In this work, the physical and chemical properties of the catalyst and reactants involved in the degradation of the acid orange 7 dye are studied to design new photocatalytic materials active and efficient under solar radiation. In the first section, the arguments that have contributed for building the selection criteria of an efficient photocatalyst are presented. These criteria are: a) the proposed materials have to exhibit an oxidation potential similar to the TiO2; b) the photo-generated charge carriers must reach the reactive sites; c) the charge carrier mobility plays an important role in the degradation reaction; d) the energy states generated by the impurities must be located at the energy bands edges; and at last e) the absorbance of visible radiation must be enough to generate the necessary amount of charge carriers to produce the HO● radicals. To tune the optical and electronic properties of the TiO2, based upon these criteria, the doping with two sets of atoms was performed: the main group elements C, N, S, and F and the transition metals Co, Fe, Ni, Pd, and Pt. The calculations were done using the solid state calculations – obtaining the electronic density of states and band structures – and using density functional theory – for the electronic and geometric description of the systems. C-TiO2 and S-TiO2 systems, within the first set, and Pd-TiO2 and Pt-TiO2, within the second, enhance the TiO2 photocatalytic properties. These system generate the least amount of unoccupied states within the energy band gap of the materials – both transition metals generate electronic states in the boundaries of the valence and conduction band and do not reduce the charge carrier mobility. Oxygen vacancies fill the empty states of the dopants and shift them towards to the valence band, “cleaning” the gap and reducing the recombination sites. Finally, the codoping of TiO2 was done using the best candidates of both element sets. The Pt-C-TiO2 codoped system is the most efficient according to the described rules. This codoped material introduces occupied states at the valence band edge, moreover in the (101) surface, the only unoccupied state of the dopant is mixed with the surface unoccupied TiO2 states.