Methylene blue degradation by DBD: combined effects of pH, Cl^-, and black TiO₂

This study aims to investigate a multi-component synergistic strategy for methylene blue (MB) degradation by coupling dielectric barrier discharge (DBD) plasma oxidation, black titanium dioxide (${\mathrm{TiO}}_2$)-assisted photocatalysis, and chloride ion (${\mathrm{Cl}}^{-}$)-mediated oxidation. A gas-liquid needle-plate discharge configuration was employed with MB solution as a simulated wastewater model. The ${\mathrm{TiO}}_2$ and ${\mathrm{Cl}}^{-}$ were introduced for synergistic treatment. The effects of discharge voltage, treatment duration, the presence of catalyst, and solution conditions (pH and ${\mathrm{Cl}}^{-}$) on degradation performance and energy efficiency were systematically investigated and finite element simulations were conducted to explore the underlying mechanisms. The results indicate that degradation performance is positively correlated with discharge voltage and treatment time. Acidic environments favour the reaction process, and the introduction of both the catalyst and ${\mathrm{Cl}}^{-}$ significantly improves degradation performance. Under the best-performing conditions within the investigated range (9 kV${}_{\mathrm{pp}}$, pH = 3, ${\mathrm{Cl}}^{-}$ and catalyst concentrations of 3 g/L, treatment time 2 h), a degradation rate of 97% and an energy yield of 150.9 mg/(kWh) were achieved, outperforming treatment with DBD alone. This enhancement may be associated with the synergistic interaction among plasma-generated reactive species, $\mathrm{Ti}{O}_2$-assisted photocatalysis, and ${\mathrm{Cl}}^{-}$-mediated reactive chlorine oxidation. This work provides new insights into DBD-based MB degradation and offers experimental evidence for energy-efficient textile wastewater remediation.