Constructing Highly Uniform Onion-Ring-like Graphitic Carbon Nitride for Efficient Visible-Light-Driven Photocatalytic Hydrogen Evolution

The introduction of microstructure to the metal-free graphitic carbon nitride (g-C₃N₄) photocatalyst holds promise in enhancing its catalytic performance. However, producing such microstructured g-C₃N₄ remains technically challenging due to a complicated synthetic process and high cost. In this study, we develop a facile and in-air chemical vapor deposition (CVD) method that produces onion-ring-like g-C₃N₄ microstructures in a simple, reliable, and economical manner. This method involves the use of randomly packed 350 nm SiO₂ microspheres as a hard template and melamine as a CVD precursor for the deposition of a thin layer of g-C₃N₄ in the narrow space between the SiO₂ microspheres. After dissolution of the microsphere template, the resultant g-C₃N₄ exhibits uniquely uniform onion-ring-like microstructures. Unlike previously reported g-C₃N₄ powder morphologies that show various degrees of agglomeration and irregularity, the onion-ring-like g-C₃N₄ is highly dispersed and uniform. The calculated band gap for onion-ring-like g-C₃N₄ is 2.58 eV, which is significantly narrower than that of bulk g-C₃N₄ at 2.70 eV. Experimental characterization and testing suggest that, in comparison with bulk g-C₃N₄, onion-ring-like g-C₃N₄ facilitates charge separation, extends the lifetime of photoinduced carriers, exhibits 5-fold higher photocatalytic hydrogen evolution, and shows great potential for photocatalytic applications.