Nanostructured Carbide Research Articles

Green synthesis of nanostructured SiCs by using natural biopolymers (guar, tragacanth, Arabic, and xanthan gums) for oxidative desulfurization of model fuel

Mesoporous SiC ceramics were prepared using different natural biopolymers (guar, tragacanth, Arabic, and xanthan gum) as both template and carbon sources. Natural biopolymers are safe, biocompatible, and inexpensive materials that can be green candidates for carbon sources. Low-temperature magnesiothermic technique was used to form porous silicon carbide. In this study, tetraethylorthosilicate was prepared by sol–gel method and used as silica precursor. The mixture of silica and carbon sources was carbonized under argon atmosphere at 750 °C, and then, the reaction continued by adding magnesium powder at 700 °C. Products were characterized using SEM, BET/BJH, XRD, FTIR, and Raman spectroscopy. The produced SiC materials showed mesoporous structures with high surface area and identical structures related to their carbon precursors. The results suggest that the natural gums can be potentially used as carbon templates in controlled formation of nanostructures. Also the synthesized silicon carbide nanostructures were used as catalyst supports in oxidative desulfurization of a model fuel. For this purpose, MoO3 was immobilized on the surface of SiC supports by using peroxo molybdenum complex. Such excellent catalytic performance was attributed in the presence of silicon carbide (99, 98, 94, and 93% conversion for SiCs produced from Arabic, xanthan, guar, and tragacanth, respectively).

Synthesis of Fe5C2@SiO2 core@shell nanoparticles as a potential candidate for biomedical application

A new strategy for water-dispersibility of hydrophobic carbide nanostructures was proposed. In this regard, hydrophobic Fe5C2 nanoparticles (NPs) with size ranging 25–40 nm were synthesized and coated with 12–15 nm silica shell for biomedical applications. X-ray diffraction (XRD) results revealed that Fe5C2 NPs with monoclinic structure were successfully prepared. The crystalline structure of Fe5C2 NPs was remained unchanged and saturation magnetization of core remained nearly constant after coating with silica shell. Moreover, Raman spectroscopy identified D-band of amorphous carbon shells which was also confirmed by transmission electron microscopy (TEM). Finally, Fe5C2@SiO2 core@shell NPs demonstrated no significant cytotoxicity and appropriate heat generating which makes them a promising candidate for magnetic fluid hyperthermia applications.

Nitrogen-doped carbon encapsulating molybdenum carbide and nickel nanostructures loaded with PVDF membrane for hexavalent chromium reduction

Molybdenum carbide and Ni0 nanoparticles (NPs) embedding into N-doped carbon materials (MoxNiy@N-C) were prepared by one-step thermolysis of Ni, Mo, N, C precursors, and then loaded on poly (vinylidene fluoride) (PVDF) film to obtain the catalytic membranes (MoxNiy@N-C/PVDF). The membranes effectively catalyzed the reduction of toxic CrVI to benign CrIII by employing formic acid (FA) as the reducing agent. The effects of parameters, such as initial concentrations of CrVI (5–25 mg/L) and FA (0.117–0.702 M), solution pHs (2.12–5.43) and temperatures (15–55 °C), as well as HCOONa concentrations (0–0.20 M) on CrVI reduction were analyzed in view of scalable industrial applications. Owing to the synergistic effects amongst Ni0, MoxC, doped nitrogen, and oxygen groups as catalytic active sites, and carbon shell protection of metal NPs from leaching out, MoxNiy@N-C/PVDF catalysts exhibited excellent catalytic activity and recyclable capability for CrVI reduction. The membrane’s unique porous structure and large chemically active surface area not only minimize the NPs agglomeration, but also allow the facile transport of catalytic reactants to the active surface without suffering from high mass-transfer resistance. This study demonstrates MoxNiy@N-C/PVDF catalytic membranes with the morphological and structural features provide a green, economic, and fast method for the treatment of CrVI containing waters.

