Raman spectroscopic investigation of carbon nanowalls

Remote Plasma-Induced Synthesis of Self-Assembled MoS2/Carbon Nanowall Nanocomposites and Their Application as High-Performance Active Materials for Supercapacitors

The objective of this study is to investigate the synthesis and influence of MoS2 on carbon nanowalls (CNWs) as supercapacitor electrodes. The synthesis of MoS2 on CNW was achieved by the introduction of hydrogen remote plasma from ammonium tetrathiomolybdate (ATTM) without deterioration of the CNWs. The topographical surface structures and electrochemical characteristics of the MoS2–CNW composite electrodes were explored using two ATTM-dispersed organic solvents—acetonitrile and dimethylformamide (DMF). In this study, CNW and MoS2 were synthesized using an electron cyclotron resonance plasma. However, hydrogen radicals, which transform ATTM into MoS2, were provided in the form of a remote plasma source. The electrochemical performances of MoS2–CNW hybrid electrodes with various morphologies—depending on the solvent and ATTM concentration—were evaluated using a three-electrode system. The results revealed that the morphology of the synthesized MoS2 was influenced by the organic solvent used and affected both the electrochemical performance and topographical characteristics. Notably, considerable enhancement of the specific capacitance was observed for the MoS2 with open top edges synthesized from DMF. These encouraging results may motivate additional research on hybrid supercapacitor electrodes and the rapid synthesis of MoS2 and other transition metal dichalcogenides.

Efficient and selective removal of Congo red by a C@Mo composite nanomaterial using a citrate-based coordination polymer as the precursor

To research the effect of structural diversity on citrate-based coordination polymers (CPs), citric acid (H4cit) was selected to combine with Cu(ii) under hydrothermal conditions. A new CP [Cu2(cit)(H2O)2] (1) was synthesized and structurally characterized. The title complex shows a 3D 2,4,6-connected topology with the point symbol of {43·63}{44·66·85}{4}. Inspired by the decomposition and functional molybdenum component, 1 was used as a catalyst precursor to synthesize a carbon-based material (C-1) and a C@Mo material (C-Mo-1) by the chemical vapor deposition (CVD) method and characterized in detail. The selective removal of a contaminant (Congo red) by complex 1, C-1 and C-Mo-1 in the aqueous phase was also comparatively investigated.

In Situ Construction of CNT/CuS Hybrids and Their Application in Photodegradation for Removing Organic Dyes

Herein, a coprecipitation method used to synthesize CuS nanostructures is reported. By varying the reaction time and temperature, the evolution of the CuS morphology between nanoparticles and nanoflakes was investigated. It was found that CuS easily crystallizes into sphere-/ellipsoid-like nanoparticles within a short reaction time (0.5 h) or at a high reaction temperature (120 °C), whereas CuS nanoflakes are readily formed at a low reaction temperature (20 °C) for a long time (12 h). Photodegradation experiments demonstrate that CuS nanoflakes exhibit a higher photodegradation performance than CuS nanoparticles for removing rhodamine B (RhB) from aqueous solution under simulated sunlight irradiation. Carbon nanotubes (CNTs) were further used to modify the photodegradation performance of a CuS photocatalyst. To achieve this aim, CNTs and CuS were integrated to form CNT/CuS hybrid composites via an in situ coprecipitation method. In the in situ constructed CNT/CuS composites, CuS is preferably formed as nanoparticles, but cannot be crystallized into nanoflakes. Compared to bare CuS, the CNT/CuS composites manifest an obviously enhanced photodegradation of RhB; notably, the 3% CNT/CuS composite with CNT content of 3% showed the highest photodegradation performance (η = 89.4% for 120 min reaction, kapp = 0.01782 min-1). To make a comparison, CuS nanoflakes and CNTs were mechanically mixed in absolute alcohol and then dried to obtain the 3% CNT/CuS-MD composite. It was observed that the 3% CNT/CuS-MD composite exhibited a slightly higher photodegradation performance (η = 92.4%, kapp = 0.0208 min-1) than the 3% CNT/CuS composite, which may be attributed to the fact that CuS maintains the morphology of nanoflakes in the 3% CNT/CuS-MD composite. The underlying enhanced photocatalytic mechanism of the CNT/CuS composites was systematically investigated and discussed.

