Oxygen Species Research Articles

Effects and Mechanism of Plasma-Activated Medium on Angiogenesis of Vascular Endothelial Cells

After cell culture medium is treated with low temperature plasma (LTP), the liquid is rich in reactive oxygen and nitrogen species (RONS), and becomes plasma-activated medium (PAM). PAM, as the supplier of RONS, can affect the angiogenesis of cells. The purpose of this study is to investigate the effects and related mechanism of PAM on human umbilical vein endothelial cells (HUVECs). Cell viability and cell cycle were evaluated after HUVECs were treated with PAM for 24 h. Changes in cell angiogenesis, migration and adhesion, secretion of cytokines such as VEGF and bFGF, expression of VEGFR-2 and phosphorylation of the key proteins in the MEK/ERK signaling pathway, concentrations of H2O2 and NO2− in PAM and in cells were also investigated. The results showed that PAM obtained by LTP treatment had dual effects on the angiogenesis of HUVECs: PAM obtained by short-term LTP treatment promoted the angiogenesis of HUVECs, while PAM obtained by long-term LTP treatment inhibited the angiogenesis of HUVECs. The mechanism may be that PAM treatment changes the content of RONS, affects the VEGF-VEGFR-2 signaling pathway, and ultimately affects the angiogenesis of HUVECs.

Nanoporous Graphene via a Pressing Organization Calcination Strategy for Highly Efficient Electrocatalytic Hydrogen Peroxide Generation.

Nanoporous graphenes (NPGs) have recently attracted huge attention owing to their designable structures and diverse properties. Many important properties of NPGs are determined by their structural regularity and homogeneity. The mass production of NPGs with periodic well-defined pore structures under a solvent-free green synthesis poses a great challenge and is largely unexplored. A facile synthetic strategy of NPGs via pressing organization calcination (POC) of readily available halogenated polycyclic aromatic hydrocarbons is developed. The gram-scale synthesized NPGs have ordered structures and possess well-defined nanopores, which can be easily exfoliated to few layers and oxidized in controllable approaches. After being decorated with oxygen species, the oxidized NPGs with tunable catalytic centers exhibit high activity, selectivity, and stability toward electrochemical hydrogen peroxide generation.

The Role of PPAR Alpha in the Modulation of Innate Immunity.

Peroxisome proliferator-activated receptor α is a potent regulator of systemic and cellular metabolism and energy homeostasis, but it also suppresses various inflammatory reactions. In this review, we focus on its role in the regulation of innate immunity; in particular, we discuss the PPARα interplay with inflammatory transcription factor signaling, pattern-recognition receptor signaling, and the endocannabinoid system. We also present examples of the PPARα-specific immunomodulatory functions during parasitic, bacterial, and viral infections, as well as approach several issues associated with innate immunity processes, such as the production of reactive nitrogen and oxygen species, phagocytosis, and the effector functions of macrophages, innate lymphoid cells, and mast cells. The described phenomena encourage the application of endogenous and pharmacological PPARα agonists to alleviate the disorders of immunological background and the development of new solutions that engage PPARα activation or suppression.

Do We Need "Ionosorbed" Oxygen Species? (Or, "A Surface Conductivity Model of Gas Sensitivity in Metal Oxides Based on Variable Surface Oxygen Vacancy Concentration").

The author provides an opinion on direct experimental evidence available to support the "ionosorption theory" often employed to interpret "electrophysical" measurements made during a gas sensing experiment. This article then aims to provide an alternative framework of a "surface conductivity" model based on recent advances in theoretical and experimental investigations in solid state physics, and to use this framework as a guide toward design rules for future improvement of gas sensor performance.

Synthesis of Sodium Alginate-Silver Nanocomposites Using Plasma Activated Water and Cold Atmospheric Plasma Treatment.

