We first studied how (ZnO) 3 is absorbed on the graphene sheet in both the parallel and vertical directions followed by adsorption on the GO models. Since determining the exact structure of synthetic GOs is difficult, we modeled the GO surfaces by adding functionality to the optimized graphene sheet using carboxyl, hydroxyl, and epoxy groups similar to the study by Huang and Gubbins. The graphene sheet was computed following the periodic boundary conditions (PBC) explained in the Gaussian tutorial using a benzene ring. A numbered graphene layer of 30 C atom layer is shown in Figure1. We introduced the required functional groups to C atoms 21, 10, 8, and 11 to produce different GO models. We then studied the adsorption of (ZnO) 3 on the graphene sheet and on the functional groups of the GO model systems already attached to the graphene sheets. The optimized (ZnO) 3 is shown in the figure2. All the above structures were optimized using the Becke-Lee-Yang-Parr (B3LYP) exchangecorrelation functional and DGDZVP2 Dunning basis set using DFT. The calculation method and specific ZnO cluster system were chosen based on our previous benchmark and basis set studies of small ZnO nanoclusters. We recall that the exchange functional/basis set combination was chosen by us as the best of 30 such combinations of exchange functionals and basis sets and the optimal size of the (ZnO) n was chosen as n=3 for the best match energy singlet-triplet energy gap with n= 6 as an alternative. We used only n=3 nanocluster and calculated the binding energy of (ZnO) 3 on graphene and on the functional groups of each GO model using the same level of theory considering the complexity and the computational time for n=6 clusters. We also calculated and compared the geometric properties, and the free energy and enthalpy changes that accompanied (ZnO) 3 adsorption. To each optimized graphene-(ZnO) 3 and GO-(ZnO) 3 models, we introduced one water molecule to study not only the corresponding binding energy but other properties such as Mulliken charges and changes in the bond length of atoms in (ZnO) 3 . The hydration and hydrolysis reaction on the selected systems was continued using the second water molecule. We used the hydrolyzed products of the GO1-(ZnO) 3 to study the reaction pathway of H 2 and O 2 production.