Comparative Studies of g-C3N4 and C3N3S3 Organic Semiconductors-Synthesis, Properties, and Application in the Catalytic Oxygen Reduction

Exfoliated g-C3N4 is a well-known semiconductor utilized in heterogenous photocatalysis and water splitting. An improvement in light harvesting and separation of photogenerated charge carriers may be obtained by polymer doping with sulfur. In this work, we incorporate sulfur into the polymer chain by chemical polymerization of trithiocyanuric acid (C3N3S3H3) to obtain C3N3S3. The XRD measurements and TEM images indicated that C3N3S3, in contrast to g-C3N4, does not exist in the form of a graphitic structure and is not exfoliated into thin lamellas. However, both polymers have similar optical properties and positions of the conduction and valence bands. The comparative studies of electrochemical oxygen reduction and hydrogen evolution indicated that the overpotentials for the two processes were smaller for C3N3S3 than for g-C3N4. The RDE experiments in the oxygen-saturated solutions of 0.1 M NaOH have shown that O-2 is electrochemically reduced via the serial pathway with two electrons involved in the first step. The spectroscopic experiments using NBT demonstrated that both polymers reveal high activity in the photocatalytic reduction of oxygen to superoxide anion radical by the photogenerated electrons.

Automated summary

In this study, sulfur is incorporated into the polymer chain by chemical polymerization to obtain C3N3S3. Unlike g-C3N4, C3N3S3 does not exist in the form of a graphitic structure and cannot be exfoliated into thin lamellas. However, both polymers have similar optical properties and positions of the conduction and valence bands. Comparative studies show that C3N3S3 exhibits smaller overpotentials for electrochemical oxygen reduction and hydrogen evolution compared to g-C3N4. Additionally, spectroscopic experiments demonstrate that both polymers have high activity in the photocatalytic reduction of oxygen to superoxide anion radical by the photogenerated electrons.