In this study, sodium alginate (SA)-based, eco-friendly nanocomposites films were synthesized for potential food packaging applications using silver nitrate (AgNO3) as the metal precursor, reactive nitrogen and oxygen species (RNOS) created within plasma activated water (PAW), or through cold plasma treatment (CP) as reducing agent and SA as stabilizing agent. The formation of silver nanoparticles (AgNPs) was confirmed via the absorption peaks observed between 440 and 450 nm in UV-vis spectroscopy. The tensile strength (TS) and tensile modulus (TM) of the nanocomposite films were significantly higher than those of the SA films. An increase in the TS was also observed as the AgNP concentration was increased from 1 to 5 mM. The storage modulus (G’) of the nanocomposite solution was higher than that of the SA solution. The synthesis of AgNPs resulted both in a higher solution viscosity and a more marked shear-thinning effect. The synthesized AgNPs showed antimicrobial activity against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria. The AgNPs were spherical in shape with an average size of 22 nm.

Oleocanthalic acid from extra-virgin olive oil: Analysis, preparative isolation and radical scavenging activity

Oleocanthal is a nutraceutical compound present in extra-virgin olive oil (EVOO), endowed with several health properties, such as anti-inflammatory, neuroprotective and anticancer effects. During the EVOO storage, oleocanthal can undergo oxidative processes that lead to the formation of oleocanthalic acid. The aim of this work was to develop a reproducible and efficient method for isolation and purification of oleocanthalic acid with the purpose to obtain enough amount of this compound for further pharmacological investigations. We heated an EVOO rich in oleocanthal at 80 °C for 14 days to favour the oxidation of oleocanthal. Subsequently, the oleocanthalic acid was extracted from this EVOO and purified through a combination of direct phase and reverse phase chromatography. The pure oleocanthalic acid was used to develop a HPLC method for qualitative and quantitative analysis of oleocanthalic acid content in EVOO. A preliminary assessment of the radical scavenging potential against oxygen species (superoxide anion radical (O2−), hypochlorous acid (HOCl) and peroxyl radical (ROO)) was also screened. The results showed the quenching efficiency of oleocanthalic acid for HOCl followed by O2−.

Building the Digital Extended Specimen: A case study of invasive European frog-bit (Hydrocharis morsus-ranae L.)

The Extended Specimen was first described by Webster (2017). He defined a “constellation of specimen preparations and data types,” centered around an occurrence of an organism, which captures the breadth of empirical facts about an organism’s phenotype, genotype, and ecology in space and time. The Extended Specimen Network was embraced by the collections community in the Biodiversity Collections Network Extended Specimen Report (Lendemer et al. 2020) and the National Academies of Science, Engineering, and Medicine Future of Collections report (Lendemer et al. 2020, National Academies of Science, Engineering, and Medicine 2020). Several global discussions are underway to build a common definition of the Digital Extended Specimen (DES) and elucidate next steps in building the infrastructure to support Digital Extended Specimens and their network of associated data (including efforts among Distributed System of Scientific Collections (DiSSCo), Biodiversity Collections Network (BCoN), GBIF’s Alliance for Biodiversity Knowledge, TDWG's Task Group on Minimum Information about a Digital Specimen (MIDS), and others.) At the foundation of the DES is the occurrence of an organism in time and space, which is represented by physical specimens or observations serving as tokens of reality. Tokens are translated to digital records, which can be extended through a network of linkages between them and with derived and associated data, e.g. project methodologies, environmental conditions, habitat characteristics, and associated taxa. For digital records to be integrated with the larger network of Digital Extended Specimens, they must become FAIR digital objects that are Findable, Accessible, Interoperable, and Reusable (Wilkinson et al. 2016). By translating the Digital Extended Specimen concept to the local project scale, we provide opportunities to move beyond a theoretical understanding of the DES and towards a practical framework for its implementation. Here we present and discuss the power, limits, and questions in the implementation of the Digital Extended Specimen framework by applying it to the case study of an invasive aquatic plant in the Laurentian Great Lakes region. European frog-bit (Hydrocharis morsus-ranae L.; EFB) is native to western and northern Eurasia and invasive in North America and India. Dense mats of EFB may hinder commercial and recreational use of waterways and decrease light, dissolved oxygen, and native species diversity. We describe a multi-taxonomic study that examined EFB along with associated plant species, animal species, and environmental characteristics (Monfils et al. 2021). The integration of such diverse types of empirical data is a necessary prerequisite for determining the factors associated with EFB establishment, the impacts of EFB on native coastal wetland ecosystems, and the development of suitable management regimes for the conservation of native biodiversity. Data gathered from this study are housed in a local database. In our database, we consider both physical specimens and recorded observations as tokens of concrete occurrences of EFB, which define the base units. These tokens are linked to their collection events, which provide environmental and sampling context, as well as co-occurrences of other taxa including plants, invertebrates, fish, anurans, reptiles, and birds. Digitally linked, these extensions of each digital representation of a collected token provide not only empirical evidence of an EFB occurrence, but also directly connect it with all additionally sampled, derived, and associated information. Through this network of extensions we gain a more holistic understanding of EFB’s species associations, habitats, and ecosystem impacts at the level of populations and communities. The application of the Digital Extended Specimen framework at the project level illustrates how the DES can be used in a real-world context and highlights challenges in translating the concept from a theoretical to a practical perspective.

