Carbon Nanowalls Research Articles

Synthesis of Carbon Nanowalls using Plasma-Irradiated Solid Carbon and Absorption of Cs in Water

Synthesis of Carbon Nanowalls using Plasma-Irradiated Solid Carbon and Absorption of Cs in Water

Effects of Plasma Ions/Radicals on Kinetic Interactions in Nanowall Deposition: A Review

Recent advances in the growth of carbon nanowalls (CNWs) and vertical graphene nanosheets using various plasma‐enhanced chemical vapor deposition (PECVD) methods are reviewed in this article. Growth methods are classified into hot‐ and cold‐wall reactors equipped with diverse plasma generation systems, and their respective characteristics are summarized, with particular attention to the behavior of reactive species, such as ions and radicals, generated within the plasma. Recent progress in this research domain is outlined for each method, and an organized account of the chemical kinetic phenomena occurring within the plasma is provided. Finally, future perspectives are discussed. Fundamental data are obtained through real‐time in situ measurements of ions and radicals, and the construction of a database from these data offers microscopic insights that significantly enhance processing outcomes for macroscopically controlling the mechanical shapes and chemical properties of CNWs.

Tailoring Defects in B, N-Codoped Carbon Nanowalls for Direct Electrochemical Oxidation of Glyphosate and its Metabolites.

Tailoring the defects in graphene and its related carbon allotropes has great potential to exploit their enhanced electrochemical properties for energy applications, environmental remediation, and sensing. Vertical graphene, also known as carbon nanowalls (CNWs), exhibits a large surface area, enhanced charge transfer capability, and high defect density, making it suitable for a wide range of emerging applications. However, precise control and tuning of the defect size, position, and density remain challenging; moreover, due to their characteristic labyrinthine morphology, conventional characterization techniques and widely accepted quality indicators fail or need to be reformulated. This study primarily focuses on examining the impact of boron heterodoping and argon plasma treatment on CNW structures, uncovering complex interplays between specific defect-induced three-dimensional nanostructures and electrochemical performance. Moreover, the study introduces the use of defect-rich CNWs as a label-free electrode for directly oxidizing glyphosate (GLY), a common herbicide, and its metabolites (sarcosine and aminomethylphosphonic acid) for the first time. Crucially, we discovered that the presence of specific boron bonds (BC and BN), coupled with the absence of Lewis-base functional groups such as pyridinic-N, is essential for the oxidation of these analytes. Notably, the D+D* second-order combinational Raman modes at ≈2570 cm-1 emerged as a reliable indicator of the analytes' affinity. Contrary to expectations, the electrochemically active surface area and the presence of oxygen-containing functional groups played a secondary role. Argon-plasma post-treatment was found to adversely affect both the morphology and surface chemistry of CNWs, leading to an increase in sp3-hybridized carbon, the introduction of oxygen, and alterations in the types of nitrogen functional groups. Simulations support that certain defects are functional for GLY rather than AMPA. Sarcosine oxidation is the least affected by defect type.

Sp2-rich dendrite-like carbon nanowalls as effective electrode for environmental monitoring of explosive nitroaromatic

Nitroaromatic compounds are commonly used explosive materials that pose a risk to human health and ecosystems due to their acute toxicity and carcinogenicity. Nitroaromatics have numerous pathways into the environment via discarded munitions (e.g. into the Baltic Sea after World War II), after use in mining operations, and in industrial run-off from factories producing these compounds (which are produced across the world to date). The current detection method relies on chromatography and mass spectrometry methods, which are time-consuming, expensive, and require specialist equipment and training. Carbon-based electrochemical sensors offer a low-cost, fast, and easy on-site method for the detection of a variety of compounds. This study demonstrates an efficient approach for rapid electrochemical sensing of Tetryl (N-methyl-N-2,4,6-tetranitroaniline) through the use of boron-doped sp2-rich carbon structures. These structures, known as dendrite-like carbon nanowalls (D:CNW), were fabricated in one-step deposition and extensively characterized to understand the structure and surface chemistry. Electrodes were used to detect a range of nitroaromatic compounds, most notably tetryl in both laboratory and real environmental samples, with an excellent sensitivity of 153.0 µA cm−2 ppm−1 and a detection limit of 17 ppb. The analytical and electrochemical capabilities of D:CNW electrodes indicate their suitability for extensive environmental monitoring.

