Catalytic Chemical Vapor Deposition Process Research Articles

Understanding the Reaction Chemistry of 1,1,3,3-Tetramethyldisilazane as a Precursor Gas in a Catalytic Chemical Vapor Deposition Process.

The reaction chemistry of 1,1,3,3-tetramethyldisilazane (TMDSZ) in catalytic chemical vapor deposition (Cat-CVD), including its primary decomposition on a heated W filament and secondary gas-phase reactions in a Cat-CVD reactor, was studied using 10.5 eV vacuum ultraviolet single-photon ionization and/or laser-induced electron ionization in tandem with time-of-flight mass spectrometry. It has been demonstrated that TMDSZ initially breaks down to form various species, including methyl radical (•CH3), ammonia (NH3), and 1,1-dimethylsilanimine (DMSA). The activation energies (Ea) for the formation of •CH3 and NH3 were determined to be 61.2 ± 1.0 and 42.1 ± 0.9 kJ mol-1, respectively, in the temperature range of 1400-2000 and 900-2400 °C. It was found that the formation of DMSA may have two different contributing routes, i.e., a concerted one (Ea = 33.6 ± 2.3 kJ mol-1) at lower temperatures of 900-1500 °C and a stepwise one (Ea = 155.0 ± 7.8 kJ mol-1) at higher temperatures of 2100-2400 °C. The secondary gas-phase reactions occurring in the Cat-CVD reactor environment were found to stem from two competing processes. The first one, free-radical short-chain reactions initiated by •CH3 formation and propagated by H abstraction reactions, is the dominating chemical process, producing many high-mass stable alkyl-substituted or silyl-substituted disilazane or trisilazane products via radical recombination reactions. Head-to-tail cycloaddition of unstable DMSA is the second contributing chemical process, which forms cyclodisilazane species. In addition, evidence was found for the conversion of NH3 into H2 and N2 in the Cat-CVD reactor.

Ni3Fe@N-doped carbon nanotubes 3D network induced by nanoconfined symmetry breaking for high-performance microwave absorption, corrosion protection, and pollutant purification

It remains challenging to develop multifunctional electromagnetic wave (EMW) absorbers with anti-corrosion and pollutant purification capabilities suitable for extremely harsh ocean environments. This study exploits symmetry breaking to construct a three-dimensional (3D) network of bamboo-like N-doped carbon nanotubes (NCNT) encapsulated with magnetic Ni3Fe nanocatalysts via facile coordination and catalytic chemical vapor deposition process. The resulting Ni3Fe@NCNT composite demonstrates outstanding EMW absorption performance, anti-corrosion behavior, and adsorption purification function. Its excellent EMW absorption performance, including a minimum reflection loss of −57.3 dB and a maximum effective absorption bandwidth of 6.0 GHz, is achieved by magnetic-dielectric match, inert space platform, and porosity architecture. The Ni3Fe@NCNT composite also shows corrosion resistance and self-cleaning function simultaneously because of the physical shield provided by the intrinsically impermeable, inert NCNT shells and their considerable chemically active site and high porosity. For the first time, the EMW absorber is endowed with cooperative multi-functionalities. Our findings may pave the way to manufacture versatile EMW materials for applications in complicated environments.

Polyolefin-derived carbon nanotubes as magnetic catalysts for wet peroxide oxidation of paracetamol in aqueous solutions

This work deals with developing feasible valorization technologies to prepare carbon nanotubes (CNTs) from plastic solid waste and demonstrate their application in catalytic wet peroxide oxidation (CWPO). CNTs were synthesized by catalytic chemical vapor deposition (CCVD) at 850 ºC, considering low-density polyethylene (LDPE), high-density polyethylene (HDPE), and polypropylene (PP) as carbon precursors representative of urban plastic solid waste. Iron oxide nanoparticles supported in alumina, previously synthesized by sol-gel, were used as catalysts in the CCVD process. TEM micrographs allow us to determine 41 nm as the average outer diameter of the CNTs and to visualize magnetic iron nanoparticles (ca. 10 nm) embedded inside the CNTs (ca. 6.4 % of content measured as ashes). These magnetic nanoparticles were kept in the CNT structure even after the purification of the CNTs with sulphuric acid, allowing to obtain magnetic CNTs. All purified and non-purified CNTs prepared from the polyolefins were assessed as catalysts in CWPO of paracetamol (PCM), used as a model pharmaceutical contaminant in water at CPCM,0 = 100 μg mL−1 (CH2O2,0 = 472 μg mL−1, CCNT = 2.5 g L−1, pH0 = 3.5 and T = 80 °C). The concentrations of PCM, H2O2, aromatic and total phenolic compounds were monitored for 24 h. All CNTs showed catalytic activity, allowing the complete degradation of PCM at 6 h of reaction time. The stability and reusability of materials are tested and proved in CWPO.

