S-doped meso/macroporous g-C3N4 spheres (SMCN) were successfully synthesized via an in situ novel method utilizing millimeter-scale porous silica spheres as template and thiourea as precursor and S source. Such SMCN possessed millimeter-scale spherical morphology with continuous channels at 20-80 nm in the interior of the spheres, and exhibited increased H-2 generation rate (15 times) and phenol degradation rate (5 times) under visible light irradiation compared with that over pristine g-C3N4, mainly due to the enlarged surface area, enhanced mass transfer and improved efficiency of charges separation all stemming from the synergetic effects of the S doping and pore creating. Notably, density functional theory (DFT) calculations were employed to further understand the mechanism of the photocatalytic enhancement with regard to the optical absorption property at atomic level. Combined with the finite difference time domain (FDTD) simulations aiming at evaluating the effect of the nanoscale pore architecture on the optical absorption ability, it was revealed that not only the S doping but also the meso/macroporous structure resulted in the enhancement of the optical absorption, which was considered to be an essential role for the enhanced photocatalytic performances over SMCN. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.