Nitrogen admixture effects on growth characteristics and properties of carbon nanowalls

The plasma functionalization of carbon nanowalls (CNWs) is of great interest due to their potential applications in electron field emission and energy storage devices. In this study, the effects of nitrogen on the growth and properties of CNWs are thoroughly investigated by varying a wide range of the N2 concentrations in the CH4/H2/N2 discharge plasma. Nitrogen-doped carbon nanowalls (NCNWs) were synthesized in a single-step growth using the hydrogen radical injection plasma-enhanced chemical vapor deposition technique. The formation of dense NCNWs was found to be enhanced by nitrogen and was three times higher in the sample with a 150 sccm N2 flow rate than in the sample without N2 addition (N-0). As the N2 concentration increased from 0 to 200 sccm, the morphology of CNWs changed from relatively straight to curly-like nanowall structures. A high-resolution optical emission spectroscopic observation shows that as N2 flow increased, CN radicals became the dominant species, suppressing the formation of C2 and CH. Photoelectron spectroscopy analysis revealed the nitrogen doping effect on graphene layers at high N2 concentrations. According to Raman and Transmission Electron Microscopy analyses, the NCNWs had more branched and thicker nanowalls with higher defect concentrations than the N-0 sample. The wettability of NCNWs was improved, particularly for the sample with a N2 flow rate of 150 sccm.

Low-temperature growth at 225 °C and characterization of carbon nanowalls synthesized by radical injection plasma-enhanced chemical vapor deposition

The synthesis of carbon nanowalls (CNWs) necessitated a substrate heating temperature above 600 °C. This study describes a low-temperature growth at 225 °C and characterization of CNWs synthesized by the radical injection plasma-enhanced chemical vapor deposition. To investigate the effect of temperature on the growth process, CNWs were synthesized at various temperatures ranging from 200 °C to 700 °C. The morphology of the CNWs observed with a scanning electron microscope shows that wall density increases as substrate temperature decreases. The Raman spectroscopy analysis indicates that CNWs grown at 225 °C have higher defect levels than those grown at higher temperatures, such as 700 °C. Transmission electron microscopy confirmed the presence of multiple graphene layers in the CNWs grown at 225 °C. The water contact angle results revealed that CNWs grown at 225 °C had higher hydrophobicity than those grown at higher temperatures, opening up the potential for CNW applications.

Raman study on the pressure-induced phase transformation of nanographite at room temperature

Pressure-induced phase transformation of graphite at room temperature has attracted considerable interest for understanding the mechanism and the pathways of its structural transformation. The transformation can be influenced by the crystallites or nanographite domains in graphite samples with crystal defects. However, few systematic studies have been conducted on the effects of nanographite on transformation. In this study, we use carbon nanowalls (CNWs) composed of nanographite domains with different sizes to present a Raman study on the phase transformation of nanographite under compression and decompression at room temperature. The pressure-induced phase transformation is clearly observed in CNWs as sp2 to sp3 transformation in graphite at room temperature. The compressed phase returns to the initial phase via decompression; however, transformation under compression and decompression exhibits a large hysteresis. The transition pressure under compression decreases with a decrease in the size of the nanographite domains. The smaller the domain size, the easier it is for the phase transition to occur. The phase transition can be attributed to the sp2 to sp3 transformation induced by sliding graphene layers in nanographite. The domain boundaries in CNWs can serve as a nucleation site of sp3 formation in phase transition and as a buffer for shrinking or expanding nanographite associated with phase transition. Our findings can provide important insights into understanding the phase transition of nanographite and for synthesizing new materials.

