Non-catalytic Chemical Vapor Deposition Research Articles

Novel Graphene Wool Gas Adsorbent for Volatile and Semivolatile Organic Compounds.

Volatile and semivolatile organic compounds in ambient air and occupational settings are of great concern due to their associated adverse human health and environmental impacts. Novel graphene wool samplers have been developed and tested to overcome limitations of commercially available sorbents that can only be used once and typically require solvent extraction. Graphene wool (GW) was synthesized by non-catalytic chemical vapor deposition with optimized conditions, resulting in a novel fibrous graphene wool that is very easy to manage and less rigid than other forms of graphene, lending itself to a wide range of potential applications. Here, the air pollutant sampling capabilities of the GW were of interest. The optimal packing weight of GW inside a glass tube (length 178 mm, i.d. 4 mm, o.d. 6 mm) was investigated by the adsorption of vaporized alkane standards on the GW, using a condensation aerosol generator in a temperature-controlled chamber and subsequent detection using a flame ionization detector. The optimized GW packing density was found to be 0.19 mg mm–3 at a flow rate of 500 mL min–1, which provided a gas collection efficiency of >90% for octane, decane, and hexadecane. The humidity uptake of the sampler is less than 1% (m/m) for ambient humidities <70%. Breakthrough studies showed the favorable adsorption of polar molecules, which is attributed to the defective nature of the graphene and the inhomogeneous coating of the graphene layers on the quartz wool, suggesting that the polar versus non-polar uptake potential of the GW can be tuned by varying the graphene layering on the quartz wool substrate during synthesis. Oxidized domains at the irregular edges of the graphene layers, due to a broken, non-pristine sp2 carbon network, allow for adsorption of polar molecules. The GW was applied and used in a combustion sampling campaign where the samplers proved to be comparable to frequently used polydimethylsiloxane sorbents in terms of sampling and thermal desorption of non-polar semivolatile organic compounds. The total alkane concentrations detected after thermal desorption of GW and PDMS samplers were found to be 17.96 ± 13.27 and 18.30 ± 16.42 μg m–3, respectively; thus, the difference in the alkane sampling concentration between the two sorbent systems was negligible. GW provides a new, exciting possibility for the monitoring of organic air pollutants with numerous advantages, including high sampling efficiencies, simple and cost-effective synthesis of the thermally stable GW, solvent-free and environmentally friendly analysis, and, importantly, the reusability of samplers.

Mechanism of non-catalytic chemical vapor deposition growth of all-inorganic CsPbX3 (X = Br, Cl) nanowires

Non-catalytic chemical vapor deposition growth of CsPbX3 (X = Br, Cl) nanowires on both amorphous and crystalline substrates through nucleation and physiological transformations: ‘nanoparticles → capsules → dumbbells → coalescence of dumbbells → NWs’.

Improved tribological behavior of lubricating oil dispersed with hybrid nanoparticles of functionalized carbon spheres and graphene nano platelets

A novel synthesis method of Functionalized Carbon Spheres (FCS) coated with Graphene nanoplatelets (GNP) using a simple sonication technique is reported. The FCS/GNP hybrid nanoparticles were found to be effectively improving the tribological characteristics of lubricating oils. For the synthesis of FCS, Carbon Spheres (CS) synthesized via non-catalytic chemical vapor deposition was functionalized using nitric acid. The hybrid nanoparticles were characterized using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Raman spectroscopy. The tribological behavior of CASTROL-20 W 40 engine oil dispersed with different concentrations of FCS and GNP using ultrasonication was investigated using a four-ball tester. The tribological behavior of FCS and GNP were investigated separately to compare the tribological performance of the FCS/GNP hybrid nanoparticles. The neat oil dispersed with 0.275 wt% of FCS/GNP hybrid nanoparticles in 10:1 ratio shows excellent dispersion and stability for 30 days without the addition of any surfactant. The results indicate that the addition of these hybrid nanoparticles causes a remarkable reduction (~18%) in the Coefficient of Friction (COF) of the neat oil. The optical image of wear scar on the ball immersed in neat oil shows a significant reduction in the Wear Scar Diameter from 425.6 µm to 390.0 µm with the addition of hybrid nanoparticles. The Raman mapping of the wear scar on chromium steel ball reveals that the FCS/GNP hybrid nanoparticles remain unseparated after the tribology test.