Rational Construction of 3D-Networked Carbon Nanowalls/Diamond Supporting CuO Architecture for High-Performance Electrochemical Biosensors

Tremendous demands for highly sensitive and selective nonenzymatic electrochemical biosensors have motivated intensive research on advanced electrode materials with high electrocatalytic activity. Herein, the 3D-networked CuO@carbon nanowalls/diamond (C/D) architecture is rationally designed, and it demonstrates wide linear range (0.5 × 10^-6 -4 × 10^-3 m), high sensitivity (1650 µA cm^-2 mm^-1 ), and low detection limit (0.5 × 10^-6 m), together with high selectivity, great long-term stability, and good reproducibility in glucose determination. The outstanding performance of the CuO@C/D electrode can be ascribed to the synergistic effect coming from high-electrocatalytic-activity CuO nanoparticles and 3D-networked conductive C/D film. The C/D film is composed of carbon nanowalls and diamond nanoplatelets; and owing to the large surface area, accessible open surfaces, and high electrical conduction, it works as an excellent transducer, greatly accelerating the mass- and charge-transport kinetics of electrocatalytic reaction on the CuO biorecognition element. Besides, the vertical aligned diamond nanoplatelet scaffolds could improve structural and mechanical stability of the designed electrode in long-term performance. The excellent CuO@C/D electrode promises potential application in practical glucose detection, and the strategy proposed here can also be extended to construct other biorecognition elements on the 3D-networked conductive C/D transducer for various high-performance nonenzymatic electrochemical biosensors.

Enhancement of Heat Dissipation in Ultraviolet Light-Emitting Diodes by a Vertically Oriented Graphene Nanowall Buffer Layer

For III-nitride-based devices, such as high-brightness light-emitting diodes (LEDs), the poor heat dissipation of the sapphire substrate is deleterious to the energy efficiency and restricts many of their applications. Herein, the role of vertically oriented graphene (VG) nanowalls as a buffer layer for improving the heat dissipation in AlN films on sapphire substrates is studied. It is found that VG nanowalls can effectively enhance the heat dissipation between an AlN film and a sapphire substrate in the longitudinal direction because of their unique vertical structure and good thermal conductivity. Thus, an LED fabricated on a VG-sapphire substrate shows a 37% improved light output power under a high injection current (350 mA) with an effective 3.8% temperature reduction. Moreover, the introduction of VG nanowalls does not degrade the quality of the AlN film, but instead promotes AlN nucleation and significantly reduces the epilayer strain that is generated during the cooling process. These findings suggest that the VG nanowalls can be a good buffer layer candidate in III-nitride semiconductor devices, especially for improving the heat dissipation in high-brightness LEDs.

Transparent Electrothermal Heaters Based on Vertically-Oriented Graphene Glass Hybrid Materials

Transparent heating devices are widely used in daily life-related applications that can be achieved by various heating materials with suitable resistances. Herein, high-performance vertically-oriented graphene (VG) films are directly grown on soda-lime glass by a radio-frequency (rf) plasma-enhanced chemical vapor deposition (PECVD) method, giving reasonable resistances for electrothermal heating. The optical and electrical properties of VG films are found to be tunable by optimizing the growth parameters such as growth time, carrier gas flow, etc. The electrothermal performances of the derived materials with different resistances are thus studied systematically. Specifically, the VG film on glass with a transmittance of ~73% at 550 nm and a sheet resistance of ~3.9 KΩ/□ is fabricated into a heating device, presenting a saturated temperature up to 55 °C by applying 80 V for 3 min. The VG film on the glass at a transmittance of ~43% and a sheet resistance of 0.76 KΩ/□ exhibits a highly steady temperature increase up to ~108 °C with a maximum heating rate of ~2.6 °C/s under a voltage of 60 V. Briefly, the tunable sheet resistance, good adhesion of VG to the growth substrate, relative high heating efficiency, and large heating temperature range make VG films on glass decent candidates for electrothermal related applications in defrosting and defogging devices.

Preparation of the CNTs/AG/ITO electrode with high electro-catalytic activity for 2-chlorophenol degradation and the potential risks from intermediates

A novel carbon nanotubes (CNTs)/agarose (AG)/ITO electrode with high electro-catalytic activity was prepared using a simple sol-gel method. Characterization results showed that the prepared CNTs/AG membrane, coated on the ITO conductive glass, was consisted of C and O. The electro-catalytic degradation for 2-chlorophenol (2-CP) and the influence factors were investigated. The results meant that electro-catalytic degradation for 2-CP was highly dependent on pH, bias voltage, and catalyst dosage. At pH 2, 4 V bias voltage, and 5 wt% CNTs dosage, the electro-catalytic efficiency of CNTs/AG/ITO electrode for 2-CP (20 mg/L) achieved 98% within 180 min. Afterwards, the electro-catalytic properties of recycling electrode, roles of the generated reactive oxygen species, and the reaction pathways were also investigated and proposed. In addition, the toxicities of the generated intermediates from the electro-catalytic degradation were calculated by easy methods. The results indicated that the toxicities of some intermediates were higher than the parent pollutant, especially the formation of 2-CP dimer which was seldom reported in the advanced oxidation process. The findings of using AG as the carrier and conductive adhesive for catalytic material and the assessment methods for the possible increasing risks from the intermediates were reported firstly in this paper.

