In order to develop efficient visible light driven photocatalysts for environmental applications, novel polymeric g-C3N4 layered materials with high surface areas are synthesized efficiently from an oxygen-containing precursor by directly treating urea in air between 450 and 600 °C, without the assistance of a template for the first time. The as-prepared g-C3N4 materials with strong visible light absorption have a band gap around 2.7 eV. The crystallinity and specific surface areas of g-C3N4 increases simultaneously when the heating temperatures increases. The g-C3N4 materials are demonstrated to exhibit much higher visible light photocatalytic activity than that of C-doped TiO2 and g-C3N4 prepared from dicyanamide for the degradation of aqueous RhB. The large surface areas, layered structure and band structure in all contributed to the efficient visible light photocatalytic activity. The efficient synthesis method for g-C3N4 combined with efficient photocatalytic activity is of significant interest for environmental pollutants degradation and solar energy conversion in large scale applications.