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

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 H-2 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 H-2-production rate of 750.2 mu mol g(-1) h(-1) under the visible light (lambda > 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 center dot was formed as intermediate in H-2 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 H-2 evolution.