Selectivity of direct plasma treatment and plasma-conditioned media in bone cancer cell lines

Atmospheric pressure plasma jets have been shown to impact several cancer cell lines, both in vitro and in vivo. These effects are based on the biochemistry of the reactive oxygen and nitrogen species generated by plasmas in physiological liquids, referred to as plasma-conditioned liquids. Plasma-conditioned media are efficient in the generation of reactive species, inducing selective cancer cell death. However, the concentration of reactive species generated by plasma in the cell culture media of different cell types can be highly variable, complicating the ability to draw precise conclusions due to the differential sensitivity of different cells to reactive species. Here, we compared the effects of direct and indirect plasma treatment on non-malignant bone cells (hOBs and hMSCs) and bone cancer cells (SaOs-2s and MG63s) by treating the cells directly or exposing them to previously treated cell culture medium. Biological effects were correlated with the concentrations of reactive species generated in the liquid. A linear increase in reactive species in the cell culture medium was observed with increased plasma treatment time independent of the volume treated. Values up to 700 µM for H2O2 and 140 µM of NO2− were attained in 2 mL after 15 min of plasma treatment in AdvDMEM cell culture media. Selectivity towards bone cancer cells was observed after both direct and indirect plasma treatments, leading to a decrease in bone cancer cell viability at 72 h to 30% for the longest plasma treatment times while maintaining the survival of non-malignant cells. Therefore, plasma-conditioned media may represent the basis for a potentially novel non-invasive technique for bone cancer therapy.

Efficient nitrate adsorbent applicable to wide pH range derived from polyacrylonitrile (PAN) fiber

A thermally stabilized polyacrylonitrile (PAN) fiber was activated with sodium carbonate (Na2CO3) at 800 °C (PYR-8SC1) followed by annealing at 950 °C (PYR-8SC1-9.5HT30) to remove negatively charged surface oxygen and supplied for adsorption of nitrate in aqueous solution from acidic to weak basic range. Nitrogen adsorption-desorption analysis was conducted to examine the textural properties of PYR-8SC1-9.5HT30 sample comparing with the non-annealing sample of PYR-8SC1. Elemental analysis was performed to know the content of nitrogen and oxygen in the samples and X-ray photoelectron spectroscopy (XPS) was also applied to determine the amount of quaternary nitrogen (N-Q) species favorable for the nitrate adsorption. PYR-8SC1-9.5HT30 exhibited a stable high adsorption capacity in a wide equilibrium solution pH (pHe) range, particularly around neutral pHe, whereas PYR-8SC1 worked well only in acidic condition at pHe close to 3 or lower. Maintaining high adsorption capacities of nitrate on PYR-8SC1-9.5HT30 could be caused by not only surface exposure of positively charged graphitic N-Q species, but also the presence of positively charged oxygen and the absence of negatively charged pyridine N-oxide (N-X) and the other negatively charged nitrogen and oxygen species that might hinder the nitrate adsorption onto the surface of PAN activated carbon fiber (ACF).

