Surface Carbon Layer Research Articles

Mechanism and Observation of Pore Formation during Carbonitriding

Abstract Carbonitriding enhances properties of many steels and is therefore an attractive alternative for surface hardening of steel components in the mechanical industry. However, pore formation in the carbon and nitrogen enriched surface layer may occur under certain process conditions. For a given steel and case depth specification, pore formation can be managed by reducing the nitrogen activity of the carbonitriding atmosphere below a defined limit, depending on process temperature and process time. Recent progress in process control allows automatic and independent adjustments of the carbon and nitrogen activities and corresponding potentials of the carbonitriding atmosphere. This study contributes to the practical evaluation of pore formation limits under selected carbonitriding conditions for a range of commonly used engineering steel grades.

Cocatalyst Engineering with Robust Tunable Carbon‐Encapsulated Mo‐Rich Mo/Mo2C Heterostructure Nanoparticle for Efficient Photocatalytic Hydrogen Evolution

AbstractCocatalyst engineering with non‐noble metal nanomaterials can play a vital role in low‐cost, sustainable, and large‐scale photocatalytic hydrogen production. This research adopts slow carburization and simultaneous hydrocarbon reduction to synthesize carbon‐encapsulated Mo/Mo2C heterostructure nanoparticles, namely Mo/Mo2C@C cocatalyst. Experimental and theoretical investigations indicate that the Mo/Mo2C@C cocatalysts have a nearly ideal hydrogen‐adsorption free energy (ΔGH*), which results in the accelerated HER kinetics. As such, the cocatalysts are immobilized onto organic polymer semiconductor g‐C3N4 and inorganic semiconductor CdS, resulting in Mo/Mo2C@C/g‐C3N4 and Mo/Mo2C@C/CdS catalysts, respectively. In photocatalytic hydrogen evolution application under visible light, the Mo/Mo2C@C with g‐C3N4 and CdS can form the Schottky junctions via appropriate band alignment, greatly suppressing the recombination of photoinduced electron‐hole pairs. The surface carbon layer as the conducting scaffolds and Mo metal facilitates electron transfer and electron‐hole separation, favoring structural stability and offering more reaction sites and interfaces as electron mediators. As a result, these catalysts exhibit high H2 production rates of 2.7 mmol h−1 g−1 in basic solution and 98.2 mmol h−1 g−1 in acidic solution, respectively, which is significantly higher than that of the bench‐mark Pt‐containing catalyst. The proposed cocatalyst engineering approach is promising in developing efficient non‐noble metal cocatalysts for rapid hydrogen production.

Formation of carbon and oxygen rich surface layer on high purity magnesium by atmospheric carbon dioxide plasma

Formation of carbon and oxygen rich surface layer on high purity magnesium by atmospheric carbon dioxide plasma

Flame retardant polypropylene with a single molecule intumescent flame retardant based on chitosan

A single molecule intumescent flame retardant was synthesized through in-situ polymerization by chitosan-based ammonium polyphosphate microencapsulated by melamine-formaldehyde resin. The multiple reactive hydroxyl and amino groups in its molecular chain made it a positively charged polymer with excellent coordination. The decomposition of melamine-formaldehyde resin produced a large amount of incombustible gas, which reduced the heat absorption on the surface of the composite material and inhibited its decomposition. Through thermogravimetric analysis, it was found that its thermal stability was better at high temperatures. Due to the decomposition of melamine-formaldehyde resin, a large amount of incombustible gas was produced, which reduced the heat absorption on its surface and inhibited its decomposition, so that polypropylene composites containing the flame retardant had a smooth decomposition process. The burning results showed that the limiting oxygen index and vertical combustion grade of the polypropylene composites containing the flame retardant had been improved, which the vertical combustion rating was V-1, and the limiting oxygen index was 25.7%. At the same time, it was clearly observed that composites containing the single-molecule intumescent flame retardant had an excellent anti-dripping effect. The surface temperature of the composite material was greatly reduced during combustion, from 343.7 ℃ to 156.9 ℃. Raman spectra and SEM of the surface carbon layer of the burned spline revealed the composite containing the flame retardant with a lower ID/IG value, indicating that the carbon layer it formed had more excellent crystallinity. Therefore, its carbon layer had a better structure and stability. It could be borne out that our single-molecule intumescent flame retardant had a good flame retardant effect on PP.

