Synergistic Effects of the Ni3B Cocatalyst and N Vacancy on g-C3N4 for Effectively Enhanced Photocatalytic N2 Fixation

The photocatalytic fixation of N2 is a promising technology for sustainable production of ammonia, while the unsatisfactory efficiency resulting from the low electron-transfer rate, narrow light absorption range, and limited active sites of the photocatalyst seriously hinder its application. Herein, we designed a noble metal-free Schottky junction photocatalyst constructed by g-C3N4 nanosheets with N vacancies (VN-CN) and metallic Ni3B nanoparticles (Ni3B/VN-CN) for N2 reduction to ammonia. The ammonia yield rate over the optimized Ni3B/VN-CN is 7.68 mM g-1 h-1, which is 6.7 times higher than that of pristine CN (1.15 mM g-1 h-1). The superior photocatalytic N2 fixation performance of Ni3B/VN-CN can be attributed not only to the formation of Schottky junctions between Ni3B and VN-CN, which facilitates the migration and separation of photogenerated electrons, but also to the incorporation of VN into g-C3N4, which enhances visible light absorption and improves electrical conductivity. More importantly, Ni3B nanoparticles can act as the cocatalyst, which provide more active sites for the adsorption and activation of N2, thereby improving the N2 reduction activity. This work provides an effective strategy of designing noble metal-free-based cocatalyst photocatalyst for sustainable and economic N2 fixation.