  We have studied the interaction of water and graphene doped with nitrogen in
different configurations, namely, graphitic and pyridinic nitrogen, by means of
the van der Waals density functional. We found that the local nitrogen
configuration plays a key role in determining the stable water configuration,
while the dispersion force is responsible for the water adsorption. With the
graphitic nitrogen, water prefers to orient with its oxygen toward the surface,
whereas for the pyridinic nitrogen it prefers to orient with its hydrogens
toward the surface, because nitrogen is positively and negatively charged for
the former and the latter, respectively. Our results have great implications
for the modeling of the interface between water and nitrogen-doped graphitic
systems.
