  We have investigated ozone adsorption on graphene using the ab initio density
functional theory method. Ozone molecules adsorb on graphene basal plane with
binding energy of 0.25 eV, and the physisorbed molecule can chemically react
with graphene to form an epoxide group and an oxygen molecule. The activation
energy barrier from physisorption to chemisorption is 0.72 eV, and the
chemisorbed state has the binding energy of 0.33 eV. These binding energies and
energy barrier indicate that the ozone adsorption on graphene is gentle and
reversible. Atomic layer deposition experiment on ozone treated graphite has
confirmed the presence of uniform hydrophilic groups on graphene basal plane.
This finding can be applied to diverse chemical functionalization of graphene
basal planes.
