Enhanced synergistic system for the persulfate activation under visible light using novel N-ZnO photocatalyst...

Herein, a novel nitrogen-doped ZnO photocatalyst supported on biochar (N-ZnO@LBC) was synthesized using the Lantana camera as a green source of biochar. The synthesized photocatalyst was applied as an activator of persulfate (PS) for the photodegradation of methylene blue (MB) under visible light irradiation. The properties of the synthesized photocatalyst were explored before and after photocatalysis using different characterization analyses. The results revealed that the nitrogen doping of ZnO@LBC could reduce the band gap energy from 2.83 eV to 2.78 eV resulting in higher activity under visible light. The synergetic effect of the N-ZnO@LBC/PS/visible process was investigated under various reaction conditions. Surprisingly, about 95.7% of MB photodegradation could be achieved using N-ZnO@LBC/PS/visible process under optimal conditions. Moreover, a prediction model with an excellent correlation between the actual and predicted data (R² = 0.9844) was established to forecast MB removal. Interestingly, the scavenging tests exhibited that various reactive species could induce MB degradation in an order of O₂^-• > h⁺ > SO₄^-• >^•OH with the highest contribution of O₂^-•. Additionally, the presence of functional hydroxyl groups in the N-ZnO@LBC structure could lead to the generation of additional radicals as confirmed by FT-IR analysis after photocatalysis. The reusability test showed that the photocatalyst could be reused for up to five cycles without a significant loss in the photocatalytic activity indicating its high stability. The cost of wastewater treatment by N-ZnO@LBC/PS/Visible process was estimated to be US$ 9.79/m³ based on an economic analysis. It worth mentioning that the proposed process was investigated for the degradation of other dyes including Congo red (CR) and methyl orange (MO) and the efficiencies were 65.41% and 59.23% for CR and MO, respectively. Overall, the proposed process could be a promising and cost-effective approach for the degradation of various dyes in real applications.