Investigations on tribological properties of non-catalytic CVD synthesized carbon spheres in lubricant

The effect of Carbon Spheres (CS) on the tribological properties of lubricating oil was studied. Relatively uniform Carbon Spheres of size ranging from 200 to 350 nm were obtained using the non-catalytic Chemical Vapor Deposition (CVD) method. The synthesis of CS was carried out using the C2H2/H2/Ar gas mixture at 950 °C. Morphological studies and material structure characterizations were carried out using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Raman Spectroscopy and X-ray Diffraction (XRD) techniques. The tribological properties of oil (Castrol 20W-40) samples containing different wt% of CS were explored using a four-ball tester conforming to the ASTM 4172-94 standard for wear prevention properties of lubricating oil. The concentration of CS in neat oil was varied from 0.01 wt% to 0.5 wt%, and the maximum reduction in the coefficient of friction obtained was 10–11% corresponding to 0.3 wt% of CS without the addition of surfactants. The optical image of the contact surface of the balls confirms a reduction in the wear corresponding to the diameter of the worn scar.

Preparation of carbon nanospheres by non-catalytic chemical vapor deposition and their formation mechanism

Preparation of carbon nanospheres by non-catalytic chemical vapor deposition and their formation mechanism

A non-catalytic vapor growth regime for organohalide perovskite nanowires using anodic aluminum oxide templates.

In this work, a novel and facile synthesis process to fabricate single crystalline organometal halide perovskite nanowires has been successfully developed. Nanowires were grown in a high density ordered array from metal nanoclusters inside anodic aluminum oxide templates using a non-catalytic chemical vapor deposition method. Specifically, perovskite NWs were grown as a result of the reaction between methylammonium iodide (MAI) and the Pb/Sn (Pb or Sn) metal in anodic aluminum oxide templates under optimal conditions. The characterization results show that there is a reaction zone at the interface between the perovskite material and metal, at the bottom of the anodic aluminum oxide nanochannels. In order to sustain perovskite NW growth, MAI molecules have to diffuse downward through the perovskite NWs to reach the reaction zone. In fact, the reaction is facilitated by the formation of an intermediate product of the metal iodide compound. This suggests that the Pb/Sn metal is converted to PbI2/SnI2 first and then perovskite NWs are formed as a result of the reaction between MAI and PbI2/SnI2 through a vapor-solid-solid process. The optical characterization results demonstrate that the as-synthesized NWs with an ultra-high nanostructure density can serve as ideal candidates for optoelectronic devices, such as solar cells, light-emitting didoes, photodetectors, etc. And the reported growth approach here is highly versatile combining the merits of excellent controllability, cost-effectiveness and tunability on material composition and physical properties.

Preparation of carbon nanospheres by non-catalytic chemical vapor deposition and their formation mechanism

Carbon spheres with different sizes were prepared by non-catalytic chemical vapor deposition fromgas mixtures of CH4 and H2. The influence of the deposition temperature, pressure, and gas ratio on the formation and growth mechanism of the spheres was investigated. The carbon spheres obtained were characterized by XRD, SEM and TEM. Results indicated that carbon nanospheres (50–100 nm) could be obtained at 1150°C and 5 kPa from a gas mixture with a CH4/H2 volume ratio of 0.25. The deposition temperature had no obvious effect on the sphere size and structure. The sphere size increased with the deposition pressure and the gas ratio. A model was proposed to elucidate their formation and growth.

Fabrication and characterization of single ZnO microwire Schottky light emitting diodes

ZnO microwires were grown using noncatalytic chemical vapor deposition method. The average diameter of the ZnO microwires were about 30μm with length of up to 1–1.5cm. Single ZnO microwire Schottky light emitting diode was fabricated using Au as Schottky contact electrode and using Al as ohmic contact electrode. The current–voltage (I–V) characteristics of Schottky diodes reveal good rectifying behavior. The Schottky barrier height and ideality factor were calculated to be 0.78eV and 4.3, respectively. Furthermore, distinct electroluminescence with ultraviolet and visible emissions was detected from this device at room temperature.

Electrochemical and photo-electrochemical properties of carbon spheres prepared via chemical vapor deposition

A noncatalytic chemical vapor deposition method was used to prepare graphitized carbon spheres (CSs) from acetylene. The CSs (diameter of 115±10nm) with n type conductivity were found to be photo-electrochemically active with a diffuse reflectance spectrum band gap of 1.01eV. The electrical conductivity followed an Arrhenius type law with an activation energy of 0.53eV. From the capacitance measurements, the flat band potential (Vfb=−0.75VSCE) and the electron density (ND=3.46×1015cm−3) were determined.

