Improved charge separation and transport with l-aspartic acid derived carbon-doped g-C3N4 for efficient visible-light photocatalytic H2 production

Abstract

In recent years, polymeric graphitic carbon nitride (g-C₃N₄ termed as CN) has emerged as a favorable candidate for solar energy conversion. However, its practical applications are limited due to rapid charge carrier recombination and poor visible-light absorption response. In this study, we report a simple one-step annealing strategy employing urea and L-aspartic acid (LAA) as precursors to prepare a series of carbon (C)-doped CN denoted as CCN-X, where X represents the nominal weight of LAA (X = 1, 4, 8, 12, and 16 mg). The results show that the introduction of C-atoms onto CN effectively improves visible-light absorption, narrows bandgap energy, and promotes the separation and transport of photogenerated electron–hole (e⁻/h⁺) pairs, culminating in a significantly higher photocatalytic hydrogen (H₂) production from water splitting. The optimal CCN-8 sample achieves a maximum H₂ production rate of 2192.2 μmol h⁻¹ g⁻¹ under visible light (λ ≥ 420 nm), which is 6.6 times higher than that of pristine CN (333.0 μmol h⁻¹ g⁻¹). Additionally, the CCN-8 sample shows an apparent quantum efficiency (AQE) of 6.57% at 420 nm and outstanding photocatalytic stability of 16 hours during recycling tests. The doping of C-atoms into CN speeds up the transfer of holes (h⁺) to triethanolamine (TEOA) and electrons (e⁻) to a Pt cocatalyst, thus augmenting the visible-light photocatalytic H₂ production from water splitting. This work provides a promising strategy for employing elemental doping to enhance semiconductor photocatalysts for efficient solar-driven H₂ production.