Cobalt nanoparticle with tunable size supported on nitrogen-deficient graphitic carbon nitride for efficient visible light driven H2 evolution reaction

Abstract

Cobalt nanoparticle with tunable size supported on nitrogen-deficient graphitic carbon nitride (Co/g-C3N4-x) was successfully realized in this work. The formation of metallic Co nanoparticle and N-deficiency generation were performed by H2 reduction in simple one step. The size of the Co nanoparticle was tuned by changing the reduction temperature and the amount of cobalt salt precursor. The Co/g-C3N4-x catalyst with the cobalt nanoparticle size in the range of (3.6 ± 2.2) nm exhibited the best H2-production rate of 750.2 μmol g−1 h−1 under the visible light (λ > 420 nm), which is 101.4 times higher than pure g-C3N4. In addition, some Co atoms were embedded in the lattice structure of g-C3N4. According to the experimental and DFT computational results, the band gap of the photocatalyst was narrowed by both Co doping into the g-C3N4-x lattice and the generation of N deficiency. The metallic Co loaded on g-C3N4-x surface promoted the electron transfer rate and electron-hole separation efficiency of the photocatalyst. EPR spectroscopy using a trapping agent had been able to determine that H was formed as intermediate in H2 generation and its concentration increased due to the presence of Co nanoparticles as co-catalysts. Our work provided a simple method for producing large scale photocatalyst with high efficient H2 evolution.