Raman spectroscopy study of the transformation of the carbonaceous skeleton of a polymer-based nanoporous carbon along the thermal annealing pathway

We report a multi-wavelength Raman spectroscopy study of the structural changes along the thermal annealing pathway of a poly(furfuryl alcohol) (PFA) derived nanoporous carbon (NPC). The Raman spectra were deconvoluted utilizing G, D, D′, A and TPA bands. The appropriateness of these deconvolutions was confirmed via recovery of the correct dispersive behaviours of these bands. It is proposed that the ID/IG ratio is composed of two parts: one associated with the extent of graphitic crystallites (the Tuinstra–Koenig relationship), and a second related to the inter-defect distance. This model was used to successfully determine the variation of the in-plane size and intra-plane defect density along the annealing pathway. It is proposed that the NPC skeleton evolves along the annealing pathway in two stages: below 1600 °C it was dominated by a reduction of in-plane defects with a minor crystallite growth, and above this temperature growth of the crystallites accelerates as the in-plane defect density approaches zero. A significant amount of transpolyacetylene (TPA)-like structures was found to be remaining even at 2400 °C. These may be responsible for resistance to further graphitization of the PFA-based carbon at higher temperatures

Competition of Desolvation and Stabilization of Organic Electrolytes in Extremely Narrow Nanopores

Organic electrolytes are widely used for electric double-layer capacitors. However, the molecular mechanism involved is far from being understood. We demonstrate the structures and stabilities of tetraethylammonium and tetrafluoroborate ions in propylene carbonate solution in carbon nanopores using Monte Carlo simulations. These ions were significantly desolvated at nanopore widths below 1.0 nm. The nanopore potential compensated for the loss of stability of the ions as a result of desolvation for nanopore widths of 0.7–1.2 nm for Et₄N⁺ and 0.6–0.9 nm for BF₄^–. High-capacitance electrodes can therefore be obtained using such nanoporous carbons

Facilitation of Water Penetration through Zero-Dimensional Gates on Rolled-up Graphene by Cluster–Chain–Cluster Transformations

We demonstrate a water penetration mechanism through zero-dimensional nanogates of a single-walled carbon nanohorn. Water vapor adsorption via the nanogates is delayed in the initial adsorption stage but then proceeds at a certain rate. The mechanism is proposed to be a water cluster–chain–cluster transformation via the nanogates. The growth of water clusters in internal nanospaces facilitates water penetration into these nanospaces, providing an intrinsic mechanism for zero-dimensional water

Effect of Pretreatment Conditions on the Precise Nanoporosity of Graphene Oxide

Nanoscale pores in graphene oxide (GO) control various important functions. The nanoporosity of GO is sensitive to low-temperature heating. Therefore, it is important to carefully process GO and GO-based materials to achieve superior functions. Optimum pretreatment conditions, such as the pre-evacuation temperature and time, are important during gas adsorption in GO to obtain accurate pore structure information. This study demonstrated that the pre-evacuation temperature and time for gas adsorption in GO must be approximately 333–353 K and 4 h, respectively, to avoid the irreversible alteration of nanoporosity. In situ temperature-dependent Fourier-transform infrared spectra and thermogravimetric analysis–mass spectrometry suggested significant structural changes in GO above the pre-evacuation temperature (353 K) through the desorption of “physically adsorbed water” and decomposition of unstable surface functional groups. The nanoporosity of GO significantly changed above the aforementioned pre-evacuation temperature and time. Thus, standard pretreatment is indispensable for understanding the intrinsic interface properties of GO

Rapid Water Transportation through Narrow One-Dimensional Channels by Restricted Hydrogen Bonds

Water plays an important role in controlling chemical reactions and bioactivities. For example, water transportation through water channels in a biomembrane is a key factor in bioactivities. However, molecular-level mechanisms of water transportation are as yet unknown. Here, we investigate water transportation through narrow and wide one-dimensional (1D) channels on the basis of water-vapor adsorption rates and those determined by molecular dynamics simulations. We observed that water in narrow 1D channels was transported 3–5 times faster than that in wide 1D channels, although the narrow 1D channels provide fewer free nanospaces for water transportation. This rapid transportation is attributed to the formation of fewer hydrogen bonds between water molecules adsorbed in narrow 1D channels. The water-transportation mechanism provides the possibility of rapid communication through 1D channels and will be useful in controlling reactions and activities in water systems