Constructing mixed-dimensional lightweight flexible carbon foam/carbon nanotubes-based heterostructures: An effective strategy to achieve tunable and boosted microwave absorption

Taking full advantage of interface engineering to strengthen interface polarization is an effective strategy to improve microwave absorption. Therefore, constructing the mixed-dimensional heterostructures and/or three-dimensional (3D) interconnected network structures should be attractive pathways to create the abundant interfaces for enhanced interfacial effect. Herein, mixed-dimensional framework structure carbon foam (CF)/carbon nanotubes (CNTs)@Fe3C@Fe3O4 samples consisting of 3D CF, one-dimensional (1D) CNTs and zero-dimensional (0D) Fe3C@Fe3O4 nanoparticles were elaborately designed and produced through a simple catalytic chemical vapor deposition process. The as-prepared CF/CNTs@Fe3C@Fe3O4 heterostructures with the different contents of CNTs could be selectively produced by regulating the pyrolysis time. Owing to the unique structure and excellent synergistic effects, the obtained mixed-dimensional CF/CNTs@Fe3C@Fe3O4 samples presented the excellent comprehensive electromagnetic wave absorption performances (EMWAPs) including strong absorption capabilities, broad absorption bandwidths, thin matching thicknesses and low densities. Furthermore, the obtained results demonstrated that the enhanced content of CNTs greatly boosted their conduction and polarization loss abilities, which resulted in the enhanced comprehensive EMWAPs. Therefore, our findings not only offered a simple strategy to produce the mixed-dimensional framework structure magnetic CF/CNTs-based heterostructures as excellent lightweight high-efficiency microwave absorbers, but also provided an effective pathway to make the best of interface engineering for enhancing interface polarization.

Nanocomposite Foams with Balanced Mechanical Properties and Energy Return from EVA and CNT for the Midsole of Sports Footwear Application

Polymer foam that provides good support with high energy return (low energy loss) is desirable for sport footwear to improve running performance. Ethylene-vinyl acetate copolymer (EVA) foam is commonly used in the midsole of running shoes. However, EVA foam exhibits low mechanical properties. Conventional mineral fillers are usually employed to improve EVA's mechanical performance, but the energy return is sacrificed. Here, we produced nanocomposite foams from EVA and multi-walled carbon nanotubes (CNT) using a chemical foaming process. Two kinds of CNT derived from the upcycling of commodity plastics were prepared through a catalytic chemical vapor deposition process and used as reinforcing and nucleating agents. Our results show that EVA foam incorporated with oxygenated CNT (O-CNT) demonstrated a more pronounced improvement of physical, mechanical, and dynamic impact response properties than acid-purified CNT (A-CNT). When CNT with weight percentage as low as 0.5 wt% was added to the nanocomposites, the physical properties, abrasion resistance, compressive strength, dynamic stiffness, and rebound performance of the EVA foams were improved significantly. Unlike the conventional EVA formulation filled with talc mineral fillers, the incorporation of CNT does not compromise the energy return of the EVA foam. From the long-cycle dynamic fatigue test, the CNT/EVA foam displays greater properties retention as compared to the talc/EVA foam. This work demonstrates a good balanced of mechanical-energy return properties of EVA nanocomposite foam with very low CNT content, which presents promising opportunities for lightweight-high rebound midsoles for running shoes.

Precise Characterization of CNF-Coated Microfibers Using Transmission Electron Microscopy

