Preparation Of Cobalt Sulfide-Based Materials And Their Application In PMS Activation For Rapid Degradation Of Emerging Contaminants Such As Chloroxylenol In Water

In recent years,emerging contaminants have been detected in groundwater and surface water in various regions.Among them,chloroxylenol(PCMX),which possesses antibacterial properties,is frequently detected in the influent water of wastewater treatment plants.It poses a serious threat to water safety and human health.Advanced oxidation processes based on peroxymonosulfate(PMS)offer significant advantages in treating emerging contaminants at low concentrations,with cobalt-based materials being recognized as the most effective catalysts for activating PMS.However,current research on cobalt-based materials is primarily focused on catalytic efficiency and degradation pathways,with a lack of correlation between their physical properties and reactivity.Additionally,some cobalt-based materials exhibit serious metal leaching,high preparation costs and poor stability.To address the above problems,a series of cobalt sulfide-based nano-catalysts were constructed in this paper,and the parameters optimization,mechanism analysis and practical applications were carried out around the activation process of PMS.The main research contents and results are as follows:(1)Three cobalt sulfide nano-catalysts(CoS2,Co3S4 and Co9S8)were successfully prepared by a one-step solvothermal method using cobalt tetrahydrate acetate and thiourea as precursors and ethylene glycol as solvent,and applied to activate PMS to degrade PCMX in water.The cobalt-sulfur molar ratio in the precursor solution was found to significantly affect the physical properties(crystal structure,morphology and specific surface area,etc.)of cobalt sulfide,which largely determines its catalytic activity.Co9S8 and CoS2 showed nanoflower and nanosphere morphologies,respectively.Co3S4 showed a mixture of hollow nanospheres and nanosheets.With the increase of cobalt-sulfur ratio,the specific surface area of cobalt sulfide increased significantly and the surface active sites(Co2+surf.)were exposed more fully.Therefore,the degradation efficiency of PCMX followed the order of Co9S8>Co3S4>CoS2.In the pH range of 6.6-11.0,Co9S8/PMS system was basically able to achieve complete removal of 20 mg/L PCMX within 3 min.The mechanistic studies showed that the main reactive oxygen species responsible for PCMX degradation were SO4·-,HO·and 1O2.Sulfur vacancies and sulfur species S2’ played a crucial role in accelerating the Co2+/Co3+cycle and improving the catalytic efficiency.Meanwhile,the PMS catalytic activity of Co9S8 was less affected by inorganic anions and humic acids in water.And Co9S8 showed good catalytic stability in pollutant cyclic degradation experiments.(2)On the basis of the above research,it is urgent to solve the key problem of cobalt ion leaching during the application of cobalt sulfide nano-catalysts.From the perspective of economy and stability of catalyst preparation,this paper utilized chitosan adsorption of cobalt ions to generate Co9S8/CS in situ vulcanization and further pyrolytically constructed a chitosan-derived carbon loaded Co9S8 composite(Co9S8/C).The catalytic efficiency and mechanism of Co9S8/C/PMS system were investigated.As a carrier,chito san-derived biochar plays a role in dispersing Co9S8,alleviating metal agglomeration and cobalt ion leaching.Co9S8/C-1 composites almost completely degraded 20 mg/L PCMX within 5 min.Compared with Co9S8,the cobalt leaching concentration of Co9S8/C-1 was reduced by nearly 10 times.It was only 0.62 mg/L after 5 cycles.Both free radical and non-free radical degradation pathways exist in Co9S8/C1/PMS system,in which SO4·-and 1O2 play a dominant role.The adsorption states of SO4·-and HO· and Co(Ⅳ)on the surface of Co9S8/C-1 also play a certain role in the degradation of PCMX.In addition,Co9S8/C-1/PMS system has the ability to resist the actual water matrix interference.It possesses great potential for practical application because of its broad spectrum of degradation of multiple pollutants(bisphenol A and phenol,etc)in single and mixed pollutant systems and high catalytic activity and low metal leaching in continuous flow long-term operation tests(10 d).In this paper,the correlation between the crystal structure,morphology and specific surface area of cobalt sulfide nano-catalysts and the cobalt-sulfur molar ratio in precursor solution and its PMS catalytic activity was confirmed.Meanwhile,the Co9S8/C/PMS catalytic system was constructed in order to alleviate the leaching of cobalt ions and reduce the preparation cost of the catalyst.It provides theoretical and technical support for the application of cobalt sulfide-based materials to the advanced treatment process of emerging contaminants such as PCMX.