Graphitic carbon nitride facilely modified with pyromellitic diimide with enhanced photocatalytic activity and good selectivity towards the photodegradation of cationic dyes

Framework modification of graphitic carbon nitride (g-C3N4) with organic molecules is recognized as an effective strategy to enhance its photocatalytic performance by improving the charge separation in g-C3N4. In this work, pyromellitic diimide (PD) with strong electron-withdrawing ability and conjugated structure was linked to g-C3N4 skeleton by simple solution blending to prepare a composite of g-C3N4 @PD. It is found that the resultant composite exhibited much higher photocatalytic activity than pristine g-C3N4 in the photodegradation of an anionic dye of sulforhodamine B (SRB). Specifically, the composite with PD of 1% in weight ratio showed a degradation rate constant 3.8 times and 5.1 times that of g-C3N4 under the illumination of visible light and ultra violet light, respectively. Moreover, g-C3N4 @PD revealed highly selective photodegradation in favor of a cationic dye of malachite green in its mixture with the anionic dye of SRB, which is attributed to preferential adsorption of the cationic dye onto the negatively charged photocatalyst. In addition, the composite maintained a high photodegradation efficiency of 98.2% at the end of five cycles of the photodegradation of SRB, suggesting good photocatalytic stability. It is proposed that enhanced photocatalytic activity of the composite is related to the electron-withdrawing effect of PD, which facilitates the separation of photo-induced electrons from the g-C3N4 skeleton to the boundary PD to inhibit the recombination of the photogenerated electron/hole pairs in g-C3N4 skeleton. The facilely prepared g-C3N4 @PD is a promising photocatalyst in environmental remediation.