Study On G-C₃N₄-based Fenton-like Catalytic Degradation Of Organic Wastewater

Refractory organic pollutants have become the focus and difficulty for research workers with high stability and strong toxicity,which cannot be treated by traditional biochemical methods.In contrast,Advanced Oxidation Process?AOP?is considered as a promising technology that can generate highly active free radicals and completely mineralize organic pollutants into water and carbon dioxide.Fenton oxidation technology is a kind of AOPs.The traditional Fenton oxidation technology uses Fe²⁺as a catalyst for homogeneous Fenton catalysis,however,it has the disadvantages of narrow p H response range and difficult recovery of iron ions.Heterogeneous Fenton-like catalysis overcomes the shortcomings of traditional homogeneous Fenton catalysis and exhibits excellent catalytic activity.In this paper,Rhodamine B was used as a simulated organic pollutant to investigate the Fenton-like catalytic performance on g-C₃N₄-based material.XRD,FTIR,SEM and XPS were used to characterize the synthesized catalyst.Graphitized carbon nitride?g-C₃N₄?is a typical inorganic non-metallic material,which attracts huge concern mainly as a photocatalyst,but its Fenton-like catalytic performance has been overlooked.In the third chapter of this paper,metal-free catalyst g-C₃N₄was synthesized by conventional urea pyrolysis without any modification,and then the Fenton-like catalytic performance of g-C₃N₄was evaluated for the first time by degrading Rhodamine B over a wide p H range.The results showed that the g-C₃N₄was an efficient metal-free heterogeneous Fenton-like catalyst.The highest activity occurred under a weakly alkaline condition of about p H10.The experiment of catalyst recycling indicated that g-C₃N₄had long-term stability.The reactive oxidizing species of·OH,generated by the g-C₃N₄activating H₂O₂,was identified by ESR and further supported by a scavenging experiment of·OH using isopropanol as the scavenger.The HNO₃oxidation of g-C₃N₄resulted in catalytic deactivation,implying the catalytic activity originated from the surface reduced groups of g-C₃N₄.The structure of synthesized g-C₃N₄before and after the HNO₃oxidation was characterized by XRD,FTIR,XPS,and a possible catalytic mechanism was proposed.In the fourth chapter of this paper,a small amount of Cu²⁺was introduced into the g-C₃N₄heterogeneous Fenton-like system.The results showed that Cu²⁺and g-C₃N₄had obvious synergistic effect.Under the concentration of Cu²⁺was 0.64mg/L,The results showed that the Cu²⁺/g-C₃N₄system exhibited excellent Fenton-like catalytic performance for a variety of dyes over a wide p H range.The content of Cu²⁺in the supernatant was determined by flame atomic absorption spectrometry after absorption-desorption equilibrium.The result showed that the Cu²⁺content decreased significantly,and the reduced Cu²⁺may be adsorbed to the active site of g-C₃N₄.Nitric acid oxidation experiments proved that the reducing active sites in the g-C₃N₄structure played an important role in the catalytic process of the Cu²⁺/g-C₃N₄system.Low concentration of Cu²⁺was also necessary in the catalytic process of Cu²⁺/g-C₃N₄system.EPR experiments and the radical trapping experiments showed that·OH radicals were the major reactive oxidizing species in the reaction process,During the catalytic reaction,g-C₃N₄provides reducing active sites for the Cu⁺/Cu²⁺redox cycle,and promotes Fenton-like catalytic processes through strong electronic interactions.In the fifth chapter of this paper,Cu@g-C₃N₄composite was prepared by one-step hydrothermal method.Cu²⁺was existed in the form of Cu?II?-N?copper porphyrin?in Cu@g-C₃N₄composite.Cu@g-C₃N₄composite exhibited excellent catalytic performance at room temperature?25°C?and p H5.Rhodamine B degradation rate reached 90.3%after 60 min catalytic reaction.The apparent activation energy of degradation calculated was 7.09 k J/mol,implying a lower reaction barrier.The radical trapping experiments proved that·OH radicals were the major reactive oxidizing species.The electron-donating effect of N made the reduction product[Cu-N]⁺more stable than Cu⁺,which is beneficial to the redox reaction of Cu⁺.