In situ synthesis of cobalt and cobalt carbide nanostructures using decomposition of cobalt acetate

A green chemical route is reported for the synthesis of cobalt and cobalt carbide nanostructures using decomposition of cobalt acetate salt in a carbon matrix in situ during spark plasma sintering (SPS). The effect of SPS pressure on the phase formation was studied in detail and it revealed that with increase in pressure from 30 to 60 MPa the interaction between Co and C atoms increases resulting in the formation of only pure face centered cubic Co at 30 MPa to predominantly Co2C phase at 60 MPa. The magnetization measurements revealed a decrease in magnetization (M) value accompanied by an increase in coercivity (Hc) value with increase in pressure. For a sample with predominant Co2C phase a M value of 35 emu/g and Hc value of 786 Oe was obtained.

Growth of Boron Carbide Nanostructures on Silicon Using Hot Filament Chemical Vapour Deposition

Boron carbide nanostructures were grown on Si wafers through introduction of a mixture of B2O3dissolved in methanol using hot filament chemical vapour deposition. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), Raman spectroscopy and the four-point probe technique were applied to characterise the properties of the boron carbide nanostructures. The XRD results showed that two kinds of boron carbide chemical compounds (B4C and B2C2) were deposited and the effect of boron concentration was significant. The FESEM images showed that the boron carbide nanostructures are made of crystal clusters with a cauliflower-like shape, in which the grain boundaries appear more clearly with increasing boron concentration. In addition, the AFM results showed that the surface roughness of the boron carbide films decreased with increasing boron concentration due to grain boundary diffusivity. The Raman spectrum results confirmed the presence of a B4C network and G and D bands. The results of the four-point probe method indicated that samples with higher boron incorporation showed the lowest sheet resistance (0.06 ω sq−1), which may be because of the decrease in inter-grain boundaries caused by the larger cluster size. This study suggests that higher boron incorporation in boron carbide nanostructures results in larger crystal clusters, higher thickness and lower film resistivity.

A mesoporous tungsten carbide nanostructure as a promising cathode catalyst decreases overpotential in Li-O2 batteries.

Lithium–oxygen (Li–O2) batteries as promising energy storage devices possess high gravimetric energy density and low emission. However, poor reversibility of electrochemical reactions at the cathode significantly affects the electrochemical properties of nonaqueous Li–O2 batteries, and low charge–discharge efficiency also results in short cycle-life. In this work, functional air cathodes containing mesoporous tungsten carbide nanoparticles for improving the reversibility of positive reactions in Li–O2 cells are designed. Mesoporous tungsten carbides are synthesized with mesoporous carbon nitride as the reactive template and carbon source. And mesoporous tungsten carbides in cathode materials display better electrochemical performance in Li–O2 cells in comparison with mesoporous carbon nitride and hard carbon. Tungsten carbide-1 (WC-1) with larger specific surface area promotes reversible formation and decomposition of Li2O2 at the cathode and lower charge overpotential (about 0.93 V) at 100 mA g−1, which allows the Li–O2 cell to run up to 100 cycles. In addition, synergistic interaction between WC-1 and LiI could further decrease the charging overpotentials of Li–O2 cells and improve the charge–discharge performances of the Li–O2 cells. These results indicate that mesoporous electrocatalysts can be utilized as promising functional materials for Li–O2 cells to decrease overpotentials.

Phenolic resin as a carbon source for the synthesis of monometallic Mo and bimetallic CoMo carbides via carbothermal reduction route

ABSTRACTIt was the first time that phenolic resin (PR) was used as a carbon source for the synthesis of nanostructured monometallic Mo and bimetallic CoMo carbides via carbothermal reduction route. The results showed that phase-pure β-Mo2C can be formed under an Ar atmosphere at 900°C or a H2 atmosphere above 700°C. However, almost pure CoMo carbides (Co3Mo3C and Co6Mo6C) can be obtained only under a H2 atmosphere at a low temperature of 630°C for 24 and 48 h, respectively. The role of PR in the preparation process has been investigated and a detailed formation mechanism was proposed based on the experimental results.