Nonwetting “white graphene” films

Nonwetting (superhydrophobicity) is currently of great interest in advanced materials research for self-cleaning applications, although it has been a well-known phenomenon in nature (e.g. in lotus leaves) for a long time. Aiming at widening the potential applications of synthetic superhydrophobic films, we have used a noncatalytic chemical vapor deposition method to prepare superhydrophobic films consisting of boron nitride (BN) nanosheets, also known as “white graphenes”. A mixture of boron (B) and boron trioxide (B2O3) powder was used as a new precursor to grow such nano-rough films. The peculiar surface topography of the films induced a nonwetting behavior which was manifested by the picking up of external particles through water droplets rolling on their surface. The nonwetting tendency of the films is explained based on the interactions of the dipole moments of polar water molecules and BN nanosheets.

Simultaneous electrochemical sensing of ascorbic acid, dopamine and uric acid at anodized nanocrystalline graphite-like pyrolytic carbon film electrode

Nanocrystalline graphite-like pyrolytic carbon film (PCF) electrode fabricated by a non-catalytic chemical vapor deposition (CVD) process was used for the simultaneous electrochemical sensing of ascorbic acid (AA), dopamine (DA), and uric acid (UA). The electrode was studied with respect to changes in electrocatalytic activity caused by a simple and fast electrochemical pretreatment. The anodized electrode exhibited excellent performance compared to many chemically modified electrodes in terms of detection limit, linear dynamic range, and sensitivity. Differential pulse voltammetry (DPV) was used for the simultaneous determination of ternary mixtures of DA, AA, and UA. Under optimum conditions, the detection limits were 2.9μM for AA, 0.04μM for DA, and 0.03μM for UA with sensitivities of 0.078, 5.345, and 6.192AM−1, respectively. The peak separation was 219mV between AA and DA and 150mV between DA and UA. No electrode fouling was observed and good reproducibility was obtained in all the experiments. The sensor was successfully applied for the assay of DA in an injectable drug and UA in human urine by using standard addition method.

Noncatalytic chemical vapor deposition of graphene on high-temperature substrates for transparent electrodes

A noncatalytic chemical vapor deposition mechanism is proposed, where high precursor concentration, long deposition time, high temperature, and flat substrate are needed to grow large-area nanocrystalline graphene using hydrocarbon pyrolysis. The graphene is scalable, uniform, and with controlled thickness. It can be deposited on virtually any nonmetallic substrate that withstands ∼1000 °C. For typical examples, graphene grown directly on quartz and sapphire shows transmittance and conductivity similar to exfoliated or metal-catalyzed graphene, as evidenced by transmission spectroscopy and transport measurements. Raman spectroscopy confirms the sp2-C structure. The model and results demonstrate a promising transfer-free technique for transparent electrode production.

Nanocrystalline graphite-like pyrolytic carbon film electrode for electrochemical sensing of hydrazine

Pyrolytic carbon film (PCF) electrode fabricated by a non-catalytic chemical vapor deposition (CVD) process was used as an electrochemical sensor for the detection of hydrazine. The electrode response was found to be electrocatalytic producing a reduction in the overpotential compared to other unmodified carbon-based electrodes such as glassy carbon (GC), basal-plane pyrolytic graphite (BPPG), and edge-plane pyrolytic graphite (EPPG) electrodes. The overall number of electrons involved in the electro-oxidation of hydrazine, the number of electrons involved in the rate-determining step, and diffusion coefficient of hydrazine at PCF electrode were estimated using cyclic voltammetry and chronoamperometry. The performance of PCF electrode was comparable to and in some cases even better than many chemically modified electrodes in terms of detection limit, linear dynamic range, and sensitivity. Moreover, the sensor exhibited fast response time (within 2 s), high response stability, and reproducibility. All the results indicated this sensor is suitable for hydrazine analysis.

Flexible field emitter arrays with adjustable carbon nanotube distances and bundle generation

A template assisted technique was used to synthesize carbon nanotubes (CNTs) in a highly ordered manner by a noncatalytic chemical vapor deposition technique. Special self-organized anodic alumina films control the syntheses of highly aligned carbon nanotube arrays with desired tube geometry, adjustable intertube distances, and unique CNT bundle generation, which are extremely important for CNT array optimization with high field enhancement factors and high current densities. These CNT arrays also meet industrial demands such as uniformity, low cost, and easy preparation. The CNT bundle generation was adjusted by the CNT tube-diameter, wall-thickness, and length-controlled growth. Field emission tests showed that the turn-on field of the CNT cathode arrays could be lowered by adjusting the intertube distance. A vacuum field emission triode with self-aligned gate using these CNT arrays as field emitter is also presented. The proposed CNT configuration allows the realization of cathode arrays on flexible su...