IN SITU Raman analysis of electrochemical phenomena in carbon nanowalls

IN SITU Raman analysis of electrochemical phenomena in carbon nanowalls

Carbon nanowall-based gas sensors for carbon dioxide gas detection

Carbon nanowalls (CNWs) have attracted significant attention for gas sensing applications due to their exceptional material properties such as large specific surface area, electric conductivity, nano- and/or micro-porous structure, and high charge carrier mobility. In this work, CNW films were synthesized and used to fabricate gas sensors for carbon dioxide (CO2) gas sensing. The CNW films were synthesized using an inductively-coupled plasma (ICP) plasma-enhanced chemical vapor deposition (PECVD) method and their structural and morphological properties were characterized using Raman spectroscopy and electron microscopy. The obtained CNW films were used to fabricate gas sensors employing interdigitated gold (Au) microelectrodes. The gas sensors were fabricated using both direct synthesis of CNW films on interdigitated Au microelectrodes on quartz and also transferring presynthesized CNW films onto interdigitated Au microelectrodes on glass. The CO2 gas-sensing properties of fabricated devices were investigated for different concentrations of CO2 gas and temperature-ranges. The sensitivities of fabricated devices were found to have a linear dependence on the concentration of CO2 gas and increase with temperature. It was revealed that devices, in which CNW films have a maze-like structure, perform better compared to the ones that have a petal-like structure. A sensitivity value of 1.18% was obtained at 500 ppm CO2 concentration and 100 °C device temperature. The CNW-based gas sensors have the potential for the development of easy-to-manufacture and efficient gas sensors for toxic gas monitoring.

Synthesis and growth mechanism of vertically aligned graphene sheets with precise control over the number of layers for lithium–oxygen batteries

Engineering carbon nanowall (CNW) nanostructures is a daunting task. Machine learning powered analysis can assist the synthesis of vertical few-layer graphene (FLGs) nanostructures with precise control over the layers.

(Invited) Plasma Sources for Growth of Carbonaceous Materials for Energy Efficient Water Treatments

Plasmas can not only be considered as a green technology for the treatment or synthesis of various types of materials, with applications from microelectronics to astrophysics, but they also serve as an excellent source for the green production of 2D materials that are often claimed to be crucial for applications in energy efficient water cleaning processes (in a passive or active way). Two typical examples are carbon nanotubes or nanowalls, stable grown on electrodes, which can be doped with nitrogen or oxygen, decorated with different oxides, or synthesized as MoS2 /C hybrids.The most important point for the production of such multimaterials in plasmas is targeting the material and control of the synthesis. We show that one of the long known, and yet forgotten parameters important for the growth control concerns the plasma wall conditions.

Synthesis of carbon nanowalls by oxy-acetylene torch method

This work presents a relatively new method for the synthesis of carbon nanowalls (CNWs) based on oxy-acetylene torch as a function of deposition time. The morphological and structural properties of the obtained CNW films were studied by scanning electron microscopy and Raman spectroscopy. Changes in the morphology and structural properties of the CNW films depending on the synthesis time were revealed. Shorter growth times lead to the formation of thinner CNW films with a dense labyrinth-like structure, while longer growth times lead to thicker CNW films with a petal-like structure. In addition, this study opens up the possibility of synthesizing CNWs on a production scale, since the proposed method is relatively environmentally friendly and efficient from an economical point of view.

Hydrogen peroxide sensing with nitrogen-doped carbon nanowalls

The fabrication of miniaturized, low-cost, enzyme-free sensors based on nanomaterials via high-performance techniques is expected to provide important benefits for applications in biological detection. In this work, nitrogen-doped carbon nanowalls (CNWs) were synthesized and used to fabricate electrochemical sensor for hydrogen peroxide (H2O2) sensing. The CNWs were grown on Ti\\SiO2\\Si substrates by radical-injection plasma-enhanced chemical vapor deposition (RI-PECVD) method with different nitrogen concentration. Structural and morphological properties of the obtained CNWs were analyzed using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and electron microscopy. Cyclic voltammetry and chronoamperometry were used to analyze the electrochemical properties of N-doped CNWs. This study demonstrates the effectiveness of CNWs doping with nitrogen during the synthesis process to improve the electrochemical characteristics of the sensor. It was shown that CNWs doped at high nitrogen flow rate (N2: 20 sccm) exhibited the highest amperometric response. Cyclic voltammetry results indicate that the CNWs doped at high nitrogen flow rate demonstrate excellent electrochemical activity for the reduction of H2O2. These results could pave the way for the development of easy-to-manufacture and highly efficient metal-free biosensors for H2O2 detection.

