Enhanced Hydrogen Evolution by Deep-Sea Marine Sediment Photocatalysts: Surface Modification with Bismuth Subnitrate

• Surface morphology composition synergy governs photocatalytic activity. • Deep-sea sediment morphology increases water microdroplet interface area. • Metallic minerals generate LSPR effects that enhance electron excitation. • Bi subnitrate donates electrons for faster HER; NO 3 − groups balance charge. • AL-6 microstructure offers highest water LSPR interface and HER rate. Deep-sea marine sediments are abundant natural materials rich in iron oxides, offering a sustainable platform for green hydrogen production through photocatalysis. In this study, deep sea marine sediment samples collected from various ocean depths were examined as photocatalysts for the hydrogen evolution reaction (HER). Surface morphology and chemical composition were characterized using XRD, SEM-EDX, and FTIR, revealing the presence of hematite and goethite as active mineral phases. To enhance photocatalytic performance, surface modification was conducted using bismuth subnitrate. The modified samples demonstrated improved hydrogen generation, attributed to enhanced charge separation and increased active surface sites. Among all samples, the AL-6 sediment modified with bismuth subnitrate exhibited the highest hydrogen evolution rate under UV-A irradiation, achieving 3873 µmol g⁻¹, which represents a 3.4-fold enhancement compared to the AL-13+BBN sample. This quantitative improvement underscores the critical role of the AL-6 microstructure and its synergistic interaction with bismuth species in promoting charge separation and catalytic efficiency providing a green and cost-effective approach for hydrogen production.