Etna ash-derived photocatalysts for the solar H₂ production

Volcanic ash formed by eruptions of Mount Etna is classified as special waste in eastern Sicily , causing environmental and management issues. In this work, Etna ash-derived materials were investigated for the first time as sustainable photocatalysts for solar-driven hydrogen production. The ash was modified through a combined chemical treatment and microwave-assisted crystallization approach (70°C, 2 h, 5° C/min heating ramp)avoiding conventional high-temperature calcination routes and thus reducing the overall energy demand of the synthesis process. In this way the chemical composition of the etna ash was modified, with an increase of the Ti/Fe wt ratio from 0.1 to 0.9 that promoted the photocatalytic perfomance with the contentuxtual removal of the alkaline metal oxides present in the bare ash. The obtained material was evaluated both as a bare photocatalyst and as a support for a Nb₂O₅/graphitic carbon nitride composite (50:50 ratio) synthesized via a hydrothermal method. The modified Etna ash photocatalyst achieved a solar H₂ production rate of 920 μmol gcat⁻¹ h⁻¹ during triethanolamine (TEOA) photoreforming experiments. After incorporation of the Nb-based composite, the hydrogen evolution rate increased by approximately 2.5 times, reaching 2370.5 μmol gcat⁻¹ h⁻¹, highlighting a pronounced synergistic interaction between the support and the active phases. Remarkably, all the developed photocatalysts largely outperformed commercial P25 TiO2, which exhibited only 25 μmol gcat⁻¹ h⁻¹ under the same experimental conditions.The enhanced photocatalytic performance was attributed to the structural and textural modifications induced in the ash, including increased porosity and partial reorganization of the aluminosilicate framework, which promoted a more favorable dispersion of photocatalytically active TiO₂ and iron oxide species. Furthermore, the Nb₂O₅/g-C₃N₄ composite supported on modified Etna ash demonstrated excellent stability over six consecutive photocatalytic cycles without significant activity loss. These findings demonstrate a sustainable strategy for valorizing volcanic waste into efficient multifunctional photocatalysts for solar H₂ production.