Low-Temperature Transformation of C/SiO2 Nanocomposites to β-SiC with High Surface Area

Mesoporous silicon carbide (SiC) nanostructures were synthesized by magnesiothermic reduction of carbon–silica (C/SiO2) nanocomposites at a low temperature of 700 °C by using furfuryl alcohol as the carbon source. The phase, morphology, and structure of the samples were characterized by a combination of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectra, X-ray photoelectron spectroscopy, thermogravimetric analysis, and N2 adsorption. The starting C/SiO2 composites exhibited an interpenetrating network and the resulting SiC preserved the mesoporous properties of the original templates. The SiC products were of β-SiC phase and showed a high surface area of 786 m2/g. The reaction mechanism and role of intermediate species (Mg2Si) were explored in detail. Furthermore, the resulting β-SiC exhibits remarkable electromagnetic wave absorption performance with a minimum reflection loss of −17.2 dB and reflection loss bandwidth less than −10 dB of 3...

Impact of Processing on Photoluminescence Properties of 4H-SiC for Potential Qubit Applications

Single silicon vacancies VSi in silicon carbide nanostructures hold great promise for future technological applications in scalable quantum computing and information processing for simulation, sensing, and communication. These defects are typically created by ion implantation or neutron/electron irradiation. Identification of these defects, knowledge of their characteristics, control of their concentrations, isolation of single spin defects and understanding the effects of semiconductor processing on their properties are crucial to the applications of SiC in quantum electronic and integrated photonic devices. These vacancies embedded in photonic crystal cavities (PCC) have the capability of high efficiency emission of single photons which can significantly improve the performance of on-chip photonic networks and long-distance quantum communication systems, as compared to conventional solid-state emitters. Here we investigate the impact of processing on the photoluminescence properties of PCCs fabricated using three approaches: hydrogen implantation to form thin SiC layers on an oxide layer that can be easily etched away to form an air gap under the PCC, wafer bonding and mechanical thinning of the SiC, also on an oxide layer, and selective photo-electrochemical etching of an n-p epitaxial SiC structure to form an air gap. We also assess the impact of electron irradiation for these three fabrication approaches.

Mo2C@onion-like carbon/amorphous carbon nanocomposites as outstanding anode materials for ideal lithium-ion batteries

Abstract Tremendous effort has been made to seek outstanding anode materials for ideal lithium ion batteries. One-pot synthesis of Mo 2 C@onion-like carbon/amorphous carbon nanocomposites is reported in this work. The obtained nanocomposite possesses a unique structure, in which Mo 2 C nanoparticles covered by onion-like carbon layer are embedded in amorphous carbon. The Mo 2 C nanoparticles shorten ion/electron diffusion distance. The onion-like carbon layer can enhance the conductivity of Mo 2 C nanoparticles, accompanied by holding the volumetric expansion/shrinkage during the repeated lithium ion insertion/extraction processes. Moreover, amorphous carbon can effectively promote the generation of stable solid electrolyte interphase film and keep the integrity of Mo 2 C nanoparticles. The combination of these advantages makes the nanocomposite a promising anode material. The nanocomposite exhibits a high specific capacity of 1065 mA h g −1 at 0.1 A g −1 , good cycle stability (remaining the specific reversible capacity of 708 mA h g −1 after 100 cycles at a current density of 0.1 A g −1 ), and a stable rate capability (the discharge capacity with retention of 98.5% when the current density returns from 2 to 0.1 A g −1 ). This work will reveal the design of nanostructured carbides for outstanding anode materials in ideal lithium ion batteries.

Erratum to: Structural properties of silicon carbide nano structures grown on quartz substrate using CVD method

Silicon carbide (SiC) nanostructures were obtained by the chemical deposition of hexamethyldisiloxane (C6H18OSi2) from the vapor phase onto quartz with a supported cobalt catalyst. A study was carried out on the structural and optical properties of the SiC nanostructures obtained at 650, 700, 750, and 800 °C using scanning electron microscopy, XRD, and electron spectroscopy. All the films were found to have crystalline structure. The optical transmittance in the visible region increases with increasing synthesis temperature.