The synthesis and characterization of fibrous materials with a hierarchical structure are of great importance for materials sciences. Among this class of materials, microfibers of different natures coated with carbon nanofibers attract special interest. Such coating modifies the surface of microfibers, makes it rougher, and thus strengthens its interaction with matrices being reinforced by the addition of these microfibers. In the present work, a series of hierarchical materials based on carbon microfibers, basalt microfibers, and fiberglass cloth coated with up to 50 wt% of carbon nanofibers was synthesized via the catalytic chemical vapor deposition technique. The initial items were impregnated with an aqueous solution of nickel nitrate and reduced in a hydrogen flow. Then, the catalytic chemical vapor deposition process using C2H4 or C2H4Cl2 as a carbon source was carried out. A simple and cost-effective technique for the preparation of the samples of hierarchical materials for transmission electron microscopy examination was developed and applied for the first time. The proposed method of sample preparation for sequential TEM visualization implies an ultrasonic treatment of up to four samples simultaneously under the same conditions by using a special sample holder. As was found, the relative strength of carbon nanofibers coating the surface of microfibers decreases in the order of CNF/CMF > CNF/BMF > CNF/FGC. Two effects of the ultrasonic action on the carbon coating were revealed. First, strongly bonded carbon nanofibers undergo significant breakage. Such behavior is typical for carbon and basalt microfibers. Secondly, carbon nanofibers can be completely detached from the microfiber surface, as was observed in the case of fiberglass cloth. In the case of CNF/CMF material, the graphitized surface of carbon microfiber is coherent with the structure of carbon nanofiber fragments grown on it, which explains the highest adhesion strength of the carbon nanolayer coated on carbon microfibers.

Development of Ag-doped on multi-walled carbon nanotubes for the treatment of fish pond effluent

The treatment of fish pond wastewater utilizing nanocomposites by batch adsorption using purified carbon nanotubes and silver-doped carbon nanotubes (CNTs) as nano-adsorbents was explored in this study. Ultraviolet spectroscopy, X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM) were used to confirm the biosynthesized AgNPs. The metallic silver is associated with the peaks in the XRD pattern, and HRTEM studies indicated that AgNPs are between particle sizes of 11.12 and 15.39 nm. Purified carbon nanotubes (P-CNTs) and silver-doped carbon nanotubes (Ag-CNTs) were produced using a Fe–Ni/kaolin catalyst in a catalytic chemical vapour deposition process, followed by acid purification and doped with silver nanoparticles, respectively. HRTEM, HRSEM, FTIR, and BET were used to characterize the as-synthesized CNTs, P-CNTs, and Ag-CNTs. Both unpurified and purified CNTs were tube-like, extremely porous, and crystalline, with Ag-CNTs having a higher surface area (1068 m2/g) greater than P-CNTs (268.40 m2/g). The batch adsorption process was used to investigate the adsorption behaviour of P-CNTs and Ag-CNTs to remove Fe, Mn, and Zn from fish pond effluent as a function of contact time, adsorbent dosage, and temperature. The Freundlich isotherm described equilibrium sorption data better than the Langmuir isotherm, and the adsorption kinetics fit well with the pseudo-second-order model. A thermodynamic study of the adsorption process found that the change in Gibbs free energy was negative, indicating that the adsorption process was feasible and spontaneous. Consequently, it has been demonstrated that removing heavy metals from aquatic effluent using Ag-doped CNTs is effective in aquaculture.

Critical Role of the Acetylene Content and Fe/C Ratio on the Thickness and Density of Vertically Aligned Carbon Nanotubes Grown at Low Temperature by a One-Step Catalytic Chemical Vapor Deposition Process.

The present work explores the role of the carbon source content and the Fe/C ratio on the synthesis of vertically aligned carbon nanotubes (VACNTs) by one-step aerosol-assisted CCVD operated at a medium temperature (615 °C) on aluminum substrates. The main objective was to overcome the limitations of VACNT growth, constituting a drawback for applications requiring thick VACNTs. By using acetylene as carbon feedstock and ferrocene as a catalyst precursor, we demonstrate that when acetylene content is reduced to 1.5 vol%, it is possible to grow VACNT carpets up to 700 µm thick while maintaining constant VACNT growth for a long duration (up to 160 min). The carbon conversion yield is significantly improved when the acetylene content reaches 1.5 vol%. The Al surface roughness also influences VACNT growth. An optimum Fe/C ratio of 0.8 wt.% coupled with a low acetylene content gives the highest growth rate (5.4 µm/min) ever reported for a thermal aerosol-assisted CCVD process operated at such a low temperature. The CNT number density can be controlled by varying the Fe/C ratio, enabling high density growth (e.g., 1.3 × 1011 CNT/cm2).

