A comparative study of morphology, spectral and photocatalytic properties of graphene-like C3N4 samples prepared by liquid-phase exfoliation of the bulk (l-C3N4) and mechanochemically delaminated g-C3N4 (m-C3N4) was performed for the first time. It was established that the particles of the mechanochemically prepared m-C3N4 are predominantly monolayer whereas the particles of l-C3N4 possess few-layer morphology. It was shown that m-C3N4 exhibits higher photocatalytic activity in the photocatalytic hydrogen evolution from aqueous solution of lactic acid under AM1.5G irradiation due to monolayer morphology, higher reduction potential, as well as more efficient separation and transfer of the photogenerated charges. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.