Carbon最新文献

Biomass char is very promising in developing microwave absorbing materials with low minimum reflection loss (RL_min) and ultrawide effective absorption bandwidth (EAB) owing to its low cost and natural availability of various pores, but however is facing a dilemma between the conduction loss and interface polarization loss where new heating technology is highly desirable. In this work, a microwave confined plasma/microwave hybrid heating technology is developed based on the unique interaction between porous carbon and microwave for simultaneous enhancement of conduction loss and interface polarization loss of cellulose char. Compared to the conventional heating product at the same temperature, the as-prepared microwave char showed almost doubled conductivity which is beneficial for conduction loss, higher content of C–O bond that has longer bond length and dielectric susceptibility than CO bond, and more condensed carbon nanoparticles embedded in the carbon matrix which is responsible for increasing the heterointerface polarization loss. As such the tangent loss of MW900-40 % ranges from 0.69 to 0.97 while that of CH900-40 % only ranges from 0.34 to 0.64 in the frequency range of 2.0–18.0 GHz. Further, based on multilayer impedance gradient principle, a double-layer absorber is constructed with products of different MW900 loading, yielding a RL_min of −59.0 dB at 15.9 GHz with an EAB of 10.0 GHz at 4.0 mm, whose working mechanism is comprehensively studied by simulations in terms of impedance matching and microwave dissipation distribution.

The photothermal effect has been recognized as a universal promoter in various photocatalytic reactions. However, in many promising nanocomposite systems, the integration of heterogeneous photothermal materials with photocatalysts remains a significant technical challenge. Focusing on the emerging graphitic carbon nitride (g-C₃N₄) based photocatalyst, we identified that the segregation of the introduced photothermal particles results from the dynamic instability of the original solid-solid dispersion system, which essentially origins from a sluggish two-step solid-liquid-solid phase transformation of urea towards g-C₃N₄. By taking advantages of the photothermal particles to be loaded, we developed a photothermal-polymerization strategy to create a rapid heating to overcome their undesired segregation during g-C₃N₄ formation. The strategy enables a one-step loading of various photothermal particles on the g-C₃N₄, presenting a versatile methodology. This sustainable technique enhances the synthesis yield of g-C₃N₄ by 352 % with reduced energy consumption. The derived photothermal particles-dispersed g-C₃N₄ shows 290 % improvement in photocatalytic CO₂ reduction compared to the separated system, which is obtained from the traditional heating synthesis. Beyond enriching the accessible categories of composite catalysts, this study may deepen physiochemical insights into the dynamic transformation of the novel dispersion system.

Modern electronic equipment puts forward stricter requirements for the performance of electromagnetic interference (EMI) shielding materials to cope with the increasingly complex electromagnetic environment. Here, a high-performance polyimide-MXene-multi-wall carbon nanotubes (PI-MXene-MWCNT) nanocomposite films were prepared by a highly controllable electrospinning-spraying process using the design strategy of integrating conductive gradient with the sandwich structure. The top layer and bottom layer of the composite films are PI electrospun fiber films, and the middle layer is composed by MXene and MWCNT. The design strategy of the conductive gradient structure significantly enhances the EMI shielding performance without increasing the filler content, as evidenced by the nanocomposite film's high EMI shielding effectiveness of 66.8 dB and a satisfactory absolute shielding efficiency of 13153.8 dB cm² g⁻¹. The design strategy of PI sandwich structure endows the nanocomposite film with excellent comprehensive performance. The nanocomposite film not only maintains efficient EMI shielding performance in various extreme conditions, but also has excellent thermal insulation performance (30.5 mW/(m·K)) and flame retardation performance. Meanwhile, the nanocomposite film exhibits good mechanical properties and flexibility, as evidenced by an elongation at break of up to 35.4 %. This work provides inspiration for the preparation of a high-performance EMI shielding material that can be used in extreme environments, which has broad application potential in the field of EMI shielding.

Ensuring long-lasting lubrication is vital for sustainable machinery operation, made possible by self-regenerating carbon-based tribofilms via tribocatalysis. Conventional methods use expensive catalytic coatings, posing challenges for replacement and maintenance in practice. Here, we are proposing catalytic layered double hydroxide (LDH) nanoparticles as cost-effective and easily replenished lubricant additives to engineer catalytically active surfaces in situ where binary and ternary LDHs with Ni²⁺, Co²⁺, and/or Cu²⁺ divalent cations alongside Al³⁺ trivalent cations are investigated for lubrication performance. Under 100 °C sliding condition equivalent to the lubricating temperature in an internal combustion engine, NiCoAl–CO₃ LDH exhibits the lowest wear losses alongside the durable low-friction regime. This excellent performance is attributed to Co-containing spinel and oxide phases in the catalytic tribo-oxide layer which help stabilize and maintain the microstructures of the tribo-oxide layer. In contrast, deterioration in lubrication performance at this temperature was observed for copper-containing LDHs, especially NiCuAl–CO₃ LDHs, which is due to the reduction of metallic oxides that drive phase separation in the catalytic oxide tribo-layers. The more stable tribo-oxide layers can result in thick, durable carbon-based tribofilm during sliding along with higher resistance to plastic deformation bulk interlayer. This study offers valuable insight into the synergy of catalytic oxide materials, opening avenues for a rational design of innovative catalytic nano-materials for tribocatalysis processes.

