CN Layer Research Articles

Flower-like CN layer-doped WO3/W photoanode as an efficient sun-light photoelectrocatalyst for PFOA degradation and electricity generation

Photoelectrocatalysis (PEC) system has been proven to be effective in degrading perfluorooctanoic acid (PFOA) and generating electricity as a goal to solve the problems of environmental pollution and energy shortages simultaneously. In this study, we utilized a flower-like WO3in-situ generated on tungsten foil (WO3/W), and then doped with a CN layer by immersing it in urea solution and then undergoing calcination (CN-WO3/W), to degrade PFOA and generate electricity. The growth mechanism of WO3/W with different morphologies prepared under various experimental conditions was analyzed in order to explain the reasons for the superior performance of the flower-like structure compared to other morphologies. Under the irradiation of simulated sun-light, the power density reached its peak at 0.11 mW/cm2 when current density was 0.14 mA/cm2 with PFOA as fuel. CN-WO3/W displayed a steady state photocurrent density of 6.1 mA/cm2 at 1.2 V (vs. Ag/AgCl) under simulated sun-light irradiation and a high PFOA degradation of 95 %, which is much higher than that of WO3/W. Due to distinctive flower-like structure, stable W–N–C bond, narrower energy band (from 2.67 to 2.41 eV), more acquisition of visible light, and strong oxidation capability, the CN-WO3/W exhibited high stability and reusability for simultaneous PEC degradation of PFOA (almost unchanged after 9 cycles) and electricity generation (without activity loss during the 24 h test) under simulated sun-light irradiation. Based on the scavenger-quenching experiments the possible degradation pathways of PFOA were suggested. This work provides a way to design and synthesize the photoanode to construct reaction system for high-performance photocatalytic PFOA degradation and electricity generation.

Photoelectrochemical water oxidation using hematite modified with metal-incorporated graphitic carbon nitride film as a surface passivation and hole transfer overlayer

Hematite (α-Fe2O3) is renowned as a promising photoanode for water oxidation, even though it displays poor photoconversion efficiency. In this study, ∼5 nm-thick graphitic carbon nitride (g-C3N4; CN) and metal-incorporated CN (M-CN; M = Ag, Fe, Co) films are uniformly deposited on hematite via a facile one-step evaporation method. Herein, the Co-CN layer leads to the highest photoelectrochemical activity with hematite-based photoanode. The subsequent loading of Co-CN layer with oxygen evolution catalysts (FeNiOOH and CoOOH) further enhances photocurrent density to ∼3.5 mA cm−2 and oxygen evolution at > 95 % of Faradaic efficiency over 24 h at E = 1.23 V. Detailed analysis based on spectroscopic and electrochemical measurements demonstrate that the primary role of CN layer is improving the charge separation efficiency by passivating the hematite surface. Then the incorporated metals contribute to reducing charge transfer resistance and thereby mediating hole transfer to interfacial water.

Antibacterial Effects of a Carbon Nitride (CN) Layer Formed on Non-Woven Polypropylene Fabrics Using the Modified DC-Pulsed Sputtering Method.

In the present study, the surface of non-woven polypropylene (NW-PP) fabric was modified to form CN layers using a modified DC-pulsed (frequency: 60 kHz, pulse shape: square) sputtering with a roll-to-roll system. After plasma modification, structural damage in the NW-PP fabric was not observed, and the C-C/C-H bonds on the surface of the NW-PP fabric converted into C-C/C-H, C-N(CN), and C=O bonds. The CN-formed NW-PP fabrics showed strong hydrophobicity for H2O (polar liquid) and full-wetting characteristics for CH2I2 (non-polar liquid). In addition, the CN-formed NW-PP exhibited an enhanced antibacterial characteristic compared to NW-PP fabric. The reduction rate of the CN-formed NW-PP fabric was 89.0% and 91.6% for Staphylococcus aureus (ATCC 6538, Gram-positive) and Klebsiella pneumoniae (ATCC4352, Gram-negative), respectively. It was confirmed that the CN layer showed antibacterial characteristics against both Gram-positive and Gram-negative bacteria. The reason for the antibacterial effect of CN-formed NW-PP fabrics can be explained as the strong hydrophobicity due to the CH3 bond of the fabric, enhanced wetting property due to CN bonds, and antibacterial activity due to C=O bonds. Our study presents a one-step, damage-free, mass-productive, and eco-friendly method that can be applied to most weak substrates, allowing the mass production of antibacterial fabrics.

