大場 友則

Graphene is a fundamental unit of carbon materials and, thus, primary sp2-bonded carbon material. Graphene is, however, easily broken macroscopically despite high mechanical strength, although its natural degradation has rarely been considered. In this work, we evaluate the natural degradation of two-layer graphene in vacuo, in low-humidity air, and in high-humidity air at 300, 400, 450, and 500 K. Over 1000 days of degradation at 300 K, the graphene structure was highly maintained in vacuo, whereas the layer number of graphene tended to decrease in high- and low-humidity air. Water was slightly reacted/chemisorbed on graphene to form surface oxygen groups at 300 K. At 450 and 500 K, graphene was moderately volatilized in vacuo and was obviously oxidized in high- and low-humidity air. Surprisingly, the oxidation of graphene was more suppressed in the high-humidity air than in the low-humidity air, indicating that water worked as an anti-oxidizer of graphene by preventing the chemisorption of oxygen on the graphene surface.

BaTiO₃ nanocatalysts chemisorb and reduce CO₂ efficiently at 700 K and 0.1–1.0 MPa.

TiO2 anatase, which exhibits the highest catalytic performance, transforms to rutile at 800 K. To inhibit the transition of anatase to rutile, several strategies, such as metal and/or non-metal doping, oxygen enrichment, and surface coating, have been studied, resulting in stable anatase within 773-1273 K. However, highly stable anatase without dopants is still required. Here, a new approach, which involves the synthesis of anatase nanocatalysts in carbon nanotubes (CNTs), was proposed to inhibit the anatase-to-rutile transition. The nanocatalysts exhibited high thermal anatase stability along with a suppression of the crystal growth up to 1200 K. The highly stable anatase in CNTs also exhibited high photocatalytic activity, which was evaluated based on methylene blue decomposition under visible- and UV-light irradiation. This was attributed to the maintenance of the small crystal size of the nanocatalysts in addition to a synergetic effect between the TiO2 nanocatalysts and CNTs.

Low temperature CO₂ reduction and mechanism on BaTiO₃ nanocatalysts from 500 K, CO₂ physical adsorption at 300–500 K, CO₂ chemisorption above 450 K, CO₂ reduction at 500–850 K, and CO₂ and CO release above 800 K.