Oxygen Doping Research Articles

Effect of plasma modulation on the nucleation and crystal evolution of nanodiamond seeds during CVD diamond growth

This study investigated the effect of plasma modulation on the nucleation and crystal evolution of nanodiamond seeds during chemical vapor deposition (CVD) diamond growth. To this end, secondary nucleation and growth of nanodiamond seeds on a mirror-polished silicon (100) substrate in nitrogen, oxygen, and nitrogen–oxygen co-doping environments were investigated using a 5500-W microwave plasma-assisted CVD (MPCVD) reactor. Plasma diagnosis was performed to determine the impact of auxiliary gas addition on plasma modulation using optical emission spectroscopy (OES). The results demonstrate that although nitrogen doping can promote secondary nucleation and growth of nanocrystalline diamond (NCD), it leads to the formation of twinned crystal defects and NCD aggregates, which reduce the quality of diamond growth. Similarly, although a small amount of oxygen doping can promote the competitive growth of nanodiamond seed crystals and catalyze the transition of diamond from the (111) to (220), excessive oxygen can inhibit diamond nucleation and growth. However, controlled plasma modulation can be achieved through appropriate nitrogen and oxygen additions. This study provides theoretical and experimental data for diamond nucleation, grain size, and orientation regulation in CVD diamond growth, and it can serve as a reference for studies on NCD and coatings. Furthermore, this study provides new insights into the growth of nitrogen–oxygen co-doped diamond films.

Synthesis and Structural Characterization of Layered Ni+1/+2 Oxides Obtained by Topotactic Oxygen Release on Nd2−xSrxNiO4−δ Single Crystals

Layered nickelate oxides containing Ni1+/Ni2+ are isoelectronic to Cu2+/Cu3+ compounds and of present interest with respect to recent findings of superconductivity in a series of different compositions. It is thereby questionable why superconductivity is still rare to find in nickelates, compared to the much larger amount of superconducting cuprates. Anisotropic dz2 vs. dx2−y2 orbital occupation as well as interface-induced superconductivity are two of the main advanced arguments. We are here interested in investigating the feasibility of synthesizing layered nickelate-type oxides, where the Ni1+/Ni2+ ratio can be tuned by oxygen and/or cation doping. Our strategy is to synthesize Sr-doped n = 1 Ruddlesden–Popper type Nd2−xSrxNiO4+δ single crystals, which are then reduced by H2 gas, forming Nd2−xSrxNiO4−δ via a topotactic oxygen release at moderate temperatures. We report here on structural studies carried out on single crystals by laboratory and synchrotron diffraction using pixel detectors. We evidence the general possibility to obtain reduced single crystals despite their increased orthorhombicity. This must be regarded as a milestone to obtain single crystalline nickelate oxides, which further on contain charge-ordering of Ni1+/Ni2+, opening the access towards anisotropic properties.

First-principles studies of oxygen interstitial dopants in RbPbI3 halide for perovskite solar cells

Recently perovskite solar cells (PSCs) have caught much attention. Oxygen atom (O1) and molecule (O2) are important dopants to influence the stability of the structural, electronic and optical properties, thus the performance of PSCs. RbPbX3-type perovskites have fantastic chemical stability and good power conversion efficiency. Here we have studied the effects of interstitial O1 and O2 on the structural properties, and hence the electronic structure of RbPbI3 from first principles. We have included the van der Waals (vdW) forces into our density-functional-theory calculations. The formation of dopant level within the pristine band gap has been found when incorporating oxygen. The defect level, dominated by oxygen and iodine, is above the valence band maximum by 0.5–1.3 eV, depending on the location of the defects in the bulk. In addition, we can see the bandwidths of the defect levels are very narrow, which could trap the electron and affect the transport properties. In addition, a metallic state has been found in our calculations for interstitial oxygen molecule when there are strong O–O, O–Pb, and O–I bonds, indicating the complex nature of oxygen-doped PSCs. The comparison between the defect formation energies when doping oxygen atom and molecules is consistent with the previous report about oxygen-molecule passivation of PSCs. Our work has therefore provided important theoretical insight to the effect of oxygen dopants on the electronic structure of RbPbI3.

