Porous/super-hydrophobic Carbon Cathode Prepared For Organics Degradation By Electro-fenton

The performance of H₂O₂ electro-generation by cathode was an essential factor for the degradation of organic pollutants by electro-Fenton.To enhance the capability of reducing O₂ to H₂O₂,two carbon cathodes with high-efficiency H₂O₂ electro-generation were fabricated by pore-creating or improving the hydrophobicity of the cathode’s surface.The efficiency of H₂O₂ generation was investigated on the basis of its characterization.The prepared cathodes were used to construct the two electro-Fenton oxidative systems,by which,to learn the degradation and mineralization ability of rhodamine B（Rh B）or cefepime.The intermediate products produced during the Rh B and cefepime degradation were analyzed.Thereafter,the possible degradation pathways in electro-Fenton oxidation were proposed.（1）A porous carbon cathode was prepared using graphite,polytetrafluoroethylene（PTFE）and degreasing cotton（DC）through sintering treatment.The carbonization of DC by heat treatment played an ideal role in pore-creating,enlarging the average pore diameter of the cathode and enhancing its surface hydrophobicity,which not only increased the reaction sites of O₂ reduction,but weakened the mass transfer resistance,and as a result,the adoption of degreasing cotton significantly improved the performance of H₂O₂ electro-generation.The optimal cathode was able to generate 567 mg L^-1 H₂O₂with the current efficiency（CE）of 86.7%by the electrochemical reaction of 60 min in the reactor with a cation membrane.The excellent effect of Rh B degradation was exhibited by an electro-Fenton oxidative system using the optimal cathode and a Ti/Sn O₂-Sb₂O₅-Ir O₂ anode.The Rh B solution of 50 mg L^-1 could be decolorized completely by the treatment of 10 min and the degradation of 50～90 mg L^-1 Rh B solution presented over 90%TOC removal by the treatment of 120 min,indicating the ideal mineralization of organic pollutants.（2）Polyurethane sponge was used to change the surface morphology of the cathode to obtain a certain rough surface.It was found that the hydrophobic property of the prepared cathode surface could be greatly enhanced by changing its surface morphology,which successfully allowed the preparation of super-hydrophobic carbon cathode.The improvement of the hydrophobic properties led to the increase of the gas affinity of the cathode surface,thereby enhanced the adsorption capacity and accessibility of the cathode to O₂,thus the ability of electro-reduction to generate H₂O₂was significantly increased.Based on the above finding,using a mixed material of carbon nanotube and graphite as the outer layer and graphite as the inner layer,a sandwich-like super-hydrophobic carbon cathode was fabricated.The recommended cathode exhibited an ideal performance for H₂O₂ electro-generation as well as a favorable stability.The cathode submerged in air-aeration solution（p H 3.0）has produced 376 mg L^-1 H₂O₂ with an observed current efficiency（CE）of 40%via the electrolysis of 60 min at the optimum potential.The electro-Fenton process developed with the recommended cathode exhibited an excellent performance for cefepime degradation.60 mg L^-1 cefepime could be completely degraded within 10 min and remove 30.0%TOC after 60 min treatment with 11.5%mineralization current efficiency.（3）It was found that the large number of hydroxyl radicals（·OH）and the oxidation of the anode were the main reasons for the degradation of organics.The organic intermediates formed during Rh B and cefepime degradation were identified by GC-MS or LC-MS,and on basis of the obtained results,the possible pathways for the degradation of the two organics in electro-Fenton oxidative system were proposed.（4）The improvement of the surface hydrophobicity and the lower initial p H were able to endue the cathode with a self-cleaning ability,which was conducive to the continuous and stable electro-generation of H₂O₂ in electro-Fenton oxidative system.Thereby,it would contribute to the electro-Fenton oxidation of organics.（5）The electro-Fenton degradation of cefepime evidently improved the biodegradability of the solution,indicating that biological methods could be adopted for further treatment after improving the biodegradability using electro-Fenton oxidation pretreated.Carbon cathodes with efficient H₂O₂ generation could be fabricated by pore-creating using the adoption of natural fibers or changing the morphology of the cathode surface,making the industrial application of electro-Fenton oxidative technology in the organic wastewater treatment possible.