Doping of graphitic carbon nitride with oxygen by means of cyanuric acid: Properties and photocatalytic applications

Bare and oxygen doped graphitic carbon nitride were synthetized by the thermal polymerization of melamine (CN-M) and the mechanical mixtures of melamine and cyanuric acid, respectively, at 550 °C for 4 h. The ratios of melamine and cyanuric acid were 1:0.5, 1:1 and 1:2 (CN-MCA1, CN-MCA2 and CN-MCA3). The content of oxygen increased from 1.88 wt% (CN-M) to 3.93 wt% (CN-MCA3) and the specific surface area increased from 14 to 41 m2 g−1. The prepared CN materials were characterized by the elemental analysis, UV-Vis diffuse reflectance, X-ray diffraction, Fourier transform infrared spectrometry, the physisorption of nitrogen, scanning electron and high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, the determination of zeta potentials, and the Mott-Schottky method. The addition of cyanuric acid led to partial changes in the CN morphology, as documented by occurrence of CN tubes, increase in the specific surface area and was a source of additional -O- and -OH moieties which modified the CN surface in addition to the spontaneous oxygenation observed in CN-M. The above effects positively influenced photocatalytic activity of the CN materials as demonstrated using Rhodamine B (RhB) and the Ofloxacin antibiotics. The photocatalytic decomposition of Ofloxacin was more efficient than that of RhB and differed in kinetics (first-order vs. zero-order reaction). The reusability and stability of the CN materials was verified by repeating batch photocatalytic decompositions of Ofloxacin experiments for five times.