Catalytic Chemical Vapor Deposition Method Research Articles

Low-Temperature Synthesis of Linear Carbon Chain inside Single-Walled Carbon Nanotubes

Linear carbon chain (LCC) has attracted much interest concerning its structure and applications. It has been reported that LCC possesses higher strength, elastic modulus, and stiffness than any known material, which provides a possibility for LCC as a new composite material, yet its chemical stability remains an issue [1]. Therefore, finding a method to efficiently synthesize LCC has become a meaningful research topic in recent years. A landmark study on LCC synthesis was given by using double-walled carbon nanotubes (DWCNTs) as the template combined with a high-temperature annealing treatment at 1460°C to acquire long chains composed of more than 6,000 carbon atoms [2]. Except for DWCNTs, LCC synthesis starting from single-walled carbon nanotubes (SWCNT) as templates was also reported. However, given the instability of SWCNTs at higher temperature [2] the synthesis efficiency is not as good as for DWCNTs. As far as we know, there is still no report on an efficient LCC synthesis inside SWCNTs. Herein, we report the low-temperature (400°C) efficient LCC synthesis starting from a SWCNT template.To this end, a SWCNT dispersion [3] underwent a surfactant exchange process and was fabricated into a SWCNT film by the filtration method. The SWCNT film was annealed under 400°C in an argon atmosphere to synthesize LCC. Raman spectroscopy (laser wavelength 532 nm) was used to characterize the efficiency of the LCC synthesis. A strong peak at 1863 cm-1 appeared after annealing, originating from the well-known C-mode of the linear carbon chain [4] thereby confirming its existence inside SWCNTs. SWCNTs synthesized by a low-pressure alcohol catalytic chemical vapor deposition (ACCVD) method [5] were also adopted for the LCC synthesis template, resulting in a similar LCC Raman peak at 1863 cm-1. We attribute this successful low-temperature LCC synthesis to the appropriate surfactant which could be encapsulated inside CNTs and converted to LCC during the annealing process.Keywords: Linear Carbon Chain, Single-walled Carbon Nanotubes, Surfactants

Upcycling of composite packaging waste to carbon nanotubes via chemical vapor deposition of pyrolysis gas

Based on the necessity of evaluating composite packaging wastes from both environmental and economic perspectives, it aimed to obtain carbon nanotube (CNT) from the pyrolysis gas product of this material by the catalytic chemical vapor deposition method (CCVD) via an upcycling approach. In the first stage, composite packaging wastes were pyrolyzed. Secondly, the composition of the gas via gas chromatography was determined. In the third stage, CNT production studies were carried out by the CCVD method in a tubular reactor at four different temperatures between 600 and 900 °C with nickel catalyst. The effects of temperature and carbon source feeding ratio on the properties of the obtained CNTs were investigated. CNTs produced in this study were compared with a commercial product. As a result, high-quality multi-walled carbon nanotube of 20–30 nm diameter and in micrometer scale length comparable to commercial products were produced from the gaseous product at 800 °C under Ni-catalysis.

Influence of platinum content (X) in the LaNi5PtX catalyst and reaction conditions on the properties of ferromagnetic Ni-filled CNTs

This research highlights the synthesis of carbon nanostructures using the catalytic chemical vapor deposition (CCVD) method, a hybrid process combining chemical vapor deposition (CVD) and Gas-Solid Heterogeneous Catalysis (GSHC). Intermetallic catalysts, LaNi5Ptx (x = 0, 0.05, 0.5, 1.0), were fabricated through an arc melting procedure to serve as templates for the catalytic conversion of carbon precursors into solid materials. These catalysts, featuring the ferromagnetic transition metal Ni, tend to aggregate into larger particles, reducing the rate of hydrocarbon cracking at the catalyst surface. Rare earth metals like Lanthanum were introduced to form an alloy with a higher melting point to prevent thermal aggregation. Additionally, Pt was incorporated to modify the catalytic properties of the alloy. The study primarily explores the impact of catalyst composition on carbon nanotube (CNT) production. The introduction of platinum content to the catalyst influences the rate at which Ni is filled. The research aimed to alter the catalyst's composition by varying platinum doping in the Pauli paramagnetic lanthanum nickel alloy (LaNi5) to understand the growth mechanism and morphological variations of Ni-filled CNTs. Platinum and lanthanum oxides significantly influence nickel filling in CNTs, resulting in an increased filling rate as the catalyst's Pt content varies from 0 to 1.0. However, higher Pt doping content disrupts the CNT structure with spontaneous nickel encapsulation.

