Efficient exciton dissociation in isomeric BINOL-based porous polymers for sacrificial agent-free H2O2 photosynthesis and biomass valorization

Abstract

Achieving sustainable, sacrificial agent-free hydrogen peroxide (H₂O₂) production at the millimolar scale through molecular-level modulation of organic semiconductors is a crucial global challenge. In this study, novel hierarchical porous polymers incorporating triphenylamine and BINOL (1,1′-bi-2-naphthol) were synthesized using FeCl₃-mediated homopolymerization, forming BINOL in situ, unlike conventional approaches that rely on pre-formed derivatives. These polymers, designed with varied linkage positions, exhibit remarkable optoelectronic properties, enabling efficient artificial photosynthesis of H₂O₂ up to 2.5 mmol·g⁻¹·h⁻¹ from natural water sources (river, tap, and seawater) without any additives. A direct 2e⁻ oxygen reduction and water oxidation pathway facilitated stable H₂O₂ generation, achieving 6.47 mmol·g⁻¹·h⁻¹ in pure water under AM 1.5 G illumination, with a significantly high solar-to-chemical conversion efficiency of 1.6%. This rate was further increased to 27.5 mmol·g⁻¹·h⁻¹ in isopropanol/water (1 : 1), ranking among the highest reported values thus far. Biomass-derived sacrificial agents such as 5-hydroxymethyl furfural and tetrahydrofuryl alcohol (THFA) further increased the generation rate (5.17 mmol g⁻¹ h⁻¹ in 1 : 10 THFA/water), mitigating energy demands in both ways: H₂O₂ production and biomass valorization. Notably, the polymers were recycled up to ten consecutive runs without any loss in their catalytic efficiency. In addition, DFT calculations confirmed the BINOL served as the potential oxygen reduction site with thermodynamic feasibility for H₂O₂ formation, with a free energy release of 2.86 eV in IPA/water (1 : 10) and 0.38 eV in pure water.