In recent years graphitic carbon nitride ( g-C₃N₄) has been considered the most popular candidate for replacing graphene and other similar materials in various applications. The g-C₃N₄ has unique electronic and mechanical properties, huge photoluminescence in the wide optical region, and promising properties in energy conversion and storage, water splitting, etc. Here we show a simple method of bulk g-C₃N₄ (BCN) synthesis using thermal polymerization of melamine and ultrathin 2D g-C₃N₄ nanosheets (NCN) prepared by ultrasonic exfoliation of BCN in water. The g-C₃N₄ samples were tested with XRD, FTIR, Raman, luminescence spectroscopy, and N₂ adsorption at 77 K. We characterize its photocatalytic properties in H₂ evolution by direct water splitting. We utilize the low-cost 10 W white LEDs photoreactor with visible light and flow conditions. In the water-splitting reaction, we found that the NCN were about 5 times more reactive than the primary BCN sample.