The Construction Of Ion Diffusion Pathways In Nanosheet-assembled Materials For Lithium Storage And Water Contaminant Removal

Fast energy storage and contaminant removal become two research cores recently,all of which are related to the ion diffusion rates of active materials.The ion diffusion of the heterogeneous reaction has three steps:liquid,solid-liquid interface and solid diffusion.Limited by sizes and transport modes,solid-liquid interface and solid diffusion are generally the rate-limiting steps in reactions,particularly solid diffusion which relies on pore channels in crystal structures.Therefore,the construction of ion diffusion pathway is significant,which is the topic of this dissertation.By regulating the hierarchical structure of nanosheet-assembled materials,firstly,the ion transport at solid-liquid interface of nanocatalysts is promoted by using mesopores and hollow nanotubes with open ends.Secondly,the similar structure is applied in micron-sized catalysts to enhance the ion transport at interface and improve the mass transport efficiency of bulk materials.Thirdly,the effective solid-liquid interface and solid diffusion pathways are constructed for lithium storage by increasing the diffusion dimensionality of assembled units and changing assembled structures.Finally,the solid diffusion of anode materials is transformed to solid-liquid diffusion by using ultra-small nano-sized assembled units,enhancing the diffusion kinetics of the materials.The concrete contents are as below:1.Regulation of secondary structures of hollow manganese silicate nanotubes with open ends for excellent catalytic degradation of organic dyes:Efficient mass transport at solid-liquid interface is crucial for catalysts.Therefore,hierarchical manganese silicate hollow nanotubes(MnSNTs)assembled by tunable secondary structures are precisely fabricated by the self-sacrifice of the template and systematically investigated as Fenton-type catalysts.The open ends and mesoporous walls of the hollow nanotubes effectively shorten the diffusion pathway of ions,increase the contact area of solid-liquid phase,and enhance the mass transport at the interface.MnSNTs exhibit different secondary structures by tuning the hydrothermal reaction time.Compared with large nanosheets and nanoparticles,numerous standing small nanosheets endow MnSNTs with a higher specific surface area and larger pore volume,and thus those MnSNTs expose more active sites.MnSNTs have highly efficient catalytic degradation performance towards cationic dyes with an excellent recycling stability.50 ppm of methylene blue(MB)can be degraded in 45 min at an ambient temperature.When the temperature increases to 60?,the degradation only needs 2 min.2.Construction of hierarchical mesoporous cobalt silicate architectures for highly efficient catalytic degradation of organic contaminants:Large-sized bulk catalysts are more beneficial for sedimentation and separation in practical application than nanocatalysts.However,inferior contact of solid-liquid phase restrains their catalytic performance.Therefore,the mesoporous hierarchical hollow nanotubes are constructed in a micron-sized catalyst,creating massive solid-liquid diffusion pathways in the bulk material.A series of metal silicates,including cobalt silicate(CoSiOx),copper silicate,nickel silicate,iron silicate,and magnesium silicate,are synthesized from Indocalamus tessellatus leaves as the biomass-derived silica source and investigated their catalysis in sulfate-radical-based advanced oxidization processes Among them,CoSiOx presents an analogical sandwich structure as the leaf-derived template with not only micron-level sizes but also abundant pore channels,increasing the contact area of solid-liquid phase.More importantly,the interior hollow nanotubes assembled by small nanosheets provide numerous pathways for ion diffusion and resolve the mass transport problem in such large bulk materials.Hence,CoSiOx exhibits excellent catalytic performance with 0.242 and 0.153 min-1 rate constants for the degradation of MB and phenol,respectively3.Fabrication of layered K2Mn4O8/reduced graphene oxide nanocomposites for high-performance lithium storage and adsorption of lead ions:Mesoporous hierarchical structures can effectively enhance the ion transport at solid-liquid interface,whereas the solid diffusion problem remains unresolved.Therefore,layered K2Mn4O8(KMO)nanoplates are fabricated with a mild solution process,and in-situ anchored on reduced graphene oxide(RGO),constructing layered KMO/RGO nanocomposites for lead-ion adsorption and lithium storage.The interlayer space of KMO is as high as 0.70 nm,which provides two-dimensional pathways for solid diffusion,increases diffusion dimensionality,and promotes ion diffusion rates.Simultaneously,the homogeneous distribution of KMO on RGO sufficiently exposes the active sites of KMO,further accelerating ion transport at solid-liquid interface.Additionally,RGO can prevent the aggregation of the KMO nanoplates,suppress their volume expansion,and increase the electrical conductivity of the nanocomposites.Hence,the prepared KMO/RGO nanocomposite exhibits an excellent lead-ion-adsorption capability with the maximum capacity of 341 mg g-1,higher than those of pure KMO(305 mg g-1)and RGO(63 mg g-1).More importantly,KMO/RGO also have highly effective lithium storage performance.With an optimal RGO content,KMO/RGO exhibits a first cycle charge capacity of 739 mA h g-1,much higher than that of KMO(326 mA h g-1).After 100 cycles,it still retains a capacity of 664 mA h g-1.4.Conversion-type manganese silicate/reduced graphene oxide anodes with enhanced diffusion kinetics for high-performance lithium-based dual-ion batteries:The solid diffusion is still more difficult than other diffusion modes,even if the diffusion dimensionality is increased.Therefore,one of the ideal approaches to decrease the diffusion limit is transforming solid diffusion to solid-liquid interface diffusion.Based on that theory,ultra-small manganese silicate(MS)nanosheets are uniformly anchored on RGO,constituting a MS/RGO(MSR)conversion-type anode with enhanced diffusion kinetics,and realizing the construction of high-performance lithium-based dual-ion batteries(LDIBs).The ion diffusion coefficient of MSR is promoted by in situ coating Li4SiO4 ionic conductor on the electrode surface during lithiation process.More importantly,the sufficiently exposed active sites create pseudocapacitance,which partially converts the diffusion-controlled bulk reaction to surface reaction and dramatically transforms solid diffusion to solid-liquid interface diffusion,shortening ion diffusion pathways and decreasing diffusion limits.Consequently,the MSR based LDIB exhibits superior electrochemical performance with discharge capacities of 191 mA h g-1 at 0.5 C and 128 mA h g-1 at 2C after 150 cycles,benefiting the future electrode design of LDIBs.