Highly Aligned Carbon Nanotubes Sandwiched Between Facially Arranged Ceramic Alumina Layers

A novel approach is presented for the integration of highly aligned carbon nanotubes in ceramic alumina layers perpendicular to the tube axes. A template method is used to form carbon nanotubes by a noncatalytic chemical vapor deposition inside the pores of porous alumina before consequent thermal treatment of the resulting composite on the frontal surface. The thermal treatment leads to a well-defined layered phase transition accompanied by heterogeneous etching behavior of the alumina phases. Almost freestanding carbon nanotubes sandwiched in facial-oriented corundum layers are obtained after removal of the soluble phases. These ceramic layers drastically improve the handling and stability of highly aligned carbon nanotubes.

Fabrication of Hierarchical ZnO Architectures and Their Superhydrophobic Surfaces with Strong Adhesive Force

Grid-structured ZnO microsphere arrays assembled by uniform ZnO nanorods were fabricated by noncatalytic chemical vapor deposition, taking advantage of morphologies of alumina nanowire pyramid substrates and ZnO oriented growth habits. Every ZnO microsphere (similar to the micropapilla on a lotus leaf surface) is assembled by over 200 various oriented ZnO nanorods (similar to the hairlike nanostructures on mircopapilla of a lotus leaf). This lotus-leaf-like ZnO micro-nanostructure films reveal superhydrophobicity and ultrastrong adhesive force to liquid. The realization of this hierarchical ZnO nanostructure film could be important for further understanding wettability of biological surfaces with micro-nanostructure and application in microfluidic devices.

A facile approach to simultaneous fabrication of microsize hollow and solid carbon spheres from acetylene directly

Simultaneous production of microsize hollow and solid carbon spheres has been successfully achieved via non-catalytic chemical vapor deposition of acetylene under mild conditions, of which the unique feature is that the as-made ball-like carbons can be collected separately as two individual products. The parameters such as the reaction temperature, the flow rate and the composition of the carrier gas especially H2 are found to be critical for the selective synthesis of microsize hollow and solid carbon spheres. A possible growth model for these ball-like carbon products is proposed and discussed in terms of the process parameters.

Catalyst free growth of a carbon nanotube–alumina composite structure

Aligned arrays of multiwall carbon tubes (CNTs) were prepared within cylindrical pores of compact porous anodic aluminum oxide (PAOX) by a non-catalytic chemical vapor deposition (CVD) method. Optimum CNT synthesis conditions were determined for two crucial reaction parameters, e.g. the precursor gas flow and the reaction time for a given fixed reaction temperature. Gas phase oxidation followed by a wet chemical dissolution allows selective removal of carbon by-products from the surface of the CNT/PAOX composite without destroying its structure. The developed procedure opens up the way to obtain CNT/alumina composites with open, 2D arranged pores by a selective gas phase and solution chemical etching technique.

Effect of Graphitization on the Wettability and Electrical Conductivity of CVD-Carbon Nanotubes and Films

The use of carbon nanomaterials in various applications requires precise control of their surface and bulk properties. In this paper, we present a strategy for modifying the surface chemistry, wettability, and electrical conductivity of carbon tubes and films through annealing in a vacuum. Experiments were conducted with 60-300 nm nanotubes (nanopipes), produced by noncatalytic chemical vapor deposition (CVD) in a porous alumina template, and with thin films deposited by the same technique on a glassy carbon substrate having the same structure and chemistry of the CNTs. The surface of the as-produced CVD-carbon, treated with sodium hydroxide to remove the alumina template, is hydrophilic, and the bulk electrical conductivity is lower by a factor of 20 than that of fully graphitic multiwalled nanotubes (MWNT) or bulk graphite. The bulk electrical conductivity increases to the conductivity of graphite after annealing at 2000 degrees C in a high vacuum. The analysis of CNTs by transmission electron microscopy (TEM) and Raman spectroscopy shows the ordering of carbon accompanied by an exponential increase of the in-plane crystallite size, L(a), with increasing annealing temperature. Environmental scanning electron microscopy (ESEM) was used to study the interaction of CNT with water, and contact angle measurements performed using the sessile drop method on CVD-carbon films demonstrate that the contact angle increases nearly linearly with increasing annealing temperature.