Catalytic Chemical Vapor Deposition Research Articles

Synthesis of graphitic nanofibers and carbon nanotubes by catalytic chemical vapor deposition method on nickel chloride alcogel for high oxygen evolution reaction activity in alkaline media

The carbonaceous materials containing high density of active sites are desirable to develop efficient oxygen evolution reaction electrocatalyst for the production of hydrogen gas in alkaline water electrolyzer. In this work we report facile synthesis method to produce graphitic nanofibers and carbon nanotubes by catalytic chemical vapor deposition method at 650 °C temperature on nickel chloride alcogel catalyst for efficient oxygen evolution reaction activity in alkaline media. It was found that relatively low molar concentration of nickel i.e. 0.333 molar ratio with respect to tetra ethylene ortho silane in the alcogel resulted into predominantly carbon nanotubes formation with the diameter in the range 15–45 nm, while higher concentration of nickel in the alcogel i.e. 0.495 molar ratio with respect to tetra ethylene ortho silane yielded the predominant graphitic nanofibers of the diameter 40–100 nm. The results showed that nickel particles of relatively bigger diameter exceeding 50 nm preferably produce graphitic nanofibers while smaller particles allow the formation of carbon nanotubes during in-situ catalytic chemical vapor​ deposition process. Moreover, the oxygen evolution reaction activities of synthesized carbon nanomaterials were compared with one another and it was found that the sample containing predominantly graphitic nanofibers outperformed the carbon nanotubes and commercial Ir/C (20 wt % Ir) electrocatalysts in OER electrocatalysis by exhibiting overpotential just 280 mV at current density of 10 mA/cm2. The better oxygen evolution reaction activity exhibited by graphitic nanofibers was attributed to the exposed aligned graphene layers at an angle to fiber axis constituting large number of edges, which might have served as active sites and facilitated the adsorption/desorption of hydroxide ions intermediates in alkaline media for subsequent oxygen evolution.

Development of Catalytic-CVD SiNx Passivation Process for AlGaN/GaN-on-Si HEMTs

We optimized a silicon nitride (SiNx) passivation process using a catalytic-chemical vapor deposition (Cat-CVD) system to suppress the current collapse phenomenon of AlGaN/GaN-on-Si high electron mobility transistors (HEMTs). The optimized Cat-CVD SiNx film exhibited a high film density of 2.7 g/cm3 with a low wet etch rate (buffered oxide etchant (BOE) 10:1) of 2 nm/min and a breakdown field of 8.2 MV/cm. The AlGaN/GaN-on-Si HEMT fabricated by the optimized Cat-CVD SiNx passivation process, which had a gate length of 1.5 μm and a source-to-drain distance of 6 μm, exhibited the maximum drain current density of 670 mA/mm and the maximum transconductance of 162 mS/mm with negligible hysteresis. We found that the optimized SiNx film had positive charges, which were responsible for suppressing the current collapse phenomenon.

Fe-assisted catalytic chemical vapor deposition of graphene-like carbon nanosheets over SrO

The application of graphene-like carbon nanosheets (GCN) for energy storage has attracted tremendous interest in industry. Thus, synthesis pathways producing GCN with high yield, good electrical conductivity and large accessible surface area are interesting option to obtain the desirable electrode materials. Here, a method to increase yield and functional properties of GCN is proposed using Fe-assisted catalytic chemical vapor deposition (CCVD) over SrO catalyst. In this process design, the ethanol vapor is passed through iron particle bed before reaching SrO catalyst for a CCVD synthesis at 950 °C. It is found that Fe modified conversion pathways of ethanol producing a material with 65% higher yield, better crystallinity and lower defect density compared to GCN synthesized over SrO only. Furthermore, the higher yield and low density of defects can also be retained in GCN after KOH activation (800 °C) resulting in a 3D hierarchically porous material with 34% higher specific capacitance, 12% higher capacitance retention and lower charge transfer resistance than materials obtained through a conventional CCVD process with SrO only. The obtained data suggest that the proposed Fe-assisted CCVD synthesis is a promising strategy towards the synthesis of advance functional materials, e.g. with applications in supercapacitors.

