Environmental Protection And Energy Storage Oriented Layered Double Hydroxides(LDHs) Functional Materials:Fabrication And Application

The environmental pollution and energy crisis induced by the booming development of the global economy are becoming more and more serious,which gives rise to a great impact on human survival and health.Therefore,it is extremely urgent to develop new environmental protection and energy storage materials to alleviate environmental degradation and energy shortage.Layered double hydroxides?LDHs?are a class of anionic intercalated two-dimensional layered inorganic functional materials,which are widely used in wastewater treatment,energy materials and biomedicine.Based on the structure and functions of LDHs,a series of environmental and energy storage guided functional nano/micro materials were fabricated.The performance of LDH-based materials as adsorbents or electrodes were systematically evaluated,and the relationship between the structure,as well as the chemical composition and the properties were analyzed.The main research contents and results are as follows:1.LDHs,served as high-efficiency adsorption unit of anionic dye,are decorated onto biomass porous carbon to fabricate the functional hybrid material?Ni/Al@PAB?for simultaneous removal of Cr?VI?and MO.The uniform distribution of ultra-thin Ni/Al LDH nanosheets on the PAB surface contributes to high specific surface area(1273.0 m² g^-1)and large pore volume(1.48 cm³ g^-1).In the one-component pollutant system,the maximum adsorption for Cr?VI?and MO by Ni/Al@PAB can achieve 271.5 mg g^-1 and 412.8 mg g^-1,respectively.In the Cr?VI?+MO binary system,the results reveal the synergistic removal of heavy metals and dyes by Ni/Al@PAB.Moreover,the mixed Cr?VI?and MO pollutants are treated by a fixed adsorption column and the effluent quality satisfies the industrial discharge standard(Cr?VI?<0.5 mg L^-1,MO<1.0 mg L^-1).Based on the chemical structure changes of Ni/Al@PAB before and after the adsorption of single and binary pollutants adsorption,the mechanism of synergistic adsorption includes Cr?VI?reduction,isomorphic substitution,electrostatic interaction,pore filling,chelation,hydrogen bonding and thermal compensation.2.Intercalated LDHs,served as the electroactive shell material,are constructed as flexible core-shell electrodes on carbon fiber cloth?NiMn-G-LDH@NiCo₂S₄@CFC?by in-situ growth and further used for all-solid-state flexible supercapacitors.Benefited from the three-dimensional core-shell structure of the composite electrode,the interlayer space expansion caused by glucose intercalation and the chemical composition of the core-shell material,the NiMn-G-LDH@NiCo₂S₄@CFC electrode exhibits high specific surface area(31.2 m² g^-1)and excellent specific capacity(mass ratio capacity up to 1018 C g^-1 at the current density of 1 A g^-1).When assembled into an all-solid-state flexible device,excellent flexibility and an ultrahigh energy density 60.3 W h kg^-1 can be achieved.Moreover,the device exhibits remarkable cycling stability of 86.4%retention after 10000 cycles.The outstanding electrochemical performance is mainly attributed to the sufficient electroactive sites and electrode/electrolyte contact interfaces provided by the conductive core NiCo₂S₄ hollow nanotube array,the electroactive sites and extended interlayer spaces provided by the NiMn-G-LDH shell,the unimpeded highways for ion/electron transfer and structural stability provided by the three-dimensional core-shell structure.3.LDHs,served as the adsorption and catalytic active sites for polysulfides,are constructed as core-shell structural sulfur host material?NiAl@PAB?by introducing conductive network porous carbon as a carrier.Based on the modification of NiAl-LDH,the P doping and the high conductivity of PAB,the NiAl@PAB/S electrode exhibits excellent electrochemical performance.At a current density of 0.2 C,the electrode delivers an initial capacity of 1216.3 m Ah g^-1,and maintains 614.2 mAh g^-11 when the current density is raised to 3C.During 300 charge-discharge cycles,the specific capacity decay rate is 0.13%per cycle,with a stable coulombic efficiency above 98%.By comparing the performance with commercial carbon,analyzing with DFT theoretical calculation,and Li₂S₆ symmetric battery experiments,the adsorption and catalytic conversion of LiPSs by P-containing functional groups and NiAl-LDH are revealed,and the leading role of Ni Al-LDH is verified.4.LDHs,served as structural precursors and functional sites,in-situ grow on a sacrificial template of ZIF67 and further transform to hollow dodecahedral heterogeneous composite sulfur host material?LDH/Co₉S₈?by sulfidation.Based on the hollow nanocage structure of the composite,a high sulfur loading of 73.4%is achieved.Taking advantage of the high conductivity(663.9 S m^-1)and dual functional sites of the LDH/Co₉S₈ heterostructure,the S@LDH/Co₉S₈ electrode realizes the ultra-long cycle lifespan:during 1500 cycles at 1C,the capacity decay rate is only 0.047%per cycle with the stable coulombic efficiency above 98%.Through the analysis of four-probes,static adsorption,XPS,Li₂S₆ symmetric battery,lithium sulfide deposition and Tafel tests,the LDH/Co₉S₈ can realize high-speed ion/electron transfer,efficient capture and quick conversion of LiPSs to suppress the shuttle effect and improves the utilization of sulfur during long cycles.5.Intercalated LDHs,served as a structure-guiding agent,are in situ transformed to a highly conductive cobalt-embedded nitrogen-doped hollow flower-like porous carbon?H-Co-NCM?sulfur host by the interlayer-confined reaction.Benefited from the unique micron-cavity,H-Co-NCM endowed with high specific surface area and porous structure can achieve a high sulfur loading of 82%and an excellent high conductivity skeleton(716 S m^-1).The structural and interfacial chemistry advantages of the S@H-Co-NCM electrode give rise to excellent electrochemical performance:at the current density of 0.1C,the electrode delivers an initial capacity of 1374 mAh g^-1,and retains a capacity of 611 mAh g^-11 when the current density is increased to 2C.Moreover,after 500 cycles at 0.5C,the capacity decay rate is 0.069%per cycle with the coulombic efficiency close to 100%.The static adsorption combined with XPS revealed that Co and N mainly anchored LiPSs by forming Li-N and Co-S bond.In addition,by means of Li₂S₆ symmetric battery,constant voltage discharge and Tafel tests,the kinetic promotion of H-Co-NCM on soluble LiPSs conversion and Li₂S nucleation growth is confirmed.