Degradation of Chloroform by Zerovalent Iron: Effects of Mechanochemical Sulfidation and Nitridation on the Kinetics and Mechanism.

Chloroform (CF) is a widely used chemical reagent and disinfectant and a probable human carcinogen. The extensive literature on halocarbon reduction with zerovalent iron (ZVI) shows that transformation of CF is slow, even with nano, bimetallic, sulfidated, and other modified forms of ZVI. In this study, an alternative method of ZVI modification─involving simultaneous sulfidation and nitridation through mechanochemical ball milling─was developed and shown to give improved degradation of CF (i.e., higher degradation rate and inhibited H2 evolution reaction). The composite material (denoted as S-N(C)-ZVI) gave synergistic effects of nitridation and sulfidation on CF degradation. A complete chemical reaction network (CRN) analysis of CF degradation suggests that O-nucleophile-mediated transformation pathways may be the main route for the formation of the terminal nonchlorinated products (formate, CO, and glycolic polymers) that have been used to explain the undetected products needed for mass balance. Material characterizations of the ZVI recovered after batch experiments showed that sulfidation and nitridation promoted the formation of Fe3O4 on the S-N(C)-ZVI particles, and the effect of aging on CF degradation rates was minor for S-N(C)-ZVI. The synergistic benefits of sulfidation and nitridation on CF degradation were also observed in experiments performed with groundwater.

Selective nitridation-corrosion process to recover vanadium, titanium, chromium, and iron from vanadium slag.

Vanadium slag (V-slag) is an important secondary V source, but other valuable elements are discarded in the tailings in industry. Herein, a green nitridation-corrosion process is proposed for the comprehensive recovery of valuable elements (V, Ti, Cr, Fe) from V-slag without producing hazardous waste. Thermodynamic results indicate that ammonia gas (NH3) can selectively reduce Fe and nitride V, Cr, and Ti. The main phase composition of the nitrided V-slag included metallic Fe, nitrides, and diopside under optimal conditions, and their relative contents were 42.5, 26.2, and 31.3%, respectively, after roasting at 1000 °C for 6 h. The effects of the main parameters on corrosion test were investigated, and the highest weight-gain ratio attained was 19.6%. FeOOH crystallizes on the surface of the nitrided V-slag due to the oxidization of metallic Fe. The phase evolution during the entire process is spinel/olivine/diopside → Fe/nitrides/diopside → FeOOH/nitrides/diopside. Owing to finer particle sizes, most FeOOH is separated by wet sieving (<1400 mesh). The purity of the enriched nitrides attained was 43% after pickling to remove excess Fe. The total recovery rates of Fe, V, Ti, Cr were 87.76%, 95.92%, 92.92%, 92.11%, respectively. This paper provides a sustainable strategy for the comprehensive utilization of V-slag, and guides the cleaner treatment of other similar minerals.

Even Incorporation of Nitrogen into Fe0 Nanoparticles as Crystalline Fe4N for Efficient and Selective Trichloroethylene Degradation.

Surface modification of microscale Fe powder with nitrogen has emerged recently to improve the reactivity of Fe0 for dechlorination. However, it is unclear how an even incorporation of a crystalline iron nitride phase into Fe0 nanoparticles affects their physicochemical properties and performance, or if Fe0 nanoparticles with a varied nitridation degree will act differently. Here, we synthesized nitridated Fe0 nanoparticles with an even distribution of N via a sol-gel and pyrolysis method. Nitridation expanded the Fe0 lattice and provided the Fe4N species, making the materials more hydrophobic and accelerating the electron transfer, compared to un-nitridated Fe0. These properties well explain their reactivity and selectivity toward trichloroethylene (TCE). The TCE degradation rate by nitridated Fe0 (up to 4.8 × 10-2 L m-2 h-1) was much higher (up to 27-fold) than that by un-nitridated Fe0, depending on the nitridation degree. The materials maintained a high electron efficiency (87-95%) due to the greatly suppressed water reactivity (109-127 times lower than un-nitridated Fe0). Acetylene was accumulated as the major product of TCE dechlorination via ß-elimination. These findings suggest that the nitridation of Fe0 nanoparticles can change the materials' physicochemical properties, providing high reactivity and selectivity toward chlorinated contaminants for in situ groundwater remediation.

