Hydrogen production by semiconductor photocatalysis using abundant sunlight and water is an ideal method to address the globe energy and environment issues. Here, we present a facile synthesis of bromine doped graphitic carbon nitride (g-C3N4) photocatalysts for hydrogen evolution with visible light irradiation. Bromine modification is shown to enhance the optical, conductive and photocatalytic properties of g-C3N4, while still keeping the poly-tri-s(triazine) core structure as the main building blocks of the materials. This modification method can be generally applicable to several precursors of g-C3N4, including urea, dicyandiamide, ammonium thiocyanide, and thiourea. The optimal sample CNU-Br-0.1 shows more than two times higher H-2 evolution rates than pure CNU sample under visible light irradiation, with high stability during the prolonged photocatalytic operation. Results also found that the photocatalytic O-2 evolution activity of CNU-Br-0.1 was promoted when the sample was subjected to surface kinetic promotion by loading with cobalt oxide as a cocatalyst. This study affords us a feasible modification pathway to rationally design and synthesize g-C3N4 based photocatalysts for a variety of advanced applications, including CO2 photofixation, organic photosynthesis and environmental remediation. (C) 2016 Elsevier B.V. All rights reserved.