We investigated the heat loss of the metal wire to the gases in the free molecular region, whose pressure is below 10⁻³ Pa. The heat transfer characteristics at the interface between the metal surface and the gases are only accessible when the conductional heat loss along the wire is comparable to or less than 100 nW/K. Unfortunately, such an infinitesimal heat flow is not controllable from typical metal wire. For this reason, we have synthesized a new material, metal-carbon hybrid wire (MCHW). In the free molecular flow region, the resistance of MCHW is inversely proportional to the pressure (P), R∼1/P, regardless of gas species, which contradicts the gas-dependent heat loss theory. At a pressure <1 × 10⁻⁴ Pa, we observe a deviation from reciprocal linearity attributed to a growing radiational heat loss. Our results realize the thermal conductive sensing of the pressure below 10⁻⁵ Pa, which has been unprecedented.

Harnessing the phenomena of quantum coherence and destructive interference, we have successfully engineered and synthesized a three-dimensional (3D) graphene-based film exhibiting remarkable properties, including metallic thermal conductivity (κ ≈ 150 Wm⁻¹K⁻¹) and electrical conductivity (σ ≈ 320 kSm⁻¹) at room temperature. Notably, these films demonstrate colossal transport anisotropies, reaching approximately 10³ for thermal and 10⁵ for electrical conductivity. This places them among the conducting materials with the highest anisotropies known to date, surpassing even the performance of one-dimensional (1D) carbon nanotubes and two-dimensional (2D) materials like h-BN and MoS₂. These films are synthesized by self-assembly and cross-linking of edge-hydrolyzed graphene flakes. The electron transport between flakes is phonon mediated and at low temperatures the films present quantum critical behavior of a metal to Anderson insulator transition. We measure the electron transport properties in a Hall bar geometry and extract the critical exponents as a function of the sample mobility.

The ever-increasing presence of electronic devices and communication equipment imposes a critical demand for the development of highly efficient microwave absorption materials, as a means to combat the detrimental effects of electromagnetic (EM) wave pollution. The extraordinary advantages offered by heterointerface and defect engineering, coupled with their distinctive electromagnetic traits, infuse boundless energy into the development of MXene-based absorbers for EM attenuation. However, there is still a lack of understanding regarding the consequences of irreversible oxidation on the surface chemistry and dielectric properties of MXenes. Through the employment of heterointerface engineering strategy to promote interfacial charge accumulation and polarization, remarkable EM absorption properties coupled with corrosion resistance have been realized. The partially oxidized MXenes, particularly Ti₃C₂T_x and V₂CT_x, displayed remarkable reflection loss (RL) values of −56.83 dB and −52.13 dB, respectively. Additionally, the Nb₂CT_x composites showcased exceptional performance, offering a significantly broader bandwidth of 9.84 GHz. By conducting an extensive examination of the structural changes in MXenes, this work aims to elucidate the oxidation mechanisms and proposes a feasible method for producing MXenes with excellent absorption properties.

We report the effective synthesis of polyaniline (PANi)-layered nitrogen-doped carbon-coated Fe₃O₄ (FNC@PANi) nanocapsules (NCs) for electrocatalysis of oxygen evolution reaction (OER) as well as anode material for lithium (Li)-ion batteries (LIBs) via a simple hydrothermal method and oxidative polymerization technique. The prepared FNC@PANi NCs revealed a dual core-shell structure, in which an intermediate carbon layer allowed excellent electrical conduction between the Fe₃O₄ NCs and PANi. The dual core-shell structure also allowed the Fe₃O₄ NCs to expand freely during the Li-ion insertion/extraction and OER processes without breaking the outer layer, thus providing a high surface area (147.85 m² g⁻¹) and enhanced electrical conductivity. These properties facilitate the application of the dual core-shell FNC@PANi NCs as an advanced electrode material for LIBs, delivering a high reversible specific capacity of 1556.48 mAh g⁻¹ at 0.1 A g⁻¹, excellent rate performance (896.96 mAh g⁻¹ at 1 A g⁻¹), and durable cycling life (680.12 mAh g⁻¹ at 5 A g⁻¹ for 3000 cycles). The dual core-shell FNC@PANi NCs exhibited high electrocatalytic activity in the OER, with a small Tafel slope of 108.7 mV dec⁻¹ owing to synergistic effects between the copious active sites of the Fe₃O₄ NCs and the carbon core-shell structure and a modest overpotential of 219 mV at 10 mA cm⁻². The electrodes showed excellent stability over 10 h, as determined by chronopotentiometry at 10 mA cm⁻¹. The resultant dual-core-shell FNC@PANi NCs are efficient iron-oxide-based electrode materials for LIBs and OER electrocatalysts.

Prussian blue analog (PBA) derivatives are widely utilized as high-performance electromagnetic wave absorption (EMWA) materials. Despite their potential, the specific impact of different metal ions on the morphology and EMWA performance of 3d-4f PBAs has remained unclear. Herein, using a coprecipitation method and different transition metal ions, we synthesized DyM(CN)₆ (M = Fe, Co) PBAs of different morphologies: six-petal flower-like structure for DyFe(CN)₆ and an elliptical seed shape for DyCo(CN)₆. Upon annealing, Dy₂O₃/Fe@CNT and Dy₂O₃/Co@CNT composites (CNT = carbon nanotube) maintaining their original shapes were prepared. The Dy₂O₃/Co@CNT composite, in particular, showed excellent EMWA properties with an RL_min of −48.32 dB at 15.44 GHz and an EAB of 5.68 GHz at an ultrathin thickness of only 1.75 mm. This performance is attributed to optimized impedance matching and synergistic magnetic-dielectric effects, along with interfacial polarization from Dy₂O₃, Co, and CNT interfaces. The simulated radar cross-section (RCS) confirms the excellent EMW attenuation capability of Dy₂O₃/Co@CNT and shows immense potential for practical application. This work offers a new approach to developing high-performance EMWA materials of 3d-4f PBA derivatives.