Microstructure and mechanical properties of WC-TiC0.4 composites doped with ZrO2 or 3Y-ZrO2

The ZrO2 or 3Y-ZrO2 incorporated WC-TiC0.4 composites were consolidated employing spark plasma sintering (SPS) technology at different temperatures. The impacts of ZrO2 and 3Y-ZrO2 as toughening agents on the densification, phase composition, microstructure and mechanical properties of the WC-based composites were assessed. The results revealed that the WC-5 wt% TiC0.4–9 wt% ZrO2 (W5Ti9Zr) composite required a lower sintering temperature of 1700 °C for nearly full densification than WC-5 wt% TiC0.4–9 wt% 3Y-ZrO2 (W5Ti9Zr-3Y) composite. The diffraction peaks of monoclinic ZrO2 (m-ZrO2) existed only in the W5Ti9Zr composite. The evenly dispersed ZrO2 and 3Y-ZrO2 achieved the relatively homogeneous and fine microstructure in W5Ti9Zr and W5Ti9Zr-3Y composites. Moreover, the semi-coherent interfaces of (W1-x, Tix)Cn layer with WC, (W1-x, Tix)Cn layer with m-ZrO2, and (W1-x, Tix)Cn with m-ZrO2 brought about a rise in the fracture toughness of W5Ti9Zr composite. The W5Ti9Zr composite yielded the better comprehensive mechanical properties with a combination of hardness (20.8 GPa) and fracture toughness (9.9 MPa·m1/2) as compared to those of W5Ti9Zr-3Y composite. Furthermore, the main toughening mechanisms of W5Ti9Zr and W5Ti9Zr-3Y composites included grain refinement of WC matrix, a mixed transgranular and intergranular fracture, stress-induced transformation of t-ZrO2 to m-ZrO2, and crack deflection.

In Situ Visualizing the Interfacial Failure Mechanism and Modification Promotion of LAGP Solid Electrolyte toward Li Metal Anode

AbstractIn‐depth understanding the failure process of solid‐state electrolyte (SSE) and providing potential solutions are crucial for the development of solid‐state batteries (SSBs). Typical techniques are powerful to investigate the chemical/electrochemical degradation of SSE. While, mechanical failure, which would undoubtedly affect battery performance, is difficult to detect by normal techniques and lack effective characterizations. Herein, via in situ electrochemical SEM, the dynamic failure process of SSE is observed, revealing the continuously generated side‐reaction layer and the stress‐induced cracks are the main origins. C3N4 (CN) is introduced as the modification layer for Li and SSE. Via in situ scanning electron microscope, Li growth is regulated by CN from dendrite‐like to particulate‐like growth. The properties of electronic transportation and ionic migration in CN are quantitatively measured, and CN promotion mechanism is revealed. Thanks to CN layer, the interfacial side‐reaction is restrained, simultaneously, Li+ flux becomes well‐distributed for dense Li deposition, preventing stress‐induced mechanical failure in SSE. Li symmetrical batteries with CN can endure the maximum current density up to 2.0 mA cm−2 and stably cycle for 3000 h at 300 µA cm−2. This work suggests a promising method to circumvent SSE degradation against Li and open opportunities for future SSBs.

