Chirality-dependent transport in double-walled carbon nanotube assemblies: the role of inner tubes

The MADS-Box Transcription Factor CaRIN Positively Regulates Chlorophyll Degradation During Pepper (Capsicum annuum L.) Fruit Ripening by Repressing the Expression of CaLhcb-P4

Pepper (Capsicum spp.) is an important global vegetable and spice, with fruit color being a key determinant of its commercial quality. However, the regulatory mechanisms underlying pepper fruit color are still not fully understood. This study focuses on the MADS-RIPENING INHIBITOR (MADS-RIN), a MADS-box transcription factor that regulates various aspects of fruit ripening, including pigmentation. We identified CaRIN, a homolog of tomato's SlRIN, whose expression is closely associated with fruit ripening in pepper. Silencing CaRIN through virus-induced gene silencing (VIGS) resulted in increased chlorophyll and chlorophyll a content, reduced carotenoid accumulation, and uneven fruit coloration. Integrative analysis of the RNA-seq and DAP-seq data identified 77 target genes regulated by CaRIN, which was involved in processes such as chlorophyll metabolism and plant hormone signaling. Yeast one-hybrid (Y1H) and dual-luciferase (LUC) assays demonstrated that CaRIN directly bound to the promoter of CaLhcb-P4, repressing its expression. Downregulation of CaLhcb-P4 in pepper fruits via VIGS accelerated chlorophyll degradation. Additionally, CaRIN indirectly regulated multiple genes associated with chlorophyll and carotenoid metabolism, sugar transport, and cell wall degradation. These findings provide novel insights into the regulatory mechanisms of chlorophyll degradation during pepper fruit ripening, offering a foundation for further research and potential genetic improvement strategies.

Interlayer Interactions in 1D Van der Waals Moiré Superlattices

Studying two-dimensional (2D) van der Waals (vdW) moiré superlattices and their interlayer interactions have received surging attention after recent discoveries of many new phases of matter that are highly tunable. Different atomistic registry between layers forming the inner and outer nanotubes can also form one-dimensional (1D) vdW moiré superlattices. In this review, experimental observations and theoretical perspectives related to interlayer interactions in 1D vdW moiré superlattices are summarized. The discussion focuses on double-walled carbon nanotubes (DWNTs), a model 1D vdW moiré system, and the authors highlight the new optical features emerging from the non-trivial strong interlayer coupling effect and the unique physics in 1D DWNTs. Future directions and questions in probing the intriguing physical phenomena in 1D vdW moiré superlattices such as, correlated physics in different 1D moiré systems beyond DWNTs are proposed and discussed.

Direct Measurement of Folding Angle and Strain Vector in Atomically Thin WS2 Using Second-Harmonic Generation

Structural engineering techniques such as local strain engineering and folding provide functional control over critical optoelectronic properties of 2D materials. Local strain engineering at the nanoscale level is practically achieved via permanently deformed wrinkled nanostructures, which are reported to show photoluminescence enhancement, bandgap modulation, and funneling effect. Folding in 2D materials is reported to tune optoelecronic properties via folding angle dependent interlayer coupling and symmetry variation. The accurate and efficient monitoring of local strain vector and folding angle is important to optimize the performance of optoelectronic devices. Conventionally, the accurate measurement of both strain amplitude and strain direction in wrinkled nanostructures requires the combined usage of multiple tools resulting in manufacturing lead time and cost. Here, we demonstrate the usage of a single tool, polarization-dependent second-harmonic generation (SHG), to determine the folding angle and strain vector accurately and efficiently in ultrathin WS₂. The folding angle in trilayer WS₂ folds exhibiting 1-9 times SHG enhancement is probed through variable approaches such as SHG enhancement factor, maxima and minima SHG phase difference, and linear dichroism. In compressive strain induced wrinkled nanostructures, strain-dependent SHG quenching and enhancement is observed parallel and perpendicular, respectively, to the direction of the compressive strain vector, allowing us to determine the local strain vector accurately using a photoelastic approach. We further demonstrate that SHG is highly sensitive to band-nesting-induced transition (C-peak), which can be significantly modulated by strain. Our results show SHG as a powerful probe to folding angle and strain vector.

Recent progress on nanostructured carbon-based counter/back electrodes for high-performance dye-sensitized and perovskite solar cells

Dye-sensitized solar cells (DSSCs) and perovskite solar cells (PSCs) favor minimal environmental impact and low processing costs, factors that have prompted intensive research and development. In both cases, rare, expensive, and less stable metals (Pt and Au) are used as counter/back electrodes; this design increases the overall fabrication cost of commercial DSSC and PSC devices. Therefore, significant attempts have been made to identify possible substitutes. Carbon-based materials seem to be a favorable candidate for DSSCs and PSCs due to their excellent catalytic ability, easy scalability, low cost, and long-term stability. However, different carbon materials, including carbon black, graphene, and carbon nanotubes, among others, have distinct properties, which have a significant role in device efficiency. Herein, we summarize the recent advancement of carbon-based materials and review their synthetic approaches, structure-function relationship, surface modification, heteroatoms/metal/metal oxide incorporation, fabrication process of counter/back electrodes, and their effects on photovoltaic efficiency, based on previous studies. Finally, we highlight the advantages, disadvantages, and design criteria of carbon materials and fabrication challenges that inspire researchers to find low cost, efficient and stable counter/back electrodes for DSSCs and PSCs.

