify the difference in electrical properties of lanthanide-doped CBN ceramics at high temperatures. As a result, the anomalous electrical properties are attributed to the extrinsic oxygen vacancies induced by the Ce doping. These results could assist to tailor the electrical properties of Aurivillius phase ceramics with lanthanide modifications.

Influence of manganese rate on structural, optical and electrochemical properties of CeO2 thin films deposited by spray pyrolysis: Supercapacitor applications

The present work aimed to investigate the electrochemical properties of ITO substrates in propylene carbonate (PC) with 0.5 mol/L lithium perchlorate (LiClO4) medium in the presence of elaborated thin films of cerium dioxide pure and doped with manganese at varying percentages. Ce1–xMnxO2 (x = 0 wt%, 2 wt%, 4 wt% and 6 wt%) were successfully deposited by the spray pyrolysis (SP) technique on the glass substrate and ITO at 450 °C. The effects of manganese (Mn) doped thin films Ce1–xMnxO2 were studied and investigated by using different analyses namely X-ray diffraction (XRD) analysis, Raman spectroscopy method, UV–Vis spectrophotometer technique, atomic force microscopy (AFM) analysis and electrochemical properties. XRD data obtained present a polycrystalline with a face-centred cubic structure of fluorite type. Raman results of undoped and Mn doped thin films show two peaks at 465 and 600 cm−1, due to the formation of extrinsic oxygen vacancies by the incorporation of Mn into Ce1–xMnxO2 matrix. Energy dispersive spectroscopy (EDS) data show the presence of Ce, O, and Mn elements in the elaborated films. The AFM results reveal that the surface roughness decreases with increasing Mn rate. Further, band gap energy of thin films decreases with increasing in Mn rate due to the formation of defect state between valence and conduction band. The storage capacity of the elaborated Ce1–xMnxO2/ITO/PC + LiClO4 electrode reaches a maximum of 1.997 mF in the presence of 6 wt% of Mn.

Modulation of Ferroelectric and Optical Properties of La/Co-Doped KNbO3 Ceramics.

The phase transition, microscopic morphology and optical and ferroelectric properties are studied in a series of La- and Co-doped KNbO3-based ceramics. The results show that the doping induces the transformation from the orthorhombic to the cubic phase of KNbO3, significantly reduces the optical bandgap and simultaneously evidently improves the leakage, with a slight weakening of ferroelectric polarization. Further analysis reveals that (i) the Co doping is responsible for the obvious reduction of the bandgap, whereas it is reversed for the La doping; (ii) the slight deterioration of ferroelectricity is due to the doping-induced remarkable extrinsic defect levels and intrinsic oxygen vacancies; and (iii) the La doping can optimize the defect levels and inhibit the leakage. This investigation should both provide novel insight for exploring the bandgap engineering and ferroelectric properties of KNbO3, and suggest its potential applications, e.g., photovoltaic and multifunctional materials.

Role of oxygen vacancy defects in piezoelectric thermal stability characteristics of Mn-doped (K,Na,Li)NbO3 piezoceramics

Piezoelectric thermal stability characteristics of (K,Na,Li)NbO3 ceramics were investigated with a particular focus on the role of oxygen vacancy defects, by excluding the lattice distortion or microstructural effects with the help of a low level of Mn doping (less than 1.0 mol%). Benefiting from the reduction of intrinsic oxygen vacancy defects, controlled Mn doping (0.25 mol%) could achieve excellent ferroelectric/piezoelectric activity and superior thermal aging resistance. Beyond this doping level, however, the defect dipoles combined with extrinsic oxygen vacancies, although advantageous to the hardening effect, deteriorated the piezoelectric thermal stability and aging resistance including room-temperature properties. The thermal dissociation and migration of oxygen-vacancy-associated defect dipoles were considered mainly responsible for negating the ability to restore the initial poled domain state with defect-dipole-induced polarization. Results demonstrated the importance of keeping the intrinsic and extrinsic oxygen vacancy levels as low as possible for lead-free (K,Na)NbO3 systems with more thermally stable domain structure.