Two Sprayer CVD Synthesis of Nitrogen-doped Carbon Sponge-type Nanomaterials

CO2-Derived Nanocarbons with Controlled Morphology and High Specific Capacitance

The conversion of CO2 to nanocarbons addresses a dual goal of harmful CO2 elimination from the atmosphere along with the production of valuable nanocarbon materials. In the present study, a simple one-step metallothermic CO2 reduction to nanocarbons was performed at 675 °C with the usage of a Mg reductant. The latter was employed alone and in its mixture with ferrocene, which was found to control the morphology of the produced nanocarbons. Scanning electron microscopy (SEM) analysis reveals a gradual increase in the amount of nanoparticles with different shapes and a decrease in tubular nanostructures with the increase of ferrocene content in the mixture. A possible mechanism for such morphological alterations is discussed. Transmission electron microscopy (TEM) analysis elucidates that the nanotubes and nanoparticles gain mainly amorphous structures, while sheet- and cloud-like morphologies also present in the materials possess significantly improved crystallinity. As a result, the overall crystallinity was preserved constant for all of the samples, which was confirmed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. Finally, electrochemical tests demonstrated that the prepared nanocarbons retained high specific capacitance values in the range of 200-310 F/g (at 0.1 V/s), which can be explained by the measured high specific surface area (650-810 m2/g), total pore volume (1.20-1.55 cm3/g), and the degree of crystallinity. The obtained results demonstrate the suitability of ferrocene for managing the nanocarbons' morphology and open perspectives for the preparation of efficient "green" nanocarbon materials for energy storage applications and beyond.

Nitrogen-phosphorus codoped carbon nanotube sponges for detecting volatile organic compounds: experimental and DFT calculations

The sensing of harmful gases and vapors is of fundamental interest to control the industrial emissions and environmental contamination. Nitrogen/phosphorus codoped carbon nanotube sponges (NP-CNTSs) were used to detect ethanol, acetone, cyclohexane, isopropanol, and methanol. The NP-CNTSs were produced through the aerosol-assisted chemical vapor deposition (AACVD) method using acetonitrile and triphenylphosphine as precursors at 1020 °C. The sensors based on NP-CNTSs were tested with varying operating temperatures (25-100 °C) and gas vapor concentrations (5-50 ppm). For instance, for a gas vapor concentration of 30 ppm and an operating temperature of 65 °C, the sensors showed changes in the electrical resistance of 1.12%, 1.21%, 1.09%, 2.4%, and 1.34% for ethanol, acetone, cyclohexane, isopropanol, and methanol, respectively. We found that the response and recovery times for isopropanol gas vapor are up to 43.7 s and 95 s, respectively. The current sensor outperformed the sensors reported in the literature by at least two times in the response measurement. Additionally, we performed van der Waals density functional theory calculations to elucidate the role of nitrogen and phosphorous codoped single-walled carbon nanotubes (SWCNTs) and their interaction with the considered gas molecule. We analyzed the molecular adsorption energy, optimized structures, and the density of states and calculated the electrostatic potential surface for N-doped, P-doped, NP-codoped, and OH-functionalized NP-codoped metallic SWCNTs-(6,6) and semiconducting SWCNTs-(10,0). Adsorption energy calculations revealed that in most cases the molecules are adsorbed to carbon nanotubes via physisorption. The codoping in SWCNTs-(6,6) promoted structural changes in the surface nanotube and marked chemisorption for acetone molecules.

A Simple Approach to Control the Physical and Chemical Features of Custom-Synthesized N-Doped Carbon Nanotubes and the Extent of Their Network Formation in Polymers: The Importance of Catalyst to Substrate Ratio

