Carbon最新文献

Electric vehicle (EV) mobility represents a transformative shift in achieving better energy security, environmental cleanliness, and economic prosperity. Despite recent advancements in EV technology, several challenges persist in tribology and lubrication fronts that can hamper their long-term reliability, performance, and efficiency. In this work, we explored the tribological performance of four commercially available driveline lubricants under non-electrified and electrified sliding conditions using AISI 52100 bearing steel. The results confirmed that passing of electricity through the contact interface exacerbate the wear damage (causing as much as a 5-fold increase in wear volume). Using Raman Spectroscopy, XPS, SEM, ToF-SIMS, and HRTEM, we confirmed that such accelerated wear primarily results from the formation of highly abrasive soot-like amorphous carbon, iron carbide, and other carbonaceous products which result from the decomposition of long-chain hydrocarbon molecules of lubricating oils under electrification. These findings confirm the existence of very complex wear mechanisms in electrified contacts and suggest the need for much improved lubricants and/or materials for future EV applications.

Particles derived from combustion processes, mainly composed of soot agglomerates, are acknowledged to be among the main contributors to climate change. Their effects depend mostly on their size, shape, and internal structure. Specifically, the latter has a significant effect on their optical properties, mainly through the refractive index. This index has been widely evaluated, but scarcely correlated with the soot internal characteristics. In this work, relationships between the nanostructural parameters (such as the degree of graphitization, among others) obtained with conventional analytical techniques and the input parameters of the dispersion model (a representation of the electromagnetic radiation through the Lorentz-Drude approach) are proposed with the aim to determine the refractive index. From experiments in a chassis dynamometer, it has been observed that as the vehicle speed increases, the soot samples have, in general, higher degree of graphitization, due to increased combustion temperature. The method proposed allows quantifying how both the real and imaginary parts of the complex refractive index increase as the degree of graphitization increases. Much lower dependence on the average crystal length has been observed. Different combinations of techniques can be used to determine the nanostructural parameters, depending on the analytical technique used. As far as the resulting parameters are reliable, the effect of the technique selected is minor, thus providing flexibility to the application of the method.

Macro-assembled graphene-based films can been considered as a potential materials for the electromagnetic shielding (EMI) and thermal management in portable electronics. Here, a carbon nanotubes and graphene composite film with covalent bond (CNT-gGF) was fabricated through graphitized welding. The fabricated covalent-bonding CNT-gGF was feature with sandwich structure based carbon nanotubes welding graphene layers as the skeleton, resulting in an excellent conductivity of 13000 S cm^-1 exceeding the pure graphene film. These unique structures endow CNT-gGF film with a prominent mechanical property and flexibility (folding resistant with 1000 cycles). Importantly, an outstanding EMI value is over 55 dB with a thickness of merely 20 μm in the broad frequency of 5-22 GHz. And the CNT-gGF was proven to exhibit a steady EMI property in a variety of extreme environments including high and low temperatures and burns. Moreover, the thermal conductivity of CNT-gGF could be up to 912 W m^-1 K^-1, then CNT-gGF present well heat dissipation application for different voltages and mobile phone. Therefore, this large-size CNT-gGF film has a good application potential for high-performance EMI and thermal management, and this study provides favorable guidelines for the graphene-based films toward extreme demands in wearable electronics and 5G communication.

A series of non-porous zinc-containing coordination compounds with mono- and polydentate ligands has been used to produce carbon materials with a hierarchical porous structure. Adjustment of the carbonization mode enables to increase the target product yield by an average of three times. The obtained carbons have a combination of micro- and mesopores with a pronounced maximum at 3.5 nm. The gas-sorption behavior of the obtained carbons has been studied over a wide range of temperatures and pressures. It has been established that the amount of excess adsorption for hydrogen and methane reaches 2.7 and 15 wt.%, respectively. The extension of the proposed approach to the use of simple bimetallic complexes as precursors may be promising for obtaining effective catalysts based on a carbon matrix with controlled porosity and encapsulated nanoscale particles of a catalytically active metal.

The development of high-efficiency titanate-based electromagnetic wave (EMW) absorbers presents a significant challenge, primarily due to the limited number of loss mechanisms available in such materials. Herein, an innovative approach has been employed, utilizing g-C₃N₄ as a connecting bridge linking KTi₈O_16.5 nanorods with Fe₂O₃ nanoparticles, thereby crafting a KTO/Fe₂O₃–CN absorber with a dual heterojunction architecture. This sophisticated structure is realized through a detailed freeze-drying process followed by heat treatment. In this structure, g-C₃N₄ and KTi₈O_16.5 originate from melamine and MXene precursors, respectively, while Fe₂O₃ component is derived from the thermal decomposition of FeSO₄. The integrated KTO/Fe₂O₃–CN system fosters enhanced interfacial and dipole polarization, as well as conduction and magnetic loss, all collaboratively aiding in the attenuation of EM waves. In addition, the specially designed EMW absorber is notable for its lightweight nature, along with impressive heat dissipation and resistant performance. It demonstrates exceptional thermal stability, capable of withstanding temperatures as high as 500 °C and sustaining repeated thermal cycles at 400 °C. This strategy not only elevates the efficacy of titanate-based EMW absorbers but also paves the way for the conceptualization of high-performance, multifunctional EMW absorption materials. Such advancements hold the promise of transforming a wide range of applications that necessitate effective EM wave attenuation, marking a significant leap forward in the field.

