Se-modified g-C3N4 was synthesized from sonicated aqueous suspensions of melamine cyanurate and SeO2. The different thermal condensation temperatures in the 500-650 degrees C range were found to influence the photophysical properties and hydrogen evolution rates. H-2 evolution increased dramatically by two orders of magnitude when Pt co-catalyst (1 wt.%) was incorporated, reaching an HER of 75 mu mol H-2/h. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.