Producing hydrogen from biomass and seawater using immobilized carbon nitride photocatalysts

• Carbon nitride-based photocatalyst has high potential for H₂ evolution under visible light. • Low-concentration saccharides are identified as alternatives for photocatalytic H₂ reforming. • H 2 evolution is shown to depend on the -OH groups present in electron donors. • Robust 3D-structured photocatalyst exhibits high stability for H 2 production from saccharides. • Significant potential of seawater in driving photocatalytic H 2 generation. To address the challenges related with using powdered catalysts and freshwater in photocatalytic hydrogen (H 2 ) production, this study explores the performance of carbon nitride-based catalyst immobilized on a 3D structure, employing seawater as a proton source. Methanol and saccharides such as cellobiose, fructose, glucose, saccharose and sorbitol were used as sacrificial agents to accelerate H 2 production via photoreforming. The results using immobilized photocatalyst showed that, at similar molar concentrations, glucose reveals higher efficiency compared with methanol, achieving an amount of H 2 evolution of 102 µmol after 180 min under visible light, compared to 45 µmol with methanol. Among the mono- and polysaccharides used, cellobiose has emerged as the most promising for H 2 evolution, achieving the highest amount of H 2 (124 µmol) after 180 min reaction. This result suggests a correlation between the efficiency of scavenging holes and the number of hydroxyl groups in the electron donor's structure. Despite a slight decrease in H₂ evolution compared with the powdered catalysts, the use of immobilized photocatalyst exhibited remarkable stability in both ultrapure water and seawater, maintaining its performance across multiple reuse cycles. The photocatalytic system demonstrated remarkable efficiency for H₂ production, avoiding phases separation processes, promotes the transition to continuous flow reactors and preserve freshwater resources.