Construction of 1D/0D/2D Zn0.5Cd0.5S/PdAg/g-C3N4 ternary heterojunction composites for efficient photocatalytic hydrogen evolution

A high-efficiency and easy-available approach was developed to obtain a ternary heterojunction composites with advanced hydrogen evolution reaction (HER) performance under visible light by water split. PdAg bimetallic nanoparticles make a close contact interface between g-C3N4(CN) and Zn0.5Cd0.5S(ZCS). Under visible light irradiation, CN and ZCS are both excited to generate electron-hole pairs, PdAg bimetallic nanoparticles act as a bridge between CN and ZCS. Not only can the photogenerated electrons from CN be captured, but they can also be quickly transferred to the surface of ZCS and participate in the photocatalytic reaction to release H2, and the recombination of charge carriers between the contact interface of ZCS and CN can be significantly inhibited. In addition, the thin CN layer reduces the photocorrosion of the ZCS and enhances the specific surface area of the composite material. After testing, the composite material with 30 wt% ZCS and 4 wt% PdAg demonstrates hydrogen evolution performance, up to 6250.7 μmol g−1h−1, which is 753 times the hydrogen evolution rate of single-component CN and 12.6 times of ZCS/CN. Compared with single-component and two-component photocatalysts, the ternary ZCS/PdAg/CN photocatalyst achieves significantly enhanced photocatalytic activity.

Carbon Nitride‐Based Photoanode with Enhanced Photostability and Water Oxidation Kinetics

AbstractCarbon nitrides (CN) have emerged as promising photoanode materials for water‐splitting photoelectrochemical cells (PECs). However, their poor charge separation and transfer properties, together with slow water‐oxidation kinetics, have resulted in low PEC activity and instability, which strongly impede their further development. In this work, these limitations are addressed by optimizing the charge separation and transfer process. To this end, a nickel–iron based metal‐organic framework, Ni/Fe‐MIL‐53, is deposited, that acts as an oxygen evolution pre‐catalyst within the CN layer and incorporate reduced graphene oxide as an electron acceptor. Upon electrochemical activation, a uniform distribution of highly active oxygen evolution reaction (OER) catalysts is obtained on the porous CN surface. Detailed mechanistic studies reveal excellent hole extraction properties with high OER catalytic activity (83% faradaic efficiency) and long‐term stability, up to 35 h. These results indicate that the decrease in performance is mainly due to the slow leaching of the catalyst from the CN layer. The CN photoanode exhibits a reproducible photocurrent density of 472 ± 20 µA cm−2 at 1.23 V versus reversible hydrogen electrode (RHE) in 0.1 m KOH, an exceptionally low onset potential of ≈0.034 V versus RHE, and high external quantum yield.

Ternary heterostructural CoO/CN/Ni catalyst for promoted CO2 electroreduction to methanol

Methanol is one of the most desirable C1 products in the electrocatalytic CO2 reduction reaction (CO2RR). The intricate nature of the reaction pathway involving six-electron transfer, however, makes the process highly challenging. In this work, we report a ternary heterostructural catalyst CoO/CN/Ni, with cobalt as catalytic centers supported on N-doped carbon with underlying nickel, which presents a remarkably promoted Faraday efficiency (70.7%) and current density (10.6 mA/cm2) towards methanol, compared with CoO/CN. It appears that the nickel underneath plays an essential role by donating electrons to outer CN layer and thus changes the electronic state of surface and then of the cobalt species which act as catalytic centers. Notably, the unique catalyst shows not only high electrocatalytic activity and selectivity to CH3OH, but also suppression of H2 formation and well-preserved catalytic performance during the long-term test of reaction. Simultaneously, isotropic labeling and electrochemical experiment prove the carbon source.

