Crown Ether-Modified Carbon Nitride for Augmented Visible-Light Photocatalytic H₂ Production from Water Splitting

Photocatalytic water splitting, which converts solar energy into hydrogen fuel, is one of the most viable methods to address future energy demands. Herein, by introducing 1,4,7,10,13,16-hexaoxacyclooctadecane (crown ether) on the surface of graphitic carbon nitride (CN) via H-bonding and CH-π interactions, we prepare highly efficient potassium-18-crown-6 ether-modified carbon nitride (CN/K-5CE) nanocomposite photocatalysts by a simple modification method for augmented photocatalytic hydrogen production. The optimized CN/K-5CE hybrid photocatalyst displays an enhanced photocatalytic hydrogen production rate of 126.33 μmol h^-1, which is 6.83-fold higher than that of CN (18.47 μmol h^-1) and 3.76 times higher than that of CN/CE (33.58 μmol h^-1). The optimal CN/K-5CE sample exhibits an AQE of 8.93% at λ = 420 nm. Furthermore, the stability test indicates no significant activity loss over the CN/K-5CE sample after 4 consecutive cycles. The experimental results and corresponding characterization unravel that the electride formation by the complexation of 18-crown-6 ether (CE) with an alkali metal potassium ion (K⁺) provides excess electrons in CN/K-5CE, resulting in a reduced band gap and increased electrical conductivity and hydrophilicity. Synergistic effect from the van der Waals (vdW) force interaction between CE and CN leads to efficient interfacial charge transportation and separation. Moreover, the presence of K⁺ cations facilitates water adsorption and dissociation on the catalyst, thus enhancing photocatalytic H₂ evolution. Our study opens up an avenue to fabricate highly efficient and stable hydrophilic CN-based hybrid materials with tuned surface properties and electronic structures for practical solar-to-fuel conversion.