Non-Noble Metal Oxygen Reduction Reaction Catalysts Based on Tungsten Carbide Supports and Fe-N Structures: Rrde Studies in Acid and Alkaline Media

Tungsten carbide (WC) has been receiving considerable attention in recent years due to its interesting properties, such as, a Pt-like catalytic behavior, [1] high electrical conductivity, chemical stability in acidic electrolytes, and much lower cost compared to platinum. [2] Non-noble catalysts of the type Fe-N/C (iron atoms coordinated to nitrogen atoms in a graphene packed structure) have also been considerably studied given their high catalytic activity toward the oxygen reduction reaction in both, alkaline and acid electrolytes. In this work, Fe-N structures were incorporated into various tungsten carbide nanostructures and their catalytic activities toward the oxygen reduction reaction are assessed in both, acid and alkaline media. Nanostructured tungsten carbides supported on carbon (WC(20, 30, 40%)/C) were prepared by depositing suitable amounts of WO3 on the Vulcan XC72R carbon black, followed by a thermal treatment at 850 0C for 4 hours in a controlled CH4/H2 atmosphere with a subsequent passivation step in a Ar/O2 (99%/1%) atmosphere for 12 hours at 25 oC. The Fe-N structure precursor was obtained by complexing an iron salt ((NH4)2Fe(SO4)2 x 6 H2O) with a nitrogen ligand (2,4,6-Tris(2-pyridyl)–1,3,5–Triazina), followed by deposition on the various WC/C supports with a subsequent pyrolysis step at 700 0C or 800 0C for 2 hours in a controlled N2 atmosphere. The electrocatalysts were physically characterized by X-ray Diffraction, X-ray Photoelectron Spectroscopy and Energy-dispersive X-ray spectroscopy. XRD spectra revel that the WC(30%)/C presents the highest WC proportion among the different supports, while the deconvoluted XPS spectra (W4f peak) evidence the presence of W+6, W+4 and W+2 at the surface of the material, with a much higher proportion of W+2 compared to insignificant amounts of W+6 and W+4. In contrast, when Fe-N structures are prepared on the WC(30)/C support, a higher proportion of W+6 is observed. The catalytic activity of these composites were assessed through cyclic voltammetry on a thin catalyst layer rotating ring-disk electrode, where the durability of the catalysts were conducted, followed with EDX analyses of the thin layer. Considering the ORR electrocatalytic activity, as a trend, it was seen that the Fe-N/WC/C catalyst presents higher activity compared to the support itself (WC/C) in both acidic and alkaline media with a prevalence of the direct 4e- reaction pathway. Further results for the dissolution of Fe upon accelerate durability test revels loss of metal along the cycling, and this information was important for the understanding of the ORR characteristics in these hybrid nanomaterials. Acknowledgements: Authors acknowledge the São Paulo Research Foundation (FAPESP - Procs. 2013/16930-7, 2016/07848-3), Brazil, for financial supports. The authors also wish to thank Brazilian Nanotechnology National Laboratory (LNNano) for assisting with the XPS measurements.

Highly Porous Molybdenum and Tungsten Carbides for Hydrogen Evolution Reaction Synthesized from a Sacrificial Leaching

