Carbon Letters最新文献

Diamond/SiC composites were prepared by vacuum silica vapor-phase infiltration of in situ silicon–carbon reaction, and the thermophysical properties of the composites were modulated by controlling diamond graphitizing. The effects of diamond surface state and vacuum silicon infiltration temperature on diamond graphitization were investigated, and the micro-morphology, phase composition, and properties of the composites were observed and characterized. The results show that diamond pretreatment can reduce the probability of graphitizing; when the penetration temperature is greater than 1600 °C, the diamond undergoes a graphitizing phase transition and the micro-morphology presents a lamellar shape. The thermal conductivity, density, and flexural strength of the composites increased and then decreased with the increase of penetration temperature in the experimentally designed range of penetration temperature. The variation of thermal expansion coefficients of composites prepared with different penetration temperatures ranged from 0.8 to 3.0 ppm/K when the temperature was between 50 and 400 °C.

Nitrogen-doped carbon nanomaterials (N-CNMs) were prepared using Ni(NO₃)₂ as a catalyst in the laminar diffusion flame. Doping the structure of carbon nanomaterials (CNMs) with nitrogen can significantly change the characteristics of CNMs. The purpose of this research is to study the effect of adding ammonia (NH₃) on the evolution of CNMs structure in the laminar flame of ethylene. Raman analysis shows that the intensity ratio (I_D/I_G) of the D-band and G-band of N-CNMs increases and then decreases after the addition of NH₃. The intensity ratio is a maximum of 0.99, which has a good degree of disorder and defect density. The binding distribution of nitrogen was analyzed by X-ray photoelectron spectroscopy (XPS), and a correlation was found between the amount of nitrogen and the morphology of N-CNMs. Nitrogen atoms predominantly present in the forms of pyrrolic-N, pyridinic-N, graphitized-N and oxidized-N, with a doping ratio of nitrogen atoms reaching up to 2.44 at.%. This study found that smaller nickel (Ni) nanoparticles were the main catalysts for carbon nanotubes (CNTs), and their synthesis followed the ‘hollow growth mechanism’ and carbon nanofibers (CNFs) were synthesized from larger Ni nanoparticles according to the ‘solid growth mechanism’. Furthermore, a growth mechanism for the synthesis of bamboo-like CNTs using a specific particle size of the Ni catalyst is proposed. It is noteworthy that the synthesis and modulation of high-performance N-CNMs by flame method represents a simple and efficient approach.

Graphical Abstract

Graphene-based solar cells and supercapacitors integrated into photosupercapacitors represent a pioneering advancement. These devices leverage the exceptional properties of graphene, such as high conductivity and large surface area, to enhance both solar energy conversion and energy storage. The integration of these technologies into photosupercapacitors creates a multifunctional device capable of harnessing solar energy and storing it efficiently. This innovative approach holds promise for sustainable and versatile energy solutions, marking a significant step towards developing efficient and compact energy storage systems. This integration addresses the intermittent nature of solar power generation by providing a continuous and reliable power supply through energy storage. Supercapacitors are one such energy device with a high-power density and excellent specific capacitance which is integrated will a dye-sensitized solar cell (DSSC) comprising a single system of photosupercapacitor. A novel electrode material of NiO/CuO/Co₃O₄/rGO was synthesized which serves as the Pt-free counter electrode of DSSC and working or storage electrode of supercapacitor later was used as the intermediate electrode and storage electrode of a photosupercapacitor. The integrated photosupercapacitor device had a photovoltage of 0.81 V with areal-specific capacitance, energy and power density of 190.12 mF cm⁻², 17.325 μW h cm⁻² and 0.162 mW cm⁻², respectively. The device self-discharged in 385 s with an overall conversion efficiency of 2.17%, resulting in a self-charged energy device.

A simple and effective method was developed to prepare fluorescent carbon quantum dots (CQDs) for the detection of Fe³⁺ and Cu²⁺ in aqueous solution. The water-soluble CQDs with the diameter around 2–5 nm were synthesized using anthracite coal as the precursor. In addition, the as-prepared CQDs exhibits sensitive detection properties for Fe³⁺ and Cu²⁺ metal cations with a detection limit of 18.4 nM and 15.6 nM, respectively, indicating that the coal-derived CQDs sensor is superior for heavy metal recognition and environmental monitoring.

