Exfoliated g-C3N4 materials were prepared by thermal treatment of bulk materials synthesized from melamine at 4 different temperatures in range from 500 to 600 degrees C. The exfoliated g-C3N4 synergically increased the photo catalytic degradation of phenol as effects like the fast production of H2O2, the presence of more active holes for direct phenol degradation and the use of high-power visible (416 nm) LEDs as irradiation source. The amount of phenol initially present was 99% converted in 15 min. All materials were also tested for comparison only in UVA region by using high-power UV (370 nm) LEDs. All prepared materials were thoroughly characterized by several analytical methods. In this work, the combination of g-C3N4 after thermal treatment and high-power visible LEDs reduced the time needed for complete phenol degradation from several hours to just a few minutes. The mechanism of phenol degradation was also studied by introducing different active species scavengers into the reaction medium.