Metal-free graphitic carbon nitride (g-C3N4) shows tremendous potentials in energy and environmental domains. Nonetheless, amelioration on the crystal configuration, electronic structure and microstructure of g-C3N4 for high-performing visible-light photocatalysis is still challenging and anticipated. Here we report the development of chlorine (Cl) intercalated g-C3N4 via co-pyrolysis of melamine and excessive ammonium chloride (excessive is very pivotal). This protocol renders not only Cl intercalation in the interlayer of g-C3N4, but also a homogeneous porous structure, thereby endowing g-C3N4 with multiple superiority effects, including significantly promoted charge migration by establishing interlayer pathway, up-shifted conduction-band level, narrowed band gap as well as enhanced surface area. The as-prepared CI intercalated mesoporous g-C3N4 parades outstanding photocatalytic performance for water splitting into H-2, CO2 reduction, liquid and air contaminants removal. The most enhanced photocatalytic performance was obtained at Cl-C3N4-3 for H-2 evolution activity, which shows a 19.2-fold increase in contrast to pristine g-C3N4, accompanying with a high apparent quantum efficiency of 11.9% at 420 +/- 15 nm. Experimental and OFT calculations results co-disclose that the aforementioned advantageous factors account for the profoundly boosted photooxidation and photoreduction capabilities of g-C3N4 under visible light. The present work may furnish a bottom-up tactic for integrally advancing g-C3N4, and also hold huge promise to be extended to other layered materials for photochemical or photoelectrochemical applications. (C) 2016 Elsevier B.V. All rights reserved.