A highly active isotype graphitic carbon nitride (g-C3N4) derivatives were fabricated by a one-step thermal treatment with the aim to promote the charge separation. The molecular composite precursor melamine-urea, melamine-thiourea, and urea-thiourea were treated simultaneously under the same thermal conditions, in situ creating a novel heterojunction. Coupling of g-C3N4 with different electronic band structure precursor produces different isotype heterojunctions. Different characterizations were studied using Fourier transform infrared spectroscopy, X-ray diffraction, Field emission scanning electron microscopy, Transmission electron microscopy, X-ray photoelectron spectroscopy, photoluminescence spectroscopy and UV visible diffused reflectance spectroscopy. The prepared metal-free isotype heterojunction evidenced the separation of photoinduced charges, which promote the photocatalytic activity for degrading Methylene Blue (MB) under visible-light irradiation. The hetereojunction system shows 99% photodegradation for MB which is about 10% higher when compared to single precursor g g-C3N4 semiconductor. Moreover, photoactivity of the controlled bandgap design g-C3N4 composite semiconductors was greatly enhanced and possessed excellent stability even after four recycles. (C) 2017 Elsevier B.V. All rights reserved.