Supramolecular hydrogen-bond control enables low-temperature synthesis of sulfur-modified carbon nitride

Supramolecular precursor engineering can alter the formation pathway and electronic structure of carbon nitride materials. Here, we investigate a low-temperature route to sulfur-containing carbon nitride based on hydrogen-bond-driven preorganization of a melamine-thiobarbituric acid assembly. Thermal treatment at 305 °C yields a partially condensed, triazine-rich carbon nitride-derived framework, below the 500-600 °C range commonly used for conventional molecular precursors. X-ray diffraction and Fourier-transform infrared spectroscopy show progressive framework formation within 2-3 h, while scanning electron microscopy indicates preservation of the precursor-scale morphology, consistent with a pseudomorphic transformation in the morphological sense. Multi-rate isoconversional analysis gives a high, conversion-dependent apparent activation energy; the low observable transformation temperature is therefore interpreted as arising from a compensation-controlled, entropy/topology-assisted kinetic regime rather than from a simple lowering of the activation barrier. X-ray photoelectron spectroscopy, elemental mapping, and evolved-gas analysis support retention of chemically bound sulfur-containing motifs without assigning a unique substitutional doping configuration. Electronic characterization gives an optical band gap of 2.26 eV and sub-bandgap states. Photoactivity is demonstrated by DMPO spin-trapping EPR detection of reactive oxygen species under 405 nm irradiation, Rh6G degradation absent in the no-catalyst control, and low-rate hydrogen evolution without a cocatalyst. The principal contribution is therefore the coupling of supramolecular precursor design, low-temperature framework formation, sulfur retention, and mechanistic kinetic analysis rather than record photocatalytic performance.