Passivation of textured crystalline silicon with small pyramids by silicon nitride films formed by catalytic chemical vapor deposition and phosphorus catalytic impurity doping

Abstracts Silicon nitride (SiNx) films formed by catalytic chemical vapor deposition (Cat-CVD) and phosphorus (P) catalytic impurity doping (Cat-doping) are applied on textured crystalline silicon (c-Si) wafers with a pyramid size of 1–2 µm to reduce the surface recombination of minority carriers. SiNx single layer passivation realizes a surface recombination velocity (SRV) of less than 10 cm/s. The addition of a P Cat-doped layer results in a reduction in a SRV to ~7 cm/s owing to field-effect passivation. These values are comparable to those obtained in our previous study for textured c-Si surface with larger-sized pyramids, indicating the high passivation ability of Cat-CVD SiNx films and P Cat-doping independent of the size of pyramids. In addition to the double-side textured wafers, we also prepare a single-side textured wafer using Cat-CVD SiNx as an etching barrier. We find that Cat-CVD SiNx films can be utilized as an etching barrier against alkali solution, and a high effective minority carrier lifetime (τeff) of 2.3 ms has been obtained by the passivation with Cat-CVD SiNx films. These achievements will contribute to an improvement in the performance of back-contact c-Si solar cells.

Diatom-frustule catalyst supported multiwalled carbon nanotubes: Scalable and cost-effective synthesis and stable anode for lithium-ion battery

Multiwalled carbon nanotubes have interesting electrochemical properties that can be utilized for the energy storage application. However, the practical application of multiwalled carbon nanotubes is limited by the current techniques to provide large scale production. So, the large scale production of multiwalled carbon nanotubes is obtained by catalytic chemical vapor deposition of acetylene/liquified petroleum gas on diatom supported Mischmetal based nickel alloy catalyst. The developed multiwalled carbon nanotubes are uniform in diameter and the method of production does not require any process of purification. The multiwalled carbon nanotubes along with the presence of diatom is used as the high capacity anode for the lithium-ion battery. The interaction of lithium ions with both multiwalled carbon nanotubes and diatom increases the specific capacity to 1090 mAh g−1 at 0.05 A g−1 with cyclic durability of 2000 cycles. This work demonstrates a scalable method for the production of multiwalled carbon nanotubes from a cost-effective catalyst with the benefit of utilizing it as a high capacity anode material for lithium-ion battery.

Semi-transparent graphite films growth on Ni and their double-sided polymer-free transfer

Nanorange thickness graphite films (NGFs) are robust nanomaterials that can be produced via catalytic chemical vapour deposition but questions remain regarding their facile transfer and how surface topography may affect their application in next-generation devices. Here, we report the growth of NGFs (with an area of 55 cm2 and thickness of ~ 100 nm) on both sides of a polycrystalline Ni foil and their polymer-free transfer (front- and back-side, in areas up to 6 cm2). Due to the catalyst foil topography, the two carbon films differed in physical properties and other characteristics such as surface roughness. We demonstrate that the coarser back-side NGF is well-suited for NO2 sensing, whereas the smoother and more electrically conductive front-side NGF (2000 S/cm, sheet resistance − 50 Ω/sq) could be a viable conducting channel or counter electrode in solar cells (as it transmits 62% of visible light). Overall, the growth and transfer processes described could help realizing NGFs as an alternative carbon material for those technological applications where graphene and micrometer-thick graphite films are not an option.