Degradation of toxic textile effluent rhodamine-B dyes using oxygen doped graphitic carbon nitride nanosheets

A metal-free oxygen-doped graphitic carbon nitride (O-gCN) is prepared by thermal decomposition techniques using urea and oxalic acid (OA). The O-gCN physio-chemical properties are obtained by using different analytical analyses. The O-gCN is utilized as a photocatalyst and applied to degrade rhodamine-B toxic environmental dye. The higher photocatalytic ability of O-gCN is ascribed to the nanostructure with a porous nature. In addition, the porous nature of prepared O-gCN initiated more reactive sites for the degradation of target pollutants. The dopant oxygen atoms in the gCN tri-s-triazine units have extended enormous light absorption capability in the visible range. Radical scavenging experiments exhibited that the reactive radicals played a key role in the photocatalytic degradation of rhodamine B (RhB). The treated waters' toxic and non-toxic nature is observed using mung bean seed germination. Hence, this present study portrayed a simple, eco-friendly, and cost-effective technique to prepare O-gCN nanosheets for environmental remediation applications.

Retarding the effect of Ta on high-temperature oxidation of sputtered nanocrystalline coatings

The presence of excess Ta in high-temperature protective coatings can compromise the integrity of the Al2O3 scale on the surface, which has a negative impact on the oxidation behavior and reduces the service life. The effects of oxygen doping on the isothermal oxidation of three sputtered nanocrystalline coatings were investigated at 1100 °C. The results indicated that oxygen doping inhibited the diffusion of Ta from the coating to the oxide scale, which was primarily attributed to the preferential oxidation of the Al in the coating. However, excess oxygen doping decreased the amount of Al available for the formation of the Al2O3 scale on the coating, thus reducing the inhibitory effect on Ta oxidation. Moreover, doping with excess O caused spalling of the oxide scale. Therefore, the right balance in O doping is crucial for suppressing Ta oxidation while maintaining the integrity of the oxide scale.

Probing the Optoelectronic Properties and Energy Conversion of Boron Nitride Quantum Dots: Impact of Oxygen Doping and Chemical Functionalization

Boron nitride quantum dots (BNQDs) are emerging nanomaterials with promising applications in photocatalysis and optoelectronics. Chemical functionalization effectively tunes the optoelectronic properties and photocatalytic performance of BNQDs. This study investigates the impact of oxygen doping and functionalization with urea, thiourea, and p‐phenylenediamine (PPD) on BNQD properties. Density functional theory calculations reveal that these functional groups introduce new electronic states within the bandgap, shifting absorption spectra and reducing the bandgap due to ligand molecular orbital contributions. Functionalization also adjusts the energy‐level alignment between BNQDs and cocatalysts, enhancing interfacial charge transfer. Oxygen‐doped, chemically functionalized BNQDs exhibit significantly higher first‐order hyperpolarizability, up to 17 times greater than pristine BNQDs, enabling superior optical nonlinearities. Additionally, PPD functionalization leads to a remarkable 18.2% photocatalytic energy conversion efficiency under simulated solar irradiation. These achieved quantum yields result from bandgap engineering, expanded light harvesting, increased exciton densities, prolonged exciton lifetimes, and improved charge separation and transfer dynamics. This study provides crucial insights into property tuning mechanisms, establishing the promising potential of chemically functionalized BNQDs for energy conversion and optoelectronic technologies.

Enabling high-areal-capacity zinc-iodine batteries: Constructing high-density microporous carbon framework with large surface area

The aqueous zinc-iodine batteries hold great potential for next-generation energy storage device owing to their exceptional advantages in cost-effectiveness and intrinsic safety. However, the iodine loading is below 2 mg cm−2 in most of the reported aqueous zinc-iodine batteries, resulting in a low practical energy density, which is still the key challenge in implementing their practical applications. Herein, the hierarchical porous carbon with high-density microporous was successfully prepared by a sample one-step alkali activation strategy using 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) as carbon source. The resultant product possesses a large specific surface area (2693 m2 g−1), a typical three-dimensional framework comprised of high-density microporous (Vmicropore = 0.77 cm3 g−1) with suitable pore size distribution, together with an appropriate oxygen doping. Benefiting from the efficient physical adsorption of high-density micropores, the iodine electrode demonstrated low polarization, high iodine utilization and excellent electrochemical stability. The assembled Zn-I2 battery exhibited high discharge capacity (140.7 mAh g−1 at 0.1 A g−1) and capacity retention (∼ 90% retention upon 6000 cycles). Most importantly, ultra-high area capacity of 2.89 mAh cm−2 can be obtained with a loading of 24 mg cm−2 electrode, showing superior application potential.