Mussel chemistry inspired synthesis of Pd/SBA-15 for the efficient reduction of 4-nitrophenol

In this study, N-doped platelet-like metal-loaded Zr/SBA-15 was synthesized and employed for reducing 4-nitrophenol to remove this contaminant from water. Dopamine hydrochloride was used as a novel CN source for the modification of ZrSBA-15. The N doping process occurred readily at a low temperature due to the polymerization of dopamine, which could save energy and simplify the experimental fabrication of catalysts. In addition, polydopamine can immobilize Pd ions in a facile manner and the trapped Pd ions are reduced to Pd nanoparticles due to the reducibility of the polydopamine polymer. The utilization of dopamine allows the catalyst to be obtained in a facile and cost-effective synthetic process, while the production of the CN layer as well as the reduction and immobilization of the Pd ions can occur simultaneously. Characterization of the product showed that the catalyst had a platelet-like structure after decoration with elemental Zr, which enhanced the catalytic reaction compared with the natural fiber-like SBA-15. The optimal Pd loading capacity was determined as ~3.0 wt% and the materials obtained could reduce 4-nitrophenol to 4-aminophenol within 120 s with a conversion ratio above 90%.

Carbon Nitride Materials for Water Splitting Photoelectrochemical Cells.

Graphitic carbon nitride materials (CNs) have emerged as suitable photocatalysts and heterogeneous catalysts for various reactions thanks to their tunable band gap, suitable energy-band position, high stability under harsh chemical conditions, and low cost. However, the utilization of CN in photoelectrochemical (PEC) and photoelectronic devices is still at an early stage owing to the difficulties in depositing high-quality and homogenous CN layer on substrates, its wide band gap, poor charge-separation efficiency, and low electronic conductivity. In this Minireview, we discuss the synthetic pathways for the preparation of various structures of CN on substrates and their underlying photophysical properties and current photoelectrochemical performance. The main challenges for CN incorporation into PEC cell are described, together with possible routes to overcome the standing limitations toward the integration of CN materials in PEC and other photoelectronic devices.

Temperature dependence of protection layer formation on organic trench sidewall in H2/N2 plasma etching with control of substrate temperature

For the etching of organic films in H2/N2 plasma, etched profiles are significantly determined by substrate temperature. Here, we control the substrate temperature variation within 3 °C during processing by modulating the plasma-discharge time. The evolution of the cross-sectional profile of line-and-space patterns was observed every 10 s. At 60 and 100 °C, sidewall etching was observed during overetching, but not at 20 °C. During the main etching, the sidewalls were protected by the adsorption of by-products at various temperatures. Moreover, we investigated the temperature dependence of protection layer formation by analyzing the surface components of the organic film. The CN layer formed by N radicals has a protective effect that depends on the components of the CN layer. It was found that the ratio of C–N sp3 to C–N sp2 in the sidewall was highest at 100 °C. By evaluating the radical contribution to CN layer formation, C–N sp3 bonds were observed to be formed by ions and radiation-assisted reaction.

Development and application of CN PLIF for single-shot imaging in turbulent flames

A laser-induced fluorescence concept for improved interference-free imaging detection of the cyano radical (CN), an intermediate species in nitrogen combustion chemistry, has been investigated. Both a standard Nd:YAG-pumped dye laser and a solid-state alexandrite laser were employed for excitation of CN B–X (1–0) lines near 359nm in combination with detection of the (1–1) band near 387nm, providing a direct comparison of interferences and achievable detection sensitivity. Measurements in ammonia-doped premixed methane–air flames showed that the alexandrite laser, with longer pulse duration (∼30ns) and broader line width (2.5cm−1), can provide around 4 times stronger CN signal than that achievable with conventional Nd:YAG pumped dye laser system. Enhanced CN detection using alexandrite laser excitation is demonstrated that signal-to-noise ratio ∼5 is achieved for single-shot fluorescence imaging at conditions with CN concentration levels experimentally estimated to be a few hundred ppbs. This improved detection sensitivity, however, might still not be sufficient for pure methane/air flames due to low CN concentration. Observations of local extinction, represented by CN layer dis-continuation, in turbulent flames suggest that the improved CN detection will be useful for deepened understanding of interactions between fuel-nitrogen chemistry and local turbulent transport in combustion.

