| Recently,the effective treatment and discharge of wastewater has been paid more and more attention as a hot topic.In this process,printing and dyeing wastewater has the characteristics of high organic content and alkalinity,and the water quality changes greatly,so effective catalysts are urgently needed.Hydrotalcite is widely used in catalysis and environmental remediation because of its adjustable structure,large specific surface area and stable chemical properties.Graphene has shown excellent development potential in various fields since it was first prepared in 2004,its ideal crystal structure,excellent mechanical strength and huge surface area make it a common material in catalytic field.The study shows that the composite of hydrotalcite and graphene can effectively enhance the electrical conductivity of metal materials,so this kind of composite has been widely used in advanced oxidation technology and electrocatalytic system.Therefore,a Mn-Co layered double hydroxide/graphene composites was prepared as cathodes,the electrode morphology was characterized at different Mn/Co ratios and its redox properties was tested by electrochemical means.On the other hand,rhodamine B?RhB?wastewater was degradation under optimal conditions and preliminary mechanism was explored.?1?The Mn-Co-LDH materials were prepared by hydrothermal method,in which Mn/Co elements were set at 3:1,1:1 and 1:3 molar ratios?LDH1?LDH2?LDH3?,graphene oxide?GO?was prepared by the modified phosphoric acid method proposed by Tour group,and the Mn-Co-LDH/rGO composites?LDH1/rGO?LDH2/rGO?LDH3/rGO?were prepared by hydrothermal method.The XRD and XPS results showed that the material was composed of C?O?Mn?Co elements,and the main valence states of the two metals were 2 valence.The results of BET characterization showed that the maximum surface area of the material could reach 244.5 m2·g-1,and the pore size was mainly distributed in 010 nm.?2?The oxygen reduction reaction?ORR?and oxygen evolution reaction?OER?properties of the electrode were tested.ORR results showed that oxygen reduction peak appeared at-0.425 V,with the increase of Co element ratio and the addition of rGO,the peak current of the material increased from 0.486 mA·cm-22 to 0.749 mA·cm-2.Rotating disk electrode?RDE?resulted show that the number of transferred electrons in the reaction process was 2,that is,the two electron reduction process occured.OER results showed that the initial oxygen evolution potential of the LDH3/rGO electrode was 1.48 V,Tafel the slope was 47.8 mV dec-1.Otherwise,when the current density was 10 mA·cm-11 during the reaction,the overpotential was 346 mV,which was almost comparable to the commercial IrO2,indicating that the material had good stability.?3?The LDH3/rGO electrode was used as cathode to investigate the degradation effect under different conditions.The experimental results showed that the optimum conditions for the reaction were:dye initial concentration 20 mg·L-1,catalyst dosage 1 g·L-1,current density30 mA·cm-2,initial pH 11.Under the optimal conditions,the electrode could degrade 98.5%of the RhB dye within 120 min,and the degradation rate could still reach 95.7%after recycling the electrode for 3 times.The results of radical quenching experiment and EPR test showed that the main radical was·OH. |
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