Abstract:

Objective In order to enhance the efficiency of dyeing wastewater treatment and decrease the presence of transition metals in the process, Ti₃C₂ MXene was employed to reduce trace Fe³⁺ for rapid activation degradation of C.I. Reactive Black 5 (RB5) wastewater by sodium persulfate (SPS).

Method The RB5 solution was used as the research subject, and the degradation rate was employed as the evaluation criterion. The relationship between the concentrations of sodium persulfate (SPS), FeCl₃, and MXene, initial pH was investigated, and the influence of MXene on the degradation of RB5. The contribution rate of free radicals in the process of dye degradation was investigated through free radical quenching experiments.

Results The results showed that the degradation rate of RB5 simulated wastewater was up to 99.3% when a mixture of 2.0 g/L SPS, 0.06 mmol/L FeCl₃, and 60 mg/L MXene was stirred at 25 ℃ for 30 min. After MXene was applied, particle structures adhered to the surface. Furthermore, the formation of numerous Ti—O bonds and the reduction of Ti element introduced Fe element, leading to a 1.13% decrease in the crystallinity of the characteristic peak. The Fe³⁺/SPS/MXene system effectively degraded RB5. This is mainly attributed to MXene's role in promoting the reduction of Fe³⁺ to Fe²⁺, thereby accelerating the activation of SPS. RB5 degradation followed quasi-first-order reaction kinetics. Both Fe³⁺ and MXene demonstrated significant effects on the activation of SPS. The degradation efficiency of organic pollutants was modulated by changing the concentrations of Fe³⁺ and MXene. The degradation rate of RB5 was decreased as the pH value increased. Under alkaline conditions, iron ions were transformed into precipitates and lost their catalytic ability. This, in turn, hindered the effective degradation of dye molecules. In addition, MXene effectively prevented the hydrolysis of Fe³⁺ ions in water through its interlayer confinement effect. After the utilization of Ti₃C₂ MXene, the elemental O content was increased from 22.37% to 49.71%, suggesting that Ti₃C₂ MXene underwent oxidation. MXene before and after use revealed the presence of interfacial reactions between Fe³⁺ and MXene, resulting in the reduction of Fe³⁺ to Fe²⁺ by MXene. The degradation rate of RB5 in the Fe³⁺/SPS/MXene system for 30 min was 2.49% higher than that in the Fe³⁺/SPS/hydroxylamine process, indicating that MXene can continuously reduce Fe³⁺ under these conditions. When reactive dyes were degraded by the Fe³⁺/SPS/MXene system, the ·OH played a major role. Inorganic salts significantly altered the decolorization rate of the dye solution, but have little impact on the final decolorization rate.

Conclusion For 0.05 g/L of RB5 simulated wastewater, the optimal degradation conditions were found to be 2.0 g/L SPS, 0.06 mmol/L FeCl₃, and 60 mg/L MXene. Under these conditions, the degradation rate reached as high as 99.3% after being treated at 25 ℃ for 30 min. During the degradation process, while inorganic salts like NaCl significantly altered the decolorization rate of the dye solution, but had little impact on the final decolorization rate. The strong reducing MXene not only inhibited the hydrolysis of iron ions, but also continuously reduced Fe³⁺ to Fe²⁺. When the Fe³⁺/SPS/MXene system was adopted to degrade RB5 simulated wastewater. Neutral pH conditions could be achieved for degrading the wastewater, with ·OH playing a major role in degradation process.

Key words: reactive dye, MXene, sodium persulfate, free radical, dye wastewater, degradation rate