Fabrication and Photocatalytic Application of Aromatic Ring Functionalized Melem Oligomers

This paper reports the fabrication of aromatic ring functionalized melem oligomers (AFMOs) and the study of their synergistic photodegradation properties. Highlights include the following: (1) the fabrication of various carbon nitrides (CNs) through thermal polycondensation; (2) the intrinsic modulation of the molecular nature of polymeric CNs using different amounts of melamine precursors; and (3) the extrinsic functionalization of melem oligomers (MOs) with aromatic rings, which enhanced visible light absorption, reduced dark absorption, and enhanced π electron delocalization, thus inhibiting electron-hole (e^--h⁺) pair recombination. X-ray diffraction and UV-vis spectroscopy qualitatively indicated the fabrication of MOs after washing with 135 °C dimethyl sulfoxide. ¹⁵N solid state nuclear magnetic resonance spectroscopy revealed that the MO sample consisted mainly of trimers before and after aromatic ring functionalization. Fourier-transform infrared spectroscopy indicated the structures of polymerized heptazine rings and the effective functionalization of aromatic rings. A scavenger study demonstrated that •O₂^- predominated in the AFMO photodegradation mechanism of methylene blue solutions. The AFMO sample exhibited a photodegradation rate constant of approximately 9.8 × 10^-3 min^-1, which was nearly 8 times higher than that of melon. The superior photocatalytic properties were attributed to the substantial improvement in visible light absorption and poor e^--h⁺ pair recombination because of π electron delocalization, which were verified using UV-vis and photoluminescence spectra, respectively.