Carboxylated Resin Microspheres As Hard Template To Regulate The Structure Of Hollow Microspheres And Their Applications

Hollow microspheres possess high surface areas,controlled structures and compositions,ionic permeable shells and good stability,which allow them to find extensive applications in energy storage and catalysis areas.Hard template method is the common method to synthesize hollow microspheres,as it can control structure,morphology and composition more accurately compared to template free and soft template method.At present,carbon,SiO₂ and polystyrene microspheres are the main hard templates.However,there are still difficult problems such as the difficulty in adsorption of metal ions by hard template and the complexity of the preparation process,difficulty in controlling and adjusting of the shell numbers,spacing,exterior shell structure,compositions and cores.The carboxylated resin microspheres are three-dimensional network structure,stable,low price and easy to be removed by calcination,which is an ideal hard template for the preparation of hollow microspheres.Therefore,in this thesis,2,4-dihydroxy benzoic acid-formaldehyde carboxylated resin microspheres are proposed as hard templates,the adsorption of metal ions is strengthened by the electrostatic effect of carboxyl and metal cation,shell numbers,space,thickness,exterior shell structure,compositions and core are tuned by changing the adsorption capacity and the formation process of shells.The optimized structure has large surface area,low impedance,ionic permeable shells and stable structure,which improve the performance of hollow microspheres in energy storage and catalysis.Carboxylated resin microspheres are proposed as hard templates to strengthen the adsorption of Ni²⁺.Single-,double-,triple-,and quadruple-shelled NiO hollow ticrospheres Vwith a thin exterior single shell or closed exterior double shells are prepared by modifying Ni²⁺ precursor concentration,adsorption time and heating ramp rate to control the Ni²⁺adsorption amount and shell formation process,which solves the problems of difficulty in adsorption of metal ions by hard template and the complexity of the preparation process,difficulty in controlling and adjusting of shell numbers,spacing and exterior shell structure.What's more,the formation mechanism of multishell microspheres is proposed,at the initial stage of calcination,the exterior shell is formed first,with the extension of calcination time,the resin template is further removed,and the NiO shell is formed from the outer shell to the inner shell layer by layer.The hollow microspheres are used in supercapacitors,triple-shelled NiO hollow microspheres with a thin exterior single shell have large surface area?93.28 m2/g?,low internal resistance?0.76 Q?and Warburg impedance compared to closed exterior double shells,resulting in an improved energy storage performance,which show a remarkable specific capacitance of 1280 F/g at a current density of 1A/g.The specific capacitance gradually increased and reached 108%of its initial value after 2500 cycles.The 3S-NiO-HMS//RGO@Fe₃O₄ asymmetric supercapacitor shows an ultrahigh energy density of 51 Wh/kg at a power density of 800 W/kg.The simultaneous adsorption of Ni²⁺ and Co²⁺ by carboxylated resin microspheres are studied,single-,double-and triple-shelled NiCo₂O₄ hollow microspheres with different shell thickness are prepared by modifying solvent,precursor concentration and heating ramp rate to control the metal ions adsorption amount and shell formation process,which solves the problems that different metal ions are difficult to be adsorbed,shell numbers and thickness are difficult to be controlled in preparing mixed metal oxide multi-shell hollow microspheres as the physical and chemical properties of different metal ions are different.What's more,NiCo₂O₄ hollow microspheres are used in supercapacitors,thin triple-shell NiCo₂O₄ hollow microspheres provide more electroactive sites,thin shell with more porosity is beneficial for the diffusion of ions/electrolyte,the hollow structures also act as "ion-buffering reservoir" to facilitate a quicker permeation of electrolyte,the multishells support each other to improve the structural stability compared to thick shell,which improve energy storage perpormace with a specific capacitance of 720 F/g at a current density of 2 A/g and 580 F/g at 25 A/g,demonstrating an excellent rate capability retention of 81%.Based on the above research results,carboxylated resin microspheres are further used to adsorb Ni²⁺.Co²⁺,Fe³⁺ simutaneously,Ni and Co doped Fe₂O₃ hollow microspheres of-yolk-shell type are synthesized,and the effective control of pore structure in exterior shell and metal doping are realized by modifying precursor concentration to control the metal ions adsorption amount.It is proved that carboxylated resin microspheres can strengthen the adsorption of metal ions and the hard template method is universal.Furthermore,the mechanism research shows that,with the extension of calcination time,the exterior shell is formed first,and then resin template is further removed to form the core shell structure,which further verify the above mentioned formation mechanism of multi-shell NiO hollow microspheres.Ni and Co doped Fe₂O₃ hollow microspheres are used in lithium-ion battery,Ni and Co doped Fe₂O₃ hollow microspheres with small porous and mesoporous shells have relatively stable hollow structures compared to large porous shell,which improve the energy storage performance with specific capacitances of 415.7 and 414.1 mA h/g up to 200 cycles,respectively.Carboxylated resin microspheres not only can adsorb metal ions to prepare hollow microspheres,but also can carry precious metal to prepare hollow microspheres.It is proposed to use the hard template to load Pt nanoparticles and to prepare Pt@SiO₂ hollow microspheres,hollow and porous SiO₂ shells produced by the removal of resin template and CTAB are used to control the amount of Ni²⁺ into the reactor,Pt nanoparticles not only lead to Ni deposition on Pt cores but also catalyze the reduction of Ni²⁺,the amount of Ni²⁺increases in the nanometer reactor through mesoporous SiO₂ shell when the penetration time of Ni²⁺ is increased?0.5,1,2,4 h?,it is realized that Pt nanoparticles are covered by partial Ni shell and further complete Ni shell.The hollow microspheres are applied to catalyze the hydrolysis of ammonium borane,electronic structure change at the interface with the formation of Ni coating and the synergistic effect improve the catalytic activity,the Pt@Ni nanoparticles with partial Ni shell make the hydrogenation rate of the hydrolysis of ammonium borane up to 1475.02 mL/min·g.Carboxylated resin is further used to encapsulate Au and Pt simutaneously,CTAB forms micelles with F127 to adsorb and stabilize noble metal precursors,then the RF-COOH monomers aggregate and polymerize on the micelles to encapsulate Au and Pt simutaneously,AuPt@RF-COOH microspheres hard template are synthesized,AuPt nanoalloy nanoparticles are synthesized by one step,further AuPt nanoalloy are encapsulated into SiO₂ to obtain AuPt@SiO₂.The ratio of Au and Pt is adjusted by changing the added amount of metal precursors,and the core of Au,Pt and AuPt alloy nanoparticles is realized respectively.This method does not need to use metal template and solves the difficult problems that the preparation of bimetallic nanomaterials is tedious,wastes metal hard template,and the ratio of bimetal is difficult to control.AuPt@SiO₂ hollow microspheres are applied to catalyze the epoxidation of styrene,compared to Au or Pt,the optimized ratio of Au and Pt improves the catalytic performance,the conversion and selectivity of AuPt?1:8?@SiO₂ are 74%and 85%,respectively.