The extraordinary strength of inner graphene walls in carbon nanotube (CNT) is barely exerted due to the weak inner-wall shear resistance, which extremely limits its load-bearing capability. To overcome such deficiency, nanocarbon architecture engineering from CNT to graphene nanoribbon (GNR) was performed via longitudinal unzipping of multi-walled CNT, which was utilized to reinforce pure Al. Results show that the activation volume of composites at macroyielding point, evaluated by stress relaxation experiments, monotonically decreases from CNT/Al to GNR/Al, which results in the continuous increase of critical resolved shear stress (CRSS) called for dislocation nucleation/cross-slip at the grain boundaries. Shear-lag model and numerical simulations demonstrate the increased load-transfer effect from CNT/Al to GNR/Al. Meanwhile, the isotropic and kinematic hardening in nanocarbon/Al composites were investigated both by loading-unloading-reloading tests and strain hardening model on basis of dislocation behavior, wherein the effective stress was determined as being larger than back stress in the composites. Detailed analysis further indicates that the nanocarbon architecture from CNT to GNR increases the back stress strengthening due to the enhanced dislocation accumulation at nanocarbon/Al interface. Moreover, as CNT was unfolded to GNR, the failure mode of reinforcements in the composites gradually changed from pull-out to breakage.

Due to the superior mechanical properties and electrical conductivity of multi-walled carbon nanotubes (MWCNTs), their integration into cementitious composites can improve compressive strength and self-sensing capabilities. However, balancing high mechanical strength with high conductivity is challenging as high MWCNT dosages can impede strength development. We addressed this by studying the effect of MWCNTs concentration (0 to 1.1 wt% of cementitious binders) and induced pore structures on the compressive performance and elastic modulus of ultra-high toughness cementitious composites (UHTCC), both experimentally and theoretically. It was found that as the MWCNTs concentration increased, the porosity continued to increase, while the compressive strength fluctuated. Two failure patterns were identified, i.e., quasi-brittle failure and ductile failure. Analysis showed MWCNTs could promote cement binder hydration, increasing matrix density but the strength development was curbed by increased porosity. A balance was achieved at 0.7 wt% MWCNTs. Further investigations using the Eshelby-Mori-Tanaka method discussed how MWCNT concentration, mechanical properties, distribution, porosity, and pore geometry influenced the elastic modulus. Ultimately, we developed a UHTCC-MWCNT composite with 1.1 wt% MWCNTs, which exhibited substantial improvements in compressive strength (44.85 MPa) and conductivity (9.78✕10^-3 S/m), showing increases of 22.18% and 18,132.6% respectively, compared to the reference group.

Efficient photocatalytic hydrogen evolution can be achieved by adjusting the morphology and constructing suitable heterojunction. In this work, an 2D/3D S-scheme graphdiyne (g-C_nH_2n-2)/carbon-nitrogen vacancies hollow Ni-Fe prussian blue analogues (Ni-Fe-CN PBA) heterojunction (GNF-CN) was prepared for photocatalytic hydrogen evolution. Ni-Fe-CN PBA were prepared by chemical etching and high temperature calcination. The hollow structure can realize multiple reflections of incident light and effectively improve the light utilization efficiency. The CN vacancy changes the band structure of Ni-Fe PBA and enhances its light absorption capacity. Graphdiyne nanosheets (GDY) prepared by load ball milling can increase the active site. The key lies in the construction of an S-scheme heterojunction between GDY and Ni-Fe-CN PBA, which effectively consume useless holes and increase the utilization rate of photogenerated electrons. The S-scheme electron transfer path are proved by DFT calculation, work function and in situ XPS. The GNF-CN-20 showed excellent photocatalytic hydrogen evolution activity (3755.02 μmol h⁻¹ g⁻¹) and photostability compared with GDY (1116.54 μmol h⁻¹ g⁻¹). The present study introduces a novel approach for the construction of an S-scheme heterojunction based on GDY and PBA, enabling wide‐spectrum‐responsive photocatalytic hydrogen evolution.

The surface conductivity of hydrogen-terminated diamond is a topic of great interest from both scientific and technological perspectives. This is primarily due to the fact that the conductivity is exceptionally high without the need for substitutional doping, thus enabling a wide range of electronic applications. Although the conductivity is commonly explained by surface transfer doping due to air-borne surface acceptors, there remains uncertainty regarding the main determining factors that govern the degree of band bending and hole density, which are crucial for the design of electronic devices. Here, we elucidate the dominant factor influencing band bending by creating shallow nitrogen-vacancy (NV) centers beneath the hydrogen-terminated diamond surface through nitrogen ion implantation at varying fluences. We measured the photoluminescence and optically detected magnetic resonance (ODMR) of the NV centers, as well as the surface conductivity, as a function of the nitrogen implantation fluence. The disappearance of the conductivity with increasing nitrogen implantation fluence coincides with the appearance of photoluminescence and ODMR signals from negatively charged NV centers. This finding indicates that band bending is not exclusively determined by the work-function difference between diamond and the surface acceptor material, but by the finite density of surface acceptors. This work emphasizes the importance of distinguishing work-function-difference-limited band bending and surface-acceptor-density-limited band bending when modeling the surface transfer doping, and provides useful insights for the development of devices based on hydrogen-terminated diamond.