Note: A compact microwave plasma enhanced chemical vapor deposition based on a household microwave oven

I designed an efficient and compact microwave plasma enhanced chemical vapor deposition (MW-PECVD) based on a household 2.45 GHz microwave oven. In the MW-PECVD, the microwave plasma was sparked by a piece of Cu foil in a low pressure down to 1 Pa. The SiC plate is not only used to realize rapid microwave heating-up but also to prevent the reflected power from damaging the magnetron. To test the performance of the system, vertically oriented graphene nanosheets were fabricated on the Cu foil. The products were characterized by Raman spectra and scanning electron microscope.

Upcycling Waste Lard Oil into Vertical Graphene Sheets by Inductively Coupled Plasma Assisted Chemical Vapor Deposition

Vertical graphene (VG) sheets were single-step synthesized via inductively coupled plasma (ICP)-enhanced chemical vapor deposition (PECVD) using waste lard oil as a sustainable and economical carbon source. Interweaved few-layer VG sheets, H₂, and other hydrocarbon gases were obtained after the decomposition of waste lard oil. The influence of parameters such as temperature, gas proportion, ICP power was investigated to tune the nanostructures of obtained VG, which indicated that a proper temperature and H₂ concentration was indispensable for the synthesis of VG sheets. Rich defects of VG were formed with a high I D / I G ratio (1.29), consistent with the dense edges structure observed in electron microscopy. Additionally, the morphologies, crystalline degree, and wettability of nanostructure carbon induced by PECVD and ICP separately were comparatively analyzed. The present work demonstrated the potential of our PECVD recipe to synthesize VG from abundant natural waste oil, which paved the way to upgrade the low-value hydrocarbons into advanced carbon material.

Enhanced polarization-sensitive terahertz emission from vertically grown graphene by a dynamical photon drag effect

Improving terahertz (THz) emission from graphene is a challenge for graphene-based THz photonics as graphene demonstrates a weak light-matter interaction. With a unique ultra-black surface structure, vertically grown graphene (VGG) is proposed to enhance the light-matter interaction and further enhance THz emission. Herein, enhanced THz radiation is observed by THz time-domain emission spectroscopy from VGG compared with single-layer graphene. The radiated THz amplitude shows a linear dependence on pump power, which demonstrates a second order nonlinear effect. Considering the symmetry of VGG on a substrate, we can exclude the optical rectification effect and photogalvanic effect (PGE) by the D_6h point group with centrosymmetry. Thus we analyze the transient photocurrent related to THz emission only by the photon drag effect (PDE). The polarization-sensitive THz radiation signals are wave-vector reliant and demonstrate cos 2φ and sin 2φ dependence on the polarization angles of the pump laser. This is consistent with the theoretical analysis of PDE. Our results show the enhanced, ultrafast, broadband THz radiation property of VGG, which paves the way for high performance THz emitters and THz detectors based on graphene materials.

Composites of epoxy/graphene-modified-diamond filler show enhanced thermal conductivity and high electrical insulation

In this work, we developed a single-step process to cast epoxy composites having a high thermal conductivity but a low electric conductivity.

High Current Emission from Patterned Aligned Carbon Nanotubes Fabricated by Plasma-Enhanced Chemical Vapor Deposition

Vertically, carbon nanotube (CNT) arrays were successfully fabricated on hexagon patterned Si substrates through radio frequency plasma-enhanced chemical vapor deposition using gas mixtures of acetylene (C2H2) and hydrogen (H2) with Fe/Al2O3 catalysts. The CNTs were found to be graphitized with multi-walled structures. Different H2/C2H2 gas flow rate ratio was used to investigate the effect on CNT growth, and the field emission properties were optimized. The CNT emitters exhibited excellent field emission performance (the turn-on and threshold fields were 2.1 and 2.4 V/μm, respectively). The largest emission current could reach 70 mA/cm(2). The emission current was stable, and no obvious deterioration was observed during the long-term stability test of 50 h. The results were relevant for practical applications based on CNTs.

Electroactive graphene-multi-walled carbon nanotube hybrid supported impedimetric immunosensor for the detection of human cardiac troponin-I

We report a sensitive and stable electrochemical impedance immunosensor prepared with electroactive three-dimensional graphene-multi-walled carbon nanotube hybrid deposited on a glassy carbon electrode.