Intrinsic Effect of Carbon Supports on the Activity and Stability of Precious Metal Based Catalysts for Electrocatalytic Alcohol Oxidation in Fuel Cells: A Review

Electrocatalyst supports, in particular carbonaceous materials, play critical roles in the electrocatalytic activity and stability of precious metal group (PMG)-based catalysts such as Pt, Pd, and Au for the electrochemical alcohol oxidation reaction (AOR) of fuels such as methanol and ethanol in polymer electrolyte membrane fuel cells (PEMFCs). Carbonaceous supports such as high surface area carbon provide electronic contact throughout the catalyst layer, isolate PMG nanoparticles (NPs) to maintain high electrochemical surface area, and provide hydrophobic properties to avoid flooding of the catalyst layer by liquid water produced. Compared to high surface area carbon, PMG catalysts supported on 1D and 2D carbon materials such as graphene and carbon nanotubes show enhanced activity and durability due to the intrinsic effect of the underlying carbonaceous supports on the electronic states of PMG NPs. The modification of the electronic environment, in particular the d-band centers of PMG NPs, weakens the adsorption of AOR intermediates, facilitates breaking of the C-C bonds, and thus enhances the electrocatalytic activity of PMG catalysts. The doping of heteroatoms further facilitates the electrocatalytic activity for the AOR through the structural, bifunctional, and electronic effects, in addition to the enhanced dispersion of PMG NPs in the carbon support. The prospects for the development of effective PMG-based catalysts for high-performance alcohol-fuel-based PEMFCs is discussed.

Effect of boron doping on the electrical conductivity of metallicity-separated single walled carbon nanotubes

We explored the effect of substitutional boron doping on the electrical conductivity of a metallicity-separated single walled carbon nanotube (SWCNT) assembly. Boron atoms were introduced into semiconducting (S)- and metallic (M)-SWCNT assemblies using high temperature thermal diffusion and the concentration of the doped boron atoms was controlled by the thermal treatment temperature. Depending on the conduction mechanism of the SWCNT assembly, both positive and negative effects upon boron incorporation are observed. For the S-SWCNT sheet, the electrical resistivity decreased by about 1 order on introduction of a small amount of boron atoms, due to the localized state for hopping conduction. In contrast, we observed an increase in the electrical resistivity on boron doping for M-SWCNTs. The pristine and boron doped metallic SWCNTs exhibited a tendency of decreasing electrical resistivity in the presence of an external magnetic field perpendicular to the film, which indicated two-dimensional weak localization behavior. A detailed analysis of the resistivity and the magnetoresistance implied that an increase in the inelastic scattering event at the doped boron site reduced the phase coherence length, leading to an increase in the electrical resistivity.

Are metal-free pristine carbon nanotubes electrocatalytically active?

Metal-free carbon nanotubes (CNTs) do show electrocatalytic activity for H₂ evolution, O₂ evolution and O₂ reduction reactions in alkaline solutions, but their activities strongly depend on the number of walls or inner tubes with a maximum for CNTs with 2–3 walls.

One-pot synthesis of metal-carbon nanotubes network hybrids as highly efficient catalysts for oxygen evolution reaction of water splitting

Oxygen evaluation reaction (OER) is the most important reaction in hydrogen production from water splitting. Here we developed metal-carbon nanotubes (M-CNTs) hybrids with high metal oxide catalyst loading synthesized by arc-discharge and chemical vapor deposition (CVD) methods as electrocatalysts for OER in alkaline solutions. The M-CNTs hybrids produced by arc-discharge (M-CNTs-Arc) and CVD (M-CNTs-CVD) exhibit a core-shell-like structure, in which metal nanoparticles (NPs) encapsulated by graphite shells are connected by carbon nanotubes (CNTs), forming M-CNTs network hybrids. M-CNTs-Arc has NiCo0.16Fe0.34 metal core and shows very high activity and superior stability for OER, achieving 100 A g(-1) at an overpotential (η) of 0.29 V and 500 A g(-1) at η = 0.37 V in 1 M KOH solution. This is probably the highest activity reported for OER in alkaline solutions. The reaction follows the first-order kinetics with respect to OH(-) concentration and Tafel slope of 34 mV dec(-1). The results demonstrate a highly efficient, scalable, and low-cost one-step synthesis method for developing highly active and stable catalysts for electrochemical water splitting in alkaline solutions.

Conducting linear chains of sulphur inside carbon nanotubes

Despite extensive research for more than 200 years, the experimental isolation of monatomic sulphur chains, which are believed to exhibit a conducting character, has eluded scientists. Here we report the synthesis of a previously unobserved composite material of elemental sulphur, consisting of monatomic chains stabilized in the constraining volume of a carbon nanotube. This one-dimensional phase is confirmed by high-resolution transmission electron microscopy and synchrotron X-ray diffraction. Interestingly, these one-dimensional sulphur chains exhibit long domain sizes of up to 160 nm and high thermal stability (~800 K). Synchrotron X-ray diffraction shows a sharp structural transition of the one-dimensional sulphur occurring at ~450-650 K. Our observations, and corresponding electronic structure and quantum transport calculations, indicate the conducting character of the one-dimensional sulphur chains under ambient pressure. This is in stark contrast to bulk sulphur that needs ultrahigh pressures exceeding ~90 GPa to become metallic.