Milk lymphocyte profile and macrophage functions: new insights into the immunity of the mammary gland in quarters infected with Corynebacterium bovis

BackgroundsThe present study explored the viability of bovine milk macrophages, their intracellular production of reactive oxygen and nitrogen species (RONS), and their phagocytosis of Staphylococcus aureus, as well as the profile of lymphocytes, from healthy udder quarters and udder quarters infected by Corynebacterium bovis. The study included 28 healthy udder quarters from 12 dairy cows and 20 udder quarters infected by C. bovis from 10 dairy cows. The percentages of macrophages and lymphocytes were identified by flow cytometry using monoclonal antibodies. Macrophage viability, RONS production, and S. aureus phagocytosis were evaluated by flow cytometry.ResultsMilk samples from quarters infected with C. bovis showed a lower percentage of macrophages but an increased number of milk macrophages per mL and a higher percentage of macrophages that produced intracellular RONS and phagocytosed S. aureus. No effect of C. bovis infection on macrophage viability was found. Udder quarters infected by C. bovis showed a higher percentage of T cells and CD4+ T lymphocytes, but no effect was found on the percentage of CD8+ CD4− T, CD8− CD4− T, or B lymphocytes.ConclusionsThus, our results corroborate, at least in part, the finding that intramammary infections by C. bovis may offer protection against intramammary infections by major pathogens.

Improvement of Gas Sensing of Uniform Ag3PO4 Nanoparticles to NH3 under the Assistant of LED Lamp with Low Power Consumption at Room Temperature

AbstractLight‐driven semiconductor gas sensors are attracting considerable research attention in the recent past. Among them, silver phosphate (Ag3PO4) material has excellent photocatalytic activities due to its high separation efficiency of electron‐hole pairs under visible light. Inspired by the above point of view, in this study, Ag3PO4 nanoparticles were successfully synthesized via simple precipitation method. The microstructure of Ag3PO4 nanoparticles were characterized by scanning electron microscopy (SEM). The crystalline phase and the composition of the elements and the chemical bonding states of the material were characterized by X‐ray diffraction (XRD) and X‐ray photoelectron spectroscopy (XPS), respectively. Then the gas sensing performance of Ag3PO4 to ammonia (NH3) was systematically explored at room temperature under the illumination of LED lamp and the same was compared with the dark condition as well. Interestingly, the response value to NH3 under LED lamp was 30 % higher than that of dark condition and the detection limit was found to be as low as 10 ppm at room temperature. This can be ascribed to the generation of more oxygen species under visible light, which benefitted for enhancing the gas sensing performance of the sensor. Surprisingly, Ag3PO4 sensor exhibited superior selectivity to NH3 under mixed target gases, which can be attributed to the lone pair electrons of NH3 that tend to coordinate the empty orbitals of silver atom.

Procyanidin B2 protects neurons from cypermethrin-induced oxidative stress through the P13K/Akt/Nrf2 signaling pathway

