Preparation Of Cathode And The Degradation Of Organic Pollutants In Electron-Fenton System

With the rapid development of industry,large amount of industrial wastewater containing organic pollutants has been produced,which would cause serious harm to the municipal sewage treatment system and water environment if it hasn't been efficiently treated.Among various industrial sewage treatment methods,electro-Fenton has been widely studied and used because of its good environmental compatibility,amenability of automation,and low costs.The cathode materials obviously affect the electro-reduction process of oxygen and the formation of hydrogen peroxide,and then have crucial influence on the treatment efficiency.In this thesis,three two-dimensional conductive carbon-based materials were synthesized and coated on graphite flape to prepare the corresponding cathodes.They were aza-fused-conjugated microporous polymers/graphite flake?Aza-CMP/GF?cathode,graphite phase carbon nitride/graphite flake?g-C₃N₄/GF?,and carbon quantum dots/graphene/graphite flakes?CQDs/rGO/GF?,respectively.The morphology and structure were characterized by XRD,FTIR,SEM,TEM,UV-Vis.Their catalytic effect on the electrochemical reduction of dissolved oxygen to produce H₂O₂ was studied and the degradation of p-nitrophenol?PNP?and ornidazole in the electro-Fenton system were investigated.The details are as follows:?1?In the aza-CMP/GF cathode electro-Fenton system,the experiment results of constant current electrolysis showed that aza-CMP/GF cathode has obvious catalysis for the electro-production of H₂O₂.Under the optimal conditions after 90 min of electrolysis,the production of H₂O₂ was 830.6?mol?L^-1,which was 1.7 times of that using bare GF cathode.The degradation experiment of p-nitrophenol?PNP?in the presence of Fe²⁺showed that adsorbance of the three absorption peaks of PNP in UV-Vis spectrum were all significantly reduced during the electrolysis process,indicating PNP molecular structure was destroyed.Under the optimal conditions,the degradation rate of PNP was 69.4 after 180 min of electrolysis.The COD removal was also determined and it was 48.0%after 360 min of electrolysis.?2?In the g-C₃N₄/GF and N-CQDs/g-C₃N₄/GF cathodes electro-Fenton system,the prepared g-C₃N₄ and N-CQDs were characterized by FTIR?XRD?SEM?TEM and FTIR.The experiment results of constant current electrolysis showed that g-C₃N₄/GF cathode has obvious catalysis for the electro-production of H₂O₂.Under the optimal contions,the production of H₂O₂ reaches 944.3?mol·L^-11 after 120 minutes electrolysis,which is 1.9 times of that using bare GF cathode.The electro-Fenton system was used to degrade ornidazole in the presence of Fe²⁺and the UV-Vis spectra of ornidazole were used to display the structure changing of ornidazole.The experiment results showed that the absorbance of the peaks attributed to???^*,n??^*and resonance transition all decreased with electrolysis,but the absorbance of the peak from n?s^*transition increased,indicating that the structure of ornidazole was destroyed and transferred to other non-conjugated small molecula.Using the decrease of the maximum absorption of ornidazole to calculate the degradation rate,the degradation rate was 84.5%after 120min electrolysis and reached almost 100%after 300 minutes treatment.Ornidazole degeadation reached almost 100%after 240 minutes treatment by using N-CQDs/C₃N₄/GF cathode system.The photo-assisted electro-Fenton was also investigated and the results showed that the supplied UV-light accelerated degeadation of ornidazole but didn't change the degradation process.?3?In the CQDs/rGO/GF cathode electro-Fenton system,the prepared CQDs and rGO were characterized by FTIR,TEM and SEM.The constant current electrolysis results showed that CQDs/rGO/GF cathode has the best catalysis for the electro-production of H₂O₂ during the three cathodes.Under the optimal contions,the production of H₂O₂ reaches 1416.1?mol·L^-11 after 180 minutes electrolysis,which is 3times of that using bare GF cathode.In the degradation experiment of PNP in the presence of Fe²⁺,the UV-Vis spectra of PNP showed that the absorbance of all the absorption peaks decreased obviously,indicating PNP molecule was destroyed and removed.PNP degradation was 90.6%after 180 min electrolysis and the COD removal reached 64.3%after 360 min electrolysis.The photo-assisted electro-Fenton was also investigated and the results showed that ornidazole degeadation increased to76.7%by suppling UV-light.