Preparation And Desalination Performance Of Metal Sulfides-based Electrodes For Capacitive Deionization

With the increasing scarcity of natural fresh water resources,salt water and seawater desalination are one of the strategic solutions to solve this crisis.Capacitance deionization（CDI）is a new desalination technology with rapid development,which has the advantages of low cost,low energy consumption and environmentally friendly.CDI provides a new way for obtaining fresh water.Electrode materials are an important factor affecting the desalination efficiency of CDI,so the exploration of high-efficiency desalination electrode materials is a hot research topic in the field of CDI desalination.In this study,the desalination performance of CDI electrodes prepared by metal sulfides-based materials as the main electrode materials were investigated.Specific research contents and conclusions are as follows:1.Pure SnS and SnS/CNTs composites were successfully synthesized by solvothermal method by introducing different contents of carbon nanotubes（0,5,10,15,20 wt%）.SEM and Nitrogen adsorption and desorption measurements showed that the addition of CNTs not only promoted the network distribution of SnS,but also induced changes in the morphology and pore structure of SnS during the crystallization process.In SnS/CNTs composites,especially in SnS/CNTs-10%composites,irregular two-dimensional nanosheet SnS was observed,while pure SnS was in the shape of agglomeration.According to the CV test results,the SnS/CNTs-10%composite electrode has the high specific capacitance.When the scan rate is 5 m V/s,the specific capacitance is as high as 136.2 F/g.Combined with EIS test,the SnS/CNTs-10%composite electrode has the low resistance,at the same time,it is found that the SnS/CNTs-10%composite electrode has good cycling stability through GCD tests.Through capacitive deionization（CDI）experiments,it is found that the SnS/CNTs-10%composite electrode has the better desalination capacity.The maximum electrosorption capacity is 7.83 mg/g at room temperature,when the optimal applied voltage is 1.2 V,the flow rate is 20 m L/min and initial concentration of NaCl at 100 mg/L.2.The g-C₃N₄ nanomaterials and ZnS/g-C₃N₄ nanomaterials were successfully prepared by the high-temperature calcination method.The microstructure,morphology and elemental composition of the materials were characterized by XRD,FTIR,SEM and N₂ adsorption and desorption techniques.The results show that ZnS/g-C₃N₄ composites have larger specific surface area and porosity than the g-C₃N₄.CV test shows that the specific capacitance of g-C₃N₄ and ZnS/g-C₃N₄ is 24.66 F/g and 30.27 F/g,respectively,when the scan rate is 5 m V/s,the latter has better specific capacitance.Meanwhile,EIS and GCD test show that ZnS/g-C₃N₄has relatively small resistance and higher electrochemical stability.Finally,the desalination conditions of the two materials under different desalination modes of capacitance deionization（CDI）and Membrane capacitance deionization（MCDI）were investigated,as follows:g-C₃N₄//g-C₃N₄（CDI）,g-C₃N₄//g-C₃N₄（MCDI）and ZnS/g-C₃N₄//ZnS/g-C₃N₄（MCDI）.The results show that the ZnS/g-C₃N₄//ZnS/g-C₃N₄（MCDI）electrode has the better desalination ability.When the initial concentration of NaCl was 200 mg/L,the flow rate was 5 m L/min and the voltage was 1.2 V,the electrosorption capacity of ZnS/g-C₃N₄//ZnS/g-C₃N₄（MCDI）reached 27.65 mg/g.When the initial concentration of NaCl was increased to 400 mg/L and 600mg/L,the electrosorption capacity reached 50.26 mg/g and 65.34 mg/g,respectively.3.NiCo₂S₄ nanostructure material was successfully prepared by one-step hydrothermal synthesis method.The microstructure,morphology and pore structure of the material were analyzed and characterized by XRD,SEM,TEM and N₂ adsorption and desorption techniques.The results showed that the NiCo₂S₄ nanomaterial presented the hollow structure,which could enhance more active sites.CV test shows that when the scan rate is 5 m V/s,the specific capacitance of NiCo₂S₄ nanomaterial is 75.10 F/g,which has the good specific capacitance characteristics.Meanwhile,the EIS and GCD tests show that the NiCo₂S₄ material has the small resistance and good electrochemical stability.The desalination experiments were carried out in a self-assembled hybrid capacitor deionization（HCDI）device,using NiCo₂S₄ as anode material and AC as cathode material.At the same time,different modes of AC//AC（MCDI）,NiCo₂S₄//NiCo₂S₄（MCDI）,NiCo₂S₄//AC（without membrane）and NiCo₂S₄//AC（HCDI）were compared,and the results showed that NiCo₂S₄//AC（HCDI）had higher HCDI desalination ability.When the initial concentration of NaCl was 400 mg/L,600 mg/L and 1000 mg/L,the adsorption capacity could reach 18.86 mg/g,30.64 mg/g and 58.67 mg/g,respectively,under the condition of the applied voltage of 1.2 V and the flow rate of 10 m L/min.