In‐Vitro Investigation of the α‐Amylase Inhibition Activity of Bare Bis‐Benzylidene‐Cyclohexanone Synthesized by a Highly Selective Solvent‐Free Route

AbstractCurrent work reports the highly selective, solvent‐free synthesis of an endorsed bioactive compound, Bis benzylidine cyclohexanone (BBC) through solid acid catalysed cross aldol condensation route and checks its in‐vitro bio activity. The catalytic support (Multiwalled carbon nanotube) employed was synthesized through the highly sophisticated catalytic chemical vapor deposition (CVD) method and simple mechanical grinding strategy was adopted to decorate sulfonic acid on the support. The C1s X‐ray photoelectron peak of at 290.3 eV confirms the effective interaction of sulfonic acid with MWCNT. The sharp and intense desorption peaks observed at approximately 528.7 °C and 655.15 °C in the TPD analysis unmistakably substantiate the strong acidity of the synthesized system. The alpha amylase inhibition activity of the synthesized compound was calculated to be around 88.5 %, which is in par with the commercial drug as it could inhibit only 96 %. Further, the in‐silico (Docking and Molecular Dynamic Simulation) investigations unveiled a new target site for the compound and this can further be studied in detail to advance the applications in drug design. Detailed scrutiny of various parameters was conducted to validate the bioactivity and pharmaceutical potential of the synthesized compound.

Polyethyleneglycol-polyhydroxylbutyrate functionalized carbon nanotubes for industrial electroplating wastewater treatment

This study focuses on the production and purification of multi-walled carbon nanotubes (P-CNTs) via a catalytic chemical vapor deposition method and subsequent functionalization with amino polyethylene glycol (NH2-PEG) and its mixture with polyhydroxybutyrate (PHB) through a multi-step purification process to produce NH2-PEG-CNTs and NH2-PEG-PHB-CNTs, respectively. The developed nanoadsorbents were used to treat electroplating wastewater via batch adsorption to sorb potentially toxic metals and emerging pollutants. The nanoadsorbents were characterized before and after treatment with wastewater after thermal regeneration analyzed using HRSEM/EDS/SAED, DLS Nanozetasizer, BET, TGA/DTG, and FTIR. The nanoadsorbents showed a homogeneous distribution of clean and smooth crystalline interwoven tubular/cylindrical shapes and sizes, with broad polydispersed/high aspect ratio, large surface area, mesopores, and functional groups. The batch adsorption study showed simultaneous multi-capturing of toxic metals from industrial electroplating wastewater with a directly proportional relationship between contact time, adsorbent dosage andtemperature, and electrostatic activities via the positive surface charge of the nanoadsorbents (pH > pHzpc). The highest removal of Fe (15.86 %), Ni (79.82 %), Pb (79.82 %), and Cu (84.97 %) were obtained using NH2-PEG-PHB-CNTs. In addition, the ANOVA results show that the adsorption process depends on other parameters such as the concentration of toxic metals in the wastewater, its hydration energy, electronegativity, ionic mobility in the electrostatic activities, pH of the nanoadsorbents, water holding capacity of the polymer-functionalized nanoadsorbents, and synergistic effects of the bi-polymer. Moreover, the nanoadsorbents have a stable morphology after thermal regeneration for reusability purposes, and treated wastewater can be safely reused in the electroplating industry or for other purposes, such as agriculture.

Facile constructing Ti3C2Tx/TiO2@C heterostructures for excellent microwave absorption properties

