Abstract
A green-oriented synthesis of highly photoactive nano-scaled graphitic carbon nitride (g-C3N4) is presented with water to be utilized as a critical reagent in order to tune desired physicochemical properties, and so, to elevate the photocatalytic activity. The materials’ optimization strategy involved the use of three precursors (melamine, urea or thiourea) and different thermal polycondensation (pyrolysis) durations. The synthesized materials were characterized by SEM, XRD, XPS, N2 sorption, FT-IR, and UV–vis DRS. Their photocatalytic activity against a non-steroidal anti-inflammatory pharmaceutical compound, diclofenac, was evaluated under ultraviolent irradiation, also investigating the influence of pH, photocatalyst dosage/mass and concentration of H2O2. The results revealed that the precursor, pyrolysis time and use of water effect significantly the physicochemical features and the photocatalytic activity. Urea-derived samples showed the highest specific surface areas and smallest crystalline domains, as well as the highest photocatalytic efficiency. The involved mechanisms were examined by exploring the optical properties, the role of the photo-generated radicals and the reactive oxygen species, as well as LC-MS analysis. The Orbitrap high-resolution mass-spectrometry analysis revealed the formation of 26 transformation products governed by different processes such as hydroxylation and further oxidation to keto derivatives and ring opening, decarboxylation/hydroxylation with further oxidation, dichlorination, and lactam formation.
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