Cooperative Adsorption of Supercritical CH₄ in Single-Walled Carbon Nanohorns for Compensation of Nanopore Potential

High-density CH₄ storage using adsorption techniques is an important issue in the use of CH₄ as a clean energy source. The CH₄ adsorption mechanism has to be understood to enable innovative improvements in CH₄ adsorption storage. Here, we describe the adsorption mechanism, based on CH₄ structure, and stabilities in the internal and external nanopores of single-walled carbon nanohorns, which have wide and narrow diameters, respectively. The adsorption of larger amounts of CH₄ in the narrow nanopores at pressures lower than 3 MPa was the result of strong adsorption potential fields; in contrast, the wider nanopores achieve higher-density adsorption above 3 MPa, despite the relatively weak adsorption potential fields. In the wider nanopores, CH₄ molecules were stabilized by trimer formation. Formation of CH₄ clusters therefore compensates for the weak potential fields in the wider nanopores and enables high-density adsorption and adsorption of large amounts of CH₄

Formation and Properties of Selenium Double-Helices inside Double-Wall Carbon Nanotubes: Experiment and Theory

We report the production of covalently bonded selenium double-helices within the narrow cavity inside double-wall carbon nanotubes. The double-helix structure, characterized by high-resolution transmission electron microscopy and X-ray diffraction, is completely different from the bulk atomic arrangement and may be considered a new structural phase of Se. Supporting <i>ab initio</i> calculations indicate that the observed encapsulated Se double-helices are radially compressed and have formed from free Se atoms or short chains contained inside carbon nanotubes. The calculated electronic structure of Se double-helices is very different from the bulk system, indicating the possibility to develop a new branch of Se chemistry

Essential Role of Viscosity of SWCNT Inks in Homogeneous Conducting Film Formation

Newly developed inorganic single-wall carbon nanotube (SWCNT) inks of the Zn/Al complex and colloidal silica give a quite homogeneous SWCNT film on the polyethylene terephthalate (PET) substrate by the bar-coating method, whereas the surfactant-based SWCNT inks of sodium dodecyl sulfonate (SDS) and sodium dodecyl benzene sulfonate (SDBS) cannot give a homogeneous film. The key properties of SWCNT inks were studied for the production of homogeneous SWCNT films. The contact angle and surface tension of the inorganic dispersant-based SWCNT inks were 70° and 72 mN m^–1, respectively, being close to those of water (71.5° and 71 mN m^–1). The viscosity was significantly higher than that of water (0.90 mPa·s), consequently, providing sufficient wettability, spreadability, and slow drying of the ink on the substrate, leading to homogeneous film formation. On the other hand, the surfactant dispersant-aided SWCNT inks have the contact angle and surface tension twice lower than the inorganic dispersant-based SWCNT inks, guaranteeing better wettability and spreadability than the inorganic dispersant-based inks. However, the small viscosity close to that of water induces a heterogeneous flow of SWCNT ink on rapid drying, leading to inhomogeneous film formation

High-Pressure Methane Storage in Porous Materials: Are Carbon Materials in the Pole Position?

Natural gas storage on porous materials (ANG) is a promising alternative to conventional on-board compressed (CNG) or liquefied natural gas (LNG). To date, Metal–organic framework (MOF) materials have apparently been the only system published in the literature that is able to reach the new Department of Energy (DOE) value of 263 cm³ (STP: 273.15 K, 1 atm)/cm³; however, this value was obtained by using the ideal single-crystal density to calculate the volumetric capacity. Here, we prove experimentally, and for the first time, that properly designed activated carbon materials can really achieve the new DOE value while avoiding the additional drawback usually associated with MOF materials (i.e., the low mechanical stability under pressure (conforming), which is required for any practical application)

Distorted Graphene Sheet Structure-Derived Latent Nanoporosity

High surface area graphene monoliths consist mainly of single graphene layers wider than 10 nm. The interlayer porosity of high temperature treated nanoporous graphene monoliths with tuned intergraphene layer structures is evaluated by hybrid analysis of Ar adsorption at 87 K, N₂ adsorption at 77 K, high resolution transmission electron microscopic observation, and small-angle X-ray scattering (SAXS) measurements. SAXS analysis results in surface areas that are 1.4 and 4.5 times larger than those evaluated by Ar adsorption for graphene monoliths nontreated and treated at 2273 K, respectively. A distorted graphene sheet structure model is proposed for the high surface area graphene monoliths on the basis of the hybrid analysis