Formation of a Surficial Bifunctional Nanolayer on Nb2 O5 for Ultrastable Electrodes for Lithium-Ion Battery.

Safe and long cycle life electrode materials for lithium-ion batteries are significantly important to meet the increasing demands of rechargeable batteries. Niobium pentoxide (Nb2 O5 ) is one of the highly promising candidates for stable electrodes due to its safety and minimal volume expansion. Nevertheless, pulverization and low conductivity of Nb2 O5 have remained as inherent challenges for its practical use as viable electrodes. A highly facile method is proposed to improve the overall cycle retention of Nb2 O5 microparticles by ammonia (NH3 ) gas-driven nitridation. After nitridation, an ultrathin surficial layer (2 nm) is formed on the Nb2 O5 , acting as a bifunctional nanolayer that allows facile lithium (Li)-ion transport (10-100 times higher Li diffusivity compared with pristine Nb2 O5 microparticles) and further prevents the pulverization of Nb2 O5 . With the subsequent decoration of silver (Ag) nanoparticles (NPs), the low electric conductivity of nitridated Nb2 O5 is also significantly improved. Cycle retention is greatly improved for nitridated Nb2 O5 (96.7%) compared with Nb2 O5 (64.7%) for 500 cycles. Ag-decorated, nitridated Nb2 O5 microparticles and nitridated Nb2 O5 microparticles exhibit ultrastable cycling for 3000 cycles at high current density (3000 mA g-1 ), which highlights the importance of the surficial nanolayer in improving overall electrochemical performances, in addition to conductive NPs.

Phosphorus and Fluorine Co-Doping Induced Enhancement of Oxygen Evolution Reaction in Bimetallic Nitride Nanorods Arrays: Ionic Liquid-Driven and Mechanism Clarification.

Electrocatalytic splitting of water is becoming increasingly crucial for renewable energy and device technologies. As one of the most important half-reactions for water splitting reactions, the oxygen evolution reaction (OER) is a kinetically sluggish process that will greatly affect the energy conversion efficiency. Therefore, exploring a highly efficient and durable catalyst to boost the OER is of great urgency. In this work, we develop a facile strategy for the synthesis of well-defined phosphorus and fluorine co-doped Ni1.5 Co1.5 N hybrid nanorods (HNs) by using ionic liquids (ILs; 1-butyl-3-methylimidazolium hexafluorophosphate). In comparison to the IrO2 catalyst, the as-obtained PF/Ni1.5 Co1.5 N HNs manifests a low overpotential of 280 mV at 10 mA cm-2 , Tafel slope of 66.1 mV dec-1 , and excellent durability in 1.0 m KOH solution. Furthermore, the iR-corrected electrochemical results indicate it could achieve a current density of 100 mA cm-2 at an overpotential of 350 mV. The combination of cobalt and nickel elements, 1D mesoporous nanostructure, heteroatom incorporation, and ionic liquid-assisted nitridation, which result in faster charge transfer capability and more active surface sites, can facilitate the release of oxygen bubbles from the catalyst surface. Our findings confirm that surface heteroatom doping in bimetallic nitrides could serve as a new class of OER catalyst with excellent catalytic activity.

Synthesis of AlN: Eu2+ green phosphors by a simple direct nitridation method.

Eu-doped aluminum nitride phosphors were successfully prepared using simple direct nitridation of a metallic aluminum and Eu2 O3 powder mixture in flowing ammonia. AlN formed at reaction temperatures >900°C, and Eu3+ transformed into the secondary oxide phase EuAl2 O4 in the nitridation condition. Phase pure AlN was obtained by post-heat treatment of the nitridated product at 1600°C for 3 h in a nitrogen atmosphere, with an Eu2+ doping concentration < 0.5%. The phosphors exhibited broad green emission centered at 521 nm under 363 nm excitation. The luminescence of the phosphor was significantly influenced by the post-heat treatment temperature, which affected the dissolution of Eu2+ , phase purity, crystallinity, and particle size of the AlN host.