Integrative improvement on thermophysical properties and ablation resistance of laminated carbon/carbon composites modified by in situ grown HfC nanowires onto carbon fiber cloths

HfC nanowires modified carbon fiber cloth laminated carbon/carbon (HfCnw-C/C) composites were fabricated by in situ growth of HfC nanowires on carbon cloths via catalytic CVD, followed with lamination of the cloths and densification by pyrolytic carbon (PyC). Morphologies, thermal conductivity, coefficient of thermal expansion (CTE), and ablation resistance of the composites were investigated. Due to the loading of HfC nanowires, the matrix PyC with low texture was obtained; the thermal conductivity of the composites in the Z direction was enhanced from 100℃ to 2500℃; CTE along the X–Y direction also decreased in the range of 2060 ℃ – 2500 ℃, which reaches the maximum of 24 % at 2500℃. Moreover, the 20s-ablation-resistance of HfCnw-C/C composites exhibits mass and linear ablation rates of 5.3 mg/s and 21.0 μm/s, which are 40 % and 37 % lower than those of pure C/C composites, respectively. Our work shows laminated HfCnw-C/C composites are a promising candidate for high-temperature applications.

Synthesis of multiwalled carbon nanotubes from polyethylene waste to enhance the rheological behavior of lubricating grease

Carbon nanotubes (CNTs) are attracting great interest in enhancing rheological behavior and thermal performance of lubricating grease. In this study, CNTs were synthesized by catalytic chemical vapor deposition (CCVD) method using low-density polyethylene (LDPE) waste as a cheap carbon source and Co/MgO as an effective catalyst. The effect of temperature on the catalytic pyrolysis of LDPE to produce CNTs has been studied. Catalytic pyrolysis of LDPE waste was conducted in a temperature range of 350–600 °C using the H-ZSM-5 catalyst. The structure and quality of CNTs were fully characterized using HR-TEM, XRD, and Raman spectroscopy. On the other hand, various concentrations of CNTs (0.2, 0.4, 0.6, 0.8, and 1.0 wt%) were mixed with pure lithium grease to determine the optimum percentage that improves the properties of nano-grease. The results showed that a high yield of multiwalled carbon nanotubes (MWCNTs) was obtained with high quality at temperatures ranging from 400 to 550 °C. Also, the addition of CNTs enhanced the rheological behavior of lithium grease, and the optimum percentage of CNTs was 0.8 wt%. Furthermore, the apparent viscosity and shear stress of lithium nano-grease increased by increasing the concentration of CNTs up to 0.8%. At this concentration, the penetration value of lithium nano-grease was greater than pure grease, and the dropping point increased by 12.5%. These results suggested that CNTs prepared from LDPE waste were an excellent additive to enhance the physicochemical properties of lithium grease.

Electron microscopy study of surface-treated carbon fiber for interface modification in composites

Relatively poor adhesion of carbon fibers with matrix leads to various serious concerns in high performance composites. Interface debonding during loading is the most vulnerable among them particularly when polymer matrix is used. This paper presents the results of electron microscopy investigation of four different techniques that are beneficial for improving interfacial bonding. These techniques were based on modifying the fiber surface by way of both; coating a film on the fiber and ablating a layer from it. The former employed growth of nanostructures of carbon and zinc oxide by thermal catalytic chemical vapor deposition and magnetron sputtering respectively and depositing a layer of pyrolytic carbon by CVD while the latter involved ablation of an outer layer of fiber using femtosecond laser treatment. Both the approaches relied on introducing mechanical anchoring on the fiber surface by micro roughening anticipating an improved fiber- matrix interfacial bonding. Carbon fiber surface prior and post treatment was investigated microscopically using FESEM and TEM. CNTs growth formed network like structure around the fiber, while PyC coating showed continuous layer around the fiber. HRTEM images of ZnO nanostructures; both nanowires and nanowalls possessed crystalline structure revealed by the presence of Moiré fringes formed due to overlapping of two crystals with different orientation. Laser treated fiber surface showed formation of LIPSS with average periodicity of 147 ± 10 nm.

