Comparative Studies of g-C(3)N(4) and C(3)N(3)S(3) Organic Semiconductors—Synthesis, Properties, and Application in the Catalytic Oxygen Reduction

Exfoliated g-C(3)N(4) 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 (C(3)N(3)S(3)H(3)) to obtain C(3)N(3)S(3). The XRD measurements and TEM images indicated that C(3)N(3)S(3), in contrast to g-C(3)N(4), 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 C(3)N(3)S(3) than for g-C(3)N(4). 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.