Pristine Ta3 N5 Nanotubes: Trap-Driven High External Biasing Perspective in Semiconductor/Electrolyte Interfaces.

Ta3 N5 is a promising photoelectrode for solar hydrogen production; however, to date pristine Ta3 N5 electrodes without loading co-catalysts have presented limited photoelectrochemical (PEC) performance. In particular, large external biasing has been required to run water oxidation, the origin of which is investigated herein. Ta3 N5 nanotubes (NTs) prepared by nitridation were characterized by a wide range of techniques. The bandgap was confirmed by a novel PEC technique. Nondestructive synchrotron-excited XPS has shown the presence of reduced Ta species deeper in the Ta3 N5 surface. Lower photocurrent and transient spikes that were intense at lower applied biasing were observed under water oxidation; however, spikes were inhibited in the presence of a sacrificial agent and photocurrent was improved even at low biasing. It was observed for the first time that the lower PEC performance under water oxidation can be attributed to the presence of interband trapping states associated with pristine Ta3 N5 NTs/electrolyte junction. These states correspond to the structural defects in Ta3 N5 , devastate PEC performance, and present the necessity to apply higher biasing. The key to circumvent them is to use a sacrificial agent in the electrolyte or to load a suitable co-catalyst to avoid hole accumulation under water oxidation, thereby improving the phootocurrent. The findings on the interband states could also provide guidance for the investigation of PEC properties of new types of semiconducting devices.

Nitride surface passivation of GaAs nanowires: impact on surface state density.

Surface nitridation by hydrazine-sulfide solution, which is known to produce surface passivation of GaAs crystals, was applied to GaAs nanowires (NWs). We studied the effect of nitridation on conductivity and microphotoluminescence (µ-PL) of individual GaAs NWs using conductive atomic force microscopy (CAFM) and confocal luminescent microscopy (CLM), respectively. Nitridation is found to produce an essential increase in the NW conductivity and the µ-PL intensity as well evidence of surface passivation. Estimations show that the nitride passivation reduces the surface state density by a factor of 6, which is of the same order as that found for GaAs/AlGaAs nanowires. The effects of the nitride passivation are also stable under atmospheric ambient conditions for six months.

Direct in situ nitridation of nanostructured metal oxide deposited semiconductor interfaces: tuning the response of reversibly interacting sensor sites.

Metal-oxide nanostructure-decorated extrinsic semiconductor interfaces modified through in situ nitridation greatly expand the range of sensor interface response. Select metal-oxide sites, deposited to an n-type nanopore-coated microporous interface, direct a dominant electron-transduction process for reversible chemical sensing, which minimizes chemical-bond formation. The oxides are modified to decrease their Lewis acidity through a weak interaction to form metal oxynitride sites. Conductometric and X-ray photoelectron spectroscopy measurements demonstrate that in situ treatment changes the reversible interaction with the analytes NH3 and NO. The sensor range is extended, which creates a distinct new family of responses determined by the Lewis acidity/basicity of a given analyte relative to that of the nanostructures chosen to decorate the interface. The analyte response, broadened in a substantial and predictable way by nitridation, is explained by the recently developing inverse hard/soft acid/base model (IHSAB) of reversible electron transduction.

Ammonolysis-Driven Exsolution of Ru Nanoparticle Embedded in Conductive Metal Nitride Matrix to Boost Electrocatalyst Activity.

