The In-Situ Activation Of Dissolved Oxygen By Modified Zero-Valent Metals Catalyst

Recently,along with the utilization of energy sources and the process of industrialization,the emergence of various environmental contaminants has gradually exposed the limitation of those treatment technologies for traditional pollutants.To achieve promising performance in the treatment of contaminants for the traditional Fenton/Fenton-like technology,it is necessary to consume a large number of oxidants,and sometimes the combination with other methods is also indispensable.It not only increases the cost of treatment but also raises energy consumption.According to the requirements of green and clean development in the“14th Five-Year Plan”,improving the treatment technology based on the environmental-friendly view of energy-saving and low-carbon is becoming the focus of research.Oxygen activation is a continuous process in which molecular oxygen is adsorbed on the catalyst surface,and the electron transfer on the catalyst surface is used to improve the re-dissociation of its activity.It is the crucial step in the catalytic reaction,including oxygen reduction reaction（ORR）in fuel cells,catalytic combustion of volatile organic compounds（VOCs）and so on.In this work,a series of three-dimensional graphene-wrapped nano-zero-valent metals（3D-GN@n ZVMs）,as heterogeneous Fenton-like catalysts fabricated through a self-assembly process of liquid-phase reduction under ambient conditions,played an important role in the Fenton-like reactions triggered by the oxygen activation.3D-GN@n ZVMs were featured with good three-dimensional construction wrapped nanoparticles,which effectively alleviated the problem of nanoparticles that tended to be deactivated due to aggregation,and broadened the p H application range of Fenton-like systems.The micro-cells formed between graphene matrix and n ZVMs endowed 3D-GN@n ZVMs with excellent properties of electron delivery and high reactivity,which could effectively activate dissolved oxygen（DO）to in-situ generate hydrogen peroxide（H₂O₂）and form a novel heterogeneous Fenton-like system for the efficient removal of antibiotics.The main points of this work are shown as follows:（1）Nanoscale zero-valent iron（n ZVI）,nanoscale copper and n ZVI-doped amorphous Al encapsulated in the three-dimensional graphene network（3D-GN@n ZVI,3D-GN@Cu and3D-GN@n ZVI/Al）was synthesized and characterized by scanning electron microscopy（SEM）,Brunauer–Emmett–Teller（BET）analysis,X-ray diffractometer（XRD）,Raman spectrum and density functional theory（DFT）calculations.The results showed that the nanoparticles were uniformly dispersed in the interlayer and pore structure of the three-dimensional graphene.The active metal and graphene in 3D-GN@n ZVMs formed a micro-electrolysis structure,and the active metal was the main DO activation and catalytic center.（2）The removal of antibiotics by 3D-GN@n ZVMs activated dissolved oxygen was investigated,and the effects of different catalysts,solution p H,catalyst dosage,reaction temperature and other ions on the degradation of antibiotics were studied.Through removal experiments of sulfadiazine（SDZ）,the optimal removal efficiency of SDZ（10 mg/L）reached 81%in the 3D-GN@n ZVI-DO system at p H 3.2 under 298 K.The3D-GN@Cu⁰-DO system effectively degraded metronidazole（MNZ）in a wide p H range（p H 3.2-7.2）with the removal rate of 92%-63%,and the TOC mineralization was 65%at p H 3.2.3D-GN@n ZVI/Als could effectively remove chloramphenicol（CAP）with or without DO in the p H range of 3.2-12.6.The degradation of antibiotics conformed to the pseudo-first-order kinetic model,and the thermodynamic results showed that the degradation was driven by a chemical reaction.（3）Based on the experiments of radical scavengers and electron paramagnetic resonance（EPR）spectroscopy,the active oxygen species（ROSs）generated in the 3D-GN@n ZVI-DO and 3D-GN@Cu⁰-DO systems were determined as·OH,while the main active species generated on the surface of 3D-GN@n ZVI/Als was singlet oxygen（¹O₂）.Combined with the variation of Fourier transfer infrared（FTIR）spectrum,X-ray photoelectron spectroscopy（XPS）,ORR tests and DFT calculations,the mechanisms of 3D-GN@n ZVMs activated dissolved oxygen were explored.The active metals and graphene in3D-GN@n ZVI and 3D-GN@Cu⁰ formed micro-electrolysis promoted Fenton-like reaction to enhance electron transfer on the catalyst surface,thereby activating dissolved oxygen to generate·OH.Singlet oxygen（¹O₂）was confirmed to be generated through single electron transfer from the effective activation of DO by 3D-GN@n ZVI/Als.Moreover,intermediates produced during the degradation of antibiotics were detected by LC/MS,and the possible degradation pathways were proposed.（4）The stability and economy of the 3D-GN@n ZVMs catalyst were evaluated.The results of the cyclic experiments showed that 3D-GN@n ZVI became invalid after two repetitions.After 3D-GN@Cu⁰ was used three times,the degradation rate of MNZ was63%.3D-GN@n ZVI/Al had good stability,and the degradation rate of CAP after three cycles of use was 55%.The preparation process of the 3D-GN@n ZVMs catalyst was simple,and no additional chemicals and auxiliary technologies were required during the application,which had high economic applicability.This is expected to be used for the treatment of a variety of complex organic pollutants generated in energy utilization.