Synthesis of 3-dimensional porous graphene nanosheets using electron cyclotron resonance plasma enhanced chemical vapour deposition

Microwave plasma driven chemical vapour deposition was used to synthesize graphene nanosheets from a mixture of acetylene and hydrogen gas molecules.

Thermal transformation of carbon hybrid materials to graphene films

We demonstrate a simple approach to grow graphene films on polycrystalline nickel (Ni) foils, in which polycrystalline carbon hybrid materials (CHMs) were used in sandwich structures (molybdenum-CHMs-Ni-molybdenum) as a carbon source for graphene, and pressure was then applied to the sandwich. The CHMs were transformed into single as well as few layer graphene by a segregation-precipitation process. The applied pressure not only increased the density of the graphene films but also reduced the vaporization of dissociated carbon molecules of the CHMs. We have explored the possibility to grow graphene films in low vacuum (5 × 10(-1) Pa) at relatively low temperatures (≤750 °C). The formation of the graphene films at 750 °C is simple and cost-effective and can be scaled up.

Plasma-enhanced chemical vapor deposition synthesis of vertically oriented graphene nanosheets

Vertically oriented graphene (VG) nanosheets have attracted growing interest for a wide range of applications, from energy storage, catalysis and field emission to gas sensing, due to their unique orientation, exposed sharp edges, non-stacking morphology, and huge surface-to-volume ratio. Plasma-enhanced chemical vapor deposition (PECVD) has emerged as a key method for VG synthesis; however, controllable growth of VG with desirable characteristics for specific applications remains a challenge. This paper attempts to summarize the state-of-the-art research on PECVD growth of VG nanosheets to provide guidelines on the design of plasma sources and operation parameters, and to offer a perspective on outstanding challenges that need to be overcome to enable commercial applications of VG. The review starts with an overview of various types of existing PECVD processes for VG growth, and then moves on to research on the influences of feedstock gas, temperature, and pressure on VG growth, substrate pretreatment, the growth of VG patterns on planar substrates, and VG growth on cylindrical and carbon nanotube (CNT) substrates. The review ends with a discussion on challenges and future directions for PECVD growth of VG.

Carbon nanowalls amplify the surface-enhanced Raman scattering from Ag nanoparticles

We report surface-enhanced Raman scattering (SERS) from Ag nanoparticles decorated on thin carbon nanowalls (CNWs) grown by microwave plasma chemical vapor deposition. The Ag morphology is controlled by exposing the CNWs to oxygen plasma and through the electrodeposition process by varying the number of deposition cycles. The SERS substrates are capable of detecting low concentrations of rhodamine 6G and bovine serum albumin, showing much higher Raman enhancement than ordinary planar HOPG with Ag decoration. The major factors contributing to this behavior include: high density of Ag nanoparticles, large surface area, high surface roughness, and the underlying presence of vertically oriented CNWs. The relatively simple procedure of substrate preparation and nanoparticle decoration suggests that this is a promising approach for fabricating ultrasensitive SERS substrates for biological and chemical detection at the single-molecule level, while also enabling the study of fundamental SERS phenomena.

Note: Continuous synthesis of uniform vertical graphene on cylindrical surfaces

This note describes a new reactor design for continuous synthesis of vertically oriented graphene (VG) sheets on cylindrical wire substrates using an atmospheric plasma-enhanced chemical vapor deposition (PECVD) system. Through combining a U-shaped reactor design with "dynamic mode" synthesis featuring simultaneous rotational and axial movements of the metallic wire substrate, the new setup can enable continuous synthesis of VG sheets on the wire surface with remarkable uniformity in both circumferential and axial directions. In contrast, synthesis of VG at "static mode" with a fixed substrate can only lead to non-uniform growth of VG sheets on the wire surface. Potential applications of the resulting uniform-VG-coated metallic wire could include field emitters, field-ionization-based neutral atom detectors, and indoor corona discharges.

Laser patterning of epitaxial graphene for Schottky junction photodetectors

Large-area patterning of epitaxial graphene for Schottky junction photodetectors has been demonstrated with a simple laser irradiation method. In this method, semimetal-semiconductor Schottky junctions are created in a controllable pattern between epitaxial graphene (EG) and laser-modified epitaxial graphene (LEG). The zero-biased EG-LEG-EG photodetector exhibits a nanosecond and wavelength-independent photoresponse in a broad-band spectrum from ultraviolet (200 nm) through visible to infrared light (1064 nm), distinctively different from conventional photon detectors. An efficient external photoresponsivity (or efficiency) of ∼0.1 A·W(-1) is achieved with a biased interdigitated EG-LEG-EG photodetector. The fabrication method presented here opens a viable route to carbon optoelectronics for a fast and highly efficient photoconductive detector.