∆H reaction = H P roducts -H Reactants (11) Our results are presented in table together with the HOMO-LUMO gap in the singlet state before and after the addition of one water molecule. Again the energies and free energies of adsorption in the triplet state are more negative than in the singlet state which is reflected in the total energy. Hydration is driven by the enthalpy change modulated by a substantial negative entropy contribution. Since DFT is a ground state theory, calculations of the HOMP-LUMO gaps using this theory are subject to errors that are well known, but our calculations using DFT should depict the trends in the HOMO-LUMO gap when the zinc oxide trimer is adsorbed on graphene or the functional groups of the GO models. The gap is substantially reduced from 4.42ev for the bare Zinc oxide trimer to 1.21,1.16 and 1.48 eV respectively for the Zinc oxide trimer on GO2, GO3, and GO5, suggesting that GO models will be sensitive to light and electron promotion in the visible region.