Hole injection enhancement of a single-walled carbon nanotube anode using an organic charge-generation layer

We demonstrate significant hole injection enhancement of single-walled carbon nanotube (SWCNT) anodes in flexible organic light-emitting devices (OLEDs) by the insertion of a strong electron-accepting organic charge-generation layer (CGL), hexaazatriphenylene hexacarbonitrile (HAT–CN). To clarify the origin of hole injection improvement, we investigated interfacial electronic structures using in situ ultraviolet photoelectron spectroscopy, inverse photoelectron spectroscopy, theoretical calculations, and electrical measurements. The HAT–CN layer significantly increased the work function of SWCNT anodes and acted as an efficient CGL due to its deep-lying lowest unoccupied molecular orbital level, which arises from the strong electron-accepting characteristics of the carbonitrile endgroups. We compared the energy level alignment at the interface of the N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) hole transport layer/HAT–CN/SWCNTs with that of NPB/SWCNTs, and found that the highest occupied molecular orbital level of the NPB changed from 1.20 to 0.40eV with insertion of the HAT–CN layer. As a result, flexible OLEDs with the HAT–CN layer showed an order of magnitude larger current density and luminance than those without the HAT–CN layer.

Investigation of Oxide Inclusions and Primary Carbonitrides in Inconel 718 Superalloy Refined through Electroslag Remelting Process

The effect of remelting atmosphere and calcium treatment during electroslag remelting (ESR) of Inconel 718 superalloy on the oxide inclusions and primary carbonitrides was investigated. The results show that after ESR refining combined with calcium treatment, the original oxide inclusions in the electrode, mainly MgO·Al2O3 spinels and some MgO inclusions, were modified to CaO-Al2O3 system inclusions or the inclusions of MgO·Al2O3 spinel core surrounded by CaO-MgO-Al2O3 system inclusion layer. Without the calcium treatment in ESR process, all the oxide inclusions in superalloy ingots are MgO·Al2O3 spinels. All the oxide inclusions in ESR ingots act as the nucleation site for carbonitride (Nb,Ti)CN with two-layer structure precipitation, except for those with a single (Nb,Ti)CN layer containing a small amount of Ti and N in the ingot refined by a proper amount of calcium addition in ESR process. The carbonitrides (Nb,Ti)CN formed directly on the oxide inclusion have a small amount of Nb and C as well as a relatively fixed atomic ratio of Nb/Ti (about 0.6:1). There is a Nb-rich and C-rich (Nb,Ti)CN layer on the pre-existing (Nb,Ti)CN formed on the oxide inclusion. The size of the observed carbonitrides is in the range of 5 μm to 15 μm. The calcium treatment in the ESR process has a significant effect on the morphology of carbonitrides in superalloy ingot due to modification of oxide inclusions by Ca-treatment resulting in the change of precipitation and growth conditions for carbonitrides. The morphologies of carbonitrides were changed from clustered block or single octahedral to skeleton-like after calcium treatment.

Decomposition of expanded austenite in AISI 316L stainless steel nitrided at 723K

Expanded austenite (cN), which can be produced during plasma nitriding of austenitic stainless steels, provides high levels of strength, toughness and corrosion resistance by comparison with traditional nitride layers. However, expanded austenite properties can be lost due to decomposition caused its thermodynamic metastability. In the present work, austenitic stainless AISI 316L steel was plasma nitrided at 723 K for 5 h at 500 Pa and microstructurally characterised by X-ray diffraction (XRD), and optical and transmission electron microscopy (TEM) which confirmed the presence of fcc expanded austenite with a lattice parameter up to 9?5% larger than untreated austenite. TEM analyses of thin foils showed that fine nitrides were formed in the cN layer and some areas were observed with a singular lamellar morphology very similar to the pearlite colonies found in carbon steels. Selected area electron diffraction (SAED) analysis suggests that these areas are composed of bcc ferrite and cubic chromium nitrides produced after a localised decomposition of the expanded austenite layer. Amorphous expanded austenite was observed in some areas of the investigated samples. The occurrence of cN decomposition was associated with microsegregation of ferrite stabilisers (Cr, Mo) and depletion of an austenite stabiliser (Ni) in localised regions of the expanded austenite layer.

