Sulfur- and Strontium-Doped Graphitic Carbon Nitride for Efficient Photocatalytic Hydrogen Evolution

Doping metallic and nonmetallic elements in the graphitic carbon nitride (g-C3N4) molecular layer to tune its band structure is an important strategy for improving its photocatalytic activity. Herein, sulfur- and strontium-doped g-C3N4 catalysts are synthesized by calcining the mixture of urea, 2-thiobarbituric acid, and strontium chloride hexahydrate at elevated temperature. The optimal hydrogen production rate of 6Sr-SCN (SCN, sulfur-doped graphitic carbon nitride) reaches 13.9 μmol/h, about 6.6 times that of pure g-C3N4, abridged as CN, under visible light irradiation with λ ≥ 420 nm. An experimental study and theoretical simulation demonstrate that S and Sr doping narrows the band gap, forms an intraplane heterojunction, extends the harvest in the visible light range and the transport and separation efficiency of photogenerated carriers, and increases molecular buckling and specific surface area as well. All these factors are synergistically combined to improve the photocatalytic performance of g-C3N4.