Preparation Of Carbon-based Hollow Structural Materials And Research On The Performance And Mechanism Of Removing Lead Ions From Water By Capacitive Metho

Lead（Pb）pollution has become a serious environmental problem with the development of metallurgy,chemical manufacturing,and mining,especially battery industries from wastewater disposal.Furthermore,the accumulation of Pb shows chronically harmful effects on the human,such as hematopoietic,nerve,kidney,cardiovascular and endocrine systems.Capacitive deionization（CDI）technology is a neoteric and attractive method for wastewater treatment,owing to its economization,convenient operation,regenerable electrodes and environmental friendliness,and electrode materials show crucial effect in this technology.Currently,carbon materials based on the electric double layer theory are used as conventional CDI electrode materials.Nevertheless,these carbon materials possess weak adsorption performance and low selectivity.The transition metal oxides and transition metal dihalogenated compounds based on Faradaic capacitance show excellent deionization performance,nevertheless,they possess low electrical conductivity and poor cycle performance attributed to torpid dynamics and large volume change.Therefore,the design of efficient and stable electrode materials is the key to improve the capacitive removal performance of Pb²⁺.The composite of Faradaic materials and carbon materials is an effective method for the synthesis of target materials.Molybdenum dioxide（Mo O₂）and molybdenum disulfide（Mo S₂）are two kinds of Faradaic materials.Mo O₂ shows high charging rate and reversible capacity,while Mo S₂ possess large specific surface area and large layer spacing.Both of them are ideal materials for CDI.Among various carbon materials,three-dimensional（3D）N-doped hollow carbon spheres（NHCS）show the advantages of large specific surface area,good charge transfer ability and wettability.Additionally,excellent porous structure is beneficial to improve the electrical capacity and electrochemical performance of the material.Herein,3D N-doped hollow carbon spheres are used as the substrate to synthesize hollow spherical Mo O₂@NHCS and hollow nano-flowered Mo S₂/NHCS,and the removal mechanism of lead ion was analyzed.The main achievements are as follows:（1）The Mo O₂@NHCS material was prepared by hydrothermal and calcination with silica as hard template,and then as electrodes for capacity removal of Pb²⁺from wastewater by CDI.The Mo O₂@NHCS electrodes show the high adsorption capacity of 202.14 mg/g in 50 ppm Pb²⁺solution under p H=6 and U=1.2 V.In addition,the Mo O₂@NHCS electrodes exhibit 90%Pb²⁺removal efficiency in 10 ppm Pb²⁺solution and excellent regeneration ability,especially high selective removal efficiency from mixed solution.The DFT calculations show that Mo O₂ crystals adsorb Pb²⁺in Tetrahedral mode with the highest adsorption energy(E_ads=-1.61 e V),and the charge density difference indicates that the insertion of Pb²⁺makes the transformation of the Mo O₂ crystal.The selective removal of Pb²⁺is attributed to the transformation between octahedral Mo O₂ and tetrahedral[Mo O₄]^2-.（2）In order to further improve the removal efficiency of Pb²⁺at higher concentration,NHCS are used as the substrate to synthesize hollow nano-flowered Mo S₂/NHCS by hydrothermal and calcination,and then as cathode for capacity removal of Pb²⁺from wastewater by CDI.The Mo S₂/NHCS electrodes show the high removal efficiency of 96.9%in 20 ppm Pb（NO₃）₂ solution under p H=6 and U=1.2 V.In addition,Mo S₂/NHCS electrodes show a maximum removal efficiency of 98.2%of Pb²⁺and excellent regeneration ability in 10 ppm Pb²⁺solution,with the removal efficiency still reaching 97.7%after 20 cycles,especially high selective removal efficiency from the mixed solution.The highly selective removal of Pb²⁺by Mo S₂/NHCS electrodes is attributed to the combination of Pb²⁺and S^2-to generate Pb S after Pb²⁺enters the inner space of Mo S₂,while some S ions get electrons to transform into S₂^2-and further combine with Pb²⁺to form Pb S₂.The electrode is converted to Mo S₂ again after desorption.In summary,the CDI technology was adopted to removal Pb²⁺in this manuscript.Meanwhile,the removal mechanism was analyzed through various means,providing the potential in the practical application to Lead-containing wastewater treatment.