Metal-Free Photocatalysts C3N3S3 and its Polymers: Solubility in Water and Application in Benzylic Alcohols Oxidation Under Visible Light

Metal-free photocatalysts trithiocyanuric acid (C 3 N 3 S 3 ) and its polymers were one-step synthesized and used for selective aerobic oxidation of benzyl alcohol under visible light. The S–S bridged C 3 N 3 S 3 polymers showed higher oxidation activity with increasing polymerization time and reached a maximum at 40 h. As a major factor, catalysts’ solubility in water at different temperatures (from 298.15 K to 368.15 K) was measured at atmospheric pressure. The obtained data were correlated by polynomial empirical equation and modified Apelblat equation, respectively. Experimental results proved that the solubility of C 3 N 3 S 3 and its polymers increased with increasing temperature. The solubility of C 3 N 3 S 3 polymers with lower polymerization degree (DP) were better than that of parent C 3 N 3 S 3 owing to the hydrophilicity caused by a low symmetry and disorder structure, whereas the higher DP could lead to the decrease of polymer solubility and further affect the photocatalytic activity. Thermodynamic properties of the solution system including the enthalpy ( Δ H S 0 ) and heat capacity ( c p 0 ) were calculated by the modified Apelblat equation.