Research On The Removal Of Phenol And Quinoline By Heterogeneous Fenton Method Under Partial Neutral Condition

In recent decades,the coking industry is developing rapidly,but it is accompanied by environmental pollution problems.Among this,coking wastewater has attracted a lot of attention from researchers at internal and abroad because of a large volume of water,high pollution,and difficult to treat.The traditional treatment method of coking wastewater in China is mainly the combination of physicochemical and biological method.But with the improvement of national emission standards,traditional treatment methods can no longer meet the emission requirement.Advanced oxidation methods?AOPs?has attracted researchers attention because of its green and high efficiency.The hydroxyl radical?·OH?generated by the reaction has high redox potential,which can attack pollutants without selectivity,resulting in no secondary pollution.Among AOPs,the heterogeneous Fenton method has great potential for removing refractory organic pollutants due to its simple operation,high oxidation efficiency,catalyst recycling and wide pH reaction.In this paper,CuFeO₂,a catalyst material with high activity under near-neutral conditions,CuFeO₂@C was prepared by loading nano-carbon on the catalyst surface.The two materials were used to catalyze H₂O₂ to degrade simulated wastewater such as phenol and quinoline.The catalysts were characterized by XRD and SEM.Combined with the different degradation ratios of phenol and quinoline,the optimum ratio of the two-step CuFeO₂@C catalyst was determined.The applicable range of pH in the two reaction systems,the concentration of oxidant H₂O₂ and the effect of catalyst dosage on the removal of target pollutants were investigated.The metal dissolution rate and reusability of the materials were measured.The mechanism of CuFeO₂@0.5C catalyzing H₂O₂and the degradation pathway of phenol,quinoline were inferred through the free radical identification experiment,the TOC removal rate and pH value during the reaction,and the utilization rate of H₂O₂,combined with the results of UV-Vis full spectrum scanning.SEM characterization showed that CuFeO₂ consisted of rhombohedral crystals with the size of 1³?m.The catalytic activity was greatly improved after loading nano-carbon on the surface.When the optimum molar ratio of CuFeO₂ to glucose is 1:0.5,the prepared catalyst has higher activity.In the system where the target pollutant is phenol,the main oxidation agent was·OH.When the amount of catalyst was 1.0 g/L,the H₂O₂ dosage is 20 mmol/L,and the pH=5,the removal rate of phenol up to 99%at 120 min,the TOC removal rate reached 64%.The catalyst still has higher activity after repeated use for 6 times.The total iron and copper eluted on the surface of CuFeO₂ were 2.45 mg/L and 0.35 mg/L,respectively.The total iron and total copper dissolution on CuFeO₂@0.5C were1.242 mg/L and 0.12 mg/L,respectively.During the reaction,the pH decreased first and then increased.The utilization rate of H₂O₂ in CuFeO₂+H₂O₂ system was38.3%,and the utilization rate of H₂O₂ in CuFeO₂@0.5C+H₂O₂ system was47.2%.In the system with the target pollutant was quinoline,when the catalyst usage was 2.5 g/L,H₂O₂ concentration was 40 mmol/L and pH=5,the quinoline removal rate can reach over 95%in 300 min,and the TOC removal rate was reached 65%.The total iron and total copper eluted on the surface of CuFeO₂ were3.27 mg/L and 0.52 mg/L,respectively.The total iron and total copper dissolution on CuFeO₂@0.5C were 1.73 mg/L and 0.36 mg/L,respectively,and it has high catalytic activity and stability in repeated use.The utilization rate of H₂O₂ in the CuFeO₂+H₂O₂ system was 22.3%,and the utilization rate of H₂O₂ in the CuFeO₂@0.5C+H₂O₂ system was 35.9%.The active materials of CuFeO₂ and CuFeO₂@0.5C catalyzed H₂O₂ are derived from the valence transition of Cu⁺/Cu²⁺and Fe²⁺/Fe³⁺ion pairs,while the presence of surface nano carbon accelerates the electron conduction rate of the catalyst,thereby increasing the catalytic activity.It was found that the utilization rate of H₂O₂ was low because the neutral condition causes the H₂O₂ to be decomposed inefficiently,resulting in low catalytic activity of the reaction system.In order to study the heterogeneous reaction process with high catalytic activity under neutral conditions,we selected peroxymonosulfate?PMS?which is more convenient to store and has good oxidation effect under neutral conditions as the oxidant of the heterogeneous reaction system,and then tested the catalytic performance of CuFeO₂ and CuFeO₂@0.5C.It was found that CuFeO₂ and CuFeO₂@0.5C materials have low activity in catalyzing PMS.Subsequently,?-MnO₂ with high catalytic activity was selected as a catalyst for heterogeneous Fenton system according to literature reports.The catalytic activity of the?-MnO₂-PMS system was investigated.The?-MnO₂ was characterized by XRD and SEM,and the different ratios of precursors in the preparation of?-MnO₂ materials were determined.The pH application range of the reaction system,the dosage of oxidant PMS and the dosage of?-MnO₂ to remove phenol were investigated,and the reusability of the material was investigated.The mechanism of?-MnO₂ catalyzed PMS was inferred by the free radical identification experiment,the TOC measurement results and the UV-Vis full spectrum scanning.The catalyst was characterized by catalytic activity XRD and SEM.The optimum precursor ratio in the preparation of the catalyst was KMnO₄:MnSO₄·H₂O=2:3.At this time,the catalyst exhibited a needle shape of about 2?m,which was optimized by Response Surface Methodology.The factors were obtained at pH=7,the PMS dosage was 1.15 mmol/L,and the?-MnO₂ dosage was0.25 g/L.The catalytic effect was optimized.Under this condition phenol could remove 95.6%in 75 min.By quenching the reaction of tert-butanol and methanol,it can be identified that the main active substance in the system is sulfate radical?SO₄·^-?.The pH of the reaction is decreased first and then increased.The removal rate of TOC reached 64.5%.The mechanism of?-MnO₂ catalyzing PMS mainly depends on the valence state of Mn³⁺/Mn⁴⁺on the surface of the catalyst,and the utilization rate of PMS is higher,which can reach more than 70%.