An Integrated Metal‐Free Modification Method to Construct Efficient and Durable Bulk Heterojunction Photocathode for Solar Hydrogen Production

AbstractPolymer semiconductor with bulk heterojunction (BHJ) structure has attracted increasing attention to fabricate highly efficient photoelectrode for converting solar energy and water into hydrogen, thanks to its high photocurrent output and positive onset potential beyond 0.6 V. However, BHJ‐based photoelectrodes demonstrate poor anticorrosion against irradiation in aqueous environment, thus the photoelectrochemical (PEC) stability is a very intractable problem to solve. Herein, an inside and outside integrated modification method is developed to help BHJ‐based photocathode withstand PEC erosion during hydrogen production in acidic solution. The obtained BHJ (PBDB‐T:ITIC:PC71BM)‐based photocathode with surface carbon protective layer allows sustained and fast PEC hydrogen evolution (an average photocurrent density up to 13.5 mA cm−2) for a duration up to 15 h, which is among the best results of BHJ‐based photocathodes. The internal modification with fullerene derivative of PC71BM boosts the photogenerated electron transfer to balance against relative fast hole transfer, which largely alleviates electron accumulation and improves PEC intrinsic stability as a result. The surface carbon layer effectively resists the permeation of aqueous electrolyte without hindering interfacial charge transfer. This metal‐free protective method is very promising toward construction of highly robust BHJ‐based photoelectrodes for sustainable water splitting.

Ultra-thin carbon coated amorphous N-doped CoP enhancing electron transfer for wide spectrum photocatalytic hydrogen evolution

It is necessary that develop broad spectrum responsive and noble-metal-free photo-catalysts to produce hydrogen. Herein, a novel nitrogen doped amorphous CoP with carbon coating (N–CoP@C) photo-catalyst was prepared by phosphating the Co-alanine complex precursor for wide spectrum photocatalytic H2 production. Nitrogen doping can adjust the electronic structure, promote photogenerated carrier separation, and enhance electronic density. The improvement of photocatalytic hydrogen evolution activity is due to the porous structure and surface carbon layer of amorphous N–CoP@C. The porous and thin slice structure can increase the specific surface area, thus providing more active sites and separating surface charges. The carbon layer can be used as an electron acceptor to suppress charge recombination and improve photocatalytic performance. The amorphous N–CoP@C-4 exhibits the highest hydrogen evolution rate of 60.91 μmol h−1 under visible light irradiation with EY as a photosensitizer and TEOA as an electron donor, which is about 46.7 and 2.8 times higher than Co-alanine and CoP, respectively. In particular, a high photocatalytic reaction stability was achieved over N–CoP@C-4 catalyst. This work provides an effective strategy for construction N–CoP@C to improve the photocatalytic activity.

Ultrafast flame coating of carbon and chemical vapor deposition of graphene on NiTi alloy to enhance its corrosion resistance

