Fabrication of an NTO/Ag/g-C₃N₄ self-supporting membrane for efficient photocatalytic hydrogen production from seawater

Hydrogen is now a key focus in clean energy. Splitting seawater under sunlight to produce hydrogen by photocatalytic technology, which converts solar energy directly into hydrogen energy, is an absolute green hydrogen technology. This study prepared a Z-scheme ternary composite catalyst by loading Ag nanoparticles onto sodium titanate (Na₂Ti₃O₇, NTO) nanowires, and compounding NTO with graphite phase carbon nitride (g-C₃N₄) semiconductors to form heterojunctions. The catalyst was further fabricated into a self-supporting membrane, which provides a valuable exploration for the manufacturing of panel-type hydrogen production reactors, and enables large-scale photocatalytic hydrogen production. g-C₃N₄ was dissolved in NTO/Ag solution, followed by a hydrothermal reaction at 130^∘ C for 24 h to prepare TiO₂/Ag/g-C₃N₄. The hydrogen production efficiency of the TiO₂/Ag(2%)/g-C₃N₄ powder under visible light is approximately 365 μmol/(g·h). The short nanorod structure of TiO₂/Ag/g-C₃N₄ makes fabricating a self-supporting membrane of TiO₂/Ag/g-C₃N₄ difficult. P25 powder, Ag nanoparticles and g-C₃N₄ were added to a strongly alkaline NaOH solution, followed by a hydrothermal reaction at 130^∘ C for 24 h to prepare NTO/Ag/g-C₃N₄. The hydrogen production efficiency of the NTO/Ag(2%)/g-C₃N₄ powder under visible light is approximately 660 μmol/(g·h), and the hydrogen production efficiency of the NTO/Ag(5%)/g-C₃N₄ powder reaches 1168 μmol/(g·h), both of which are much higher than that of the TiO₂/Ag(2%)/g-C₃N₄ powder. The catalytic efficiency increases with the increase of the Ag content. After suction filtration and freeze-drying, a sturdy self-supporting membrane of NTO/Ag/ g-C₃N₄ was prepared. After the 3-hour hydrogen production reaction, the self-supporting membrane still maintains its original morphology, without hydrolysis or decomposition. The enhancement of the photocatalytic performance of NTO/Ag/g-C₃N₄ is mainly attributed to the construction of the Z-scheme multi-dimensional heterostructure, in which zero-dimensional Ag nanoparticles decorated on the surface of NTO nanowires not only act as electron mediators for the formation of Z-scheme between NTO and g-C₃N₄, but also provide hot electrons due to their plasma effect, while g-C₃N₄ is non-toxic, environmentally friendly, and possesses high visible light response capability, which improves both the visible light absorption range and intensity.