Preparation And Application Of Pyrite-type Nano-cobalt Disulfide Films

The continuous development of our economy has led to an increase in the consumption of resources and energy.At the same time,environmental pollution,especially water pollution,is becoming more and more serious.During the"Thirteenth Five-Year Plan" period,the Ministry of Environmental Protection launched the "Water Pollution Prevention Action Plan’ to further improve the water pollutant discharge standards.The first-class A standard(COD 50 mg/L)has been implemented in some areas of wastewater discharge standards such as rivers,which requires a deep treatment of wastewater,often requires the use of photocatalysis,Fenton and other advanced oxidation methods.In view of the large consumption and high cost of the traditional Fenton method,a transition metal sulfide pyrite-type CoS2 film was synthesized and used as a cocatalyst for the Fenton reaction,which greatly improved the performance of the Fenton reaction to degrade the simulated dye wastewater.It is expected to reduce the amount of H2O2 oxidant and the output of iron mud.At the same time,considering the problem of H2O2 storage and transportation,this paper also studied the performance of electrocatalytic oxidation of H2O2 on the surface of pyrite-type CoS2 film by electrocatalytic method,in order to develop in-situ synthesis of H2O2 and Fenton oxidation degradation of pollutants.The method provides a theoretical basis.Main conclusions are as follows:Pyrite-type nano-CoS2 thin films were grown on graphite substrates by hydrothermal and chemical vapor deposition methods.The compositions and morphology were characterized by XRD,SEM and EDS.The results show that the synthesized product is a pyrite-type COS2 film with nano-flower structure.Using 20 mg/L Rhodamine B simulated dye wastewater as the target pollutant,CoS2 was used as the Fenton and Fenton-like promoter to degrade the dye wastewater.The reaction rate of CoS2 increased by nearly 3.8 times at 20 s.The utilization efficiency of H2O2 and the rate of catalytic oxidation reaction are significantly improved.Then,under the condition of pH=5,the Fe2+system was added with H2O2 and the H2O2 system was added with Fe2+.The former and the latter were 0.78 and 1.25 times of the traditional Fenton reaction efficiency,respectively.Fe2+and CoS2 cocatalysts are more efficient to use.The experimental results also show that factors such as pH,voltage and mass transfer affect the Fenton reaction catalyzed by CoS2.The lower the pH value,the better the catalytic effect of CoS2.When pH=2,the maximum reaction rate is increased by 587%.The application of a voltage enhanced the reduction of the cathode,and the reaction rate increased by 6%at 40 min.The increase in rotational speed enhances mass transfer,and the reaction rate is 1.38 times higher at 1600 rpm than at rest.The CoS2 catalyst can still achieve 90%decolorization rate after 420 min of circulation.XRD,EDS,SEM and other characterizations also indicate that the CoS2 catalyst does not decompose before and after the reaction.The mechanism of CoS2 promoted Fenton was investigated.The results showed that the exposed active sites in CoS2 reacted with Fe3+,a product of Fenton reaction,to produce Fe2+,which enhanced the speed limit step of the traditional Fenton reaction.In addition,the CoS2 promoted Fenton system.Among them,H2O2 first combines with Co2+to form Co-OOH and H+.Due to the stability of Co-OOH,the effect of slowly releasing H2O2 is objectively made,so that the·OH oxidation reaction can be carried out in a longer period of time,thereby improving the utilization of H2O2.The results of oxygen reduction(ORR)experiments of CoS2 electrode show that the initial potential of CoS2 electrocatalytic ORR reaction is increased by 0.05 V relative to the graphite potential,and the current density of CoS2 electrode is significantly larger than that of graphite electrode.According to the K-L equation,the number of generated electrons n is calculated.The total number of electron transfer n of the CoS2 electrode at different potentials is in the range of 2 to 2.6,and has a highly efficient 2e selectivity.It can be seen that the CoS2 electrode synthesized by the experiment has higher initial reaction potential,larger reaction current and higher reaction selectivity than the graphite electrode,and is an excellent oxygen reduction H2O2 electrode.