In this thesis, graphite-like C 3 N 4 nanomaterials (g-C 3 N 4 ) were synthesized from two inexpensive and available precursors, viz. , urea and thiourea, through the calcination method in an electrical furnace. The prepared materials were characterized using FT-IR, FE-SEM, BET, AFM, XRD, solid-state UV, and zeta potential methods. The results showed that g-C 3 N 4 nanomaterials were successfully synthesized. In the next step, g-C 3 N 4 nanomaterials were metal-doped by four transition metal salts of iron (III), ruthenium (III), cobalt (II), and nickel (II). The obtained products ( i.e., X@g-C 3 N 4 ( X = Fe, Ru, Co, and Ni)) were also characterized using FT-IR, FE-SEM, solid-state UV, ICP, EDX, BET, and zeta potential methods. The results showed that the immobilization process of metal salts on the g-C 3 N 4 surface were successfully done. In addition, the photocatalytic activity of g-C 3 N 4 obtained from two precursors urea and thiourea, as metal-free photocatalysts, and X@g-C 3 N 4 (X = Fe, Ru, Co, and Ni) samples, as metallated photocatalysts, on the photodegradation of Sky Blue and Youhao reactive K2BP pigments was investigated under visible light in aqueous solutions. The progress of the reactions was monitored by UV-Vis spectrophotometer. The results demonstrated the proper efficiency of the prepared nanomaterials in the photocatalytic degradation of organic pigments. The results also showed that the g-C 3 N 4 ample obtained from precursor urea and its metallated forms, X@g-C 3 N 4 (X = Fe, Ru, Co, and Ni) have better efficiency and higher reaction rate in the photocatalytic degradation of organic pigments in comparison to those obtained from another precursor, thiourea. Consequently, these nanomaterials were used to optimize the effective factors of the photocatalytic degradation of Rhodamine B dye under the visible light. The optimized factors are including photocatalyst quantity, concentration of the colored solution, and pH. Finally, the amounts of the photocatalyst and concentration of the colored solution were optimized at 0.015 g and 5 ppm, respectively. The optimal pH of the colored solution for the photocatalysts g-C 3 N 4 and X@g-C 3 N 4 (X = Ru, Co, and Ni) was obtained at an acidic range (pH = 3) and forFe@g-C 3 N 4 was obtained at a neutral range (pH = 7). The kinetic study of the photocatalytic degradation reactions of Rhodamine B showed that all the degradation reactions are first-order. In addition, the renewability of the photocatalysts were investigated in four successive cycles in the optimal conditions of each photocatalyst. The results showed that at the end of forth cycle, the amount of dye decomposed by the recycled photocatalysts was approximately the same as the fresh photocatalysts. This indicates the stability of the prepared photocatalysts in the reaction mixture. Finally, the photocatalytic activity of C 3 N 4 and X@g-C 3 N 4 by prepared from urea precursor was investigated for the photocatalytic degradation of Rhodamine B under sunlight. The results showed that these photocatalysts have an efficient photocatalytic activity under the sunlight exposure.