Boosting visible-light photocatalytic performance of exfoliated carbon nitride nanosheets via optimizing dopant decoration for efficient pollutant removal

Abstract

This study systematically studied the effects of Pr, Fe, and Na as representative rare earth, transition, and alkali metal dopants, respectively, on the photocatalytic activity of exfoliated graphitic carbon nitride (g-C₃N₄). The doped exfoliated g-C₃N₄ samples were prepared by integrating precursor ion intercalation into the pre-formed g-C₃N₄ with thermal treatment. The as-prepared catalysts were examined for crystal, textural, chemical, optical, and photoelectrochemical properties to explore the correlation between dopants and photocatalytic activity of the resulting composites. The detailed analyses revealed that the Pr-doped g-C₃N₄ exhibited superior photocatalytic activity in degrading methylene blue under visible light, achieving a ∼96% removal in 40 min. This was not only better than the activity of g-C₃N₄, but also much higher than that of Na-doped g-C₃N₄ or Fe-doped g-C₃N₄. The kinetic rate constant using Pr-doped g-C₃N₄ was 3.2, 5.1, and 2.0 times greater than that of the g-C₃N₄, Fe-doped g-C₃N₄, and Na-doped g-C₃N₄, respectively. The enhanced performance was attributed to its inherent characteristics after optimal tuning, including good surface area, improved porosity, enhanced visible light absorption, suitable electronic band structure, increased charge carrier density, promoted charge separation, and reduced charge transfer resistance. In addition, the optimized Pr(0.4)g-C₃N₄ was used to study the photocatalytic removal of methylene blue in detail under conditions with different initial methylene blue concentrations, types of dyes, catalyst dosages, initial solution pH, counter ions, and water matrices. Our results demonstrated the high photocatalytic activity of Pr(0.4)g-C₃N₄ under varying conditions, including in real wastewater media, which were collected from our local municipal wastewater treatment plant. The observed good reusability and stability after five cycles of photocatalytic degradation test further suggested a promising potential of Pr(0.4)g-C₃N₄ for practical application in wastewater treatment.