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

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A highly efficient 3D wood-derived carbon monolith reactor with a low tortuosity is demonstrated for high-temperature reaction applications, using catalytic steam reforming of biomass tar as the model system. Outstanding catalytic activity is achieved as the reactant gases flow through this 3D natural wood-derived catalyst, where over 99% toluene conversion and good stability at 700 °C are observed.