Enhanced Hydrogen Evolution in the Presence of Plasmonic Au-Photo-Sensitized g-C₃N₄ with an Extended Absorption Spectrum from 460 to 640 nm

<div><p>Extensively spectral-responsive photocatalytic hydrogen production was achieved over g-C₃N₄ photo-sensitized by Au nanoparticles. The photo-sensitization, which was achieved by a facile photo-assisted reduction route, resulted in an extended spectral range of absorption from 460 to 640 nm. The photo-sensitized g-C₃N₄ (Au/g-C₃N₄) photocatalysts exhibit significantly enhanced photocatalytic hydrogen evolution with a TOF value of 223 μmol g^-1 h^-1, which is a 130-fold improvement over g-C₃N₄. The hydrogen production result confirms that Au nanoparticles are effective photo-sensitizers for the visible light-responsive substrate g-C₃N₄. UV–vis diffuse reflection spectra (DRS), photoluminescence spectra (PL), electron spin resonance (ESR), and electrochemical measurements were used to investigate the transfer process of photogenerated electrons. The optimal Au/g-C₃N₄ photocatalyst displays the lowest charge transfer resistance of 18.45 Ω cm^-2 and a high electron transfer efficiency, as determined by electrochemical impedance spectroscopy (EIS). The photo-sensitized g-C₃N₄ shows a broad range of response to visible light (400–640 nm), with significantly high incident photon-to-current efficiency (IPCE) values of 14.52%, 2.9%, and 0.74% under monochromatic light irradiation of 400, 550, and 640 nm, respectively. ESR characterization suggests that Au nanoparticles are able to absorb visible light of wavelengths higher than 460 nm and to generate hot electrons due to the SPR effect.</p>