Integrating singlet oxygen-driven photocatalytic H2O2 synthesis with uranium(vi) sequestration by a pyrene-based porous aromatic framework

Abstract

Artificial photosynthesis of H₂O₂ without sacrificial agents is gaining momentum as a sustainable energy solution, especially using organic semiconductors. In this study, we introduce a porous aromatic framework (PAF), Pyrene-BINOL-4, synthesized via in situ BINOL generation during polymerization, exhibiting remarkable photoactivity towards the visible light-driven production of H₂O₂ in pure water without the need for additives. It showcases a maximum rate of 3.82 mmol g⁻¹ h⁻¹ (under AM 1.5 G), with a solar-to-chemical conversion efficiency of 1%, supported by its broad light absorption and optimal band gap. Phosphorescence (λ_em = 650 nm) and transient absorption spectroscopy confirm a stable, long-lived triplet state (τ_avg = 7.22 µs), key for efficient singlet oxygen generation. Theoretical study reveals a synergistic pyrene-BINOL geometry with a low singlet–triplet energy gap (ΔE_ST = 0.13 eV) and triplet excited state energy >1.60 eV, facilitating ³O₂ to ¹O₂ conversion. Notably, the material also generates H₂O₂ efficiently in seawater (0.89 mmol g⁻¹ h⁻¹) without sacrificial agents. Its high surface area (1595 m² g⁻¹), thermal stability (up to 365 °C), and hollow rod-like structure support the diffusion of oxygen and mass transfer. In addition, it also demonstrated sacrificial agent-free removal of uranium(VI) up to 627.5 mg g⁻¹ from natural water sources, maintaining performance over five cycles without degradation.