In Situ Construction of Globe-like Carbon Nitride as a Self-Cocatalyst Modified Tree-like Carbon Nitride for Drastic Improvement in Visible-Light Photocatalytic Hydrogen Evolution

Graphical Unique morphological structure : Three carbon nitrides with different morphologies are shown to be highly effective visible-light photocatalysts for the photocatalytic H 2 evolution reaction (HER). Globe/tree-like g-C 3 N 4 shows high visible-light photocatalytic HER activity, apparent quantum efficiency, and stability. The enhanced photocatalytic activity might arise from the globe-like carbon nitride as a self-cocatalyst and hollow-tree-branch structures. Photogenerated carriers possess high recombination efficiency in carbon–nitrogen materials, which results in lower photocatalytic H 2 evolution activity. By reviewing the literature, it was concluded that relying only on a structure-controlled technique was insufficient to reduce the combination of photogenerated carriers without introducing a foreign material or element. Hence, bulk-like g-C 3 N 4 [CN (B)], globe/strip-like g-C 3 N 4 [CN (G/S)], and globe/tree-like g-C 3 N 4 [CN (G/T)] were in situ obtained through a facile calcination method. Similar to platinum (Pt) as a cocatalyst, globe-like carbon nitride as a self-cocatalyst was found to improve the separation efficiency of photogenerated carriers effectively. Interestingly, the hollow-tree-branch morphology of CN (G/T) effectively transmitted photogenerated holes, which thereby enhanced the photocatalytic H 2 evolution activity. The H 2 production rates of CN (G/S) and CN (G/T) were almost 10.7 and 18.3 times greater, respectively, than that of CN (B) without the addition of Pt as a cocatalyst. Notably, CN (G/S) and CN (G/T) displayed considerable rates of H 2 production in water relative to that shown by CN (B) (no activity) without the use of any sacrificial agent and by using Pt as a cocatalyst. CN (G/T) showed outstanding long-term stability, as evidenced by seven cycle tests performed over 28 h. The charge separation and transfer process of the compounds were verified by photoluminescence (PL), time-resolved PL spectroscopy, and photocurrent measurements.