Construction Of Fenton Catalytic System For Copper-Based Sulfides And Its Mechanism For Degrading Organic Pollutants

Organic contaminants in industrial wastewater are a serious threat to human life and health safety,and the efficient treatment of organic contaminants in water has become an important issue in current scientific research and engineering.Advanced oxidation processes（AOPs）have been widely used in catalytic oxidation for the degradation of POPs due to the large number of non-selective radicals generated in the reaction.Fenton oxidation,a typical AOPs,has become a popular area of research in recent decades due to its high efficiency and low cost.However,the conventional Fenton reaction based on the activation of Fe（Ⅲ）/Fe（Ⅱ）by hydrogen peroxide suffers from narrow working pH range（2.5-3.0）,low oxidant utilization,and slow generation rate of reactive oxygen species（ROS）.To overcome these drawbacks,copper-based heterogenous catalysts,with their higher catalytic oxidation capacity,wider pH applicability range and faster oxidant activation process,have played an important alternative role in Fenton technology and have a promising application in the construction of catalytic systems for practical industrial wastewater treatment.Nowadays,transition metal sulfides（TMSs）have gained wide attention as high-performance heterogenous catalysts in AOPs due to their unique physicochemical properties,such as abundant redox sites,excellent photoelectric properties,good thermal stability and mechanical stability.Correspondingly,copper-based transition metal sulfide heterogenous catalysts with different components and microstructures have shown multifunctional applications in Fenton-like,photo-Fenton and electro-Fenton processes,as well as low cost,low secondary pollution,flexible and controllable material design in actual industrial pollutant treatment.It was found that the efficiency of TMSs-based Fenton catalytic systems is restricted by the thermodynamic limitations of redox cycling from high-to low-valent metals,as well as the sluggish regeneration rate of low-valent metal active species.Inefficient active species cycling will inhibit the reaction rate and sustainability of the system,thus becoming a fundamental problem affecting the efficiency of this type of catalytic system.In recent years,bimetallic heterogeneous Fenton catalytic systems have been gradually developed,and multiple synergistic catalytic interactions between the bimetallic components can effectively promote the redox cycle of the active components,thus enhancing the catalytic efficiency of the system.In the current literature,the strategy of constructing bimetallic heterogeneous Fenton systems is mainly based on promoting the transfer of electrons to the higher valence components in the system,thus breaking the thermodynamic limitation of the conversion of the higher valence metals to the lower valence ones and promoting the regeneration of the lower valence metals.Firstly,the introduction of metal components with low redox potentials promotes thermodynamically favorable reactions due to the potential difference,thus enhancing the redox cycle of high potential metals.Secondly,electron-donating metal components are introduced to provide electrons to Fenton active components to reduce high-valent components under photocatalytic and electrocatalytic conditions.At present,the researchers mainly focus on making use of the high efficiency of Cu Fenton to enhance the Fenton catalytic activity of low active components such as Fe and Co.However,the catalytic activity of copper-based Fenton catalysts is also limited by the thermodynamic limitation of the conversion of Cu（Ⅱ）to Cu（Ⅰ）,and the approaches for further promoting the efficiency of Cu-based TMSs Fenton catalytic systems are still little studied.It remains unclear whether the introduction of lower potential metal components can enhance the Fenton catalytic efficiency of Cu-based TMSs.Based on the above issues,this thesis explores the mechanism of enhanced catalytic activity in the Fenton reaction of copper-based bimetallic sulfides by introducing a second metal element to construct an efficient copper-based bimetallic sulfide Fenton catalytic system and to expand the methodology for the synthesis of copper-based transition metal sulfide materials.（1）A convenient microwave-assisted synthesis method was proposed to prepare monometallic sulfides and bimetallic alloy/complex sulfides.and the Fenton-like and photo-Fenton catalytic activities of the as-prepared monometallic catalyst CU7S4 nanoparticles and bimetallic alloy/complex sulfides were evaluated by degrading the model pollutant phenol.Under the specified reaction conditions,the Fenton-like and photo-Fenton degradation efficiencies of the monometallic catalyst CU7S4 were 25.40%and 32.05%,respectively,and the Cu-Sn,Cu-Sb,and Cu-Fe bimetallic products significantly enhanced the Fenton-like activity（86.05%,78.64%,and 24.77-40.73%,respectively）.and the Cu-Ag bimetallic products significantly enhanced the photo-Fenton activity（63.65%）.This chapter presents a simple and rapid general synthesis method for the synthesis of monometallis and bimetallic alloy/complex sulfide heterogenous Fenton catalytic materials.and provides data support for the construction of bimetallic sulfide Fenton catalytic systems.