Different Electrochemical Reactor Configurations For The Oxidative Degradation Of Typical PPCPs

Pharmaceutical and personal care products（PPCPs）are frequently detected as an emerging class of contaminants in various environmental media（e.g.soil,water bodies,river sediments,etc.）around the world,and their long-term exposure in the environment may have toxic effects on organisms and induce the emergence of drug-resistant pathogens and resistance genes.The aim of this study is to achieve the removal of PPCPs from water using a green,safe and efficient electrochemical oxidation and its coupling process.By developing new electrode materials and optimizing the electrochemical reactor configuration to solve the problems of poor catalytic activity and low mass transfer efficiency in electrochemical oxidation technology,two systems,a flow-through electrochemical filtration reactor and a three-dimensional（3D）electrochemical reactor,were used to degrade PPCPs in water.The typical antiviral drug favipiravir（FP）and the non-steroidal anti-inflammatory drug diclofenac（DCF）were selected as model contaminants to investigate the electrocatalytic performance and degradation mechanisms of the two systems.Details of the study are given below:（1）Flow-through electrochemical filtration system.Uniformly ordered Ti O₂nanotube arrays（Ti O₂-NTA）were prepared on porous titanium plate substrates by anodic oxidation and cathodic reduction,based on which a penetrating Ti/Ti O₂-NTA/Ti₄O₇electrode was prepared and a flow-through electrochemical filtration system was constructed.The properties of the electrode,such as morphology and composition,were systematically characterized using various characterization tools,and the results showed that Ti O₂-NTA as an intermediate layer greatly contributed to the electrocatalytic activity and stability of the Ti/Ti O₂-NTA/Ti₄O₇electrode.Compared with the conventional Ti/Ti₄O₇electrode,the Ti/Ti O₂-NTA/Ti₄O₇electrode has a higher oxygen deposition potential（2.40 V,vs Ag/Ag Cl）,a larger specific active surface area（1.81 m²/g）,a stronger radical generation capacity（64.42μM）and a longer accelerated life（56.0 h）.The effectiveness of the system in degrading organic matter was further investigated using the typical antiviral drug FP as a model contaminant,and the results showed that the system could remove up to 93.6%of FP within30 min at a low current density of 4 m A/cm².The flow-through electrochemical filtration system offers significantly higher degradation ratios,TOC removal ratios and mineralization current efficiencies for FP and lower energy consumption compared to conventional flat plate reactors.Quenching experiments confirmed that FP removal was a combination of^·OH and SO₄^·-（free radical pathway）and anodic direct electron transfer（non-radical pathway）.The relative contributions of^·OH and SO₄^·-to FP degradation were calculated to be 30.35%and 15.64%respectively,indicating that^·OH plays a dominant role in the free radical pathway.In addition,the system still showed good FP removal（87.7%）in real wastewater and was efficient and versatile for a wide range of typical PPCPs,indicating that the flow-through electrochemical filtration system can be applied for the effective treatment of many different PPCPs.（2）Three-dimensional（3D）electrocatalytic-PS coupled system.The Cu⁰QDs-CoO@NC multilayer core-shell nano-catalyst was successfully synthesized by solvent heat and high-temperature carbonization methods,and it has excellent activation effect on persulfate（PS）.A series of advanced characterization tools were used to systematically characterize the microstructure and chemical composition of the material.The Cu⁰QDs-CoO@NC and PS were introduced into a conventional two-dimensional（2D）electrochemical reactor to construct a 3D electrocatalytic-PS coupled system（ECO/Cu⁰QDs-CoO@NC/PS）with strong synergistic catalytic effects.The introduction of electric field not only polarizes the Cu⁰QDs-CoO@NC nanomaterials into particle electrodes,the main anode（Ti₄O₇）and the main cathode（Ti）also promote the cyclic reaction processes of S₂O₈^2-→SO₄^2-→S₂O₈^2-and Mⁿ⁺→M^（n+1）+→Mⁿ⁺,respectively.The electrocatalytic performance of the system was examined using a typical non-steroidal anti-inflammatory drug DCF as a model contaminant,and the most superior catalytic performance of the 3D electrocatalytic-PS coupled system was demonstrated by seven sets of controlled experiments with different systems.Quenching experiments and electron paramagnetic resonance analysis showed that the degradation of DCF was a combination of three processes,namely PS activation,particle electrode and anodic oxidation,and the active species contributing to the pollutant degradation included SO₄^·-,^·OH,O₂^·-and ¹O₂,with ¹O₂playing a major role.Density flooding theory（DFT）calculations show that PS adsorbs preferentially on the catalyst Cosite over the Cu and NC sites,and the NC layer can act as an electron conduction bridge,facilitating the transfer of electrons Cu⁰QDs-CoO@NC surface to PS,contributing to the activation efficiency of PS.Due to the presence of both free radical and non-free radical pathways,the system exhibits high efficiency and strong environmental adaptability over a wide p H range and real waters.