To explore whether procyanidin B2 (PCB2) regulates the P13K/Akt/Nrf2 signaling pathway to protect neurons from oxidative stress induced by cypermethrin (CYP). Primary cultures of cerebral cortex neurons from C57BL/6 mice were randomly divided into 5 groups: normal control group (cultured in serum-free neurobasal-B27 medium), PCB2 treatment group(treated with 5 μg/mL PCB2 for 24 h), CYP exposure group(treated with 50 μmol/L CYP for 24 h), PCB2 pretreatment group(pretreated with 5 μg/mL PCB2 for 30 min followed by exposure to 50 μmol/L CYP for 24 h), and LY294002 treatment group (pretreated with 20 μmol/L LY294002 for 30 min before treatment with PCB2 for 30 min and then CYP for 24 h).CCK-8 assay was used to analyze the neuronal viability after the treatments.Reactive oxygen species (ROS) production in the cells was detected using the fluorescent probe DCFH-DA and flow cytometry.The changes in nuclear morphology and mitochondrial membrane potential of the cells were examined with Hoechst 33342 and JC-1 staining, respectively.Western blotting was performed to detect the protein expressions of Nrf2, HO-1, p-Akt and Akt in the cells. In CYP exposure group, the cells showed significantly decreased viability and mitochondrial membrane potential with obvious apoptotic morphological changes and abnormal ROS production.By comparison, the cells in PCB2 preconditioning group showed improved cell survival rate, reduced abnormalities in nuclear morphology, increased mitochondrial membrane potential, and lowered intracellular ROS production.CYP exposure caused Nrf2 nuclear translocation and up-regulated Nrf2, HO-1, p-Akt protein expressions in the cells, which were inhibited by PCB2 pretreatment.Inhibition of the P13K/Akt signaling pathway obviously neutralized the protective effect of PCB2 against CYP-induced neuronal injury. PCB2 regulates the Nrf2/ARE signaling pathway by activating the P13K/Akt signaling pathway to protect mouse cerebral cortical neurons against oxidative injury induced by cypermethrin.

Understanding A-site tuning effect on formaldehyde catalytic oxidation over La-Mn perovskite catalysts

A combination study of density functional theory (DFT) calculation and microkinetic analysis was carried out to investigate A-site tuning effect on formaldehyde (HCHO) oxidation over La-Mn perovskite catalysts (A = Sr, Ag, and Sn). The oxygen mobility of A-doped LaMnO3 catalysts and reaction mechanism of HCHO oxidation on catalyst surfaces were investigated. The microkinetic simulation was performed to quantitatively determine the activity of catalysts toward the HCHO catalytic oxidation. The results indicated that A-site tuning weakens the binding energy of Mn–O bond of LaMnO3 surface and facilitates the formation of surface oxygen vacancy. The presence of dopants can significantly reduce the activation energy of O2 dissociation, which ascribes to the facilitation of electron transfer between oxygen species and catalyst surfaces. The reaction cycle of HCHO oxidation contains seven steps: HCHO adsorption, HCHO* dehydrogenation, CHO* dehydrogenation, CO2 desorption, H2O desorption, O2 adsorption and oxygen vacancy recovery. The dopants promote HCHO adsorption and reduce the activation energy of HCHO oxidation. Two elementary steps control the overall reaction rate of HCHO oxidation. CHO* dehydrogenation step has the largest degree of rate control value at low temperature and O2 adsorption step controls the whole reaction at high temperature

Xenoextracellular matrix-rosiglitazone complex-mediated immune evasion promotes xenogenic bioengineered root regeneration by altering M1/M2 macrophage polarization

Xenogenic extracellular matrix (xECM)-based organ transplantation will be a promising approach to address the problem of donor shortage for allotransplantation, which has achieved great success in organ regeneration. However, current approaches to utilize xECM-based organ have limited capacity to yield the host a biofriendly microenvironment for long-term immunity homeostasis, compromising the application of these xenografts for repairing and replacing damaged tissues. As the key innate immune cells, macrophages directly determine the prognosis of xenografts in long term. However, it has not been fully elucidated that how to modulate their biological behavior for microenvironment homeostasis in tissue reconstruction. In this study, we report a robust strategy to impart an immunosuppressive surface to naturally sponge-like porous xECM scaffolds by loading rosiglitazone (RSG) to activate peroxisome proliferators receptors-γ (PPAR-γ). The resultant xECM-RSG complex, enabling RSG to be delivered sequentially and continuously to cells without obvious systemic side effects, is recognized as “self” to escape immune monitoring in local immunoregulation by downregulating the expression of proinflammatory NOS2+ M1 macrophages and oxygen species (ROS) through suppressing NF-κB expression, greatly facilitating the regeneration of enthesis anchoring between the transplanted xenograft and host in both heterotopic and orthotopic models. The newly formed bio-root is morphologically and biomechanically equivalent to native tooth root with a significant expression of odontogenic differentiation-related critical proteins. Therefore, the PPAR-γ-NF-κB axis activated by the xECM-RSG complex enables the xenografts to converse towards M2 macrophages with a modest immunosuppressive capacity for facilitating in xECM-based tissue or organ regeneration.

