After their discovery carbon nanotubes (CNTs) have attracted significant interest due to their outstanding mechanical properties and intrinsic optical and electronic properties. The chemical functionalization of CNTs has been investigated to reveal their chemical reactivity, to increase dispersibility, to add functionalities, etc. This review focuses on the structures and reactivities of single-walled carbon nanotubes (SWCNTs) and the methods of evaluating functionalized SWCNTs. A recent topic, the formation of SWCNTs quantum defects is described, focusing on our results.

This article reviews the influence of heteroatom doping and the formation of warped graphitic layers on the catalytic activity of carbons for the oxygen reduction reaction (ORR). The development of a non-platinum cathode catalyst is key for the practical use of polymer electrolyte fuel cells (PEFCs), and carbon-based ORR catalysts are receiving special attention. First, we consider studies on the enhanced ORR activity of carbons caused by heteroatom doping. The type of dopant has been extended to elements other than nitrogen, and to multi-element doping. Possible mechanisms elucidating the enhanced ORR activity caused by heteroatom doping are given. Second, we mention the influence of the presence of the warped graphitic layers, which we consider to be an important factor for ORR activity. Finally, we show that combinations of these two factors, namely heteroatom doping and the presence of the warped graphitic layers, can further enhance ORR activity.

Nitrogen-doped carbon materials show activity as a base catalyst and an oxygen reduction reaction (ORR) electro catalyst. The origin of the activity at the atomic level has not been known for a long time. Recently, the local electronic structure of nitrogen-doped carbon surfaces has been analyzed directly by scanning tunneling spectroscopy (STS), which clearly reveals specific electronic states such as edge states or non-bonding orbitals. Here, we summarize the current understanding of the activity of nitrogen-doped graphitic carbons and their electronic structures.

The conversion of cellulose to glucose is a major challenge in biorefinery. This paper summarizes our work on the hydrolysis of cellulose by carbon catalysts with weak acid sites. Among solid catalysts carbon materials show a unique good catalytic activity for this reaction. The ball-milling pretreatment of a mixture of cellulose and a carbon material produces tight solid-solid contact, leading to a remarkable improvement in the hydrolysis rate of solid cellulose. As a result, the reaction achieves an up-to 70% yield of cello-oligosaccharides in water and an 88% yield of glucose in a 0.012% HCl aqueous solution. We have also succeeded in the hydrolysis of a real woody biomass containing lignin. A carbon catalyst is prepared from the biomass itself and the spent catalyst can be regenerated by an air oxidation process with the unconverted lignin from the hydrolysis reaction, making a self-contained system. A mechanistic study shows that the carbon adsorbs cellulose by CH-π dispersive forces and hydrophobic interactions. Afterwards, surface weak acid sites hydrolyze the adsorbed cellulose, where neighboring oxygenated groups increase the frequency factor by making strong hydrogen bonds. Accordingly, the structural characteristics of carbon, a combination of polycyclic aromatics and multiple oxygenated groups, is remarkably suited for the hydrolysis of cellulose.

The effectiveness of a new technology for the efficient manufacture of activated carbon, which is based on alkali activation and is able to recover the consumed alkali activator by oxidants at the reaction site, has been demonstrated. The in situ regeneration of the consumed alkali activator is made by intermittently supplying water vapor to the reaction site. The amount of the alkali required is reduced to about 10% of that needed by conventional methods and the yield of activated carbon is improved by nearly 60% using the activation of coconut shell char as an example.

Non-graphitizable carbon (hard carbon; HC) is expected as one of the most promising negative electrode materials for sodium ion batteries (NIB) due to its high working voltage, large capacity and superior charge-discharge cyclability. Phosphorus is also a fascinating material for NIB because its theoretical capacity is one of the highest (over 2000 mAh g⁻¹). However, it is difficult to clarify the structures and states of sodium in these anode materials by diffraction methods because the materials are amorphous. In this research, multinuclear (²³Na and ³¹P) solid state nuclear magnetic resonance (NMR) is applied to investigate the states. Models of Na and Li storage in HC based on the calculated cluster structures were proposed, which elucidates why the adequate heat treatment temperature of HC for high-capacity sodium storage is higher than the temperature for lithium storage. The fully sodiated sample prepared at higher carbonization temperature shows a higher ²³Na NMR shift associated with Na clusters. A higher dehydration temperature of the precursor is favorable to form Na clusters with the higher shift, which implies that the HC pore structure is influenced by not only carbonization temperature but also the heat treatment process. Sodium-phosphorus compounds synthesized by thermal reaction or electrochemical sodiation were characterized using NMR. The Na and P NMR spectra reveal that sodiation and desodiation processes are reversible after the second cycle. During the sodiation and desodiation, Na₃P compounds and three amorphous compositions are observed.