Photocatalytic degradation of azo dye wastewater promoted by inorganic acid post-treated carbon nitride

Abstract

A series of inorganic acid post-treated carbon nitride was synthesized to regulate the electronic structure, surface properties and then improve the photocatalytic activity. Carbon nitride displayed a thinner and smaller nanosheet structure after acid post-treatment, which could provide more exposed active sites and improve the charge carrier separation. The electronic band gap structure revealed that the phosphoric acid-treated sample (HP-CN) had a more positive valence band edge, endowing it with a higher oxidation ability. Furthermore, electron spin resonance (EPR) and transient photoinduced voltage (TPV) analyses demonstrated that the acid-treated carbon nitride had a higher electron–hole pair separation and transfer efficiency, thus boosting the photocatalytic performance. HP-CN possessed an optimal removal efficiency of 87.7% towards Reactive Brilliant Red X-3B (RBR X-3B), which was 1.62 times that of g-C₃N₄. Moreover, HP-CN showed an outstanding stability and satisfactory ability to remove RhB (rhodamine B) and TC (tetracycline), proving its potential application in environmental remediation. The photocatalytic mechanism measurement indicated that photogenerated h⁺, ˙O₂⁻ and ˙OH played critical roles during photocatalytic RBR X-3B decomposition.