High-Sensitivity H2 and CH4 SAW Sensors with Carbon Nanowalls and Improvement in Their Performance after Plasma Treatment

We have developed surface acoustic wave (SAW) sensors with high sensitivity and a reversible response at room temperature (RT). The sensitive area of the sensor was prepared from vertically aligned graphene sheets, like carbon nanowalls (CNWs), which were deposited onto the quartz SAW sensor substrate. The CNWs were obtained by RF plasma-enhanced chemical vapor deposition (PECVD) at 600 °C, and their sensitivity was subsequently enhanced through hydrogen plasma treatment. The SAW sensors were tested at H2 and CH4 at RT, and they exhibited a reversible response for both gases at concentrations between 0.02% and 0.1%, with a detection limit of a few ppm. The additional hydrogen plasma treatment preserved the lamellar structure, with slight modifications to the morphology of CNW edges, as observed by scanning electron microscopy (SEM). X-ray photoelectron spectroscopy (XPS) investigations revealed the presence of new functional groups, a significant number of defects and electron transitions after the treatment. Changes in the chemical state on the CNW surface are most probably responsible for the improved gas adsorption after plasma treatment. These results identify CNWs as a promising material for designing new SAW sensors, with the possibility of using plasma treatments to enhance the detection limit below the ppm level.

Direct determination of paraquat herbicide by square-wave voltammetry by two-step transfer mechanism at heterogeneous boron-doped carbon nanowall electrodes

Boron-doped carbon nanowalls (B:CNW) versus boron-doped diamond (BDD) materials were investigated for the effective electrochemical detection of highly toxic herbicide paraquat (PQ). Depending on the surface morphology and functional groups of BDD and B:CNWs, the electrochemical absorption and detection of the target analyte PQ revealed different detection mechanisms. The surface absorption mechanism was mainly observed for BDD, while for B:CNWs, both surficial and edge absorption were observed due to the sharp edges of carbon nanowalls. This effectually drives the high heterogenous electron transfer kinetics at absorption sites. Detection of PQ was carried out in phosphate buffer solution with an optimized pH of 10 and parameters of the square-wave voltammetry. Comparative studies show higher voltammetric current peak heights for B:CNWs (∼90.5 μA) than BDD (∼7.5 μA) at a much lower PQ concentration of 4 μM. B:CNWs show a higher sensitivity of 11 μA/μM/cm2 than BDD of 2.23 μA/μM/cm2, hence BDD shows a LOD of 1.8 μM, whereas B:CNWs have a much lower LOD of 0.47 μM. Density functional theory calculations (DFT) show a higher propensity of the B:CNW models toward electrocatalytic reduction of the PQ. Moreover, the proposed two-step detection mechanism is strongly supported by the distribution of the PQ electrostatic potential in different oxidation states in conjunction with the slab surfaces. The higher the sensitivity, the lower the LOD, and the excellent performance of B:CNWs in the detection of PQ in real water samples also suggests its potential for use in the environmental monitoring and assessment of emerging pollutants.

Achieving stable photodiode characteristics under ionizing radiation with a self-adaptive nanostructured heterojunction CNWs/CdZnTe

This study proposed self-adaptive nanostructured heterojunction UV-VIS-NIR photodiodes carbon nanowalls (CNWs)/cadmium zinc telluride (CdZnTe) exhibiting stable photoelectric characteristics under ionizing radiation conditions. We carried out a comprehensive analysis of the impact of proton radiation with an energy of 1.5 MeV and a total fluence of 1012 protons/cm2 on the properties of CNWs and CdZnTe functional layers, as well as on the main photodiode characteristics of the CNWs/CdZnTe heterojunctions, employing a set of state-of-the-art materials and device characterization techniques. Responsivity and detectivity of the prepared heterojunctions even slightly improve after exposure to harsh ionizing radiation conditions due to the unique radiation-induced self-adaptive features of the CNWs/CdZnTe heterojunction interface. The characteristics of the CNWs/CdZnTe photodiodes before and after high-energy proton bombardment demonstrate excellent stability, which is the key requirement for long-term and reliable operation of optoelectronic devices in space or radioactively contaminated environments.

Carbon Nanowalls as Anode Materials with Improved Performance Using Carbon Nanofibers.

In this paper, a new synthesis of carbon nanofibers (CNFs)/carbon nanowalls (CNWs) was performed to improve the characteristics of anode materials of lithium-ion batteries by using the advantages offered by CNWs and CNFs. Among the carbon-based nanomaterials, CNWs provide low resistance and high specific surface area. CNFs have the advantage of being stretchable and durable. The CNWs were grown using a microwave plasma-enhanced chemical vapor deposition (PECVD) system with a mixture of methane (CH4) and hydrogen (H2) gases. Polyacrylonitrile (PAN) and N,N-Dimethyl Formamide (DMF) were stirred to prepare a solution and then nanofibers were fabricated using an electrospinning method. Heat treatment in air was then performed using a hot plate for stabilization. In addition, heat treatment was performed at 800 °C for 2 h using rapid thermal annealing (RTA) to produce CNFs. A field emission scanning electron microscope (FE-SEM) was used to confirm surface and cross-sectional images of the CNFs/CNWs anode materials. Raman spectroscopy was used to examine structural characteristics and defects. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and constant current charge/discharge tests were performed to analyze the electrical characteristics. The synthesized CNFs/CNWs anode material had a CV value in which oxidation and reduction reactions were easily performed, and a low Rct value of 93 Ω was confirmed.

