Study On The Capacitive Desalination Performance And Selective Removal Of Cu²⁺ By Hollow Mesoporous Carbon Nanospheres/MoS₂ Mobile Electrod

The progress of human industry and technology as well as the development of social economy have brought about the explosive growth of population and the huge demand for water resources.Various pollutants produced by human activities further aggravate the water resources crisis in the context of the scarcity of fresh water resources.Under the current low-carbon economy,the flow-electrode capacitive deionazition technology（FCDI）,as a kind of energy-saving and environmentally friendly technology developed from capacitive deionazition technology（CDI）,is applied to water desalination.Because of its environmentally friendly,low energy consumption,continuous desalination,energy recovery and other characteristics,it has been widely concerned in the field of seawater desalination and resource recovery.However,FCDI technology still faces two technical limitations in engineering practice:（1）insufficient electron/ion transfer ability of the mobile electrode and（2）difficulty in selective separation and recovery of special ions.Based on this,this paper proposes to construct a HMCNs/MoS₂ flow electrode and carry out research ideas of enhancing capacitive desalination and selective removal of heavy metal ions,and clarifies the structure-activity relationship between the structural composition of the flow electrode material and the desalination performance and heavy metal removal performance.The main conclusions are as follows.（1）Hollow mesoporous carbon nanospheres（HMCNs）were prepared by a“silica assisted”St?ber method and used for FCDI system desalination.The structure activity relationship between electrode structure characteristics and capacitive desalination were clarified by making a reasonable comparison between HMCNs,solid mesoporous carbon nanospheres（SMCNs）and activated carbon（AC）.Compared with the control group AC and SMCNs,HMCNs showed the best performance.The average salt removal rate（ASRR）was 0.031 mg/cm²·min^-1 at 1.2 V voltage and 5%electrode loading,which was 1.19 times and 1.41 times of SMCNs and AC,respectively.The charge efficiency（CE）and mole energy consumption（E_m）were 92.9%and0.035 k Wh/mol,respectively.The mechanism confirmed that the regular geometry,central cavity and mesoporous structure were beneficial to improve the dispersion of the active material particles and the rheological properties of the fluid,reduced the resistance in the flow electrode,and thus enhanced the ability of electron conduction and ion diffusion.（2）The two-dimensional layered pseudocapacitor MoS₂ was prepared by the thermal reaction of molybdate brine,and its characteristics of large surface area,high density and fast ion conduction were used to improve the desalting performance.It was shown that the optimal ratio of AC:MoS₂ in the electrode is 4:1 by a series of methods such as material characterization and electrochemical testing.In the FCDI desalination test,the ASRR of the 5 wt%material loading flow electrode for 1000 mg/L Na Cl at 1.2 V voltage was 0.0313 mg/cm²·min^-1,CE exceeded 90%,and the energy consumption demand was 0.0368 k Wh/mol.The ASRR of 5 wt%HMCNs/MoS₂ mixed flow electrode reached 0.0344 mg/cm²·min,the charge efficiency was97%,and the energy consumption was 0.0348 k Wh/mol under the condition of 1.2 V voltage and 1000 mg/L Na Cl.Mechanism analysis confirmed that,as a capacitor additive,MoS₂intercalation reaction provides a larger capacitance value.The carbon-based active material acts a good conductive bridge and it can provide capacitance.Under the combined action of pseudocapacitance and Na⁺intercalation reaction and electric double layer capacitance,it exhibited a better FCDI performance.（3）The synergistic effect of HMCNs and MoS₂ on the Cu²⁺removal performance of FCDI was studied by using them as mixed flow electrodes.The removal rate of Cu²⁺in 50mg/L Cu²⁺solution was 88.53%,and the removal rate of copper ions in 400 mg/L high-concentration Cu²⁺solution was more than 70%.In addition,the removal rate of Cu²⁺reached 65%in the strong Na⁺background mixed solution consists of 2000mg/L Na Cl and 100mg/L Cu Cl₂,which was higher than that of Na⁺.The mechanism analysis confirmed that the excellent Cu²⁺removal selectivity should be attributed to the interlayer structure of MoS₂ and the edge exposed S element can be combined with Cu²⁺with Lewis soft bonds,thus showing a stronger affinity for divalent Cu²⁺.Finally,after 1 hour of desorption with 0.1 M HCl,the electrode was recycled.The removal rate of Cu²⁺was still above 60%after 5 cycles,and the recovery rate of Cu²⁺was57.8%.This indicated that the electrode has a good cycle stability and resource recovery ability.