Electrocatalytic Activity And Mechanism Of Doped Activated Carbon Fiber Cathode

The efficiency of electro-Fenton oxidation in wastewater treatment mainly depends on H₂O₂high effectively generated at the cathode via two-electron oxygen reduction reaction(ORR).Electrodes play a significant role in the ORR kinetics.Carbon-based cathodic materials(such as carbon felt,activated carbon fiber,carbon sponge,etc.)doped with nonmetals or metals are growing concern.The development of low-cost and environmentally friendly electrocatalysts that can be used in the synthesis of H₂O₂ have important scientific significance in the field of recalcitrant pollutant control in wastewater.In this paper,the electrocatalytic activities of carbon felt(CF),graphite felt(GF)and activated carbon fiber felt(ACF)for Reactivated Red X-3B(RRX-3B)degradation in the simulated wastewater were compared.It was found that ACF presented the best electrocatalytic efficiency.Exploiting ACF cathodes modified with cerium nitrate,ferric chloride,cobalt chloride,copper sulfate,lanthanum nitrate,phosphoric acid,boric acid and urea by hydrothermal calcination processes,which were denoted as Ce/Fe/Co/Cu/La-ACF and N/P/B-ACF,the electrocatalytic activities for 1000 mg/L RRX-3B degradation in simulated dyeing wastewater were studied.The results showed that Fe/Co/Cu/La-ACF cathodes didn't realize complete decolorization after 180 min.The UV₂₅₄ and COD removals on metals modified ACF cathodes were in the order of Ce-ACF>Cu-ACF>RACF>Co-ACF>Fe-ACF>La-ACF.The removal rate on Ce-ACF cathode(86.25%,88.63%)was significantly higher than on other cathodes.N/P/B-ACF cathodes realized decolorization of 95%after 30 min,showing the order on UV₂₅₄ and COD removals:PACF>BACF>NACF>RACF.The phosphorus modified ACF(PACF)cathode exhibited the outstanding performance(97.38%,91.33%),which was fabricated by hydrothermal treatment of65%phosphoric acid solution at 170?for 24 h and calcination at 700?for 2 h in nitrogen atmosphere.PACF as cathode,the simulated dyeing wastewater could be completely decolorized in 90 min,and the COD removal and mineralization were 91.33%and 92.97%,respectively.The morphologies and properties of ACF and PACF were characterized by SEM,BET,XRD and XPS.P=O,P-O-P and other oxygen-containing functional groups were observed on the surface of PACF.The electronegativity and electron transfer efficiency of phosphorus atoms provided abundant active sites for electrocatalytic reactions.PACF with a larger specific surface area(1697.70 m~2/g)promoted the reactants and electron transfer.The cyclic voltammetry(CV)and liner sweep voltammetry(LSV)curves indicated that P-doped benefited the enhancement of REDOX activity on PACF cathode.The influencing factors for simulated dyeing wastewater treatment in PACF/DSA electrolysis system were investigated.At p H of 3,Fe²⁺dosage of 0.6 m M and current density of 20 m A/cm~2,complete decolorization,97.13%UV₂₅₄ removal and 99.02%COD removal were realized for recalcitrant RRX-3B in simulated wastewater.It was found that COD removal on PACF/DSA electrolysis system was declined to 44.25%after five cycles,which was attributed to the loss of P active sites.Notably,PACF cathode presented superior electrocatalytic activity than raw ACF in long runs.O₂^-·dominated RRX-3B degradation,and the contribution of reactive oxygen species was in the order:O₂^-·>^·OH>~1O₂?SO₄^·-.The Fe²⁺/Fe³⁺cycling triggered chain reactions,enhancing the transition of radicals and electrocatalytic reactions.^·OH and O₂^-·attacked the azo bond N=N in RRX-3B,achieving wastewater decolorization and efficient pollutant mineralization.