Increased oxidative stress in allergic rhinitis. Attention; Ruywayda Adams

There is ample evidence that allergic disorders such as asthma, rhinitis and atopic dermatitis are mediated by oxidative stress. Excessive exposure to reactive oxygen and nitrogen species is the hallmark of oxidative stress and leads to damage of proteins, lipids and DNA. Oxidative stress occurs not only as a result of inflammation but also from environmental exposure to air pollution and cigarette smoke.

High-Quality Single-Crystalline β-Ga2O3 Nanowires: Synthesis to Nonvolatile Memory Applications.

One of the promising nonvolatile memories of the next generation is resistive random-access memory (ReRAM). It has vast benefits in comparison to other emerging nonvolatile memories. Among different materials, dielectric films have been extensively studied by the scientific research community as a nonvolatile switching material over several decades and have reported many advantages and downsides. However, less attention has been given to low-dimensional materials for resistive memory compared to dielectric films. Particularly, β-Ga2O3 is one of the promising materials for high-power electronics and exhibits the resistive switching phenomenon. However, low-dimensional β-Ga2O3 nanowires have not been explored in resistive memory applications, which hinders further developments. In this article, we studied the resistance switching phenomenon using controlled electron flow in the 1D nanowires and proposed possible resistive switching and electron conduction mechanisms. High-density β-Ga2O3 1D-nanowires on Si (100) substrates were produced via the VLS growth technique using Au nanoparticles as a catalyst. Structural characteristics were analyzed via SEM, TEM, and XRD. Besides, EDS, CL, and XPS binding feature analyses confirmed the composition of individual elements, the possible intermediate absorption sites in the bandgap, and the bonding characteristics, along with the presence of various oxygen species, which is crucial for the ReRAM performances. The forming-free bipolar resistance switching of a single β-Ga2O3 nanowire ReRAM device and performance are discussed in detail. The switching mechanism based on the formation and annihilation of conductive filaments through the oxygen vacancies is proposed, and the possible electron conduction mechanisms in HRS and LRS states are discussed.

An innovative strategy to rapidly inactivate 8.2-log Enterococcus faecalis in fresh pineapple juice using cold atmospheric plasma

Enterococcus faecalis is a life-threatening bacterium that resists high levels of antibiotics or chemical preservatives. In this study, we aimed to investigate the inactivation of E. faecalis in fresh pineapple juice (FPJ) with two different cold atmospheric plasmas (CAP) reinforced by H2O2/H2O cold vapor: a plasma jet and a surface dielectric barrier discharge (SDBD). CAP treatments for 300 s with plasma jet and 420 s with SDBD caused an 8.2 log reduction of E. faecalis. The concentration of reactive oxygen and nitrogen species induced in FPJ by plasmas was also evaluated. In terms of quality attributes of FPJ, no noticeable color changes (ΔE) were observed. Furthermore, a trifle of loss of organic content such as sugars and organic acids was observed after treatments. These results suggest that our rapid CAP strategy effectively inactivated E. faecalis in FPJ with no change of color and negligible effects on other physicochemical properties.

