Carbon Trends最新文献

We conduct a theoretical examination of the electronic and magnetic characteristics of end-modified 7-atom wide armchair graphene nanoribbons (AGNRs). Our investigation is performed within the framework of a single-band Hubbard model, beyond a mean-field approximation. First, we carry out a comprehensive comparison of various approaches for accommodating di-hydrogenation configurations at the AGNR ends. We demonstrate that the application of an on-site potential to the modified carbon atom, coupled with the addition of an electron, replicates phenomena such as the experimentally observed reduction of the bulk-states (BS) gap. These results for the density of states (DOS) and electronic densities align closely with those obtained through a method explicitly designed to account for the orbital properties of hydrogen atoms. Furthermore, our study enables a clear differentiation between magnetic moments already described in a mean-field (MF) approach, which are spatially confined to the same sites as the topological end-states (ES), and correlation-induced magnetic moments, which exhibit localization along all edges of the AGNRs. Notably, we show the robustness of these correlation-induced magnetic moments relative to end modifications, within the scope of the method we employ.

The mechanical properties of anisotropic carbons such as the pyrocarbon (pyC) matrices in C/C composites remain poorly documented, especially at elevated temperatures where these materials find most of their applications. We provide here a comprehensive molecular dynamics investigation of the high temperature – up to 4000 K – elastic behavior of six nanoscale pyC models in the context of fast temperature increases, not allowing for major structural modifications such as graphitization. We show that the structure of the most anisotropic and less disordered carbons, like the rough laminar (RL) pyC, is mostly not affected by annealing at the nanosecond timescale, aside from healing unstable defects like two-coordinated atoms at graphene edges. Conversely, highly disordered and less anisotropic carbons like the smooth laminar (SL) pyC show some significant rearrangements at grain boundaries and the development of some limited microporosity. The elastic constants of all highly anisotropic models moderately decrease with increasing temperature, somehow similarly to what is observed for graphite. Elastic constants of the SL pyC show a stronger decrease at high temperature, due to the decrease in density even though all models retain an important degree of stiffness up to 4000 K.

In this report, effects of pyrolysis conditions on the structure and magnetic properties of nitrogen-doped graphitic carbon materials prepared from 1-Buthyl-3-methyl imidazolium tricyano methanide ( [BMIm] [TCM]) ionic liquids(ILs) were investigated. It was found that nitrogen-containing graphitic carbon was formed under pyrolysis temperature of 400 °C or higher. Under the experimental conditions, the maximum nitrogen content of the obtained sample was C₄N_1.10 at a pyrolysis temperature of 400 °C and it was found that the nitrogen content in the obtained samples decreased with increasing pyrolysis temperature. Ferromagnetism was not observed in all the obtained samples to 2 K. From the value of the orbital diamagnetic susceptibility and XRD, it was found that the obtained sample had the structural characteristics of soft carbon.

Up to now, Platinum is still wildly regarded as the state-the-art catalyst toward hydrogen evolution reaction (HER) in acid, however alkaline HER is limited by its poor activity for water dissociation. In this regard, hydrogenated graphene (HG) was emerged as a functional support to boost alkaline HER for Pt catalysts. As a result, the optimized Pt/HG (4.15 % wt Pt) showed a wonderful activity in terms of an overpotential of 54 mV at 10 mA cm⁻² as well as a Tafel slope of 30.28 mV dec⁻¹, superior to the counterparts and even 20 wt% commercial Pt/C. Such a high activity was attributed to the fact HG can optimize electronic state and exposed facet of Pt to accelerate alkaline HER. In addition, density function theory (DFT) calculation revealed the energy barrier for H transfer from HG to Pt only required 0.02 eV, in line with experimental analysis. This work provides a promising strategy to design advanced catalysts toward alkaline HER and beyond.

Air-conditioning systems are on track to demand most of the electricity consumed by buildings around the world. The authors propose that dispersing quantum dots into the chilled water loops of air-conditioners represents a path towards improving the efficiency of air-conditioners. As such, the thermophysical properties of carbon-based quantum dot ‘nanofluids’ (e.g., nanoparticles dispersed in liquids) are presented in this study for sub-ambient temperatures (5–15°C)—an under-explored temperature range which requires understanding for air-conditioning applications. This study also explores dispersion stability and materials compatibility—another under-explored area in the literature which is required for commercial uptake. In this study, carbon quantum dots were synthesized via the hydrothermal route and characterized with UV–Vis, FT-IR, Raman spectroscopy, and TEM. Next, the thermophysical properties of specific heat capacity, thermal conductivity, and viscosity of the nanofluids were experimentally measured between 5 and 15°C (not previously reported for aqueous quantum dots). The highest thermal conductivity enhancement was ∼11% (compared to DI water) for 0.3 wt.% at ∼11 °C. Finally, the stability of the fluid was monitored over time and after exposing the fluids to common materials used in air-conditioning systems (e.g., copper, brass, and stainless steel). Unchanged UV–Vis spectra and the lack of sedimentation indicate that the developed dispersions are indeed suitable for chilled water air-conditioning applications.

