Fig. 4

Schematic of changes in OC300 or OC500 nanostructures. a raw Japanese oak wood, b, c freshly synthesized OC300 or OC500, and b’ and c’ OC300 or OC500 kept in air for a long period after synthesis. Small blue filled circles: OH groups in bulk of solid, small blue open circles: free OH groups on surface, small red open circles: hydrogen-bonded OH groups on surface, large light-blue filled circles: water molecules moved from outside, and large purple filled circles: water molecules produced by pyrolysis of wood constituents