Optimizing and enhancing the performance of electromagnetic wave (EMW) absorption materials relies on the modification of their composition and structure through heterogeneous interface engineering. Ti3C2Tx’s high conductivity results in an impedance mismatch, which hinders efficient EMW absorption. Herein, a one–step catalytic chemical vapor deposition (CCVD) method is used to construct the Ti3C2Tx/TiO2@C heterogeneous structure. Upon annealing at 500 °C, amorphous carbon is uniformly deposited on the Ti3C2Tx surface, thereby incorporating the scale–like TiO2 generated during the process. The inclusion of the amorphous carbon layer and TiO2 reduces the substrate’s conductivity, achieving optimized impedance matching. Additionally, building heterogeneous interfaces between Ti3C2Tx, TiO2, and C enriches multiple loss mechanisms involving dipole and interfacial polarization, ultimately enabling optimal EMW absorption performance. The minimum reflection loss (RLmin) value of Ti3C2Tx/TiO2@C–500 is –53.12 dB when its thickness and frequency are 1.15 mm and 13.80 GHz, respectively. Moreover, thermal infrared imaging confirms that coatings fabricated using Ti3C2Tx/TiO2@C–500 demonstrate a favorable heat dissipation rate, validating its effectiveness in addressing the challenge of efficient heat dissipation in electronic devices. This study significantly contributes to the progress of two–dimensional (2D) materials, enabling high–performance EMW absorption and expanding their applications in complex scenarios.

A Green Approach to Obtaining Glycerol Carbonate by Urea Glycerolysis Using Carbon-Supported Metal Oxide Catalysts.

The results of sustainable and selective synthesis of glycerol carbonate (GC) from urea and glycerol under ambient pressure using carbon-fiber-supported metal oxide catalysts are reported. Carbon fibers (CF) were prepared via a catalytic chemical vapor deposition method (CCVD) using Ni as a catalyst and liquefied petroleum gas (LPG) as a cheap carbon source. Supported metal oxide catalysts were obtained by an incipient wetness impregnation technique using Zn, Ba, Cr, and Mg nitrates. Finally, the samples were pyrolyzed and oxidized in an air flow. The obtained catalysts (10%MexOy/CFox) were tested in the reaction of urea glycerolysis at 140 °C for 6 h under atmospheric pressure, using an equimolar ratio of reagents and an inert gas flow for NH3 removal. Under the applied conditions, all of the prepared catalysts increased the glycerol conversion and glycerol carbonate yield compared to the blank test, and the best catalytic performance was shown by the CFox-supported ZnO and MgO systems. Screening of the reaction conditions was carried out by applying ZnO/CFox as a catalyst and considering the effect of reaction temperature, molar ratio of reagents, and the mode of the inert gas flow through the reactor on the catalytic process. Finally, a maximum yield of GC of about 40%, together with a selectivity to glycerol carbonate of ~100%, was obtained within 6 h of reaction at 140 °C using a glycerol-to-urea molar ratio of 1:1 while flowing Ar through the reaction mixture. Furthermore, a positive heterogeneous catalytic effect of the CFox support on the process was noticed.

Catalytic Chemical Vapor Deposition Methodology for Carbon Nanotubes Synthesis

AbstractCarbon nanomaterial is a smart material of the 21st century. This review encompasses various studies involved in carbon nanotube synthesis (CNTs) (Single and multi‐walled) using the catalytic chemical vapor deposition method (CVD). Due to their structural features, the promising branch of nanotechnology is that CNTs possess electrical, magnetic, thermal, chemical, mechanical, and optical properties. 90 to 99 % CNTs were synthesized by the CVD method (Tip growth model and Base growth model) while 80 to 80 % were by laser ablation and only 70 % by arc discharge methods. In CVD method has used a gaseous phase hydrocarbon to pass through a tube‐shaped reactor in the presence of various catalysts at 500–1000 °C to form CNTs. This is one of the significant advantages as compared to other growth methodologies. Further, various parameters responsible for CNTs production are also explored. By comparing hydrocarbons such as methane, graphite, and coal, coal is an abundant and economically viable carbon source.

Study on the law and mechanism of anisotropic conductivity of carbon nanotubes film prepared by floating catalytic chemical vapor deposition method

Carbon nanotubes (CNTs) film has attracted extensive attention in the field of electronics, sensors, and other potential applications due to their excellent electrical conductivity. The conductivity of CNTs film is one of the most important aspects of engineering applications. This study investigates the conductivity of CNTs film with varying areal density, prepared using the floating catalyst chemical vapor deposition (FCCVD) method and densified by rolling. The square resistance of pre- and post-rolling films was measured to characterize the electrical properties. Experimental results indicate that square resistance decreases with increasing areal density and stabilizes eventually. A mathematical formula was derived to explain the relationship between areal density and square resistance, incorporating volume and areal density formulas. Experimental data curves of pre- and post-rolling films were fitted, yielding mathematical relations consistent with the derived formulas. The electrical conductivity of post-rolling CNTs film was superior to pre-rolling in experiment and calculation. The charge carrier transport mechanism in CNTs film was studied by analyzing its internal structure and electrical properties. Surface conductivity was over 1000 times higher than volume conductivity, attributed to the distribution of CNTs bundles in collection and thickness directions. Charge carrier transport capacity decreased with increasing layers in thickness direction due to contact resistance and large resistance at tube–tube junctions. Layers of CNTs near the current application surface significantly contribute to charge carrier transport at high areal density levels.