Exsolution is an effective method for synthesizing robust nanostructured metal-based functional materials. However, no studies have investigated the exsolution of metal nanoparticles into metal nitride substrates. In this study, a versatile nitridation-driven exsolution method is developed for embedding catalytically active metal nanoparticles in conductive metal nitride substrates via the ammonolysis of multimetallic oxides. Using this approach, Ti1-xRuxO2 nanowires are phase-transformed into holey TiN nanotubes embedded with exsolved Ru nanoparticles. These Ru-exsolved holey TiN nanotubes exhibit outstanding electrocatalytic activity for the hydrogen evolution reaction with excellent durability, which is significantly higher than that of Ru-deposited TiN nanotubes. The enhanced stability of the Ru-exsolved TiN nanotubes can be attributed to the Ru nanoparticles embedded in the robust metal nitride matrix and the formation of interfacial Ti3+─N─Ru4+ bonds. Density functional theory calculations reveal that the exsolved Ru nanoparticles have a lower d-band center position and optimized hydrogen affinity than deposited Ru nanoparticles, indicating the superior electrocatalyst performance of the former. In situ Raman spectroscopic analysis reveals that the electron transfer from TiN to Ru nanoparticles is enhanced during the electrocatalytic process. The proposed approach opens a new avenue for stabilizing diverse metal nanostructures in many conductive matrices like metal phosphides and chalcogenides.

Synthesis of CuO and Cu3N Nanoparticles in and on Hollow Silica Spheres.

Copper oxide nanoparticles within hollow mesoporous silica spheres were prepared by binding/adsorbing Cu2+ or [Cu(NH3)4(H2O)2]2+ ions on the surface of carbon spheres, followed by formation of a mesoporous silica shell by sol-gel processing and calcination in air. The CuO nanoparticles can subsequently be converted into Cu3N nanoparticles by nitridation with ammonia. The effect of the different copper precursors, i.e. Cu2+ and [Cu(NH3)4(H2O)2]2+, on the nanocomposites was studied. CuO nanoparticles on the outer surface of hollow silica spheres were obtained by thermal treatment of hollow CuSiO3 spheres in air. Nitridation of the CuSiO3 spheres with ammonia resulted in Cu3N@SiO2 composites, with aggregated Cu3N nanoparticles on hollow silica spheres.

Obtaining of Mg-Zn Co-Doped GaN Powders via Nitridation of the Ga-Mg-Zn Metallic Solution and Their Structural and Optical Properties.

Mg-Zn co-dopedGaN powders via the nitridation of a Ga-Mg-Zn metallic solution at 1000 °C for 2 h in ammonia flow were obtained. XRD patterns for the Mg-Zn co-dopedGaN powders showed a crystal size average of 46.88 nm. Scanning electron microscopy micrographs had an irregular shape, with a ribbon-like structure and a length of 8.63 µm. Energy-dispersive spectroscopy showed the incorporation of Zn (Lα 1.012 eV) and Mg (Kα 1.253 eV), while XPS measurements showed the elemental contributions of magnesium and zinc as co-dopant elements quantified in 49.31 eV and 1019.49 eV, respectively. The photoluminescence spectrum showed a fundamental emission located at 3.40 eV(364.70 nm), which was related to band-to-band transition, besides a second emission found in a range from 2.80 eV to 2.90 eV (442.85-427.58 nm), which was related to a characteristic of Mg-doped GaN and Zn-doped GaN powders. Furthermore, Raman scattering demonstrated a shoulder at 648.05 cm-1, which could indicate the incorporation of the Mg and Zn co-dopants atoms into the GaN structure. It is expected that one of the main applications of Mg-Zn co-doped GaN powders is in obtaining thin films for SARS-CoV-2 biosensors.

Metallic Powder Promotes Nitridation Kinetics for Facile Synthesis of (Oxy)Nitride Photocatalysts.

