Graphitic carbon nitride electronic structure evolution caused by niacin-derived carbon bridging benefits for Na+ adsorption to enhance the photocatalytic H2 production from artificial seawater splitting

Abstract

Photocatalytic hydrogen evolution from seawater splitting was a sustainable energy technology, alleviating the overuse of limited freshwater resources. The exogenous carbon was successfully doped into the framework of graphite carbon nitride via ultrasonic peeling and secondary calcination, replacing the bridging N atoms within the heptazine skeleton. This approach effectively regulated the chemical structure of g-C₃N₄, and the photocatalytic hydrogen yield of as-prepared CN-NA45 in water reached 7.15 mmolg⁻¹h⁻¹. In artificial seawater, the hydrogen yield of CN-NA45 increased to 10.80 mmolg⁻¹h⁻¹, which was attributed to the larger specific surface area, reduced band gap and more negative band edge. The presence of bridging carbon facilitated the transfer of electrons from the heptazine ring to the region near the bridging position, enhancing the local delocalization of π electrons. In artificial seawater, the adsorption of Na⁺ ions on the catalyst surface were superior to other ions, facilitating the electron enrichment and providing more electrons for the photocatalytic reduction reaction. This work provided an insight into the construction of photocatalytic materials for marine environmental applications and the impact of electrolyte ions on hydrogen evolution performance.