Fabrication And Properties Of Hollow Nanoparticles And Their Composites

Hollow nanoparticles have attracted considerable attention due to their high surface area,large interior spaces and promising potential applications.Conventional template method usually destroyed the structures of hollow nanoparticles and limited the scalable fabrication.Templateless routes based on Ostwald ripening and Kirkendall effect are facile and benefit to realize the scalable preparation and application of hollow nanoparticles.Especially,Kirkendall effect strategies show distinguished advantages for producing composites with highly dispersive hollow nanoparticles.The present thesis investigates the synthesis of size tunable Sn O₂hollow nanoparticles through Ostwald ripening by ambient reflux method.Carbon composite nanofibers with embedded metal oxide hollow nanoparticles are also rationally fabricated via nanoscale Kirkendall effects.The properties of as-prepared hollow nanoentities are investigated.(1)A reflux method was designed to prepare tunable Sn O₂hollow nanospheres via Ostwald ripening based on the sol-gel theory of p H induced tunable aggregated particle sizes.The hydrolysis of Sn SO₄releases protons to decrease the p H value that arouse the variation of aggregate particle size.The particle sizes of Sn O₂are tunable from 137 nm to 66 nm by adjusting the Sn SO₄concentration without any additives.However,the Ostwald ripening process is inhibited due to the low reflux temperature.Only low Sn SO₄concentration produces Sn O₂hollow nanospheres.High Sn SO₄concentration produces solid particles.When used as anode materials of lithium ion battery,all samples of SOHSn exhibit high initial discharge capacity with poor cycling stability due to the lack of carbon coating.SOHS16 with the smallest particle size show the best lithium ion battery performances.Samples of SOHSn also exhibit gas sensing activity to acetone and formaldehyde?(2)Hollow Fe₂O₃nanoparticles incorporated carbon nanofibers HFCNFs are rationally fabricated based on nanoscale Kirkendall effect by using electrospinning,preoxidation,high temperature carbonization and post oxidation.The embedded nanoparticles experience morphology evolution of solid,voids,core-shell and hollow nanoparticles during the post oxidation process.The morphology variation confirms that the formation of Fe₂O₃hollow nanoparticles is promoted by the Kirkendall bilateral diffusion.Used as anode of lithium ion battery,HFCNFs-30displays improved rate capability and long-term cycling stability.It delivers an initial discharge capacity of 1903.8 m Ah/g that sustains 601.2 m A h/g after300cycles at 100 m A/g.The improved lithium ion battery performances of HFCNFs-30 stems from the synergetic coupling of the one-dimensional porous carbon nanofiber and the hollow structure of nanoparticles.(3)Carbon composite nanofibers with embedded hollow nanoparticles of Ni O(NOCNFs)or Co₃O₄(COCNFs)are fabricated by using electrospinning,preoxidation,carbonization and post oxidation.These results extended the generality of preparing composites of hollow nanoaprticles based on Kirkendall effect.During the post oxidation process,the formation of oxide layer is observed at the beginning.Afterwards,the Kirkendall effect occurs due to the faster migration of metal atoms and slow migration of O₂molecules.The metal species continuously migrate from inner space to the outer shell to form hollow nanoparticles.The morphology evolution and phase transformation manifest the Kirkendall mechanism of the formation hollow nanoparticles.Serving as anode for lithium ion battery,NOCNFs-2 exhibits enhanced discharge capacity,rate capability and long-term cycling stability.It delivers a high capacity of 1609m Ah/g at 0.1 C and maintains 530.5 m Ah/g after 300 cycles of rate and long-term cycling test.