To study their surface protection performance, both graphene and carbon layers have been deposited onto the surface of NiTi alloy via the common chemical vapor deposition (CVD) and a facile flame coating technique, respectively. The latter can be accomplished within tens of seconds with the combustion flame itself as the carbon source and alloy substrate as catalyst. The carbon layer not only inhibits effectively the Ni2+ releasing from NiTi alloy, but also displays lower surface roughness and higher corrosion resistance than that of the graphene coating. The effect of the flame coating time on the performance of resulted carbon layer has been studied comprehensively. The lowest corrosion current density (1.6 μA/cm2) of the flame coated alloy in simulated body fluid has been achieved by adjusting the flame time to be just 30s. This value is much less than that of graphene coating (2.4 μA/cm2) in the same test conditions. And it gets even less in 3.5 wt% NaCl solution (1.3 μA/cm2), implying the potential application of the flame coating method for more corrosive marine environments. Also, the Ni2+ releasing concentration of NiTi/C-30s is decreased to be around one fourth that of bare NiTi. Moreover, the excellent scratch resistance of the carbon layer and its strong adhesion to NiTi substrate have been also confirmed by both the cross-cut and scratching tests. Furthermore, both the elastic modulus and hardness of the alloy decreased marginally after the fast and mild-temperature flame coating process according to the nano-indentation test results. Compared with traditional surface engineering approaches, the flame coating method has many advantages, such as simple and fast process, high protective performance, environmental-friendly fabrication and protection. All of these benefit its promising application in various fields.

Antimony and carbon dual-doped hollow ZnS-Sb/C nanospheres for enhanced sodium storage performance and its full battery application

Currently, it is very necessary to find novel and practical anode materials for sodium ion batteries (SIBs) in energy research. Herein, utilizing the template of ZnS, hollow ZnS-Sb/C nanospheres were synthesized via a cation exchange reaction between Zn2+ and Sbx+ ions and annealing process. When applied as anode for SIBs, the ZnS-Sb/C nanospheres deliver an ultra-high reversible capacity of 747 mA h g−1 at 100 mA g−1 after 150 cycles, excellent cycling and rate performance. Additionally, the assembled Na3V2(PO4)3||ZnS-Sb/C full battery also exhibits good electrochemical performance. Combining the advantages of ZnS and metal Sb, the ZnS-Sb/C nanospheres can largely increase the battery capacity and maintain the phase stability, meanwhile hollow structure provides high specific surface area and carbon layer contributes stable support and excellent conductivity. All the rational design can synergistically provide buffer for the volume expansion during the Na+ intercalation/de-intercalation. Moreover, the high contribution of pseudocapacitance behavior contributes to the superior rate capability and long-term cycling stability. Therefore, ZnS-Sb/C nanospheres will provide a promising strategy for enhancing the performance of SIBs for practical industrialization.

Intersperse copper nanoparticles into 3D fibrous silica-supported carbon spheres for electrocatalytic nitrogen reduction

The electrocatalysts are critical to the electrocatalytic nitrogen reduction reaction (e-NRR) technique and its development. Herein, through morphological structure modulation, three-dimensional (3D) fibrous silica nanospheres (KCC-1) are firstly fabricated as the supporting scaffold, followed by the coating of nitrogen-doped carbon and interspersing of copper nanoparticles. The resulting carbon spheres (KNC) has very uniform interspersion of copper nanoparticles (Cu-NPs) in the 3D fibrous structure ensuring high accessible active sites for nitrogen molecules; the thin surface carbon layer offering a rich channel for electron transport; and nitrogen dopant allowing efficient electron transfer of copper atoms throng metal-nitrogen covalent bonds. When used as electrocatalysts to e-NRR, KNC exhibits good electrochemical activity, selectivity, and good stability, and can obtain an ammonia yield of approximately 6.67 µg h−1 mgcat−1 and an excellent Faraday efficiency (FE) of 8.1% in 0.1 M sodium sulfate solution at − 0.4 V (vs. RHE).

