Sodium/Potassium Doping and Nitrogen Defect Modified Graphitic Carbon Nitride for Boosted Visible Light Photocatalytic Activity

Graphitic carbon nitride (g-C3N4) is a promising semiconductor photocatalytic material to treat residual organic pollutants due to its advantages in photoelectric properties, physical chemical stability, redox properties and so on. However, the unmodified g-C3N4 catalyst has defects such as wide band gap, small specific surface area, and low efficiency of photogenerated electron hole separation, which limited its application in the field of photocatalysis. To overcome its drawbacks, herein, we presented a facile NaOH/KOH-assited thermal condensation approach to prepare a series of element doping (Na or K) and N vacancies simultaneously functionalized carbon nitride (DCN-xNa or DCN-xK). The modified g-C3N4 showed a significantly enhanced photocatalytic degradation tetracycline hydrochloride (TC-HCl) activity. Surprisingly, DCN-6Na and DCN-8K exhibited a high TC-HCl degradation activity of 50% (2.4 times as much as that of pristine g-C3N4) and a high TC-HCl degradation activity of 56% (2.7 times as much as that of pristine g-C3N4), respectively. The related characterizations confirmed that the accompanying Na/K doping and nitrogen defect structure characteristics improved the optical absorption ability and the effective separation of photogenerated carriers. The major active species in the photocatalytic process are superoxide radicals ($ \cdot \text{O}_{2}^{-} $) and photo-induced holes (h+).