rGO–gCN composites, which were prepared by the in situ photoreduction of GO using bulk gCN as the photocatalyst, exhibited higher photocatalytic activity than bare gCN due to the improved interface charge transfer.

Mesoporous carbon nitride (MCN) was used for the first time as a thermal catalyst for the removal of aniline. While bulk carbon nitride (BCN) and mesoporous silica (MCM-41) did not show any catalytic activities, the MCN showed aniline removal (33%) at 398 K. It was revealed that the much higher activity of the MCN originated from the presence of mesoporosity and suitable adsorption sites for the reaction to occur.The nature of aniline adsorption on MCN was found to fit well to the Freundlich adsorption model. The evidence on the interactions between aniline and MCN was supported by fluorescence and FTIR spectroscopies. It was suggested that the interactions between MCN and aniline involved both weak p to p stacking and strong hydrogen bonding, which were important to initiate the catalytic removal of aniline.

The fast electron-hole recombination in mesoporous carbon nitride (MCN) photocatalyst has spurred a great interest to improve its efficiency with addition of various modifiers. In the present study, the MCN was modified by reduced graphene oxide (rGO) that was synthesized via a novel photocatalytic reduction method with different ratios of GO to MCN to produce rGO-MCN composites. The synthesized rGO-MCN samples were characterized by X-ray diffractometer (XRD), diffuse reflectance UV-visible (DR UV-Vis), and Fourier transform infrared (FTIR) spectroscopies. It was confirmed that rGO was successfully combined with the MCN without affecting the structure of the MCN. With the higher amount of GO ratio, the composites showed more observable rGO peaks in the IR spectra and higher background absorption in the visible region of DR UV-Vis spectra. The photocatalytic removal of N-nitrosopyrrolidine (NPYR) was carried out at room temperature under visible light irradiation to investigate the photocatalytic efficiency of the composites. The ratio of GO was found to affect the photocatalytic activity of the rGO-MCN composites. The photocatalytic activity of the prepared composites increased with GO loading from 1 to 5 wt.%, owing to the slightly enhanced absorption in visible light as shown in DR UV-Vis spectra and the undisrupted graphitic structure of MCN upon characterizations by XRD and IR spectra. It was found that 5 wt.% was the optimum amount of GO ratio and there was no further improvement in photocatalytic activity when the GO ratio increased.

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