Strain-regulated sensing properties of α-Fe2O3 nano-cylinders with atomic carbon layers for ethanol detection

The sensitivity of ethanol sensor is of paramount importance in a variety of areas, including chemical production with ethanol, alcohol testing for driving safety, etc. Herein, α-Fe2O3 nano-cylinders with atomic carbon layers are synthesized, for the first time, through in-situ catalytic chemical vapor deposition combined with hydrothermal techniques for the detection of ethanol. The reported α-Fe2O3@C nano-cylinders with double surficial strain effects deliver an ethanol detection sensitivity of ～8 times as compared with α-Fe2O3 nano-cylinders, ∼10 times higher as compared with its detection sensitivity to ammonia, para-xylene, methanol and benzene. The sensor also exhibits over-14-day operation stability and the minimum detection limit of 10 ppm. To our best knowledge, the performances surpass those of previously reported α-Fe2O3. Such attractive performances are attributed to the enhanced charge transfer in α-Fe2O3 owing to the double surficial strain effects of α-Fe2O3@C nano-cylinders and the efficient adsorption of ethanol with atomic carbon layers.

CVD grown carbon nanofibers: an efficient DSPE sorbent for cleanup of multi-class pesticide residue in high fat and low water commodities by QuEChERS using GC-ECD.

An inexpensive, effective, and efficient dispersive solid-phase extraction (DSPE) sorbent was developed as an alternative totraditionally used sorbents (primary secondary amine and C18) for fatty matrices using theQuEChERS method. Catalytic chemical vapor deposition grown carbon nanofibers dispersed on activated carbon fibers (Ni-ACF/CNF) having aBET specific surface area of738 (m2/g) were for thefirst time evaluated as a DSPE material for sample cleanup before gas chromatographic analysis. Based on cleanup performance and recoveries, 10mg of Ni-ACF/CNF was found optimalfor the determination of twenty-seven multi-class pesticides in high fat and low water commodities/matrices (peanut, soybean, sesame, and flaxseed). The recoveries obtained for all analytes were in the range ~ 72 to ~ 117%, with relative standard deviation values ≤ 15%. The limits of detection and quantification values were 0.7-4.2ng/g and 2.3-13.9ng/g, respectively. The matrix match calibration curve was linear in the range 20-500ng/g with a correlation coefficient of ≥ 0.993. The results reveal thatthe Ni-ACF/CNF is a competent DSPE sorbent, similar to primary secondary amines and C18sorbent materials, for pesticide determination by QuEChERS methods in high fat and low water commodities. Graphical abstract.

Effects of loading rates on mode I interlaminar fracture toughness of carbon/epoxy composite toughened by carbon nanotube films

Carbon fiber reinforced resin matrix composites were toughened by the continuous and randomly distributed carbon nanotubes (CNTs), which were fabricated by floating catalytic chemical vapor deposition (FCCVD) method. Toughening was achieved by deploying CNT film of different areal density as interleaves in the carbon fiber reinforced composites. Double cantilever beam (DCB) specimens were adopted in both quasi-static and dynamic fracture tests. The electromagnetic Hopkinson bar was applied to achieve pure type I fracture mode at high loading speeds of 15 m/s and 24 m/s. The effects of CNTs and loading rates on the Mode I fracture toughness of the composites are investigated. It is shown that fracture toughness approaches a maximum value of 626 J/m2 under quasi-static loading, only if a 2-layered CNT film is being applied as an interleave, which is twice that of the neat composite (without CNT interleaves). Under dynamic loading, all the specimens either with or without CNTs show increases in the fracture toughness with the increase in loading rate. Different from the results of quasi-static tests, under dynamic loading conditions, the fracture toughness increases monotonously and approaches to a maximum value of 1380 J/m2 when 40-layered CNT film was applied, which is a remarkable increase of 140% if compared with that of the neat specimen. A detailed analysis of mechanisms responsible for the ameliorating effects of CNTs interleaves is carried out. It is believed that strengthening of interfaces between carbon fibers and matrix, deformation of resin and detachment of CNTs from the matrix are the main factors responsible for this effect.

