Hollow porous carbon nitride nanotubes with efficient photocatalytic H2O2 generation in pure water

Abstract

Hydrogen peroxide (H<inf>2</inf>O<inf>2</inf>) is an important green oxidant. However, its industrial production remains energy-intensive and environmentally burdensome. Photocatalytic generation of H<inf>2</inf>O<inf>2</inf> from O<inf>2</inf> and water under visible-light irradiation is an attractive alternative, yet its efficiency is often limited by sluggish oxygen activation and severe charge recombination. Here, we report a triazine-based graphitic carbon nitride material featuring a hollow, porous nanotube morphology, synthesized via a straightforward, salt-free approach. This method produces a narrow mesopore size distribution without the use of templates or structure-directing agents. The resulting photocatalyst exhibits enhanced visible-light absorption, a high specific surface area, and restricted charge recombination. In comparison with a heptazine-based analogue, the triazine nanotubes exhibit stronger O<inf>2</inf> adsorption and a more negative conduction-band potential, thereby facilitating a thermodynamically more favorable reduction of O<inf>2</inf> to H<inf>2</inf>O<inf>2</inf>. Their electrons are also more reactive due to higher mobility, thus allowing for rapid reaction with O<inf>2</inf>. Under visible-light irradiation (λ > 390 nm), an H<inf>2</inf>O<inf>2</inf> production rate of 115 μM h⁻¹ is achieved in pure water under O<inf>2</inf> flow, without the use of sacrificial reagents and cocatalysts. The triazine sample achieves an AQY of 1% at 420 nm in pure water. Mechanistic investigations indicate that H<inf>2</inf>O<inf>2</inf> formation predominantly proceeds via a superoxide-mediated one-electron oxygen reduction pathway.