Single layer g-C3N4 could be obtained from a protonic acid treatment of g-C3N4 or a new sandwich like orientation growth of melamine. Through the self-assembly of melamine and polyacrylamide by hydrogen bonds and electrostatic interactions, g-C3N4, with extended planarized atomic single layer, exhibits superiority in both photocatalytic hydrogen evolution and photocatalytic degradation under visible light irradiation. Besides low efficiency, the acid exfoliation will destroy the delocalized pi-system by inducing O atoms. The decrease of conjugation degree increases the optical gaps, making it hard for g-C3N4 to capture photons. On the contrary, the facile sandwich-like orientation growth of melamine highly keeps the conjugation degree of g-C3N4 and extends its delocalized ir-system. Such single layer g-C3N4 is more active even better than N-doped TiO2 under visible light irradiation. (C) 2017 Elsevier B.V. All rights reserved.