Carbon nanocapsules stabilized Cu2O nanocubes as the high-performance electrode material for metal ion battery

Volume expansion and structural instability of electrode materials are the major challenges to limit the ion battery development, especially for electrochemical conversion reactions-based materials. Herein, we developed hollow cuprous oxide nanocubes (HCON) as anode materials for lithium ion battery using a surfactant free, low-cost and large-scale synthesis approach based on self-assembly principle in NaCl solution. HCON delivered significantly high capacity of 202 mAh/g at current density of 1000 mA/g after 200 cycles for Li ion storage and 261 mA h/g at current density of 500 mA/g after 50 cycles for Na ion storage. Furthermore, catalytic chemical vapor deposition (CCVD) technique is employed to address partially crystalline carbon coating on HCON surface for stabilizing structure during Li+ insertion and extraction processes. Partially crystalline carbon decorates including nanodots and nanolayers are produced on HCON surface in relatively lower temperature range of 110–140 °C in CCVD process resulting in the formation of Cu2O/[email protected] hybrid. And Cu2O/[email protected] anode kept discharge retention of 84% for 200 cycles with reversible capacity of 265.3 mA h/g even at high rate of 2000 mA/g, significantly better than pure HCON anode and delivered discharge capacity of 11.3 times of pure HCON electrode (23.4 mAh/g). The reasonable combination of self-assembly approach and CCVD technique offers an effective way to introducing carbon nanomaterials in atomic level for designing high-performance electrode materials in ion battery.

Formation of carbon nanofibers with Ni catalyst supported on a micro-mesoporous glass

The Ni/SiO2 system is one of the most interesting to produce COx-free H2 and valuable carbon nanofibers (CNFs) by the catalytic decomposition of CH4. SiO2 is one of the most effective support while Ni catalyst displays long life and high activity. We studied the catalytic chemical vapor deposition (CCVD) process of CH4 within Ni/glass system at relatively low temperature (600 °C) during long times (3 h), varying the amount of the catalyst (2.3–17.8% Ni(%)) and the carbon source (100:200 to 100:0, CH4:N2). As the amount of Ni and CH4 increases, the formation of CNFs is enhanced giving as a result CNFs/glass materials with more amount, longer and thicker CNFs. The initial microstructure of the glass support and the way of Ni catalyst is deposited play a decisive role. Pristine porous glass displays a microstructe of interconnected mesopores which are progressively filled with Ni, producing ink-bottle pores with open ends. After the CCVD process as the amount of Ni or CH4 increases, the porosity of the Ni-doped glass is reduced due to the progressively filling of the mesopores (4 nm) with CNFs. Furthermore, due to the formation of large entanglements of CNFs new pores appear (20–70 nm) depending on the processing conditions. Fish-bone with hollow core and bamboo-like CNFs are found over the surface and also inside the porous glass support. It is observed a base-growth mechanism due to the strong interaction between the catalyst and the support, which prevents the Ni deactivation enhancing its activity for long times.

Enhancing Hydrodeoxygenation of Bio-oil via Bimetallic Ni-V Catalysts Modified by Cross-Surface Migrated-Carbon from Biochar.

Aromatics from selective hydrodeoxygenation (HDO) of biomass-derived bio-oil are an ideal feedstock for replacing industrial fossil products. In this study, biochar-modified Hβ/Ni-V catalysts were prepared and tested in the atmospheric HDO of guaiacol and bio-oil to produce aromatics. Compared with unmodified Hβ/Ni-V, higher HDO activity was achieved in catalysts with all kinds of biochar modifications. Especially, the pine nut shell biochar (PB)-modified PB-Hβ-8/Ni-V showed the highest selectivity to aromatics (69.17%), mainly including benzene and toluene. Besides, under the conditions of 380 °C and weight hourly space velocity (WHSV) of 0.5 h-1, the cleavage of CAr-OH (CAr means the carbon in the benzene ring) was promoted to form more aromatics. Moreover, great recyclability (58.77% aromatics for the reactivated run-3 test) and efficient HDO of bio-oil (44.9% aromatic yield) were also achieved. Based on the characterization results, the enhanced aromatic selectivity of PB-Hβ-8/Ni-V was attributed to the synergetic effect between PB and Hβ/Ni-V. In detail, a stable surface migrated-carbon layer was formed on Hβ/Ni-V via the metal catalytic chemical vapor deposition (CVD) process of the pyrolysis PB volatiles. Simultaneously, a carbothermal reduction driven by the migrated-carbon took place to decorate the surface metals, obtaining more Ni0 and V3+ active sites. With this synergism, increased Ni0 sites promoted H2 adsorption and dissociation, which improved the hydrogenation activity. Furthermore, the higher affinity of the reactant and increased oxygen vacancies both contributed to enhancing the selective surface adsorption of oxygenous groups and the cleavage of the CAr-OH bond, thus improving the deoxygenation activity. Therefore, the HDO activity was improved to form more target aromatics over biochar-modified catalysts. This work highlighted a potential avenue to develop economic and environmental catalysts for the upgrading of bio-oil.

