Effect of precursor on the solar photocatalytic production of hydrogen using C3N4

The production of hydrogen via photocatalytic water splitting with semiconductors is considered an eco-friendly alternative to reduce the use of traditional fossil fuels. Diverse photocatalytic semiconductors have been studied for water splitting, highlighting graphitic carbon nitride (C3N4) as one of the most promising due to its good characteristics of light harvesting and photocatalytic activity. In the present work, C3N4 photocatalysts were synthesized by thermal decomposition of different precursors, namely, urea, melamine and dicyandiamide. These materials were subsequently tested for hydrogen production under simulated solar light irradiation. For this purpose, triethanolamine, lactic acid or ethanol were selected as scavengers to improve hydrogen production. Using Pt as cocatalyst, all the scavengers yielded significant hydrogen production. The best results were obtained with the photocatalyst sample prepared from urea and using triethanolamine as a scavenger (810 µmol H2·gcat−1·h−1), while with lactic acid and ethanol, 427 and 114 µmol H2·gcat−1·h−1 were obtained respectively. This order of production, based on the scavenger used, was due to the reactivity of the hydroxyl groups present in the molecular structure and the adsorption capacity on the catalyst surface. Triethanolamine stood out due to its multiple reactive sites, maximizing the capture of photogenerated holes. Based on the band structure of the C3N4 and the radicals detection, it seems confirmed that the triethanolamine molecules consume the photo-generated holes from the valence band, thus improving the reduction of the water molecules by the photogenerated electrons located on the conduction band of C3N4. This semiconductor is postulated as a promising material for constructing novel photocatalysts, where not only the suitable band edge is a key factor for continuous hydrogen production, but also its electrochemical properties and its behavior when exposed to radiation need to be analyzed