Potential production of carbon nanotubes from liquid aromatic hydrocarbons over Fe and Ni on alumina powder via catalytic chemical vapor deposition

In this study, liquid aromatic hydrocarbons of benzene C6H6, toluene C7H8, and xylene C8H10 (BTX), which can be abundantly found in industrial waste oil and pyrolysis products of waste plastics, were used as carbon sources to produce carbon nanotubes (CNTs). CNTs were firstly synthesized from liquid benzene over powdered alumina (Al2O3) supported Fe and Ni catalysts at 700 to 850 °C via catalytic chemical vapor deposition (CCVD) method. It was found that, CNTs synthesized from Fe/Al2O3 resulted in significantly higher carbon yields at 1.0–5.6 wt% with relatively higher graphitization analyzed by Raman spectroscopy compared to those of Ni/Al2O3 with the yields only at 0.6–2.8 wt%. However, smaller sizes of CNTs at 20–29 nm could be produced from Ni/Al2O3 compared to 30–38 nm obtained from Fe/Al2O3 due to its smaller crystallite size of the initial catalyst confirmed by X-ray diffraction (XRD) analysis. For both catalysts, with increasing CCVD temperature, the yields tended to increase with a slight increase in CNT diameter and graphitization degree. The temperature of 800 °C was then chosen for further preliminary investigation on potential mass production of CNTs from BTX. By doubling the amount of catalysts, the CNT yield could be approximately twice achieved by maintaining its uniformity and quality because of remaining active sites of the catalysts. In addition, increasing the carbon atoms of aromatic hydrocarbons resulted in improved yields without changing the quality of CNTs. Finally, kinetic mechanisms of CNT growth from BTX decomposition using Fe/Al2O3 catalyst were simply investigated by varying reaction time from 10 to 60 min. At feeding flow of 0.5 ml/min, optimum reaction time was achieved at 30 min in order to produce uniform CNTs at high yields without carbon loss, unreacted BTX, and undesired by-products, which possibly occurred by hydrogenation, catalyst deactivation, and/or side reactions of as-produced gaseous hydrocarbons during CCVD reaction.

Precise engineering of Fe3O4/MWCNTs heterostructures for high-performance supercapacitors

The development of electrode materials with well-defined interfaces plays a vital role on improving the electrochemical performance of supercapacitors. The hybridization of conductive carbon materials with metal oxides is recommended to fabricate improved supercapacitor electrodes. In this work, catalytic chemical vapor deposition (CCVD) and solvothermal methods were utilized to synthesize a Fe3O4/MWCNTs heterostructure with tuned size and morphology. The heterostructure-based electrode showed supreme specific capacitance, energy density, and cycling stability. The size of Fe3O4 as well as the diameter and the number of walls of the functionalized MWCNTs were optimized. Various characterization techniques such as Scanning Electron Microscopy (SEM) combined with Energy Dispersive X-ray (EDX) spectroscopy, Transmission Electron Microscopy (TEM), X-ray diffraction spectroscopy (XRD), and Raman Spectroscopy were utilized to explore the structural and surface properties of the engineered heterostructures. The electrochemical measurements were carried out in 6 M KOH for all synthesized electrodes. The Fe3O4/MWCNTs heterostructure showed a specific capacitance of 492.3 F/g, energy density of 115.55 Wh/Kg at 1 A/g, and capacitance retention of 165.7 % after 1000 cycles. The specific capacitance of the electrodes was further calculated using CV measurement achieving 921.3 F/g at 10 mV/s for the Fe3O4/MWCNTs heterostructure. The excellent electrochemical performances of MWCNTs/Fe3O4 heterostructures were mainly due to the homogenous distribution of Fe3O4 nanoparticles with multivalent oxidation states on the surface of MWCNTs. This led to faster surface oxidation-reduction reactions and consequently, higher reversible capacity and ultrahigh energy density in addition to improved cyclability. This work sheds light on the possibility of precisely controlling Fe3O4/MWCNTs heterostructure electrodes for high-performance energy storage applications.