Nitrogen-containing semiconductors (including metal nitrides, metal oxynitrides, and nitrogen-doped metal oxides) have been widely researched for their application in energy conversion and environmental purification because of their unique characteristics; however, their synthesis generally encounters significant challenges owing to sluggish nitridation kinetics. Herein, a metallic-powder-assisted nitridation method is developed that effectively promotes the kinetics of nitrogen insertion into oxide precursors and exhibits good generality. By employing metallic powders with low work functions as electronic modulators, a series of oxynitrides (i.e., LnTaON2 (Ln = La, Pr, Nd, Sm, and Gd), Zr2 ON2 , and LaTiO2 N) can be prepared at lower nitridation temperatures and shorter nitridation periods to obtain comparable or even lower defect concentrations compared to those of the conventional thermal nitridation method, leading to superior photocatalytic performance. Moreover, some novel nitrogen-doped oxides (i.e., SrTiO3- x Ny and Y2 Zr2 O7- x Ny ) with visible-light responses can be exploited. As revealed by density functional theory (DFT) calculations, the nitridation kinetics are enhanced via the effective electron transfer from the metallic powder to the oxide precursors, reducing the activation energy of nitrogen insertion. The modified nitridation route developed in this work is an alternative method for preparing (oxy)nitride-based materials for energy/environment-related heterogeneous catalysis.

Highly Sensitive and Selective Organic Gas Sensors Based on Nitrided ZSM-5 Zeolite.

For next-generation gas sensors, conductive polymers have strong potential for overcoming the existing deficiencies of conventional inorganic sensors based on metallic oxides. However, the signal of organic gas sensors is inferior to that of inorganic metal oxide gas sensors because of organic gas sensors' poor charge carrier transport. Herein, the combination of an organic transistor-type gas sensor and a zeolite with strong gas-adsorbing properties is proposed and experimentally demonstrated. Among the various investigated zeolites, ZSM-5 with ∼5.5 Špore openings enhanced the adsorption for small gas molecules when combined with a polymer active layer, where it provided a pathway for gas molecules to penetrate the zeolite channels. Moreover, nitrided ZSM-5 (N-ZSM-5) enhanced the sensing performance of NO2 molecules selectively because N in the N-ZSM-5 framework strongly interacted with NO2 molecules. These results open the possibility for zeolite-modified organic gas sensors that selectively adsorb target gas molecules via heteroatoms substituted into the zeolite framework.

Plasma Nitridation Effect on ß-Ga2O3 Semiconductors.

The electrical and optoelectronic performance of semiconductor devices are mainly affected by the presence of defects or crystal imperfections in the semiconductor. Oxygen vacancies are one of the most common defects and are known to serve as electron trap sites whose energy levels are below the conduction band (CB) edge for metal oxide semiconductors, including ß-Ga2O3. In this study, the effects of plasma nitridation (PN) on polycrystalline ß-Ga2O3 thin films are discussed. In detail, the electrical and optical properties of polycrystalline ß-Ga2O3 thin films are compared at different PN treatment times. The results show that PN treatment on polycrystalline ß-Ga2O3 thin films effectively diminish the electron trap sites. This PN treatment technology could improve the device performance of both electronics and optoelectronics.

Preparation of AlON Powder by Carbothermal Reduction and Nitridation with Assisting by Silane Coupling Agent.

In the preparation processes of aluminum oxynitride (AlON) powders by carbothermal reduction and nitridation, the homogeneity of mixed raw powders between Al2O3 and C is a critical factor by which the final composition and related properties of AlON transparent ceramic will be decided. In this paper, a silane coupling agent was used as a dispersant to optimize the distribution uniformity of raw material of Al2O3 and C, and the preparation of AlON powder with controllable composition and its distribution is investigated. The results show that the silane dispersant could effectively improve the distribution uniformity of raw material. The silane coupling agent contains functional groups of -SiH3 and -CnH2n+1O. XPS showed that the silane could react with C and Al2O3 to form the Si-C bond and C-Al2O3 bond, respectively. The silane coupling agent provides a connected bridge for raw material powders. When the amount of the silane was 5 wt%, the mixed powder had a great distribution uniformity. The addition of silane coupling agent improved the reactivity of raw materials and decreased the synthesis temperature of AlON. The single-phase AlON powder was obtained after the Al2O3/C mixed powder was kept at 1670 °C for 30 min. Furthermore, the grain size of AlON powder was 100-200 nm with an AlN content of 27.5 mol%. With the increase of holding time to 4 h, the grain size increased to 15 µm, indicating that sintering between particles occurred, which may reduce the sintering activity of the powder.