This study intends to reveal the significance of the catalyst to substrate ratio (C/S) on the structural and electrical features of the carbon nanotubes and their polymeric nanocomposites. Here, nitrogen-doped carbon nanotube (N-MWNT) was synthesized via a chemical vapor deposition (CVD) method using three ratios (by weight) of iron (Fe) catalyst to aluminum oxide (Al₂O₃) substrate, i.e.,1/9, 1/4, and 2/3, by changing the Fe concentration, i.e., 10, 20, and 40 wt.% Fe. Therefore, the synthesized N-MWNT are labelled as (N-MWNTs)₁₀, (N-MWNTs)₂₀, and (N-MWNTs)₄₀. TEM, XPS, Raman spectroscopy, and TGA characterizations revealed that C/S ratio has a significant impact on the physical and chemical properties of the nanotubes. For instance, by increasing the Fe catalyst from 10 to 40 wt.%, carbon purity increased from 60 to 90 wt.% and the length of the nanotubes increased from 1.2 to 2.6 µm. Interestingly, regarding nanotube morphology, at the highest C/S ratio, the N-MWNTs displayed an open-channel structure, while at the lowest catalyst concentration the nanotubes featured a bamboo-like structure. Afterwards, the network characteristics of the N-MWNTs in a polyvinylidene fluoride (PVDF) matrix were studied using imaging techniques, AC electrical conductivity, and linear and nonlinear rheological measurements. The nanocomposites were prepared via a melt-mixing method at various loadings of the synthesized N-MWNTs. The rheological results confirmed that (N-MWNTs)₁₀, at 0.5–2.0 wt.%, did not form any substantial network through the PVDF matrix, thereby exhibiting an electrically insulative behavior, even at a higher concentration of 3.0 wt.%. Although the optical microscopy, TEM, and rheological results confirmed that both (N-MWNTs)₂₀ and (N-MWNTs)₄₀ established a continuous 3D network within the PVDF matrix, (N-MWNTs)₄₀/PVDF nanocomposites exhibited approximately one order of magnitude higher electrical conductivity. The higher electrical conductivity of (N-MWNTs)₄₀/PVDF nanocomposites is attributed to the intrinsic chemical features of (N-MWNTs)₄₀, such as nitrogen content and nitrogen bonding types.

Feasibility of a Spherical Hollow Carbon Framework as a Stable Host Material for Reversible Metallic Li Storage

A spherical hollow carbon framework decorated with functional heteroatoms is designed and synthesized using ultrasonic spray pyrolysis as a potential anode material for lithium metal batteries (LMBs). The pore structure of the hollow carbon framework can be tailored by melamine, which is a functional additive for integrating abundant nanopores and the uniform decoration of heteroatoms in the structure. The large surface area and pore volume of the hollow carbon framework offer enhanced reversibility and capability for metallic Li storage. In addition, the dendritic growth of Li and volume changes induced by repeated Li plating and stripping can be effectively suppressed during cycling. More importantly, atomic-scale decorations of heteroatoms can effectively lower the overpotential for the nucleation and growth of metallic Li inside the hollow carbon framework. It is mainly responsible for improving the cycle performance and rate capability, even at a high current density. Finally, the hollow carbon framework anode shows stable behavior toward Li plating and stripping without significant capacity fading in the LMBs than conventional Li metal anodes.

Fabrication of High Yield Photoluminescent Quantized Graphene Nanodiscs for Supercapacitor Devices

In this work, we produced high yield quantized nitrogen-doped graphene nanodiscs from waste tires via a one-step process under high pressure and temperature using a homemade stainless steel reactor without using any chemical additives. Reaction temperature played a vital role in the preparation process. By increasing the temperature to a level between 600 and 1100 °C, the carbon atoms rearranged themselves to build a mixed graphene structure of nanodiscs and quantum dots. The obtained graphene exhibits excellent capacitance and long life cycle stability as an electrode in supercapacitor devices. The specific capacitance rose to 161.24 F/g with a high power density of 733.3 W/kg, and the energy density reached 27.1 Wh/kg. The finding of this work is not only to provide a solution to get rid of hazardous materials but also to give awareness of turning these hazardous materials into a cost-effective and economical nanomaterial; in another, this approach sheds light on the promising power uses of waste.

Potential Use of Nitrogen-Doped Carbon Nanotube Sponges as Payload Carriers Against Malignant Glioma

Glioblastoma is the most aggressive brain tumor with a low median survival of 14 months. The only Food and Drug Administration (FDA)-approved treatment for topical delivery of the cancer drug carmustine is Gliadel. However, its use has been associated with several side-effects, mainly provoked by a mass effect. Nitrogen-doped carbon nanotube sponges (N-CNSs) are a new type of nanomaterial exhibiting high biocompatibility, and they are able to load large amounts of hydrophobic drugs, reducing the amount of carriers. This study evaluated the use of N-CNSs as potential carmustine carriers using malignant glioma cell lines. N-CNSs were characterized by nanoparticle tracking analysis and transmission electron microscopy. The biocompatibility of N-CNSs was determined in glioma cell lines and in primary astrocytes. Afterward, N-CNSs were loaded with carmustine (1:10 w/w), and the drug and liberation efficiency, as well as cytotoxicity induction, were determined. N-CNSs presented a homogeneous size distribution formed by round nanotubes, without induced cytotoxicity, at concentrations below 40 µg/mL. The N-CNSs loaded with carmustine exhibited a continuous kinetic release of carmustine with a maximum release after 72 h. The cytotoxic effect of N-CNSs loaded with carmustine was similar to that of carmustine alone. The results demonstrated that N-CNSs are a biocompatible nanostructure that could be used as carriers for the tumoral load of large amounts of chemotherapeutic agents.