The Importance of Water for Purification of Longer Carbon Nanotubes for Nanocomposite Applications

Ultralong carbon nanotubes (UCNTs) are in high demand for nanocomposites applications due to their magnificent physical and chemical properties. UCNTs are synthesized by the catalytic chemical vapor deposition (CCVD) method and, before use as fillers in nanocomposites, should be purified of residual catalyst and non-CNT particles without significant destruction or scissoring of the UCNT. This study investigates the role of water vapor for purification of UCNTs from iron catalyst particles and the importance of water assistance in this process is confirmed. It was shown that wet air treatment of products of UCNTs CCVD synthesis under mild conditions can be used to sufficiently decrease residual iron catalyst content without significant carbon losses in comparison to the results obtained with dry air, while the residual iron content was shown to significantly influence the subsequent oxidation of different forms of carbons, including UCNTs. The increasing of D/G ratio of Raman spectra after wet air treatment of products of UCNTs CCVD synthesis makes it possible to conclude that iron catalyst particles transform into iron oxides and hydroxides that caused inner structural strains and destruction of carbon shells, improving removal of the catalyst particles by subsequent acid treatment. UCNTs purification with water assistance can be used to develop economically and ecologically friendly methods for obtaining fillers for nanocomposites of different applications.

SO3H-functionalized carbon fibers for the catalytic transformation of glycerol to glycerol tert-butyl ethers

Carbon fibers (CFs) of high quality were produced from hydrocarbons such as isobutane or ethylene using the catalytic chemical vapor deposition method (CCVD) and Ni catalyst. The as-prepared samples were functionalized with acidic groups using concentrated sulfuric acid or 4-benzenediazonium sulfonate (BDS) generated in situ from sulfanilic acid and sodium nitrite. The morphological features of the materials were confirmed by transmission electron microscopy, whereas their physicochemical properties were characterized by means of elemental and textural analyses, thermogravimetric (TG) method, Raman spectroscopy, potentiometric back titration, and X-ray diffraction analysis. The obtained CFs were used as catalysts in glycerol etherification with tert-butyl alcohol at 110 °C under autogenous pressure. The BDS-modified CFs were particularly effective in the reaction, showing high glycerol conversions (of about 45–55% after 6 h) and substantial yields of mono- and di-glycerol ethers. It was found that the chemistry of the sample surface was crucial for the process. The high concentration of -SO3H groups decorating CFs boosted the formation of di- and tri-tert-butyl glycerol ethers. Surface oxygen functionalities also had a positive effect on the reaction, however, their impact on the catalytic performances of CFs was significantly weaker compared to that shown by -SO3H groups and it was probably due to the adsorption of reagents on the catalyst surface.

Crystalline multilayer graphene nanoflakes synthesized by catalytic chemical vapor deposition using reduced nanostructured hematite as catalyst precursor and 1,2-dichlorobenzene and benzylamine mixture as carbon source

Carbon solubility in the catalyst for the growth of graphene-type nanomaterials is an essential issue for their large-scale fabrication. Iron compounds are fundamental catalysts for the synthesis of carbon materials. The carbon solubility of ferrite (α-Fe) is ∼0.1% at 700 °C, which is enough to promote the growth of graphene nanomaterials. In this work, we synthesized crystalline multilayer graphene flakes (MLGFs) by a two-step catalytic chemical vapor deposition method using an α-Fe catalyst derived from the reduction of nanostructured hematite at 950 °C under an Ar–H2 environment. In the first step, nitrogen-doped multi-walled carbon nanotubes were synthesized by a benzylamine-ferrocene mixture at 850 °C and oxidized at 620 °C in air. In the second step, the reduced nanostructured hematite was exposed to a mixture of a 1:9 benzylamine-1,2- dichlorobenzene at 950 °C. Raman spectroscopy confirmed the presence of MLGFs with a G band and a significant 2D band intensity. The results of the thermogravimetric analysis show that the maximum oxidation rate was at 643.5 °C. Additional functional density calculations were performed considering graphene growth on the oriented (110) α-Fe surface. This work reasserts the possibility of using alternative carbon sources for graphene growth.

