Engineering the surface chemistry of carbon-based materials is of crucial importance in tuning their intrinsic properties, including electrical conductivity, wettability, electroactivity, adsorption potential, reactivity, physical and chemical stability. Intense research has recently focused on understanding the role of surface oxygen functional groups when carbon materials are in contact with an electrolyte or solvent in order to tailor and improve them for technological applications. For this purpose, their synthesis method and/or further oxidation treatments should be carefully selected, since they can substantially influence not only the oxygen content, but also the nature of the oxygen moieties, which could be decisive in determining the surface properties of the resulting material. The combined use of different chemical, spectroscopic and electrochemical techniques, provides unique and reliable information about the contribution of a specific oxygen-containing group in the surface (electro)chemistry of carbon-based materials. This paper provides a discussion of the role of oxygen heteroatoms in the surface electrochemistry of a carbon material as they relate to their influence on both its electroactivity and reactivity.

We performed dispersion-corrected density functional theory (DFT) calculations to investigate the energetically stable structures of armchair (m,m) carbon nanotubes containing π-conjugated molecules, such as methyl-terminated thiophene oligomers, p,p′-dimethyaminonitorostilbene (DANS) molecules, and triiodobenzene. The stability of such tube-based host-guest structures was analyzed by using their stabilization energy, which consisted of three terms. These analyses found that the long-range interaction energy between guest and a host, mainly originating from π–π and CH–π interactions, and the deformation energy of the guest molecule are what mostly control the stability of the tube-based host-guest structures considered in this paper. The long-range interactions mainly cause nanospace confinement effects in tube-based host-guest structures. To strengthen the long-range attraction interactions, a π-conjugated molecule and its aggregates inside a tube are substantially deformed, which costs energy compared to the corresponding optimized structures without surrounding tubes. Accordingly, we found a substantial impact of nanotube confinement in determining the structure of a guest and its aggregates. These structures play a dominant role in electronic properties (e.g. optoelectronic properties in thiophene oligomers and nonlinear second-order nonlinear properties in DANS molecules), and therefore nanospace confinement effects can be used to change the electronic properties of π-conjugated molecules inside a nanotube by changing its diameter.

Because the chemical features of carbon materials strongly depend on the number and the type of edge sites, it is crucial to analyze them in order to understand their performance at the molecular level. For the analysis of carbon edge sites, temperature programmed desorption (TPD) has often been used, because it is simple but effective. Recently, a new type of TPD apparatus was developed by our group which can reach a TPD temperature as high as 1800 °C and has a very high sensitivity for the detection of desorbed gases, thereby enabling an analysis of all edge sites for various types of carbon materials, even natural graphite. Such a thorough analysis has helped with the discovery of many new findings on the structure of high-temperature treated carbons and a molecular-level understanding of a carbon/rubber interface, electrochemical degradation and catalysis in cellulose hydrolysis.

A suspension of microalgae (Spirulina or Chlorella) biomass powder, a terephthalaldehyde condensation accelerator, and Mg pre-templates (MgCl₂, Mg(OAc)₂, Mg(OH)₂, or mixtures with MgO) in water was hydrothermally reacted at 220 °C for 14 h in an autoclave. The MgCl₂ additive changed the reaction solution pH to acidic, reducing the yield of the insoluble hydrothermal product. In contrast, Mg(OAc)₂, Mg(OH)₂, and the MgO mixture retained the pH of the solution as neutral to weakly alkaline, producing a large amount of non-porous hydrothermal carbon. After or before removal of the Mg template by acid washing, the particulate hydrothermal carbons were carbonized by heating from room temperature around 25 °C to 900 °C under an Ar atmosphere. The resulting Mg-free algal carbonized materials were N-containing porous carbons with specific surface areas ranging from 200–1500 m²/g, mesopore/total pore volume ratios ranging from 0.6 to 0.9, and electrochemical capacitances in the range of 150–320 F/g at 0.1 A/g in 1M H₂SO₄.

As a simple post-synthesis approach for the mesopore-size control of nanoporous carbons, we propose mechanical pressing of soft carbons at 600 °C, i.e. hot pressing. Although conventional nanoporous carbons are mechanically hard and brittle, a carbon mesosponge (CMS), which is primarily composed of randomly arranged graphene walls, is exceptionally soft with a record low bulk modulus of 0.084 GPa for a solid carbon material. As a result, its mesopores with an average size of 7.36 nm, can be made smaller by applying a small mechanical pressure of only 10 MPa. Interestingly, the specific surface area and pore volume of the CMS increase when a small mechanical pressure (<20 MPa) is applied. This is attributed to the exfoliation of weakly stacked graphene structures generated during CMS synthesis. Moreover, the average mesopore size of the CMS can be finely changed to be as small as 2.14 nm using a carefully adjusted mechanical pressure. We report structural changes that occur during the hot pressing of a CMS, focusing on its crystallinity, graphene edge sites, and framework flexibility. Although the CMS framework hardens on application of a mechanical force, it still retains its low bulk modulus. Thus, the hot pressing of CMS provides a simple method for fabricating soft and elastic mesoporous carbons with controllable mesopore sizes between 2.14 and 7.36 nm.

Despite great efforts to achieve ideal atomistic packing of carbon in the pore networks of even the largest pore zeolites, templating inaccuracies are ubiquitous in all presently synthesized zeolite-templated carbon (ZTC) materials. Idealized models suggest that the long-sought schwarzite-like structures could in principle be obtained by zeolite templating if the appropriate zeolite template were chosen (e.g., faujasite for D surface schwarzites) and if perfect template fidelity (insertion of a pristine layer of pure carbon directly on the surface of the zeolite) could be achieved. A requirement to achieve such structures is increased carbon density within the zeolite. We report the investigation of a series of alkali metal cation-exchanged zeolites to determine how the periodic trends in the group 1 elements influence zeolite templating, with a specific focus on the metric of structural packing density (SPD) as resolved by ex situ thermogravimetry. In a survey based on controlled synthesis temperature, time, and flow conditions, an increasing SPD was observed with decreasing cation size, an effect that is consistent with the increasing strength of cation-π interactions. This effect could be promising for future work to increase the SPD of ZTCs for the synthesis of closed-tube, schwarzite-like carbonaceous solids.

Zeolite-templated carbon (ZTC) is a unique porous carbonaceous material whose structure is ordered at the nanometre scale, enabling a representative periodic description at the atomistic level. Utilizing an existing, well-defined reference model for ZTCs, a structural library of varying compositions was developed by refinement using density-functional tight-binding (DFTB) potentials parameterized for materials science applications. We first determined the quantum chemical-refined structures of models with CH, CHO, CHON, CHOB, and CHOBN compositions with various degrees of heteroatom substitution. These structural models comprise the characteristic morphological features of highly porous carbon materials, such as open-blade surfaces, edges, saddles, and closed-strut formations, spanning a range of curvatures and characteristic sizes. Second, we carried out alternating compression and expansion of the CHO model unit cell to determine the lowest energy structure as well as to obtain its bulk modulus in order to demonstrate a close connection between macroscopic observations and atomic-scale structures. The agreement between experimental measurements and the computational model is remarkable and demonstrates the power of approximate density functional theory as a cost-effective computational tool with chemical accuracy for the investigation of structure/property relationships in real-world carbon-based solids.