Impact of Nitridation on Bias Temperature Instability and Hard Breakdown Characteristics of SiON MOSFETs.

We study how nitridation, applied to SiON gate layers, impacts the reliability of planar metal-oxide-semiconductor field effect transistors (MOSFETs) subjected to negative and positive bias temperature instability (N/PBTI) as well as hard breakdown (HBD) characteristics of these devices. Experimental data demonstrate that p-channel transistors with SiON layers characterized by a higher nitrogen concentration have poorer NBTI reliability compared to their counterparts with a lower nitrogen content, while PBTI in n-channel devices is negligibly weak in all samples independently of the nitrogen concentration. The Weibull distribution of HBD fields extracted from experimental data in devices with a higher N density are shifted towards lower values with respect to that measured in MOSFETs, and SiON films have a lower nitrogen concentration. Based on these findings, we conclude that a higher nitrogen concentration results in the aggravation of BTI robustness and HBD characteristics.

One-step route to a hybrid TiO2/Ti x W1-x N nanocomposite by in situ selective carbothermal nitridation.

Metal oxide/nitride nanocomposites have many existing and potential applications, e.g. in energy conversion or ammonia synthesis. Here, a hybrid oxide/nitride nanocomposite (anatase/Ti x W1-x N) was synthesized by an ammonia-free sol-gel route. Synchrotron x-ray diffraction, complemented with electron microscopy and thermogravimetric analysis, was used to study the structure, composition and mechanism of formation of the nanocomposite. The nanocomposite contained nanoparticles (<5 nm diameter) of two highly intermixed phases. This was found to arise from controlled nucleation and growth of a single oxide intermediate from the gel precursor, followed by phase separation and in situ selective carbothermal nitridation. Depending on the preparation conditions, the composition varied from anatase/Ti x W1-x N at low W content to an isostructural mixture of Ti-rich and W-rich Ti x W1-x N at high W content. In situ selective carbothermal nitridation offers a facile route to the synthesis of nitride-oxide nanocomposites. This conceptually new approach is a significant advance from previous methods, which generally require ammonolysis of a pre-synthesized oxide.

Relation between Mechanical Hardening and Nitrogen Profile of PBII Nitrided Titanium Alloy.

Surface treatments of Ti-6Al-4V alloys are of utmost importance for biomedical applications since they allow for tribological gain. Here, Ti-6Al-4V disks have been PBII nitrided at either 500, 600, 700 and 800 °C. A set of techniques (XRD, SEM-EDS, EBSD and GDOES) was used to characterize the surface microstructural and chemical changes. Nanoindentation was used to assess the induced changes in terms of mechanical properties. Two types of nitrided domains are revealed. Starting from the surface, a nitride bilayer composed of δ-TiN/ϵ-Ti2N with enhanced surface resistance is supported by an α-Ti(N) solid solution formed at depth. Hardness values peak at 12-14 GPa at the surface, which is almost twice as large as the bulk value (about 7 GPa). For the moderate temperatures used here, a deep (10-15 µm) and strong hardness (14 GPa) enhancement together with a smooth gradient can be achieved.

Liquid-Phase-Assisted Catalytic Nitridation of Silicon and In Situ Growth of α-Si3N4.

Si3N4 powders were synthesized with Fe, Co, or Ni as catalysts using Si powder at 1250 °C in a nitrogen atmosphere by liquid-phase-assisted catalytic nitridation synthesis (LPA-CNS). The catalytic effects of the metals on the nitridation of silicon powder were investigated by mixing the powder with 2 wt% by mass of Fe, Co, or Ni in a high-temperature liquid phase in flowing nitrogen. The α-Si3N4 micro-morphology could be effectively changed by adjusting the type of catalyst in the initial reaction mixtures. Fe, Co, and Ni promoted the formation of α-Si3N4 at 1250 °C and controlled the morphology of the α-Si3N4 particles. The hexagonal flakes of α-Si3N4 with a better defined morphology were obtained using Ni as the catalyst, compared to that obtained from the other two catalysts.