In this section, we present the results of our studies of graphene and 5 different GO models chosen as substrates for the ZnO photocatalyst. The top and side views of the optimized singlet state graphene structures are shown in Figure . The 5 GO models are obtained by attaching carboxyl, hydroxyl, and epoxy functional groups to the graphene layer, as shown in Table . The optimized ground state GO models are shown in Figure and the triplet state structures are displayed in the SI document. When a functional group is attached to a carbon atom (chosen as C21) in the graphene sheet in GO models 1-3, the electrons on the neighboring carbon atoms are unpaired to form a double-bond, the (π conjugated system) breaks and the unpaired carbon atoms become saturated with hydrogen atoms. The optimized energies and geometric properties of the GO models in both the singlet and triplet states are tabulated in the SI document.