Convenient one-step fabrication and morphology evolution of thin-shelled honeycomb-like structured g-C3N4 to significantly enhance photocatalytic hydrogen evolution

Synthesis of three-dimensional carbon nitride (g-C3N4) structures is a promising but challenging task for effectively photocatalytic water splitting to generate H-2. In this study, thin-shelled honeycomb-like structured g-C3N4 (g-C3N4-TSH) was successfully synthesized via facile one-step co-pyrolysis of melamine/NH4Cl mixture and the morphology evolution mechanism was revealed systematically. By varying the ratios of melamine/NH4Cl precursor and thermal preparation temperatures, thin-shelled and thick-shelled honeycomb-like structured g-C3N4 were obtained. Also, the key intermediate phases were identified by their structure characterizations, which revealed low-temperature phase transition of 1-D tube-like melamium/NH4Cl adduct, then transforming to 2-D multiple plate-like melamium/melon NH4Cl complex by sintering, and finally evolving to g-C3N4-TSH at high temperature. The final hierarchical structure has several beneficial features as hollow, mesoporous, ultrathin, and honeycomb-like form, which caused its high surface area, excellent mass transfer rate and good light absorption ability. As a result, the g-C3N4-TSH with Pt as co-catalyst showed remarkable photoactivity for H-2 evolution, with an apparent quantum efficiency of 9.86% at 420 +/- 10 nm, which is superior to many reported modified g-C3N4. This study revealed the evolution mechanism of g-C3N4-TSH, which is conducive to design various dimension oriented g-C3N4 structures via solid-state chemistry for photocatalytic H-2 evolution.