Carbon nanofibers grown on carbon fibers by chemical vapor deposition using the iron catalyst

Carbon nanofibers (CNFs) were synthesized by the catalytic chemical vapour deposition (CCVD) process using iron catalyst below the iron-carbon eutetic temperature (1147 oC). CNFs were formed on carbon fibers as substrates at the growth temperatures of 750, 800, and 850 oC. The effect of processing temperature on the formation and the morphology of CNFs was studied. Moreover, the effect of composition of gase mixture (C2H4, H2, and Ar) on the morphology of CNFs was also performed. The morphology and microstructure of as-obtained CNFs were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron diffraction (ED). Results revealed that temperature and gas composition play an important role in forming of CNFs.

Fabrication of ultralight helical porous carbon fibers with CNTs-confined Ni nanoparticles for enhanced microwave absorption

It is extraordinarily difficult to develop low-cost and lightweight microwave absorbing materials that meet the needs of modern technology. Making rational use of biomass to prepare microwave absorbers is a sustainable way. Herein, we develop the catalytic self-deposition (CSD) technology and fabricate ultralight magnetic helical porous carbon fibers (MHPFs) with surface-grown carbon nanotubes (CNTs). There is no need to use expensive, flammable and explosive exogenous gases, avoiding the high energy consumption and potential safety issues faced by traditional energy-intensive catalytic chemical vapor deposition (CCVD) processes. The combined use of in-situ dipping and CSD technology realizes the in-situ growth and morphology control of CNTs encapsulated Ni nanocatalysts. Owing to the sophisticated structure, large specific surface area, complementary loss mechanisms and well-matched impedance, MHPFs exhibit exceptional microwave absorption performance. Notably, under the ultralow filler loading (5%), the strongest reflection loss (RL) exceeds −55.39 dB at 8.4 GHz, and the maximum absorption bandwidth (EAB, RL < −10 dB) reaches 4.7 GHz at the matching thickness of 2.00 mm. The study might shed light on the ultralow filler loadings and low-cost preparation of efficient microwave absorbers.

Influence of the Fe-based catalyst incorporation method on the carbon nanotube structure of hybrid composites synthesized by CCVD method using methane and without hydrogen reduction step

Nanostructured silica (n-SiO2) synthesized by sol-gel method was used in this work as a support for multi-walled carbon nanotubes (MWCNTs) synthesis by catalytic chemical vapor deposition (CCVD) process. The syntheses were performed using methane as carbon feedstock and without previous catalyst reduction with hydrogen. Three different methods to incorporate the iron-based catalyst on the silica support have been studied to identify its influence on the structural characteristics of the synthesized MWCNTs. Such study aims to develop the production of an advanced hybrid composite with better structural properties to be applied as a strengthener additive in different material matrices. The synthesized hybrid composites were characterized to analyze the MWCNTs quality in terms of morphology, graphitization degree, and thermal stability. Regarding the silica support containing the catalyst, Infrared (FTIR) and X-ray (XRD) analyses showed that no significant differences in terms of chemical composition and crystalline phases have been observed between the analyzed samples regardless of the catalyst incorporation method used. Concerning the hybrid composite, Raman spectroscopy, electron microscopies, and thermal analyses suggested modifications in terms of graphitization degree, morphology, and thermal stability of the MWCNTs. Indeed, the catalyst incorporation method would influence the catalyst/support interaction promoting the deposition of different carbon structures, and the quality of the MWCNTs grown in the hybrid material.

One-step synthesis of highly pure and well-crystallized vertically aligned carbon nanotubes

The one-step aerosol-assisted catalytic chemical vapor deposition (CCVD) process, when operated in a H2-based carrier gas, is shown to be effective at an extremely low ferrocene content (0.1 wt% in toluene), which enables to efficiently prepare forests of vertically aligned multiwalled carbon nanotubes (VACNTs) with high purity and good crystalline level. The resulting iron content in VACNT sample is only 0.5 wt% corresponding to a high catalytic yield of 200 while the steady growth rate (20 μm/min) is maintained at a significant value. The iron content in the sample is found proportional to the ferrocene concentration in the precursor, and when it decreases, a noticeable reduction in the iron encapsulation frequency in the nanotube channel is plainly observed. Lowering the ferrocene concentration generates a reduction in the VACNT number density while the growth rate increases and CNT diameters and crystalline structure remain similar. Such significant purity and crystalline levels involves a high oxidation resistance of the VACNT forest. These results, together with the in-situ continuous growth feature of the one-step aerosol assisted CCVD process, open up towards a new VACNT range made of pure and well-crystallized multi-walled carbon nanotubes, which is of interest for industrial production and commercial applications.

