Construction Of Cobalt-based Carbon Nanotube Catalyst And Study On Electrocatalytic Production Of H₂O₂ In Situ Degradation Of Pollutants

Hydrogen peroxide（H₂O₂）,as a green oxidant,is widely used in the fields of chemical industry,medical disinfection and water treatment.At present,most industrial H₂O₂is indirectly produced through anthraquinone hydrogenation and subsequent O₂oxidation,and the process has disadvantages such as high energy consumption,required noble metal catalyst and complex process.Electrochemical oxygen reduction reaction（ORR）can reduce O₂to H₂O₂,plays a vital role in fuel cell and other green energy technologies.The generation of hydrogen peroxide by selective 2e^-oxygen reduction reaction（2e^-ORR）is considered a green alternative to anthraquinone oxidation due to mild reaction conditions and green on-site production,therefore,it is crucial to develop low-cost,high selectivity and efficient electrocatalysts for the electrosynthesis of H₂O₂.In recent years,the transition metal nitrogen coordination carbon-based electrocatalyst（M-N-C）has attracted much attention due to its adjustable electronic structure,low cost and high quality activity.Therefore,two cobalt-based carbon nanotube electrocatalysts were designed and prepared for H₂O₂production and in situ degradation of pollutants.The main contents of this paper are as follows:（1）Using core-shell MOF（ZIF-67@ZIF-8）as precursor,cobalt-based B,N co-doped carbon nanotube（Co-B,N-CNTs）electrocatalytic cathode materials were successfully prepared by chemical vapor deposition,the hollow carbon nanotube structure facilitates the transfer of electrons,and the synergistic effect of single-atom Co catalytic active sites and co-doped carbon with B and N elements makes the prepared Co-B,N-CNTs electrocatalyst with excellent electrocatalytic performance.The Co-B,N-CNTs catalysts showed excellent 2e^-ORR catalytic activity and selectivity in the acidic electrolyte,Co-B,N-CNTs exhibits a selectivity of over 80%over a potential ranging from 0.1 to 0.4 V vs.RHE.Co-B,N-CNTs catalysed the reaction at 0 V vs.RHE potential for 2 h,and the hydrogen peroxide production reached 1150 m M g^-1_cat,the current of continuous electrolysis for 10 h did not weaken significantly,indicating that the catalyst has good stability.Co-B,N-CNTs/carbon paper（CP）and stainless steel mesh（SSM）were used to construct a dual-cathode electro-Fenton system,and the in-situ generated H₂O₂reacted with electrons on SSM to convert to hydroxyl radicals（·OH）with stronger oxidizing properties.It has excellent degradation capacity to six different types of water pollutants including phenol,enrofloxacin（ENR）,ciprofloxacin（CIP）,tetracycline（TC）,rhodamine B（Rh B）and Cr（VI）,it can efficiently degrade various pollutants without adding chemical reagents,and the mechanism of the degradation process is discussed in detail using terephthalic acid as a fluorescent probe.（2）Using mesoporous molecular sieve（KIT-6）as template,cobalt acetate and zinc acetate as metal sources,the hydrogel precursors were synthesized through the complexation between polyvinylpyrrolidone,salicylic acid and metals,N-doped Zn-Co-based carbon nanotubes（Zn,Co-N-CNTs）electrocatalytic cathode materials successfully prepared by high temperature pyrolysis,and successfully extended to a general method for preparing different bimetallic nitrogen-doped carbon nanotube electrocatalytic cathode materials.The Zn,Co-N-CNTs electrocatalysts exhibit excellent 2e^-ORR in 0.1 M KOH due to the synergistic effect of monodisperse metal atomic catalytically active sites and N co-doped heterocarbons in hollow nanotubes,the H₂O₂selectivity can reach 90%in the potential range of 0.1-0.6 V vs.RHE.Zn,Co-N-CNTs catalysed the reaction at 0.2 V vs.RHE potential for 3 h,and the hydrogen peroxide production reached 3289 m M g^-1_cat,after four cycles of testing,Zn,Co-N-CNTs still has very good cycling stability.Meanwhile,Zn,Co-N-CNTs in0.1 M Na₂SO₄（p H=3）electrolyte by 3 h electrocatalytic preparation of H₂O₂production reached 0.893 m M g^-1_cat.Zn,Co-N-CNTs/CP and stainless steel mesh and SSM constructed a dual-cathode electro-Fenton system to effectively degrade levofloxacin（LEV）,chlortetracycline（AM）,and Cr（VI）,and the degradation efficiencies in 90 min were 79%,91.1%,and 97.2%,respectively,providing a green and sustainable path for the removal of pollutants.