Hydrogen has been considered as one of the most promising energy source for future due to its high-energy density and no air pollutant emission. Water electrolysis into hydrogen and oxygen is an environmentally friendly method to produce hydrogen. Water electrolysis reaction is divided into two half reactions; hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). High overpotential of both HER and OER is the most significant problems to hamper reaction rate and overall efficiency of water electrolysis, which leads to increase in hydrogen production cost. Therefore, exploring active catalysts for HER and OER is one of the major issues in water electrolysis. Platinum (Pt) has been conventionally used as an efficient catalyst for HER. But, its high cost and scarceness is not suitable for a large-scale application of water electrolysis. As for the HER, the electrocatalytic activities of carbide materials, such as molybdenum carbide (Mo2C), and tungsten carbide (WC), have been remarkable among non-precious metal based catalysts. But, it is very difficult to synthesize nanostructured carbides, which is regarded as a main obstacle for increase in HER activity of such carbide based catalyts. Herein, we report highly porous Mo2C and WC catalysts synthesized from a sacrificial leaching for hydrogen evolution reaction. We firstly synthesized Mo2C and WC composites with cobalt nanoparticles (Co-Mo2C and Co-WC) using graphitic carbon nitride (g-C3N4) as a carbon source, and then leached Co nanoparticles in 0.5 M sulfuric acid (H2SO4) solution. Through this sacrificial leaching method, we could successfully synthesize highly porous Mo2C and WC nanoparticles. Highly porous Mo2C and WC catalysts exhibited much enhanced HER activities in hydrogen saturated 0.5 M H2SO4 solution in comparison to Mo2C and WC nanoparticles synthesized from conventional carburizing method. Fig. HER activities of highly porous and conventional Mo2C nanoparticles. Figure 1

Investigation of SiC and C nanostructures synthesized by the method of chemical vapor deposition on Ni films

The paper presents the results of experiments on synthesis of SiC and C nanostructures by the method ofmicrowave plasma assisted chemical vapor deposition on Ni films. The plates of polished single-crystal andporous silicon were used, on the surface of which a thin layer of Ni was deposited. The dependence of thestructure and morphology of the samples on the plasma power is studied. Scanning electron microscopy hasshown that the formed nanostructures have a diameter of 100-170 nm and a rough surface. Analysis of theresults showed that, the growth of nanostructures on the surface of porous silicon is more massive in contrast topolished Si. By means of Raman scattering the structure of the obtained samples and its dependence on theplasma power were studied. The results of studies showed the presence of silicon carbide nanostructures with3C-SiC polytype structure. Also, the main carbon peaks in the range of ~1300 and ~1500 cm-1, whichcorrespond to carbon nanostructures were found on both types of substrates.

Effectively enhanced load transfer by interfacial reactions in multi-walled carbon nanotube reinforced Al matrix composites

The thermal expansion response of multi-walled carbon nanotube (MWCNT) reinforced Al matrix composites was employed to discuss the improvement of the load transfer at the interface between the MWCNTs and the Al matrix. An aluminum carbide (Al4C3) nanostructure at the end of the MWCNTs, incorporated in the Al matrix, was produced by appropriate heat-treatment. The stress contrast around the Al4C3 observed in the high-resolution transmission electron microscopy (HRTEM) image revealed the evidence of a trace of friction, which would lead to the enhancement of the anchor effect from the Al matrix. This anchor effect of Al4C3 may hinder the local interfacial slippage and constrain the deformation of the Al matrix. As a result, the thermal expansion behavior became linear and reversible under cyclic thermal load. It is concluded that the formation of Al4C3 could effectively enhance the load transfer in MWCNT/Al composites. The yield strength of MWCNT/Al composites was substantially increased under the appropriate quantity of Al4C3 produced at the MWCNT-Al interface by precisely controlled heat-treatment.

Mechanical Properties and Corrosion Resistance of HVOF Sprayed Coatings Using Nanostructured Carbide Powders

Abstract Nanostructured and composite WC-12Co coatings were prepared by means of the supersonic spray process (HVOF). The microstructure and composition of WC-12Co nanostructured powder were analyzed by scanning electron microscope (SEM) and transmission electron microscope (TEM). Investigations revealed nano grains of WC with the size in the range of 50-500 nm. The nanostructured sprayed coating was analysed by SEM and phase composition was investigated by X-ray diffractometer (XRD). A denser coating structure with higher hardness was observed compared to conventional coating with a small amount of W2C, WC1−x, W and some amorphous phase. Young’s modulus and hardness were determined by depth sensing indentation in HVOF sprayed WC-12Co nanostructured coatings. Results were compared to conventional coatings and the relevance of the nanostructure was analyzed. An indentation size effect was observed on the polished surface and cross-section of both coatings. Data provided by indentation tests at maximum load allow to estimate hardness and elastic modulus. Enhanced nanomechanical properties of conventional coating in comparison to nanostructured one were observed. Nanostructured coatings WC-12Co (N) revealed significantly better corrosion resistance.