Carbazole-Cyanobenzene Dyes Electrografted to Carbon or Indium-Doped Tin Oxide Supports for Visible Light-Driven Photoanodes and Olefin Isomerizations

The organic carbazole-cyanobenzene push-pull dye 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene was derivatized and attached to carbon or indium-doped tin oxide (ITO) electrodes by simple diazonium electrografting. The surface-bound dye is active and stable for the visible light photosynthetic isomerization of a wide range of functionalized stilbene and cinnamic acid derivatives. Up to 87,000 net turnovers were obtained for the isomerization of trans-stilbene. The isomerizations can be carried out in air with a 33% reduction in the rate. The ITO photoelectrodes are also active and stable toward photo-oxidations under basic and acidic conditions.

Fabrication of functionalized electrospun carbon nanofibers for enhancing lead-ion adsorption from aqueous solutions

Electrospinning technique is a simple and cheap method for fabrication of electrospun nanofibers (ENFs), which in turn can converted into electrospun carbon nanofibers (ECNFs) by carbonization process. The controlling of the ECNFs properties (e.g. surface area, porosity, diameters) during fabrication, make it superior over the other carbon nanomaterials. The aim of our study is to modify the surface of ECNFs to increase its hydrophilicity and in turn its efficiency in removing lead ions (Pb2+) from aqueous systems. The surface modification was carried out in two steps starting from oxidation of pristine ECNFs to produce oxidized ECNFs (o-ECNFs), followed by covalently bonded of melamine, and poly(m-phenylene diamine) for forming melamine-functionalized ECNFs (melam-ECNFs) and poly(m-phenylene diamine)-functionalized ECNFs (PmPDA-ECNFs), respectively. The as-prepared materials were characterized in routine way. The ability of the as-prepared materials towards adsorption of Pb2+ ions as heavy metal was investigated with the study of some factors such as pH solution, contact time, initial concentration and temperature. The adsorption process was analyzed isothermally, and kinetically. According to the values of the thermodynamic parameters, the adsorption of Pb2+ ions onto the functionalized ECNFs was endothermic and spontaneous, except with melam-ECNFs was exothermic.

Oxygenated Surface of Carbon Nanotube Sponges: Electroactivity and Magnetic Studies

We report the synthesis of nitrogen-doped carbon nanotube sponges (N-CNSs) by pyrolysis of solutions of benzylamine, ferrocene, thiophene, and isopropanol-based mixture at 1020 °C for 4 h using an aerosol-assisted chemical vapor deposition system. The precursors were transported through a quartz tube using a dynamic flow of H₂/Ar. We characterized the N-CNSs by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and thermogravimetric analysis. We found that isopropanol, isopropanol-ethanol, and isopropanol-acetone as precursors promote the formation of complex-entangled carbon fibers making knots and junctions. The N-CNSs displayed an outstanding oxygen concentration reaching a value of 9.2% for those synthesized with only isopropanol. We identified oxygen and nitrogen functional groups; in particular, the carbon fibers produced using only isopropanol exhibited a high concentration of ether groups (C-O bonds). This fact suggests the presence of phenols, carboxyl, methoxy, ethoxy, epoxy, and more complex functional groups. Usually, the functionalization of graphitic materials is carried out through aggressive acid treatments; here, we offer an alternative route to produce a superoxygenated surface. The understanding of the chemical surface of these novel materials represents a huge challenge and offers an opportunity to study complex oxygen functional groups different from the conventional quinone, carboxyl, phenols, carbonyl, methoxy, ethoxy, among others. The cyclic voltammetry measurements confirmed the importance of oxygen in N-CNSs, showing that with high oxygen concentration, the highest anodic and cathodic currents are displayed. N-CNSs displayed ferromagnetic behavior with an outstanding saturation magnetization. We envisage that our sponges are promising for anodes in lithium-ion batteries and magnetic sensor devices.