Practical implantation of Si nanoparticles in Carbon-coated α-FeSi2 matrix for Lithium-ion batteries

Silicon, one of the most promising anodes, has been facing challenges to improve continuous increased electrode expansion during the cycles, resulting in a deteriorated conducting network between the particles from the accelerated side reactions with the electrolytes and inferior long-term cycle performance of the graphite counterpart for practical application. Herein, we demonstrated an easy and scalable synthesis of Si nanoparticles in the carbon-coated and interconnected α-FeSi2 matrix where α-FeSi2 acts as a buffer matrix for the expansion of adjacent Si, and the uniformly-coated carbon surface layer on the α-FeSi2 matrix enhances conductivity and reduces the side reaction of electrolyte and structural degradation. Our results reveal that the α-FeSi2/Si/carbon (FSC) exhibits better electrochemical properties in the lithium-ion cell compared to α-FeSi2/Si (FS), benchmarking samples of α-FeSi2/Si (BM-FS) and carbon nanotubes (CNTs) grown FS (BM-FS/CNT). The FSC anode in the full cell with the areal capacity and electrode density of anodes of 2.25 mAh cm−2 and 1.7 g cc−1, respectively, exhibited quite a comparable capacity retention to a graphite counterpart, showing 83 % at a rate of 0.7C charging /0.5C discharging rate between 4.4 and 3 V after 200 cycles.

Regeneration of single-atom catalysts deactivated under acid oxygen reduction reaction conditions

Single-atom catalysts serve as a promising candidate to realize noble-metal-free electrocatalytic oxygen reduction in acid media. However, their poor stability under working conditions strictly restrains their practical applications. Therefore, regeneration of their electrocatalytic activity is of great significance. Herein, the regeneration of a Fe–N–C single-atom catalyst is demonstrated to be feasible by a facile annealing regeneration strategy. The activity after regeneration recovers to that of the pristine electrocatalyst and surpasses the deactivated electrocatalyst. The regeneration mechanism is identified to be self-etching of the surface carbon layer and consequent exposure of the previously buried single-atom sites. Furthermore, the regeneration strategy is applicable to other single-atom catalysts. This work demonstrates the feasibility of regenerating oxygen reduction electrocatalysts and affords a pioneering approach to deal with rapid deactivation under working conditions.

Synthesis of non‐agglomerating submicron/nano‐Yb2Si2O7 powders by a carbon‐coated coprecipitation method

AbstractWe herein report a novel carbon‐coated coprecipitation method to synthesize non‐agglomerating submicron/nano‐β‐Yb2Si2O7 powders. Yb(C2H3O2)3·4H2O and silica sol (alkaline) were chosen as the ytterbium source and silicon source, respectively. A carbon surface layer is processed using sucrose as carbon source to hinder the contact and sintering of β‐Yb2Si2O7 particles during heat treatment under a protective atmosphere, and then the carbon layer could be completely removed by inletting air at 900°C during cooling process. The as‐synthesized Yb2Si2O7 powders demonstrate an average size of 271 nm with a narrow distribution of 142–531 nm. The results show that the carbon layer could successfully solve the severe agglomeration or sintering of nanometer β‐Yb2Si2O7 particles during the calcination process. The as‐developed carbon‐coated coprecipitation technique is an effective method to fabricate high purity submicron/nano‐Yb2Si2O7 powders.

Using molybdenum carbiding to induce digestion of carbon in H2O2: A sustainable approach to eliminate radioactivity for hazardous graphite waste inherited from nuclear enterprise

To properly manage nuclear wastes is critical to sustainable utilization of nuclear power and environment health. Here, we show an innovative carbiding strategy for sustainable management of radioactive graphite through digestion of carbon in H2O2. The combined action of intermolecular oxidation of graphite by MoO3 and molybdenum carbiding demonstrates success in gasifying graphite and sequestrating uranium for a simulated uranium-contaminated graphite waste. The carbiding process plays a triple role: (1) converting graphite into atomic carbon digestible in H2O2, (2) generating oxalic ligands in the presence of H2O2 to favor U-precipitation, and (3) delivering oxalic ligands to coordinate to MoVI-oxo anionic species to improve sample batching capacity. We demonstrate > 99% of uranium to be sequestrated for the simulated waste with graphite matrix completely gasifying while no detectable U-migration occurred during operation. This method has further been extended to removal of surface carbon layers for graphite monolith and thus can be used to decontaminate monolithic graphite waste with emission of a minimal amount of secondary waste. We believe this work not only provides a sustainable approach to tackle the managing issue of heavily metal contaminated graphite waste, but also indicates a promising methodology toward surface decontamination for irradiated graphite in general.