Palladium decorated silicon carbide nanocauliflowers for hydrogen gas sensing application

Silicon carbide (SiC) nanostructures have attracted significant attention for device applications due to their unique structural, electronic and catalytic properties. Here, the efficiency of three dimensional SiC nano-cauliflowers (NCs) for hydrogen gas sensing application has been investigated. We have deposited a vertically aligned, ordered Pd decorated SiC NCs directly on a silver (Ag) coated porous anodic alumina (AAO) substrate by DC magnetron cosputtering and then it used as a gas sensor without additional processing. The sensor shows remarkably high and selective responses to hydrogen gas with low detection range 2–500ppm at relatively high temperature range (30–500°C). Our results demonstrate the potential application of Pd decorated SiC NCs for fabricating highly sensitive and selective hydrogen gas sensors.

Single-Crystalline, Metallic TiC Nanowires for Highly Robust and Wide-Temperature Electrochemical Energy Storage.

Customized electrode materials with good temperature adaptability and high-rate capability are critical to the development of wide-temperature power sources. Herein, high-quality TiC nanowires are uniformly grown on flexible carbon cloth as free-standing electric-double-layer supercapacitor electrode. The TiC nanowires, 20-40 nm wide and 3-6 µm long, are single-crystalline and highly conductive that is close to typical metal. Symmetric supercapacitors are constructed with ionic liquid electrolyte and TiC nanowires electrodes as wide-temperature and long-cycle stable power source. Ultrastable high-rate cycling life of TiC nanowire arrays electrodes is demonstrated with capacitance retention of 96.8% at 60 °C (≈440 F g-1 ), 99% at 25 °C (≈400 F g-1 ), and 98% at -25 °C (≈240 F g-1 ) after 50 000 cycles at 10 A g-1 . Moreover, due to high electrical conductivity, the TiC nanowire arrays show ultrafast energy release with a fast response time constant of ≈0.7 ms. The results demonstrate the viability of metal carbide nanostructures as wide-temperature, robust electrode materials for high-rate and ultrastable supercapacitors.

Embedded silicon carbide “replicas” patterned by rapid thermal processing of DNA origami on silicon

When deoxyribose nucleic acid (DNA) origami on silicon substrates are heated above 900 °C, the carbon atoms from the DNA diffuse several nanometers into the silicon to form embedded silicon carbide (SiC) nanostructures. Atomic force microscopy and scanning electron microscopy images show that the SiC structures retain the shape and lateral dimensions of the original DNA origami structures, and the SiC material resists etching by hydrofluoric acid. X-ray photoelectron spectroscopy depth profiling shows a SiC peak present at depths of up to ∼15 nm. This process is a mask-free technique for patterning SiC on silicon for possible nanoelectronic applications.

B-containing nanomaterial synthesis when a combustion wave moves within a packed bed of solid particles

This study deals with combustion behavior of B2O3/Mg/NH4Cl/C complex systems for the synthesis of amorphous boron (B), boron carbide (B4C), and boron nitride (BN) nanostructures. The raw mixtures used in the experiments were prepared on the base of a B2O3–Mg precursor mixture, which is sufficiently exothermic to maintain a self-propagating regime of the combustion reaction. Thermodynamic analysis of the combustion temperatures and experimental validation indicate that the 1000–1500°C temperature range is very effective for synthesizing the nanostructures of B, B4C, and BN. It was found that B-containing functional nanostructures are mainly spherical nanoparticles (B) or nanosheets (B4C, BN). The phase composition and microstructural characteristics of the final products were evaluated based on the combustion temperature and solid/liquid phase changes.