The Role of Boron Dopant in the Improvement of Electron Transfer in g-C3N4 Photocatalyst

In this work, graphitic carbon nitride (g-C3N4) was doped with boron by thermal treatment with NaBH4. We have shown that the morphology of the modified polymer gradually changes from graphitic-like to amorphous, with increasing amounts of NaBH4 used for annealing. On the other hand, the boron doping has a very small influence on the band gap energy, as well as on the positions of the valence and conduction band edges of the polymer, but strongly improves the activity of g-C3N4 in the photocatalytic reduction of oxygen and degradation of methyl orange (8-fold increase of the degradation rate constant with respect to that of pure g-C3N4). The enhancement of the photocatalytic properties was explained by the increased rate of charge transport, both in the polymer plane and across the film, due to formation of N-B-N bonds between the adjacent heptazine units and the interlayer Coulomb interactions. The best photocatalytic activity was obtained for samples prepared from a mixture of g-C3N4 and NaBH4 at a moderate weight ratio (4:1), while increased amounts of NaBH4 led to significant and unfavorable changes in both the morphology and molecular structure of the polymer.