Numerical Analysis of the Effect of Trapezoidal Baffles Inside Fuel and Air Channels on the Performance of a Planar-Type Solid Oxide Fuel Cell

Abstract This paper investigates the effect of trapezoidal baffles inside a planar-type solid oxide fuel cell. To achieve the objective, four cases are proposed: (1) simple planar geometry as a base case, (2) trapezoidal baffles inside the fuel channel, (3) trapezoidal baffles inside the air channel, and (4) trapezoidal baffles in both fuel and air channels. The height of the trapezoidal baffles inside the channels of the solid oxide fuel cell increases along the direction of the fluid flow. The numerical investigation is based on a three-dimensional computational fluid dynamics (CFD) model that takes into account the phenomenon of mass transfer, heat transfer, species transport, and electrochemical reactions. A detailed comparison of the performance between the four cases of the fuel cell is provided in terms of power density, fluid flow, species concentration, temperature distributions, and electric fields at a variable current density and a fixed power density of 3000 W/m2. The results show that the power density, the velocity, the availability of the hydrogen and oxygen species on the electrodes-electrolyte interfaces increases for case 2, case 3, and case 4, respectively, in comparison to case 1. Finally, the average temperature of the electrode–electrolyte interface is reduced with the baffles, and it is concluded that the configuration with baffles inside the air channel (case 3) shows better results in terms of the increment of the power density and the decrement of the average temperature.

An efficient hydrogen gas sensor based on hierarchical Ag/ZnO hollow microstructures

The design of hierarchical zinc oxide (ZnO) microstructures modified with silver (Ag) nanoparticles have emerged as an effective approach for improving the hydrogen gas sensing performance. Here, we report a simple, low-cost chemical co-precipitation method to obtain the Ag/ZnO hollow microstructures and morphologically characterized them by field emission scanning electron microscopy (FESEM). FESEM images revealed the clear hollow hexagonal tube-like morphology. The existence of Ag in ZnO was confirmed by X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS). UV visible absorption and photoluminescence (PL) spectra were also recorded to observe the effect of Ag nanofiller on the optical properties of ZnO. Furthermore, the gas sensing properties of the as-prepared bare ZnO and Ag/ZnO sensor were investigated. The thoroughly sensing experiments demonstrated that after modification with Ag nanoparticles the ZnO sensor shows superior sensitivity 479 % towards 300 ppm hydrogen gas concentration, whereas 101 % response was noted for the pure ZnO sensor at 250 °C working temperature. Meanwhile, Ag/ZnO hybrids exhibited excellent selectivity, fast response, and recovery time and also obtained a good and stable response signal at 5 ppm H2 exposure, which indicated that the lower concentration measurement is also attainable. This enhancement in the sensing performance of Ag/ZnO structures towards hydrogen is due to the chemical and electronic sensitization effect of Ag nanoparticles. As a result, such microstructure is attributed to more oxygen species and active sites, and it enhances the sensitivity of a sensor. Moreover, this type of hybrid opens a new path and supports the next generation of innovative materials to fabricate highly selective and sensitive H2 gas sensing devices.

Insight into the praseodymium effect on the NH3-SCR reaction pathways over W or Nb supported ceria-zirconia based catalysts

The partial substitution of zirconium for praseodymium in a ceria-zirconia support was studied for WO3 or Nb2O5 supported catalysts dedicated to the NOx SCR by NH3. This partial substitution favored the support reducibility, but both niobium and tungsten impregnation strongly inhibited the redox behaviors of the support. Concomitantly, Nb2O5 and WO3 also provided acidic sites but praseodymium noticeably inhibited the ammonia storage, especially for WO3-containing sample. Finally, praseodymium drastically decreased the deNOx performances. Additional NO and NH3 oxidation experiments were performed and the various redox and acidic behaviors of all the studied materials were suitable to provide an overview of the reactional pathways which begins by the oxidative dehydrogenation of NH3 on acid sites. The generated species react either with oxygen species or with gaseous NO, reflecting a strong competition between the NOx SCR and NH3 oxidation together with the formation of a key intermediate in the nitrogen oxides reduction.