Electron-rich interface of Cu-Co heterostructure nanoparticle as a cocatalyst for enhancing photocatalytic hydrogen evolution

Heterogeneous nano-metal structures are widely used in the field of photocatalysis as an efficient cocatalyst, but the structure–activity relationship has not been elucidated clearly. In this work, a classical CuCo@C nanoparticle with a core of bimetallic CuCo and a carbon shell was used as a cocatalyst to explore and reveal the mechanism of interfacial effect for enhanced photocatalytic hydrogen evolution. It was found that the bimetallic CuCo had a heterogeneous structure with abundant Cu-Co interfaces. The desirable visible-light-driven photocatalytic hydrogen evolution rate of CuCo@C/g-C3N4 was much higher than that of Cu@C/g-C3N4, Co@C/g-C3N4, and superior to that of the control group loaded with 1 wt% Pt (Pt/g-C3N4). According to the experimental characterizations and density functional theory calculations, electrons were enriched at the Cu-Co interface, which can promote the electron-hole pairs separation and accelerate charge transfer of the g-C3N4 host photocatalysts. On the other hand, the surface carbon layer and Cu-Co interface modulated the H adsorption free energy on the CuCo@C, which was favorable for hydrogen evolution. It is conceivable that further investigating and tuning different metal interfaces will facilitate the large-scale application of bimetallic cocatalysts.

Tuning the electronic structure of Co@N–C hybrids via metal-doping for efficient electrocatalytic hydrogen evolution reaction

The introduction of W optimizes the electronic structure of the Co@N–C system and promotes the transfer of electrons to the surface carbon layer, thus greatly improving the HER activity.

Insights into the mechanism of enhanced peroxymonosulfate degraded tetracycline using metal organic framework derived carbonyl modified carbon-coated Fe0

Tetracycline (TC) is a commonly used antibiotic that has gained wide spread notoriety owing to its high environmental risks. In this study, rich carbonyl-modified carbon-coated Fe0 was obtained by pyrolysis of MIL-100(Fe) in an Ar atmosphere, and used to activate peroxymonosulfate (PMS) for the degradation of tetracycline in water. The roles of Fe0, carbon and surface carbonyl on PMS activation were investigated. Fe0 continuously activated PMS, acted as a sustained-release source of Fe2+, and could effectively activate PMS to produce SO4•−, O2•− and •OH. Carbon was found to do responsible for electron transportation during the activation of PMS and slow down the oxidation of Fe0. The carbonyl group on the carbon surface layer was the active site of 1O2, which explains the enhanced performance for TC degradation. When Ca = 0.1 g/L and C0 = 0.4 mM, TC degradation rate reached 96%, which was attributed to the synergistic effect of radicals (i.e., SO4•−, O2•−, •OH) and non-radical (i.e., 1O2). Finally, the degradation pathway was proposed by combining density functional theory (DFT) calculations with liquid chromatography-mass spectrometry (LC-MS), toxicities of the intermediate products were also evaluated. All results show that carbonyl-modified carbon-coated Fe0 possesses promising capacity for the removal of antibiotics from water.

