Nb₂O₅/g-C₃N₄ Composite Photocatalysts Supported on Etna-Derived Aluminosilicate for Solar H₂ Production

In this work, Etna ash-derived photocatalysts were investigated for the first time for solar H₂ production. Volcanic ash, commonly treated as a special waste in eastern Sicily (Italy), was modified through chemical treatment followed by microwave-assisted crystallization, avoiding the conventional high-temperature thermal route. The obtained material was tested both as a bare photocatalyst and as a support for a Nb₂O₅/graphitic carbon nitride composite prepared by a hydrothermal method. The Etna-derived photocatalyst exhibited a solar H₂ production rate (by TEOA photoreforming) of 920 μmol/g_cat∙h. Upon incorporation of the Nb-based composite, the H₂ evolution rate increased by about 2.5 times, reaching 2370.5 μmol/gcat∙h, demonstrating a strong synergistic effect. Notably, the developed materials largely outperformed commercial TiO₂ P25 (25 μmol/g_cat∙h). The enhanced photocatalytic activity was attributed to the tailored modifications of Etna ash, which increased porosity and promoted aluminosilicate framework reorganization, favoring an optimal distribution of the photocatalytically active TiO₂ and iron oxide phases. The obtained Nb oxide/carbon nitride supported on modified Etna ash also showed a remarkable stability after six consecutive runs of solar photocatalytic H₂ production. This work demonstrates a sustainable strategy for converting volcanic waste into efficient multifunctional photocatalysts while minimizing the use of critical raw materials.