Physical Origin of Threshold Switching in Amorphous Chromium‐Doped V2O3

Devices made of amorphous thin films of the prototypical Mott‐insulator chromium‐doped V2O3 show a threshold and negative differential resistance effect after an electroforming step. Here, it is demonstrated that this effect is caused by the formation of a crystalline filament, in which a thermal runaway effect can occur. A compact model is developed that can describe the switching behavior as well as its inherent variability. The influence of the doping concentration and oxygen stoichiometry on the switching behavior is characterized and by fitting the model to the experimental data, the underlying physical changes are extracted.

Production of high-aspect-ratio boron nitride nanosheets via oxygen doping and exfoliation by micro fluidization

Production of high-aspect-ratio boron nitride nanosheets via oxygen doping and exfoliation by micro fluidization

Cyano-rich carbon nitride with tunable n → π* electronic transition for enhanced broad-spectrum photocatalytic H2O2 production

The development of photocatalysts that effectively utilize broad-spectrum light, which occupies a primary percentage of the solar spectrum, remains a great challenge. In this paper, we propose a salt-assisted method mediated by sodium oxalate template to achieve both oxygen doping and formation cyano group defects in carbon nitride materials (CNNO). The simultaneous introduction of oxygen and cyano defects not only induced the distortion of the heptazine structure thus effectively activated the n → π* electron transition, but also can achieve the qualitative changes of broad-spectrum photocatalytic H2O2 production from “0″ to “1” (λ ≥ 700 nm) of CNNO, which has rarely been reported in single photocatalysts. DFT calculations show that the electronic structure of CNNO is rearranged to favor O2 adsorption as well as the formation of the key intermediate OOH*. The present work achieves the co-optimization of electronic structure and light absorption of CN through the synergistic effect of oxygen doping and the construction of cyano defects, which provides a new strategy for the design and synthesis of CN materials that effectively utilize sunlight.

Effective Low-Powered Photocatalytic Disinfection via Synchronous Introduction of Oxygen Dopants and Carbon Defects in Carbon Nitride.

Establishing an effective metal-free photocatalyst for sustainable applications remains a huge challenge. Herein, we developed ultrathin oxygen-doped g-C3N4 nanosheets with carbon defects (OCvN) photocatalyst via a facile gas bubble template-assisted thermal copolymerization method. A series of OCvN with different dopant amounts ranging from 0 to 10% were synthesized and used as photocatalysts under illumination of low-power (2 × 18 W, 0.18 mW/cm2) and commercially available energy-saving light bulbs. Upon testing for photocatalytic Escherichia coli inactivation, the best-performing sample, OCvN-3, demonstrated an astonishing disinfection activity of over 7-log reduction after 3 h of illumination, boasting an 18-fold improvement in its antibacterial activity compared to that of pristine g-C3N4. The enhanced performance was attributed to the synergistic effects of increased surface area, extended visible light harvesting, improved electronic conductivity, and ultralow resistance to charge transfer. This study successfully introduced a green photocatalyst that demonstrates the most effective disinfection performance ever recorded among metal-free g-C3N4 materials. Its disinfection capabilities are comparable to those of metal-based photocatalysts when they are exposed to low-power light.

Oxygen vacancies-modified S-scheme heterojunction of Bi-doped La2Ti2O7 and La-doped Bi4Ti3O12 to improve the NO gas removal avoiding NO2 product

Monoclinic phase La2Ti2O7 and orthorhombic phase Bi4Ti3O12 with layered crystal structure constructed by the perovskite slab were widely used in photocatalysis. Their electronic structures are the most crucial factor in high photocatalytic activity. Bi-doped La2Ti2O7 gradually converts to La-doped Bi4Ti3O12 with the incorporation of bismuth ions, and the two phases build an S-scheme heterojunction. More oxygen vacancies were introduced into the S-scheme heterojunction after heat treatment in a nitrogen atmosphere. The 0.1BTO/LTO-OV sample exhibits the largest NO removal efficiency of 52% and only 5.6 ppb NO2 intermediate generation. The improved NO removal efficiency was ascribed to the synergistic effect of oxygen vacancies, doping and heterojunction, providing a new insight into the photocatalytic NO removal. The photocatalytic mechanism was eventually proposed on the basis of trapping experiments.