We investigated the effects of supercritical-CO₂ treatment on the pore structure and consequent H₂ adsorption behavior of single-walled carbon nanohorns (SWCNHs) and SWCNH aggregates. High-resolution transmission electron microscopy and adsorption characterization techniques were employed to elucidate the alterations in the SWCNH morphology and aggregate pore characteristics induced by supercritical-CO₂ treatment. Our results confirm that supercritical-CO₂ treatment reduces the interstitial pore surface area and volume of SWCNH aggregates, notably affecting the adsorption of N₂ (77 K), CO₂ (273 K), and H₂ (77 K) gasses. The interstitial porosity strongly depends on the supercritical-CO₂ pressure. Supercritical-CO₂ treatment softens the individual SWCNHs and opens the core of SWCNH aggregates, producing a partially orientated structure with interstitial ultramicropores. These nanopores are formed by the diffusion and intercalation of CO₂ molecules during treatment. An increase in the amount of H₂ adsorbed per interstitial micropore of the supercritically modified SWCNHs was observed. Moreover, the increase in the number and volume of ultramicropores enable the selective adsorption of H₂ and CO₂ molecules. This study reveals that supercritical-CO₂ treatment can modulate the pore structure of SWCNH aggregates and provides an effective strategy for tailoring the H₂ adsorption properties of nanomaterials.

Graphene shows unique electron-transport properties owing to the density of its carriers near the Dirac point. The quantum capacitance (C_Q) of graphene is an intrinsic property that has been investigated theoretically in many previous studies. However, the development of C_Q theory is hindered by the limited availability of related experimental works. In this perspective, experimental works on the C_Q of mechanically exfoliated graphene, graphene synthesized by chemical vapor deposition (CVD), and graphene mesosponge are briefly summarized. The impact of structural properties such as stacking layers, defects, and nitrogen doping on C_Q was experimentally investigated. Furthermore, the applicability of C_Q theory was extended to three-dimensional graphene frameworks. Future research on CVD-synthesized and three-dimensional graphene is expected to enhance our comprehension of the underlying nature of C_Q.

For metal-free carbocatalysts, heteroatom doping and hierarchically porous structure are the significant factors to improve their catalytic performances. Herein, N-, P-co-doped hierarchically porous carbon fiber (NPC–2–800) was prepared by pyrolyzing bamboo pulp in combination with (NH₄)₂HPO₄ and activator K₂CO₃. It was found that (NH₄)₂HPO₄ not only provides N and P atoms, but also significantly affect the morphology and pore structure of the porous carbon. An appropriate dosage of (NH₄)₂HPO₄ facilitates the formation of hierarchically porous carbon fiber in NPC-2–800. Whereas, the carbon fragments with only micropores were obtained in absence of (NH₄)₂HPO₄. The hierarchical porosity and the co-doping of N and P atoms in the NPC-2–800 contribute to its outstanding catalytic performances in the 4-Nitrophenol (4-NP) reduction assisted by NaBH₄. The NPC-2–800 exhibits an attractive turnover frequency (TOF) value of 4.29 × 10^–4 mmol mg⁻¹ min⁻¹, a low activation energy (E_a) of 24.76 kJ/mol, and an acceptable recyclability for 7 cycles without obvious decrease in activity. Kinetics analyses suggest that the 4-NP reduction proceeds through the Langmuir–Hinshelwood model. In addition, the NPC-2–800 can also efficiently catalyze the 2-NP and 3-NP reduction. Moreover, in the real water body, the NPC-2–800 also showed superior catalytic activity to catalyze 4-NP reduction. This study provides an efficient catalyst for pollutant conversion and elimination as well as guidelines for designing versatile carbon-based catalysts.

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Gold nanoparticles (Au NPs) decorated carbon nanofibers (CNFs) have been prepared by an electrospinning approach and then carbonized. The prepared Au-CNFs were employed to modifying a screen printed electrode (SPE) for simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA). Au NPs are uniformly dispersed on carbon nanofibers were confirmed by the structure and morphological studies. The modified electrodes were tested in cyclic voltammetry (CV), differential pulse voltammetry (DPV) and chronoamperometry (CA) to characterize their electrochemical responses. Compared to bare SPE, the Au-CNFs/SPE had a better sensing response to AA, DA, and UA. The electrochemical oxidation signal of AA, DA and UA are well separated into three distinct peaks with peak potential separation of 280 mV, 159 mV and 439 mV between AA-DA, DA-UA and AA-UA respectively in CV studies and the corresponding peak potential separation in DPV studies are 290 mV, 166 mV and 456 mV. The Au-CNFs/SPE has a wide linear response of AA, DA and UA in DPV analysis over the range of 5–40 µM (R² = 0.9984), 2–16 µM (R² = 0.9962) and 2–16 µM (R² = 0.9983) with corresponding detection limits of 0.9 µM, 0.4 µM and 0.3 µM at S/N = 3, respectively. The developed modified SPE based sensor exhibits excellent reproducibility, stability, and repeatability. The excellent sensing response of Au-CNFs could reveal to a promising approach in electrochemical sensor.

Graphical abstract