In-situ mechanochemical synthesis of sub-micro Si/Sn@SiOx-C composite as high-rate anode material for lithium-ion batteries

Micrometer silicon (MSi) particles are prospective anode material for high energy-density lithium-ion batteries. Aiming at the scale-up production and the improvement in rate capability, a novel sub-micro Si/Sn@SiOx-C (SSSC) composite via a facile two-step process of milling and annealing is designed and synthesized. With the structural uniqueness including in-situ introduction of metallic tin (Sn) originated from mechano-reduction of nano tin dioxide (nano-SnO2) with MSi, dual-buffering of inner SiOx matrix and uniform surface carbon layer, SSSC electrodes exhibit impressive rate capability and stable cyclability. The optimum architecture of SSSC-73 (i.e. weight ratio of precursor MSi-to-SnO2 is 7:3) delivers stable cycling with 1102 mAh g−1 (at 0.5 A g−1) over 100 cycles and exceptional rate performance with a high capacity retention of 95% over 500 cycles at 2 A g−1. Particularly, this facile and cost-effective preparation of SSSC composites has no by-products, making it competitive in practical application.

Novel and Facile Method for Photocatalytic Disinfection and Removal of Organic Material from Water Using Immobilized Copper Oxide Nano Rods

In this work, copper oxide nanorods (Cu2O NRs) were directly prepared from copper sheet as substrate. The as grown Cu2O NRs were modified through surface carbon layer deposition via a single-step thermal treatment method. The carbon modified Cu2O NRs has been characterized by scanning electron microscope (SEM), energy dispersion X-ray spectroscopy (EDX), X-ray diffraction (XRD), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), furrier transform infrared (FT-IR), and Raman spectroscopy. The results showed that Cu2O NRs were formed on the surface of the metal sheet as non-aligned rods with a diameter of 100−130 nm and 1.5–2.5 μm length. The produced reactive species (OH·) in the photocatalytic experiments was detected and quantified by coumarin as a probe. Furthermore, the inactivation of E. coli bacteria was explored as a model for antimicrobial performance. Tannic acid was used as a model of NOM. The carbon modified Cu2O NRs showed an enhanced photocatalytic degradation performance for (NOM). At the end of photocatalytic experiments, 99 % of tannic acid and 93 % of COD removal were obtained. Also, complete inactivation of E. coli bacteria is achieved. The results indicated that Cu2O NRs in a modified form could be used for five cycles of photocatalytic degradation.

Study on the preparation and tribological properties of BN@C-OA nano-additive lubricants

The advanced nano-additives can improve the lubrication performance of nanolubricants efficiently, which could greatly reduce energy consumption. Here, we prepared the BN coated with carbon layer (BN@C) by a novel hydrothermal coating method with pristine BN nanosheets as matrix material and glucose as carbon source. And the BN@C exhibited excellent lubrication performance as a lubricant additive. In order to investigate the tribological properties, BN@C was modified with oleic acid as a surfactant, and the friction tests were carried out on an MRS-10A four-ball friction and wear tester. Benefitting from the stable dispersity, ultrasmall particle size and the surface carbon layer of BN@C-OA, the lubrication performance was significantly improved. More impressively, BN@C-OA could enter the interface of friction pairs. The interlayer sliding occurred to improve the anti-wear and anti-friction properties. This study could provide a new avenue to synthesize the coating-containing nanocomposite additive to promote the lubrication properties of nanoparticles in oil.

Effect of the surface contamination layer on the thickness measurement of ultra-thin HfO2 films

Mutual calibration by a combination of a zero-offset method (ZOM) and a length-unit traceable method (LTM) was suggested as a method to determine the true thickness of ultra-thin oxide films. Although, medium energy ion scattering spectroscopy (MEIS) and x-ray photoelectron spectroscopy (XPS) were suggested as the ZOMs, the offset value of thickness is affected by the surface contamination layer.In this study, we compared the effect of the surface contamination layer on the thickness measurement of a series of HfO2 films by MEIS and XPS. The surface of the HfO2 films were contaminated by thin carbon layers with the thicknesses from 0.25 nm to 1.30 nm. In MEIS, the variation of the offset value by the surface carbon layer was negligibly small in the range of 0.020 nm. However, it was large in XPS in the range of 0.131 nm. In conclusion, MEIS can be a reliable ZOM to calibrate the offset values in the thickness measurement of ultra-thin oxide films with negligibly small effect of surface contamination.