Tuning the surface and optical properties of graphitic carbon nitride by incorporation of alkali metals (Na, K, Cs and Rb): Effect on photocatalytic removal of organic pollutants

Alkali metals have been known for their intercalation properties and can be employed for the separation of stacking in sheet-like materials. In this work, alkali metals (Na, K, Rb and Cs) have been systematically incorporated in varying concentrations in g-C3N4 sheets and their effect on resulting optical, surface and photocatalytic properties have been explored in detail. It was observed that the optical, electronic and surface properties of g-C3N4 were altered upon the incorporation of different alkali metal ions. The band gap and specific surface area of resulting materials were decreased as compared to the pristine g-C3N4. In addition, the alkali metal incorporation in g-C3N4 sheets showed the formation of cyanide groups and nitrogen vacancies in the resulted materials. Further, the photocatalytic activity of g-C3N4 and alkali metal incorporated g-C3N4 was calculated by studying the degradation of acid red 94 dye under visible light irradiation. It was observed that the photocatalytic activity of pristine g-C3N4 sheets was decreased with an increase in the concentration of alkali salt used during the synthesis of alkali metal incorporated g-C3N4. This decrease in the activity could arise due to the decreased surface area, detrimental amount of nitrogen vacancies and high concentration of alkali metal ions incorporated in the structural framework of g-C3N4 sheets. This work provides a unique example of the adverse effect of alkali metal ions on photocatalytic activity of g-C3N4 and paves future directions for the improvement of the performance of g-C3N4 based materials.