Transformation of CO2 into alcohol by using photocatalysts is one of the "green" methods to solve the environmental problem. In this study, to increase the activity, condition of Cu co-catalysts onto the substrate (Zn photocatalysts) were precisely controlled by obeying to relationship between the surface potential of substrate and the condition of metal complexes in solution by applying the metal complexes calculation using critical stability constants. By obeying to calculation results, Cu metal complexes with positively charged species, [(Cu2+)(MEA)2] and [(Cu2+)(MEA)3] and/or negatively charged species, [(Cu2+)(OH-)(cit3-)] monomer and dimmer, were stably synthesized. Absorption amount of Cu species was successfully controlled by using these solutions since surface potential of ZnO was negative. When the concentration of Cu in the solution was same, the difference of adsorption amount led the difference of the number of nuclear site of Cu particles. As a result, the size of co-catalysts in the case of MEA became smaller.