Novel nanoporous g-C3N4/MnTiO3 heterojunctions were synthesized by hydrothermal method using nanoporous g-C3N4 and nano-MnTiO3 as the raw materials. The effects of g-C3N4 content on phase, microstructure and photocatalytic activity for dye degradation were studied. Hydrothermal synthesized nanoporous g-C3N4/MnTiO3 (abbreviated as HS-CN/MT) exhibited facets coupling, well-structured heterojunctions with intimate interface, which displayed enhanced absorption intensity of visible light, as well as improved separation and migration efficiency of photogenerated carriers. The adsorption rate of HS-CN/MT for methylene blue gradually increased, while its photocatalytic degradation rate initially increased and subsequently decreased with increasing g-C3N4 content. HS-CN/MT with 65 wt% g-C3N4 presented the highest degradation rate constant of 0.0411 min(-1), which was up to 14.5, 2.4, and 3.9 times as high as that of bulk g-C3N4, nanoporous g-C3N4 and mechanical mixed nanoporous g-C3N4/MnTiO3. EIS spectra revealed that HS-65CN/MT exhibited the highest separation efficiency of hole-electron pairs. Active specie capture experiments proved that (OH)-O-center dot and O-center dot(2) were the main active species, which indicated the HS-CN/MT with significantly enhanced photocatalytic performance exhibited a direct Z-scheme heterojunction mechanism, because it retained higher oxidation and reduction potentials while preventing the electron-hole pairs recombination. These were essentially attributed to the intimate contact of nanoporous g-C3N4/MnTiO3 heterojunctions, which resulted from the synergistic effects of nanoporous adsorption and hydrothermal interaction. (c) 2017 Elsevier Ltd. All rights reserved.