The preparation methods for porous graphitic carbon materials have mostly employed a conventional two-step strategy, in which hydroxides act as the pore-forming agent and transition metal nitrates or chlorides as the graphitization catalyst. However, most of the reagents mentioned above are toxic and corrosive, and multi-step processes are time-consuming. In this work, a one-step strategy to synthesize porous graphitic g-C3N4-derived carbon materials was established, and its photocatalytic performance was studied. The g-C3N4 bulks were prepared by conventional thermal polycondensation approach from dicyandiamide. Potassium ferrate (K2FeO4) was utilized as both activating agent and catalyst to fulfil the synchronous carbonization and graphitization of g-C3N4, this method is less time-demanding, highly efficient and pollution-free, when compared with a conventional two-step strategy. The g-C3N4-derived carbon materials delivers not only significantly improved visible-light absorption but also greatly enhanced photocatalytic activity compared to pristine g-C3N4. The effect of g-C3N4-derived carbon materials with different graphitization temperature on the degradation of methyl orange (MO) solution under visible light was studied. The results indicate that the degradation rate of g-C3N4-derived carbon materials prepared at 700 ℃ is 12.4 mg/g. Photoelectrochemical measurements reveal that the porous graphitic samples exhibit improved carrier densities, charge separation, and photocurrent (a 5.4-fold increase) compared to that of the original g-C3N4. Consequently, this facile and versatile method could provide a promising and cost-effective approach to improve the absorption and photocatalysis performance of g-C3N4-derived carbonaceous materials.