Development of High Performance CNTs-Based Sensor for Electrochemical Applications

This work reports the development of a new robust electrode composed of carbon nanotubes (CNTs) for redox potentiometry to determine ascorbic acid. The electrode was fabricated via catalytic chemical vapor deposition (CVD) of ethylene on Ag substrate in the presence of H2 gas at 800 °C. The C2H2:H2 ratio was 75:90 ml/min respectively. The prepared electrode was characterized with SEM, TEM, XRD, XPS, and Raman spectrometry. SEM showed the formation of aligned CNTs. XRD and Raman spectrometry proved the formation of CNTs with a good degree of graphitization and high crystallinity. XPS analysis results showed 80% of SP2 C–C with a small presence of carbonyls and carboxylates, indicating the high perfection of the CNTs formed. CNT/Ag electrode was applied, for the first time, to zero-current potentiometry and was successfully used to determine ascorbic acid in both pure form and in pharmaceutical formula. Ascorbic acid concentrations down to 0.5 mmol/L was determined. Sigmoidal potentiometric curves were obtained and the results were comparable to those obtained from Pt electrode. The CNT/Ag electrode attained fast equilibrium and exhibited good sensitivity and reproducibility. The enhanced sensing efficiency is attributed to the rapid heterogeneous electron transfer and high electrode surface area offered by CNTs grown via CVD. Additionally, the CVD method produced CNT/Ag electrode with strong adhesion of the CNTs layer to the substrate compared to other CNT-based electrodes prepared by casting the CNTs or mixing them with Nafion. This in turn improves the performance and durability. Moreover, unlike the Pt electrode, the CNT on the surface of this electrode may easily be functionalized by immobilizing the desired moieties via various types of strategies to suit different selective routine applications. Figure 1

Scalable synthesis of SWCNT via CH4/N2 gas: The effects of purification on photocatalytic properties of CNT/TiO2 nanocomposite

Single-walled carbon nanotubes (SWCNT) were synthesized by a catalytic CVD method over Mo–Fe–MgO and Mo-Fe-Al2O3 catalysts. A systematic investigation was carried out for the purification of SWCNTs by using 20 methods including different acids, acid concentrations, temperatures, and treatment times. The method of consecutive HCl treatment, air oxidation, and second time HCl treatment was successful for the purification of SWCNTs. The purification was effective in the removal of the catalyst support, embedded metal catalysts and non-nanotube carbon materials from the as-synthesized SWCNTs. Effects of purification of SWCNTs on the photocatalytic activity of CNT-based nanocomposites were then studied. The composite SWCNT/TiO2 containing 15 wt% purified SWCNT was synthesized which showed the maximum photocatalytic activity in the degradation of the dye rhodamine B under optimized conditions. The photocatalytic activity of the composite pure-SWCNT/TiO2 was much higher than those of non-purified-SWCNT/TiO2 and neat TiO2. Overall, this work could clarify the scalable synthesis of SWCNTs, an effective purification method for SWCNTs prepared by CCVD and the purity effect on the photocatalytic activity of CNT-based nanocomposites for wastewater treatment.

Low-Temperature Ethanol Sensor via Defective Multiwalled Carbon Nanotubes.

This paper focuses on the fabrication of defective-induced nanotubes via the catalytic chemical vapor deposition method and the investigation of their properties toward gas sensing. We have developed defective multi-walled carbon nanotubes with porous and crystalline structures. The catalyst layer used in CNTs’ growth here was based on 18 and 24 nm of Ni, and 5 nm of Cr deposited by the dc-sputtering technique. The CNTs’ defects were characterized by observing the low graphite peak (G-band) and higher defect peaks (D-band) in the Raman spectrum. The defectives sites are the main source of the sensitivity of materials toward different gases. Thus, the current product was used for sensing devices. The device was subjected to various gases such as NO, NO2, CO, acetone, and ethanol at a low operating temperature of 30 °C and a concentration of 50 ppm. The sensor was observed to be less sensitive to most gas while showing the highest response towards ethanol gas. The sensor showed the highest response of 8.8% toward ethanol at 30 °C of 50 ppm, and a low response of 2.8% at 5 ppm, which was investigated here. The signal repeatability of the present sensor showed its capability to detect ethanol at much lower concentrations and at very low operating temperatures, resulting in reliability and saving power consumption. The gas sensing mechanism of direct interaction between the gas molecules and nanotube surface was considered the main. We have also proposed a sensing mechanism based on Coulomb dipole interaction for the physical adsorption of gas molecules on the surface.