Optimizing the application of high-performance supercapacitors: Utilizing 3D honeycomb mesoporous carbons derived from hybrid biomass

Biomass garbage convert into highly efficient porous carbon-based electrode materials for supercapacitors is of great significance to the current energy-friendly society. Herein, an efficient electrode material of three-dimensional honeycomb porous carbons is developed for supercapacitor by employing sunflower plate and rice husk as a precursor. Particularly, SiO2-rich rice husk plays a crucial role in the formation of porous structure and three-dimensional morphology. Benefiting from the high surface area and more defective carbon nano-framework, high contents of nitrogen and oxygen dopants, abundant porosity, the resultant optimal RSC-1-1 exhibits a specific capacitance of 448 F/g at 0.5 A/g in 6 M KOH. Furthermore, the capacitive performance of RSC-1-1 in acidic and neutral media are also analysed systematically. In addition, the energy densities of RSC-1-1 assembled supercapacitors 6 M KOH, 1 M Na2SO4 and PVA/KOH gels are 12.15 Wh/kg, 35.55 Wh/kg, and 29.06 Wh/kg, respectively. This study demonstrates the great potential of twin substance derived electrode materials in constructing high performance supercapacitor.

Effects of stacking layers and different doping elements on the electronic structures and quantum capacitance of graphene: A DFT study

The influence of boron (B), nitrogen (N), oxygen (O), and sulfur (S) doping on enhancing quantum capacitance were investigated through a series of the surface-doped trilayer graphene structures by using density functional theory (DFT) calculations. The quantum capacitance of monolayer models was enhanced through a single doping, a triple doping, and a vacancy defect. Our calculations suggested that the layer interactions within the trilayer models decreased the quantum capacitance but increased the stability of the doped structures. Interestingly, in the case of sulfur dopants with significantly larger atomic size than carbon, the stacking layers induced a surface distortion that could avoid the steric clashes with stacking layers and enhanced the stability. In conclusion, this work provided more realistic models of modified carbon-based electrodes for supercapacitors with more accurate information from the combined effects of doping and stacking layers.

Highly efficient photocatalytic degradation of refractory organic pollutants onto designed boron nitride: Morphology control and oxygen doping

Hexagonal boron nitride (h-BN) exhibits enormous potential for photocatalysis, while its performance is restricted by insufficient light absorption and rapid electron-hole pairs recombination. To address this, BN photocatalysts with various morphologies and oxygen doping were rationally prepared in this study. The results showed that band gap control and charge transfer ability regulation were achieved by oxygen doping and morphology designing. The optimized BN photocatalysts (s-BN) with 3D hierarchical spherical-like structure presented an ultra-thin edge, high oxygen content (6.1 at%), and high specific surface area (446 m2g−1), resulting in enhanced light absorption, efficient charge transfer, and abundant surface reactions. The photocatalytic tetracycline degradation efficiency and rate constant of s-BN were 18.11 times and 51.02 times higher than that of commercial h-BN, respectively. The mechanism study identified the primary active species for s-BN as superoxide radicals and holes, which facilitated the mineralization of tetracycline during the degradation process. This study provides a novel strategy for the development of high-performance and stable BN photocatalysts for efficient photocatalytic degradation of refractory organic pollutants.

Construction of Z-scheme heterojunction TiO2-ZnO@Oxygen-doped gC3N4 composite for enhancing H2O2 photoproduction and removal of pharmaceutical pollutants under visible light

In this study, the heterojunction photocatalyst of titanium dioxide-zinc oxide@oxygen-doped graphitic carbon nitride (TiO2-ZnO@OCN (TZ@OCN)) was synthesized using a simple and cost-effective hydrothermal self-assembly process. Characterization of the fabricated materials revealed that the incorporation of TiO2 and ZnO as inherent semiconductors along with the oxygen doping has effectively broadened the absorption spectrum of gC3N4, which can promote the electron generation and provide more active sites for O2 and H+ adsorption. It is noteworthy that the mentioned structure modification resulted in a superior H2O2 production rate among gC3N4-based photocatalysts with up to 3.11 mM.g−1 under visible light irradiation. Moreover, a valence band shifting from 1.57 to 2.91 eV upon doping oxygen atoms also elucidated the participation of active species in the photocatalytic degradation of ciprofloxacin (99.7 %, k = 0.030 min−1) and tetracyline (94.6 %, k = 0.017 min−1), in which superoxide radicals (•O2−) were shown to play a major role in removing the antibiotic. Besides, a Z-scheme heterojunction mechanism is additionally suggested, demonstrating the effectiveness of electron-hole pair splitting in the oxidation of antibiotics. Conclusively, the results show a novel and feasible modification pathway to enhance the photocatalytic activities of gC3N4 and other advanced semiconductor catalysts, especially for eliminating antibiotics and generating H2O2 within aqueous media.

