The interaction of H2O, O2 and H2O + O2 molecules with g-C3N4 surface:A first-principle study

The interactions between H2O, O2, H2O + O2 and graphene carbon nitride (g-C3N4) surface were investigated by using first-principle method. The results indicated that the N atoms near the bridge sites and vacancies for g-C3N4 surface have high activity, which can promote the dissociation of water molecules and form hydrogen bonds after water and oxygen adsorption. The H2O and O2 molecules are not dissociated for only H2O or O2 molecules adsorption on g-C3N4 surface, and the hydrogen bonds are formed after H2O molecule adsorption. Two oxygen atoms of O2 molecule are bonded to carbon and nitrogen atoms of g-C3N4 surface respectively after O2 adsorption. There are two stable configurations for H2O + O2 co-adsorption on g-C3N4 surface (MA and MC), and their adsorption energies are −57.35 kJ/mol, −61.10 kJ/mol, respectively. For the MA, two oxygen atoms of O2 molecule are bonded to C and N atoms of g-C3N4 surface, respectively, and one hydrogen bond is formed between H2O and O2 molecules. As for the MC, three hydrogen bonds are formed in the interface of H2O + O2 and g-C3N4 surface. H2O molecule is dissociated, and O2 molecule turns to superoxide radical by gaining electrons. The formation of superoxide radical contributes to the degradation of organic pollutants for g-C3N4.