Carbon nitride film deposition by active screen plasma nitriding

Deposition of CN-based films by a novel version of active screen plasma nitriding, aiming at surface modification of polymers, is reported. The approach relies on the use of pure graphite as the grid material, which was found to act both as an active screen and as a dry source of carbon atoms for the synthesis of thin films consisting mainly of a stoichiometric CN layer with columnar-type structure and dome-like nanostructured morphology.

Stress Technology Impact on Device Performances and Reliability for Sub-90 nm Silicon-on-Insulator Complementary Metal–Oxide–Semiconductor Field-Effect-Transistors

In this work, we investigated the thickness effect of a high-stress gate capping layer (GC layer) on <100> 90 nm partially-depleted silicon-on-insulator complementary metal–oxide–semiconductor field-effect transistor (PD-SOI CMOSFETs). Additionally, we inspected the hot-carrier reliability on body-contacted (BC) SOI devices with various thicknesses of the GC layer (1100 and 700 Å) and a conventional SiN layer (CN layer). For nMOSFETs, devices with an 1100 Å GC layer possess worse characteristics and hot-carrier degradations than devices with a 700 Å GC layer in terms of excess high tensile stress. For pMOSFETs, the GC layer only slightly affects device performance, but seriously affects hot-carrier-induced device degradation. Therefore, the thickness of this high-stress GC layer should be optimized to improve the device performance.

Photolysis of sulfuric acid vapor by visible light as a source of the polar stratospheric CN layer

We present the first microphysical calculations confirming that photolysis of sulfuric acid vapor by visible light is responsible for the formation of the springtime “CN layer” observed in the polar stratosphere. Our calculations show that the recently proposed photolysis mechanism is also sufficient to explain observations of vertically increasing SO2 mixing ratios in the upper stratosphere. Such photolysis, however, does not sufficiently explain the limited observations above 40 km of vertically decreasing H2SO4 and SO3 vapor, suggesting an additional loss mechanism there. We rule out previous speculation regarding reaction of H2SO4 with O(1D) or OH as inconsistent with observations of SO2. Rather, the loss is consistent with a permanent sink for sulfur, such as H2SO4 neutralization by metals on meteoritic dust. In light of such removal, H2SO4 photolysis to SO2 gains added importance in preserving gaseous sulfur in the upper stratosphere. We also present new cross sections derived from ab initio calculations for H2SO4 absorption at visible and Lyman‐α wavelengths and evaluate their atmospheric implications. Our atmospheric model reveals that photolysis of H2SO4 by Lyman‐α radiation is responsible for up to one third of the SO2 in the mesosphere and 10% of the particles in the polar stratospheric CN layer.

A 2D microphysical model of the polar stratospheric CN layer

Each spring a layer of small particles forms between 20 and 30 km altitude in the polar regions. We present the first self‐consistent explanation of the observed “CN layer” from a 2D microphysical model of sulfate aerosol. Our theory relies on photolysis of H2SO4 and SO3, consistent with recent laboratory measurements, to produce SO2 in the upper stratosphere and mesosphere. An additional source of SO2 may be required. Nucleation throughout the polar winter extends the top of the aerosol layer to higher altitudes, despite strong downward transport of ambient air. This may affect heterogeneous chemistry at the top of the aerosol layer in polar winter and spring.

Aerosol nucleation in the winter Arctic and Antarctic stratospheres

We calculate the formation rate of sulfuric acid ‐ water aerosol particles as a function of altitude for the conditions of the winter Arctic and Antarctic stratospheres. The theoretical results indicate that sulfate particle formation can occur in the polar winter stratosphere. Conditions for new particle formation are increasingly favorable as the altitude increases between 20 and 30 km because of the decrease in surface area of pre‐existing particles and increasing sulfuric acid vapor supply. The theoretical predictions are consistent with observations of a high altitude CN layer over Antarctica in the spring. Available vapor pressure data indicate that ternary system particles composed of sulfuric acid, nitric acid and water are not thermodynamically stable under winter stratospheric conditions.