How *CO spill-over affects C–C coupling on amorphous Cu for converting CO2 to multi-carbon products

Cu-based catalysts, especially oxide-derived Cu, exhibit high multi-carbon product selectivity, thus showing excellent industrialization prospects. Although the mechanism for the superiority is debatable, both experimental and calculation results indicate that the more disordered crystal structure is better for C–C coupling. Herein, we build an amorphous Cu model by making oxygen doping and disordered morphology to approach the actual condition. The oxygen atoms in the subsurface would diffuse to the surface, creating a vacancy that would break the C–C bond. Besides, only limited sites on the amorphous surface with low coordination number and stepped morphology are conducive to the occurrence of CO–CO coupling. Furthermore, we find that the spill-over effect on the amorphous Cu surface could promote the coupling of two *CO intermediates by reducing the reaction energy barrier rather than 50 % of the C–C coupling process on stationary positions. This beneficial strategy encourages the synthesis of C2+ products.

Enhanced photo-Fenton catalytic activity over Cu-doped Bi12O17-xCl2 nanotube for tetracycline degradation: Oxygen vacancies-induced mixed valent Cu

Fenton photocatalyst constructed by transition metal-doped semiconductor material seems to be a promising alternative to classic Fenton catalysts. A series of Cu-doped tubular Bi12O17Cl2 with sufficient oxygen vacancies (ov) was successfully prepared through a hydrothermal method. The formation of ov in the Bi12 crystal lattice can favor the Fenton reaction not only by serving as a reaction site and increasing the charge density in the photocatalyst but also by partially reducing the dopant Cu2+ to Cu+, which consequently enhances the H2O2 activation to a significantly higher rate. Notably, Cu-doped Bi12O17Cl2 ov with an optimal dopant proportion of 4 % exhibited a preferable Fenton catalytic rate 4.5 times higher than pure photocatalytic degradation. This work investigates the mutual promotion of oxygen vacancies and dopant ions in the Fenton reaction and provides a novel development scheme for the advanced oxidation process.

Impact of deoxygenation/reoxygenation processes on the superconducting properties of commercial coated conductors

We report the evolution of the superconducting properties of a commercial coated conductor during deoxygenation and reoxygenation processes. By analyzing the changes on the critical temperature, Tc, and critical current density, Jc, at 4 and 77 K, we have identified the conditions that cause a complete deoxygenation of the coated conductor and, also, the reoxygenation conditions that allow a recovery of the superconducting properties. A complete suppression of superconductivity happens at ~ 500–550 °C under a pure argon flow. After a complete deoxygenation, we observed that a reoxygenation process at ~ 400–450 °C in pure oxygen flow allows, not only a full recovery, but even an improvement in Jc, both at 4 and 77 K. Such an increase of Jc is kept or even enhanced, especially at 77 K, in the presence of magnetic fields up to ~ 6 T. A microstructural analysis by transmission electron microscopy did not give evidence of major differences in the densities of Y2O3 nanoparticles and stacking faults between the pristine and reoxygenated samples, suggesting that these defects should not be the cause of the observed enhancement of Jc. Therefore, the combined action of other types of defects, which could appear as a consequence of our reoxygenation process, and of a new level of oxygen doping should be responsible of the Jc enhancement. The higher Jc that can be achieved by using our simple reoxygenation process opens new parameter space for CCs optimization, which means choosing a proper pO2-temperature–time trajectory for optimizing Jc.

Dynamic Homogenization of Internal Strain in Multi-Principal Element Alloy via High-Concentration Doping of Oxygen with Large Mobility.

Internal strain and its distribution within the crystal lattice play crucial roles in modulating dislocation activities, thereby affecting mechanical properties of materials. Through the synergistic application of integrated differential phase contrast, in situ transmission electron microscopy characterizations, and computational simulations, a method is unveiled for homogenizing dislocation pinning in NiCoCr multi-principal element alloy (MPEA) through the introduction of a high concentration of oxygen atoms with high diffusion mobility. The doping of massive oxygen atoms creates a high density of strong local pinning points for dislocation motion. Notably, oxygen interstitials exhibit remarkable diffusion and mobility across different octahedral and tetrahedral sites within the distorted crystal lattice of NiCoCrO alloy, even at room temperature. The capability allows for the release of severe stress concentrations arising from dislocation entanglement and the establishment of new strong local pinning points at alternative locations in a uniform way, enabling the material with high strength and outstanding deformability. These findings suggest that interstitial atoms can exhibit significant mobility, even at ambient temperature, in complex MPEAs with spreading lattice distortion, opening new possibilities for dislocation engineering.