CeO2-CuO composites prepared via supercritical antisolvent precipitation for photocatalytic hydrogen production from lactic acid aqueous solution

Abstract

The global increase in energy demand requires a continuous search for renewable and clean alternative resources to fossil fuels. Hydrogen is emerging as a promising energy carrier for the future; its production via photocatalysis, driven by sunlight, can directly convert solar energy into a usable or storable energy resource. However, water splitting requires sacrificial agents or electron donors/hole scavengers, such as short-chain organic acids. This research explores the use of lactic acid as a source for photocatalytic hydrogen production, offering valuable alternatives for wastewater management and renewable energy production. This study employed the innovative supercritical antisolvent (SAS) technique to micronize the precursors of both the active phase (CeO₂) and co-catalyst (CuO), ensuring rapid and complete solvent removal and size reduction of photocatalyst precursors. The prepared samples were characterized by field emission scanning electron microscopy (FESEM), Fourier transform infrared (FT-IR) spectroscopy, dynamic light scattering (DLS) analysis, Brunauer-Emmett-Teller (BET) analysis and thermogravimetric analysis (TGA). This study has shown that the micronization process resulted in a notable improvement in CeO₂ photocatalytic activity, attributed to the reduction of the dimensions of the powders. Hydrogen production was equal to 3989 μmol L⁻¹ for the SAS-produced photocatalyst while using a commercial CeO₂ sample resulted in H₂ production of 2519 μmol L⁻¹. The enhanced photoactivity of CeO₂-CuO composites was found to be related to the presence of CuO. The optimal CuO amount was equal to 0.5 wt%, determining a hydrogen production of 9313 μmol L⁻¹ after 4 h of UV irradiation time. A photocatalytic test carried out with deuterated water (D₂O) instead of distilled H₂O demonstrated that hydrogen was preferentially produced from water splitting reaction, whereas lactic acid acted as a sacrificial agent being oxidized from positive holes photogenerated in the valence band of CuO.