Tuning Thermally Treated Graphitic Carbon Nitride for H 2 Evolution and CO 2 Photo-Reduction: The Effects of Materials Properties and Mid-Gap States Elton M. Dias † , Konstantinos C. Christoforidis †,¶ , Laia Franc` as ‡ and Camille Petit †,* † Barrer Centre, Department of Chemical Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, UK ‡ Department of Chemistry, Imperial College London, South Kensington Campus, London SW7 2AZ, UK ¶ Current address, Department of Environmental Engineering, Democritus University of Thrace, Xanthi, Greece ∗ E-mail: camille.petit@imperial.ac.uk, Phone: +44 (0)20 7594 3182 Graphitic carbon nitride (g-C 3 N 4 ) is regarded as an attractive pho- tocatalyst for solar fuels production, i.e. H 2 evolution and CO 2 photo-reduction. Yet, its structural, chemical and optoelectronic properties are very much dependent on the synthesis method and are likely to contribute differently whether H 2 evolution or CO 2 reduction is considered. Little is known about this aspect mak- ing it difficult to tailor g-C 3 N 4 structure and chemistry for a spe- cific photo-reaction. Herein, we create g-C 3 N 4 of varying chemical, structural and optical features by applying specific thermal treat- 1