A dual photoelectrode-based double-chambered microbial fuel cell applied for simultaneous COD and Cr (VI) reduction in wastewater

Cerium oxide (CeO2) and cuprous oxide (Cu2O) were used for the first time as photoanode and photocathode, respectively, in a microbial fuel cell (MFC) for simultaneous reduction of chemical oxygen demand (COD) and Cr(VI) in wastewater. The photoelectrodes, viz. Photoanode and photocathode were separately prepared by impregnating activated carbon fiber (ACF) with the respective metal oxide nanoparticles, followed by growing carbon nanofibers (CNFs) on the ACF substrate using catalytic chemical vapor deposition. The MFC, operated under visible light irradiation, showed reduction in COD and Cr(VI) by approximately 94 and 97%, respectively. The MFC also generated high bioelectricity with a current density of ~6918 mA/m2 and a power density of ~1107 mW/m2. The enhanced performance of the MFC developed in this study was attributed to the combined effects of the metal oxide photocatalysts, the graphitic CNFs, and the microporous ACF substrate. The MFC based on the inexpensive transition metal oxides-based photoelectrodes developed in this study has a potential to be used at a large scale for treating the industrial aqueous effluents co-contaminated with organics and toxic Cr(VI).

Fabrication of a CNT/Ag potentiometric sensor for redox reactions via catalytic chemical vapor deposition

This work reports the fabrication of a robust and high-performance CNT/Ag composite electrode via catalytic chemical vapor deposition of ethylene. The fabricated electrode showed the formation of aligned CNTs with strong adhesion to the Ag substrate. It was successfully applied to zero-current potentiometry and sequential injection analysis of ascorbic acid. The CVD-fabricated CNT/Ag composite electrode showed an excellent response, a fast equilibrium, good sensitivity and reproducibility, as well as durability for long term use.

Simple two-stages synthesis of Ni/P-MWCNTs nanocomposite as efficient catalyst for the hexachlorobenzene electrochemical dechlorination

The present work describes the economical two-stages catalytic CVD method of the nanocomposite of phosphorous-doped multi-walled carbon nanotubes with nickel (Ni/P-MWCNTs) from the solution of the triphenylphosphine in ethanol using Ni/CaO catalyst. The structure of Ni/P-MWCNTs nanocomposite was studied by high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (IR), X-ray diffraction (XRD), and nitrogen adsorption-desorption method. The Ni/P-MWCNTs nanocomposite are characterized as a mixture of the cylindrical and bamboo-like predominately closed nanotubes with an average outer diameter of 31 nm and SBET=186 m2/g. The P atoms covalently bonded to the carbon framework of the P-MWCNTs walls predominantly through the oxygen bridges. The metal was found in Ni(0) form on the P-MWCNTs tips that is only partially covered by graphene layers. The clusters of bulk Ni(NiO) was also detected in the sample. The glassy carbon electrode modified by the Ni/P-MWCNTs nanocomposite exhibit good electrocatalytic activity in the hexachlorobenzene stepwise degradation and showed an average potential shift of ∼200 mV and ∼130 mV for each stage to the less negative potentials compared to the unmodified glassy carbon electrode and glassy carbon electrode coated by undoped MWCNTs.

MgO/carbon nanofibers composite coatings on porous ceramic surface for CO2 capture

Ceramic materials modified by hybrid MgO/carbon nanofibers systems are synthesized and characterized. Disordered carbon nanofibers were obtained via catalytic chemical vapor deposition of ethylene over nickel nanoparticles supported on the starting porous ceramic substrate. The carbon nanofibers were functionalized by acid treatment to increase the number of carbonyl and carboxyl groups on their surface. The hybrid samples were prepared by a deep coating method using Mg (OH)2 nanoparticles. After calcination, the obtained hybrid system attained a specific surface area of 242 m2·g−1 and a pore volume of 0.8 cm3·g−1. The hybrid material shows significantly enhanced sorption capacity towards carbon dioxide (4.9 mmol·g−1 CO2 uptake) under 367 K and 1 bar partial pressure of CO2.