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.

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.

Heteroatom doped carbon nanosheets from waste tires as electrode materials for electrocatalytic oxygen reduction reaction: Effect of synthesis techniques on properties and activity

The effective method for synthesis of heteroatom doped carbon nanosheets (CNS) from waste tires was developed. The process employed NiO loaded CaCO3 catalyst for catalytic chemical vapor deposition (CCVD) of the CNS from the non-condensable pyrolysis gas. The promotion of CaCO3 with NiO had beneficial effect on carbon growth compared to pure CaCO3, increasing the carbon yield by 2.8 and 8.0 times for the CCVD at 700 and 750 °C, respectively. On the contrary, the morphology and structure of synthesized S,O-doped CNS as well as oxygen reduction reaction (ORR) electrocatalytic activity were not influenced by the NiO addition. Based on the carbon yields and ORR electrocatalytic activities, the preferred CCVD temperature was 700–750 °C, resulting in the CNS with the ORR peak reduction potentials of −0.217 V to −0.220 V (versus −0.167 V for Pt electrode). The improvement of CCVD process was proposed decreasing the ORR peak reduction potential to −0.191 V. A mixture of NH3 and H2O was added to pyrolysis gas, promoting the development of mesoporosity and incorporation of N into the material structure. The developed technique is a viable solution for the conversion of non-condensable gases from tire pyrolysis into S,N,O-doped CNS for ORR.

Oxidising and carburising catalyst conditioning for the controlled growth and transfer of large crystal monolayer hexagonal boron nitride

Hexagonal boron nitride (h-BN) is well-established as a requisite support, encapsulant and barrier for 2D material technologies, but also recently as an active material for applications ranging from hyperbolic metasurfaces to room temperature single-photon sources. Cost-effective, scalable and high quality growth techniques for h-BN layers are critically required. We utilise widely-available iron foils for the catalytic chemical vapour deposition (CVD) of h-BN and report on the significant role of bulk dissolved species in h-BN CVD, and specifically, the balance between dissolved oxygen and carbon. A simple pre-growth conditioning step of the iron foils enables us to tailor an error-tolerant scalable CVD process to give exceptionally large h-BN monolayer domains. We also develop a facile method for the improved transfer of as-grown h-BN away from the iron surface by means of the controlled humidity oxidation and subsequent rapid etching of a thin interfacial iron oxide; thus, avoiding the impurities from the bulk of the foil. We demonstrate wafer-scale (2″) production and utilise this h-BN as a protective layer for graphene towards integrated (opto-)electronic device fabrication.

Single-Step Synthesis of Vertically Aligned Carbon Nanotube Forest on Aluminium Foils.

Vertically aligned carbon nanotube (VACNT) forests are promising for supercapacitor electrodes, but their industrialisation requires a large-scale cost-effective synthesis process suitable to commercial aluminium (Al) foils, namely by operating at a low temperature (<660 °C). We show that Aerosol-Assisted Catalytic Chemical Vapour Deposition (CCVD), a single-step roll-to-roll compatible process, can be optimised to meet this industrial requirement. With ferrocene as a catalyst precursor, acetylene as a carbon source and Ar/H2 as a carrier gas, clean and dense forests of VACNTs of about 10 nm in diameter are obtained at 615 °C with a growth rate up to 5 µm/min. Such novel potentiality of this one-step CCVD process is at the state-of-the-art of the multi-step assisted CCVD processes. To produce thick samples, long synthesis durations are required, but growth saturation occurs that is not associated with a diffusion phenomenon of iron in aluminium substrate. Sequential syntheses show that the saturation trend fits a model of catalytic nanoparticle deactivation that can be limited by decreasing acetylene flow, thus obtaining sample thickness up to 200 µm. Cyclic voltammetry measurements on binder-free VACNT/Al electrodes show that the CNT surface is fully accessible to the ionic liquid electrolyte, even in these dense VACNT forests.