Freeze-dried dicyandiamide-derived g-C3N4 as an effective photocatalyst for H2 generation

Background: Hydrogen (H2) is viewed as a clean, green, and sustainable energy source. The photocatalytic H2 evolution using light-activated photocatalyst under light irradiation is attractive to convert light into chemical energy in a feasible way. In the present work, photocatalysis of H2 generation was explored, using graphitic carbon nitride (g-C3N4) synthesized from freeze-dried dicyandiamide (DICY). Methods: The DICY underwent rapid dissolution-recrystallization during the freeze-drying process, enabling more complete polymerization of the heptazine units of g-C3N4 than occurred in the same compound synthesized from untreated DICY. After loading with Pt as a cocatalyst, and under light irradiation (metal halide lamp) in the presence of triethanolamine, g-C3N4 synthesized from freeze-dried DICY (DCN) showed an increased H2 evolution rate (>> 20 mmol h-1) compared with that using g-C3N4 derived from untreated DICY (CN) (12 mmol h-1). In addition, DCN had a higher H2 generation rate than CN under light of different wavelengths (400, 450, and 550 nm). Significant Findings: The improved activity of DCN could be attributed to inhibition of charge recombination (evidenced by photoluminescence), fast charge transfer (evidenced by electrochemical impedance spectra and photocurrent measurements), and a suitable energy bandgap (evidenced by Mott-Schottky and UV-vis measurements) resulting from better-polymerized heptazine rings (evidenced by nuclear magnetic resonance spectroscopy). In summary, DCN prepared in this study could be used as a visible-light activated and effective metal-free material for photocatalytic H2 generation. (c) 2021 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.