Comprehensive experimental design on UV/H₂O₂ degradation of Rhodamine B

Rhodamine B (RhB) is a typical triphenylmethane dye with a carboxyl structure and a type of recalcitrant organic pollutant. It can cause significant damage to human health and the environment when discharged into water bodies. Ultraviolet/hydrogen peroxide (UV/H₂O₂) technology uses UV light excitation to decompose H₂O₂ into hydroxyl radicals (•OH) with strong oxidizing properties. The standard electrode potential of •OH is 2.8 eV, which is much higher than those of ordinary oxidants such as O₃, Cl₂, and H₂O₂. UV/H₂O₂ technology has the advantages of rapid reaction, low selectivity with organic compounds, and good treatment effects. In addition, the hydrolysis products of H₂O₂ are water and oxygen, which are environmentally friendly and do not cause secondary pollution. Therefore, among many advanced oxidation methods, UV/H₂O₂ technology is receiving widespread attention and research. Herein, a comprehensive experiment was designed to degrade RhB by the UV/H₂O₂ process. [Method] The effects of process conditions such as H₂O₂ dosage, pH value, and UV light intensity on the removal efficiency of RhB by UV/H₂O₂ were explored by single-factor experiments. Response surface methodology (RSM) was employed to examine the interaction of the different influencing factors. A quadratic regression model for the RhB removal rate was constructed, and its accuracy was verified through experiments. UV-Visible (UV-Vis) spectroscopy and three-dimensional fluorescence spectroscopy were applied to confirm the removal effect of RhB.

The results of the single-factor experiments indicated that the degradation process of RhB by UV/H₂O₂ followed the pseudo-first-order kinetic equation. Properly increasing the concentration of H₂O₂ improved the reaction rate and the degradation effect of RhB, but its excessive addition led to the self-loss of •OH. Weak alkaline conditions were more conducive to RhB degradation in UV/H₂O₂ systems. With the increased UV light intensity, the reaction rate constant k value significantly increased. The RSM results revealed that the interaction between H₂O₂ dosage and UV light intensity significantly affected RhB degradation. At a H₂O₂ dosage of 47.45 mL/L, the pH value was 8.11, the UV light intensity was 730 μW/cm², and the RhB removal rate could reach 92.44% after 120 min. The relative deviation between the experimental and predicted values of the model was 0.89%. The predicted values from the regression model established with Design-expert software were highly correlated with the experimental values, accurately reflecting the actual removal of RhB. The UV–Vis and three-dimensional fluorescence results showed that a large number of azo bonds were rapidly broken by the active components, and the polycyclic aromatic hydrocarbons in the molecular structure of RhB were disrupted, but some benzene derivatives were formed during the reaction.

The UV/H₂O₂ method could effectively degrade RhB dye wastewater. Single-factor experiments and RSM were used to optimize the conditions of the UV/H₂O₂ process, which helped improve students’ understanding of the influencing factors of the reaction, kinetic fitting and optimization of experimental conditions in scientific research training, and cultivating students’ scientific and rigorous style.