Comparative Study of Cu(II) Adsorption by As-prepared and Oxidized Multi-walled N-Doped Carbon Nanotubes

The laws and mechanisms of adsorption of Cu(II) ions by well characterized and oxidized N‑doped multi-walled carbon nanotubes (N-CNTs) are discussed. The samples were synthesized by catalytic chemical vapour deposition method using n-butylamine as a carbon source and their surface was functionalized by oxidation with mixture of concentrated H2SO4 and HNO3. The morphology, chemistry and charge of surface groups were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy and micro-electrophoresis methods. It has been shown that: adsorption of Cu(II) reached equilibrium value within 60 min; the degree of extraction of these ions from the solution increased with its dilution; adsorption resulted in a moderate decrease in the suspension pH for as-prepared N-CNTs (1.5 pH unit) and its considerable lowering for the oxidized sample (up to 2.5 pH unit); the adsorption isotherms can be described by the Langmuir model and the plateau amounts of adsorption (28–35 mg/g) were almost the same for both as-prepared and oxidized samples; at pH 6.5 and higher a sharp increase in adsorption was observed which was attributed to hydroxides precipitation. The spectroscopic, adsorption, electrophoretic and pH measurements data showed that below pH of hydroxide precipitation, the major mechanism of adsorption by as-prepared N-CNTs is the donor-acceptor interaction between the free electron pair of N atoms incorporated into nanotubes lattice and vacant d orbital of the adsorbing Cu(II) ions. For the oxidized N-CNTs ion-exchange processes with a release of H+ ions play also a role.

Individual arc-discharge synthesized multiwalled carbon nanotubes probed with multiple measurement techniques

Arc-discharge synthesized multiwalled carbon nanotubes (AD-MWNT), or related MWNTs, exhibit a good quality compared to the more common type of MWNT synthesized by catalytic chemical vapor deposition methods. Yet experimental measurements on these are rather few and typically have not correlated data from different measurement techniques. Here, the authors report Raman spectroscopy, scanning probe microscopy, conductivity measurements, and force microscopy on single AD-MWNTs. The results demonstrate the high quality of AD-MWNTs and are compatible with the view of them as the best approximation of MWNTs as an assembly of defect-free concentric individual single-walled carbon nanotubes. The authors also demonstrate conductance measurements over a step on the surface of an AD-MWNT, which is due to an abruptly broken outer layer(s), whereby the interlayer resistance is measured.

Catalyst-Free Growth of Two-Dimensional BCxN Materials on Dielectrics by Temperature-Dependent Plasma-Enhanced Chemical Vapor Deposition.

Traditional methods to prepare two-dimensional (2D) B-C-N ternary materials (BCxN), such as chemical vapor deposition (CVD), require sophisticated experimental conditions such as high temperature, delicate control of precursors, and postgrowth transfer from catalytic substrates, and the products are generally thick or bulky films without the atomically mixed phase of B-C-N, hampering practical applications of these materials. Here, for the first time, we develop a temperature-dependent plasma-enhanced chemical vapor deposition (PECVD) method to grow 2D BCxN materials directly on noncatalytic dielectrics at low temperature with high controllability. The C, N, and B compositions can be tuned by simply changing the growth temperature. Thus, the properties of the as-made materials including band gap and conductivity are modulated, which is hardly achieved by other methods. A 2D hybridized BC2N film with a mixed BC2N phase is produced, for the first time, with a band gap of about 2.3 eV. The growth temperature is 580-620 °C, much lower than that of traditional catalytic CVD for growing BCxN. The product has a p-type conducting property and can be directly applied in field-effect transistors and sensors without postgrowth transfer, showing great promise for this method in future applications.

The effect of various substrates and catalyst layer deposition on the incorporation of nitrogen into carbon nanotube forest structures

The incorporation of nitrogen into carbon nanotubes (CNTs) might increase their conductivity that can further enhance their excellent properties which is a very important issue nowadays. The current research focused on the fabrication of nanotube forests via catalytic chemical vapor deposition method and the investigation of nitrogen incorporation into carbon nanotubes on the surface of various substrates such as aluminum, titanium and silicon. Also, this study dealt with different catalyst layer deposition techniques in order to simplify the production of CNT forests. Besides, more complex layer construction methods such as pulsed laser deposition and dip-coating were also applied since they can influence the incorporation of nitrogen into carbon nanotubes as well. Samples were analyzed by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and Raman spectroscopy.