The effective prediction of corrosion inhibition efficiency (%IE) of modified graphene oxides (GOs); diaminohexane-modified graphene oxide (DAH-GO) and diaminooctane-modified graphene oxide (DAO-GO) is vital for advanced material applications. This study employs a dual-modelling scheme to predict the %IE, for this purpose, four stand-alone machine learning (ML) models (Multivariate Regression (MVR), Gaussian Process Regression (GPR), Adaptive Neuro-Fuzzy Inference System (ANFIS), and Neural Network (NN)), and five simple averaging (SA) ensemble paradigms (MVR-SA, GPR-SA, ANFIS-SA, NN-SA, and Decision Tree-SA (DT-SA)). Feature selection processes were carried out to develop three distinct models, leading to a comprehensive comparative analysis. The results demonstrated that the non-linear stand-alone models (GPR, ANFIS, NN) significantly outperform the linear MVR model, with the M2 model configuration yielding the highest performance across all models. Remarkably, GPR-M2 achieved perfect model tuning with zero error rates, indicating its superior predictive capabilities. Ensemble techniques further improved performance, reflecting the experimental data's complexities in %IE modelling. The hierarchical order of performance in the training phase in the testing phase is DT-SA < MVR-SA < ANFIS-SA < NN-SA < GPR-SA. The GPR-SA ensemble emerged as the most accurate technique, substantially enhancing the predictive accuracy of the ensemble models by up to 67.73% in the training phase and 50.71% in the testing phase. These findings suggest the potential of GPR-SA in boosting the performance of ensemble approaches in material science applications. The study recommended a promising future for ML in the development and application of corrosion-inhibitors.

In the direction of developing new and reliable prognostic tools, metamaterial-based biosensor device is an emergent potential field. The special design of metamaterial provides signature frequency features of healthy or diseased tissues. In the current work we have studied the single split resonance device (SSR) using graphene oxide (GO) as probe for the accelerated and selective detection of bovine serum albumin (BSA). Further, we have used different band gap GO to interpret the structure-property relationship. Spectroscopy methods have been employed to further support the SSR results. 1 ppm solution of mGO-0.5 (band gap ∼1.35 eV) shows sequential increase in sensitivity on increasing amount of BSA. Figure-of-merit (FoM) of SSR biosensor also increased from 57 to 82 and highest Q-factor calculated for mGO-1 is ∼47 making it a good candidate as probe molecule. This work lays out a correlation of degree of GO functionalization with a physical parameter, i.e., band gap for activity towards protein molecules. Also, as the SSR devices use large wavelength radiation with high resolution and accuracy for quantitative estimation of analyte, these are potential non-invasive point-of-use portable diagnostic and early disease diagnosis devices.

The energy demand has increased significantly in recent years and it is urgent to develop a renewable energy system that is highly efficient and non-noble metal-based. Hydrogen energy is an environmentally friendly energy source with abundant resources, which can be used to solve the problem of high energy demand without greenhouse gas emissions. However, the development of catalysts for hydrogen production technology by electrolysis of water is slow, mainly due to the complexity of the electrolysis hydrogen generation process, low hydrogen production efficiency, weak electrode material activity and high cost. Among the non-noble metal-based catalysts, carbon-based materials have high conductivity, tunable chemical bonding, and easily modified morphology, making them beneficial to achieving efficient hydrogen production, though pure carbon composites suffer from few surface-active sites and unmoderated hydrogen bonding energy, which need to be further optimized. The principle of electrocatalytic hydrogen production from the perspectives of reaction thermodynamics and kinetics is analyzed and discussed in this paper. Thermodynamics of electrocatalytic hydrogen production is reflected by the Gibbs free energy of hydrogen adsorption (ΔG_H*) and electrode potential (E). Reaction kinetics of the electrocatalytic hydrogen production process are reflected by overpotential, Tafel slope and exchange current density. Structural optimization methods of carbon-based composite materials and hydrogen production performance after structural optimization are also summarized. Structural optimization methods of carbon-based composite materials mainly include introducing active sites, improving conductivity, increasing specific surface area and introducing self-supporting materials. Finally, prospects are proposed for the development direction and existing problems of electrocatalytic hydrogen production performance of carbon-based composites.

Two-electron oxygen reduction reaction (2e⁻ ORR) generating hydrogen peroxide (H₂O₂) in neutral electrolytes is currently encountering significant scientific challenges. Here, we adopted a direct electron transfer and defect engineering approach for synthesizing a Co-doped NiSe hybrid catalyst to boost the efficiency of this reaction system. The Co@NiSe catalyst with long-term stability over 160 h showed a 53.1 % increase in H₂O₂ selectivity comparing with the pristine NiSe material in neutral electrolyte, indicating the effective modulation of the electronic structure of NiSe via Co doping. Impressively, the 2e⁻ ORR catalytic activity of the catalysts exhibited a positive linear dependence on the content of Ni²⁺ species. The present research proved the possibility for improving the activity of transition metal-based catalysts in neutral electrolytes via hetero-atom doping, which had built basic structure-function relations for designing highly efficient 2e⁻ ORR system.

As a star two-dimensional material, molybdenum disulfide (MoS₂) shows a good potential in the field of electrochemical hydrogen evolution reaction (HER) due to its low price, special physicochemical properties and a small theoretical Gibbs free energy of hydrogen adsorption. However, some disadvantages such as poor electroconductivity and inert basal planes hinder its further improvement of HER activity. Therefore, adopting carbon materials with good electrical conductivity and large specific surface area to composite with MoS₂ is one of the popular strategies to improve the electrical conductivity and increase the exposure of catalytically active sites for constructing highly efficient MoS₂-based electrocatalysts. Herein, in this review, we firstly gave a brief introduction of the MoS₂ structure and the basic HER principle. Then, the synthesis method, catalytic performance and reaction mechanism of utilizing different carbon materials to improve the HER activity of MoS₂ were summarized in detail. Finally, the existing problems and future opportunities for preparing highly active and low cost electrocatalysts assisted by carbon materials are prospected.