Surface-Enhanced Raman Spectroscopy (SERS) Investigation of a 3D Plasmonic Architecture Utilizing Ag Nanoparticles-Embedded Functionalized Carbon Nanowall.

Surface-enhanced Raman scattering (SERS) is a highly sensitive technique for detecting DNA, proteins, and single molecules. The design of SERS substrates plays a crucial role, with the density of hotspots being a key factor in enhancing Raman spectra. In this study, we employed carbon nanowall (CNW) as the nanostructure and embedded plasmonic nanoparticles (PNPs) to increase hotspot density, resulting in robust Raman signals. To enhance the CNW's performance, we functionalized it via oxygen plasma and embedded silver nanoparticles (Ag NPs). The authors evaluated the substrate using rhodamine 6G (R6G) as a model target molecule, ranging in concentration from 10-6 M to 10-10 M for a 4 min exposure. Our analysis confirmed a proportional increase in Raman signal intensity with an increase in concentration. The CNW's large specific surface area and graphene domains provide dense hotspots and high charge mobility, respectively, contributing to both the electromagnetic mechanism (EM) and the chemical mechanism (CM) of SERS.

Corrosion and wear resistance improvements in NiCu alloys through flame-grown honeycomb carbon and CVD of graphene coatings

To improve the corrosion and wear resistance of NiCu alloys, a protective carbon coating and graphene layer is deposited on the surface of an NiCu sample using the flame growth method and chemical vapor deposition (CVD), respectively. The physicochemical properties, nanohardness, hydrophobicity, friction, and corrosion behaviors of the carbonaceous coating layer on the alloy are characterized. The carbon coat consists of many carbon nanowalls, forming a honeycomb-like structure at the interface with the alloy. The effects of the carbon coating on both the corrosion and wear resistance of the NiCu alloy and the corresponding mechanisms are investigated. For anti-corrosion of the coated Monel alloy, the optimum flame time is determined to be 10 min, and its corrosion current density is reduced by 80.8 %, which is much higher than that of the graphene coating (60.3 %). In addition, as compared with bare NiCu, the wear rate of the carbon-coated samples is reduced by 98.9 %, which is nearly the same as that of their graphene counterparts. Nanoindentation tests indicate that the hardness of the carbon-coated Monel alloy is much greater than that of its graphene counterparts due to the lower carbon-growth temperature.

Vertical graphene nanosheets as interface current-collector for enhanced charge-storage kinetics of bimetallic MOF nano-rods and asymmetric solid-state supercapacitors

Vertical graphene nanosheets (VGN), also known as vertical-oriented graphene or carbon nanowalls emerge recently for different energy storage devices by virtue of their interesting properties that enable them to bring out as excellent current-collector and templates for the growth of different nanostructures. In the current research, we design the facile synthesis of nano-sized bimetallic NiCo MOF on VGN (NiCo MOF/VGN) to achieve improved storage performance. The enhanced capacitive contribution, wetting nature, and charge-transfer kinetics of NiCo MOF/VGN facilitate an increase in the energy-storage performance in the case of an in-situ (solvothermal) method than the drop-cast method. Further, the comparison also confirms that VGN acts as an excellent current collector for NiCo MOF than carbon paper. Due to the unique morphology of VGN and nano rod-like NiCo MOF structure, the NiCo MOF/VGN composite delivers a specific capacity of 132 mA h g−1 (475 C g−1) and a specific capacitance of 950 F g−1 at 1 A g−1 with a high rate capability of 93.2 % at 10 A g−1. Moreover, the assembled asymmetric solid-state supercapacitor device (NiCo MOF/VGN//PVA + KOH//activated carbon) exhibited a high energy density of 58.1 Wh kg−1 at a power density of 1170 W kg−1 and a high power density of 7 kW kg−1 at an energy density of 36.5 Wh kg−1 with a cycle stability of 88.5 % after 10,000 cycles of charge-discharge.