（2）A series of Cu-Sn bimetallic copper-based sulfide（CTS）catalysts were successfully prepared by a facile microwave-assisted synthetic route,and the resulting CTS catalysts exhibited excellent Fenton-like catalytic activity for H₂O₂ activation and phenol degradation.The structure-performance correlation between the chemical components,microstructure,surface electronic structure and valence state of CTS and the catalytic activity of the materials were revealed,and CTS-1 exhibited the optimal Fenton-like catalytic activity among the synthesized CTS catalysts due to its high surface Cu species content and Cu（I）ratio.The effect of the reaction parameters on the Fenton-like performance of the CTS-1/H₂O₂ system was systematically investigated,and the system showed good catalytic performance at lower oxidant dosage,wider pH range and lower reaction temperature.^·OH,and^·O₂^-is the main ROS for phenol degradation,and the comparative study of CTS-1/H₂O₂ and Cu₇S₄/H₂O₂ radical generation confirmed that the CTS-1/H₂O₂ system enhanced the radical reaction.Finally,by studying the role of Cu,Sn,and S species in the catalytic oxidation process,the synergistic effect of Cu-Sn species was achieved to promote the Cu（Ⅱ）/Cu（Ⅰ）redox cycle in the CTS-1/H₂O₂ system,enhancing the H₂O₂ activation and the efficiency of phenol degradation.The study in this chapter provides a new idea for Cu-based TMS to promote Cu（Ⅱ）/Cu（Ⅰ）cycle in Fenton-like catalytic systems with Sn species with lower redox potential and variable metal valence,further expanding the application prospects of Cu-based TMS in AOPs technology.（3）The Cu-Ag bimetallic catalyst CAS was rapidly synthesized by a facile microwave-assisted synthesis route,and the effective photo-Fenton catalytic oxidative degradation of the organic pollutant phenol was achieved by constructing the Ag/AgCuS bimetallic sulfide complex system.The structure-performance correlation between material composition,structure and photocatalytic performance was systematically investigated,and the optimal degradation efficiency of CAS-1 was obtained due to its higher Cu（Ⅰ）valence content of Cu species and lower band gap.The effects of various reaction condition factors on the CAS-1/H₂O₂ system were systematically investigated to further investigate the activity and stability of the catalyst.The free radical reaction pathways in the system were investigated,and the presence of both Fenton-like catalysis and photocatalysis in the system was demonstrated,and the mechanism of enhancing the efficient degradation of phenol by H₂O₂ with photocatalysis and Fenton-like synergistic catalysis in CAS-1,an Ag/AgCuS bimetallic sulfide complex system,was elucidated.The synergistic catalysis in the photo-Fenton process is reflected in the synergy between the photocatalytic and Fenton-like reactions and the synergy among the catalyst components,and the localized surface plasmon resonance（LSPR）effect of Ag nanoparticles further promotes the transfer of photogenerated electrons to the high-valent metal,which strengthens the photocatalytic reaction and enhances the redox cycle in the system.This part of the research provides a new idea for constructing the optical Fenton system of bimetallic sulfide materials by introducing Ag components and adjusting the optical properties such as the band gap and band position of the catalytic materials to constitute the complex system of bimetallic sulfide combined with Ag nanoparticles.The Ag/AgCuS system can intensify electron transfer under visible light,while using the synergy between material components to achieve efficient catalytic degradation of phenol.（4）A generalized ion-thermal synthesis strategy using an amino acid ionic liquids[TBP][Cys]-mediated synthesis of transition metal sulfides（TMSs）is proposed.In this strategy,TMSs crystals with regular morphology and microstructure,including hierarchical structured Cu₇S₄ microspheres,ZnS and CdS nanoparticles,PdS polyhedral particles,and Bi₂S₃ nanorods,were successfully synthesized.The unique multifunctional roles of amino acid ionic liquid[TBP][Cys]in the synthesis of TMSs nanomaterials,such as chelator/reducer and stabilizer,were elaborated through theoretical analysis of the synthesis mechanism and experimental characterization of the hierarchical structured Cu₇S₄ microspheres,indicating the integrated solvent-template-precursor strategy of this ionic liquid-mediated synthesis of nanomaterials.In addition,the synthesized hierarchical structured CU7S4 microspheres exhibit good photo-Fenton catalytic activity for the refractory organic dye methylene blue（MB）under visible light irradiation.Considering the designability of amino acid ionic liquid molecules,we expect that the amino acid ionic liquid-mediated assembly strategy will provide a safe,green and versatile synthetic methodology for engineering inorganic nanomaterials,expanding the applications of functionalized ionic liquids in materials science.