Four different C3N4 specimens have been prepared, a bulk one (MCN), a thermally etched (MCN-TE), a solid prepared by hydrothermally treating MCN with H2O2 (MCN-H2O2) and a polymeric carbon nitride-hydrogen peroxide adduct (MCN-TE-H2O2). The principal aim of this work was to correlate the capability of the prepared material to generate reactive oxygen species (ROS), under irradiation, with their photocatalytic activities in terms of conversion and selectivity for partial oxidation reactions. Photoelectrochemical studies revealed that MCN-TE represented the best material in terms of photoconductivity, whereas MCN-H2O2 was defective and evidenced a poor mobility of carriers. EPR studies showed a maximum generation of reactive oxygen species irradiating the MCN-TE sample. The photocatalytic activity of these materials in the selective oxidation of three different alcohols to the corresponding aldehydes, both under UV and natural solar light, showed that the highest conversion was obtained in the presence of the MCN-TE sample, whereas the most selective one was MCN-TE-H2O2. Under solar light irradiation the performances of the powders were generally better than those under UV light. The characterization of the C3N4-based materials well justified their photocatalytic activity. The pristine C3N4 materials were more active but less selective than those prepared in the presence of H2O2.