The synthesis of sponge-type nitrogen-doped multiwall carbon nanotubes using ball-milled natural red-leptosol as catalyst precursor: A cycle voltammetry study

Sponge-type nitrogen-doped multiwall carbon nanotubes (N-MWCNTs), synthesized via an aerosol-assisted catalytic chemical vapor deposition (AACCVD) method, were extensively studied. A ball-milled and oxidized red-leptosol (RL) was used as the catalyst precursor, and benzylamine worked as a carbon and nitrogen source. The ball-milled and oxidized RL increased their contact area and purity for the N-MWCNT synthesis. X-ray diffraction characterization revealed that raw RL contained kaolinite, quartz, graphite, hematite, and goethite. According to the electron microscopy analysis, the N-MWCNTs exhibited exotic morphologies and microstructures. The high-resolution X-ray photoelectron spectroscopy showed that the as-grown N-MWCNTs contained pyrrolic and pyridinic nitrogen species. The cyclic voltammetry studies demonstrated that the redox processes in the N-MWCNTs in 0.1 M H2SO4 were dominated by the carboxyl, pyridinic, and pyrrolic groups. Using the natural RL as a catalyst precursor in AACCVD led to a large yield of N-MWCNTs mixed with different minerals, causing the observed morphologies and influencing the electrochemical behavior, which is of interest in energy-storage and sensing applications.

Optimization of carbon nanotube growth via response surface methodology for Fischer-Tropsch synthesis over Fe/CNT catalyst

Light olefins such as ethylene, propylene, and butylene are key compounds in the chemical industry. Iron catalyst supported on carbon nanotubes (CNTs) is an appropriate candidate for light olefins production using synthesis gas in Fischer-Tropsch synthesis (FTS). First, catalytic chemical vapor deposition (CCVD) method was applied to synthesize CNTs using Fe/CaCO3 and acetylene as catalyst and hydrocarbon source, respectively. Applying response surface methodology, the optimum operating conditions were determined in CVD reactor for maximal yield and purity of CNTs. The effects of reaction time (30–60 min), reaction temperature (700–800 °C), and loading of the catalyst (10–30 wt% Fe) were investigated. The synthesized CNTs was characterized by Raman spectroscopy for its graphitic structure and purity. After acid-treatment of the synthesized CNTs, Fe/CNTs-synthesized catalyst was successfully fabricated by ultrasonic-assisted wet impregnation method. 20Fe/CNTs-synthesized, 20Fe/CNTs-commercial, and 20Fe/Al2O3 were analyzed in terms of physio-chemical properties and FTS catalytic performance. Comparison of transmission electron microscopy (TEM) and CO-chemisorption results showed that 20Fe/CNTs-synthesized reduces iron oxide agglomeration resulting in metal particles well-dispersed among the studied Fe-based catalysts. The catalytic performance of Fe-based catalysts was investigated using a fixed-bed reactor at 280 °C under 290 psi. 20Fe/CNTs-synthesized exhibited a lower rate of water-gas-shift (WGS) reaction compared with 20Fe/CNTs-commercial, with C2-C4 selectivity of 23.6% which is slightly less than that of its commercial counterpart. Analysis of FTS liquid products revealed that 20Fe/CNTs-synthesized provides liquid hydrocarbons in the range of C8-C18, while 20Fe/CNTs-commercial and 20Fe/Al2O3 obtained C9-C52 and C10-C20, respectively. After 120 h time on stream under steady state condition, higher activity had been maintained by the 20Fe/CNTs-synthesized catalyst compared to the 20Fe/CNTs-Commercial and 20Fe/Al2O3 catalysts.

Effects of total pressure on carbon nanotube synthesis, independent of feed pressure

While the effects of partial pressure of carbon feed on the growth of carbon nanotubes (CNTs) are well documented, the effects of total pressure in the growth chamber are not well understood. To shed some light, we investigated the growth of CNTs at different total pressures and a constant partial pressure using catalytic chemical vapour deposition method. It was observed that the growth height and diameter of CNTs decreased as the total pressure increased, probably due to the dilution of carbon feed, the increase in the boundary layer thickness and the decrease in the gas diffusion coefficient. Furthermore, the growth quality of the CNTs was found to be highest at intermediate total pressures. This can provide clues as to where the best temperature concentration is for high-quality CNTs.