Hydrogen from Water over Openly-Structured Graphitic Carbon Nitride Polymer through Photocatalysis

Openly-structured g-C3N4 microspheres (CNMS) are developed through a well-controlled strategy. These materials have unique features of open 3D structure, ordered hierarchical porosity, and improved optical and electronic properties. Hydrogen evolution from water is performed under a 300W Xe lamp with a cut-off filter (>420nm) and Pt nanoparticles are used as the co-catalyst (3.0wt%). The catalyst prepared at 600 degrees C (CNMS-600) has a hydrogen evolution rate (HER) of 392molh(-1) (apparent quantum yield, AQY=6.3%) at 420nm. This value is higher than that of g-C3N4 nanosheets prepared through thermal oxidation, liquid exfoliation, or chemical exfoliation. The HER value is only 27molh(-1) (AQY=0.43%) at 420nm for bulk g-C3N4 from melamine. The evolution of openly-structured CNMS was investigated by TEM, FTIR, and XRD. The improved optical and electronic properties were demonstrated through UV/Vis absorption spectra, valence-band X-ray photoelectron spectroscopy, photoluminescence spectroscopy, electron paramagnetic resonance spectroscopy, and electrochemical impedance spectroscopy.