Alkali-assisted engineering of ultrathin graphite phase carbon nitride nanosheets with carbon vacancy and cyano group for significantly promoting photocatalytic hydrogen peroxide generation under visible light: Fast electron transfer channel.

Exfoliating bulk graphite phase carbon nitride (g-C3N4) into 2D nanosheets is considered to be an effective method to enhance its photocatalytic activity. However, optical absorption capacity of the exfoliated g-C3N4 nanosheets are lower than that of the original bulk g-C3N4 due to the quantum size effect. Here, the ultrathin graphite phase carbon nitride nanosheets containing both carbon vacancy and cyano group (UCNS580) were prepared by two-step calcination in air with the assistance of KOH. The formation and position of carbon vacancy and cyano group were first investigated and determined. The simultaneous introduction of carbon vacancy and cyano group not only improved light absorption range and intensity of g-C3N4 nanosheets, but also more importantly constructed a fast transfer channel for photogenerated electrons, further enhancing the separation efficiency and migration ability of photogenerated carriers. The cyano group as the accumulation center of photogenerated electrons and the oxygen adsorption center increased the proportion of one-step two-electrons reaction path to efficiently generate H2O2. As a result, UCNS580 exhibited highly boosted H2O2 generation activity, its H2O2 production yield for 6 h reached 939 µmol/L and the formation rate was up to 4167 µM h-1 g-1, which was in priority in the reported literature under the same conditions.

Enhanced nonsacrificial photocatalytic generation of hydrogen peroxide under visible light using modified graphitic carbon nitride with doped phosphorus and loaded carbon quantum dots: Constructing electron transfer channel.

The photocatalytic production of H2O2 by graphite-phase carbon nitride (g-C3N4) using water and oxygen is a promising and sustainable method. Nevertheless, the yield of H2O2 produced by the pristine g-C3N4 is still far from satisfactory owing to limited optical absorption, rapid photogenerated electron-hole recombination and poor surface electron migration. Therefore, p-P1CN/CQDs25 was designed and synthesized by doping phosphorus (P) and loading carbon quantum dots (CQDs) to modify porous g-C3N4 (p-CN) via a facile method. Herein, P acted as an electron transfer bridge to induce electrons into CQDs, while CQDs acted as an electron trapping material to capture and stabilize photogenerated electrons. Moreover, CQDs could enhance their optical absorption due to its unique optical properties. Notably, p-P1CN/CQDs25 presented highly boosted H2O2 generation activity, its H2O2 production yield for 5 h was up to 494 µM/L and the formation rate constant Kf in the first hour was 238 µM h-1 without adding sacrificial agents and without bubbling oxygen under visible light, which took precedence among the reported results under the same conditions. It should be noted that the composite p-P1CN/CQDs25 also possessed low H2O2 decomposition behavior based on the effect of CQDs stabilizing electrons. In addition, the possible mechanism of photocatalytic H2O2 generation for p-P1CN/CQDs25 was also proposed. Our research provided a new idea for the design of novel photocatalysts to efficient generation of H2O2.