The Creation Of Inorganic Hollow Spheres Through Carbon Template Approach And Their Properties

The creation of microscopic materials has experienced a great structural evolution fromsimple to complex with the development of modern synthetic technology and analyticalinstruments because materials always show a strong correlation between their geometry andtheir function. For instance, in addition to general solid particles, the creation of hollowparticles has always been a critical issue in recent years owing to their great advantages oflarge void space area fraction, low density and special shape, which generally results inenhanced properties and novel application potentials compared to solid particles. As aconsequence, in the present study, the creation of a series of materials with unique structureincluding hollow, hollow core-shell and multiple shell hollow spheres, has been demonstrated.As follows:（1） Hollow Eu₂O₃spheres have been fabricated through a solvothermal approach byusing carbon spheres as templates. Further, through a similar two step approach, hollowNiZnFe₂O₄/SiO₂spheres have also been prepared. The products were characterized andinvestigated through XRD, SEM, TEM, TGA, nitrogen sorptions and so on. It reveals that thesol nucleates were filled into the mesopores within the templates driven by the vigorousinternal thermal motion of molecules during solvothermal treatment. However, the forming ofhollow interiors was resulted in by the transition of sol nucleates from inner to outer alongwith the mesopores within templates driven by heating. As a concequence, it is confirmed thatthe carbon spheres play a critical role as a template to direct the formation of hollow structure.（2） As increasing the adsorption layer thickness may result in the separation of hollowshells and inner cores, hollow core-shell ZnCo₂O₄、SnO₂、Tb₄O₇、CeO₂and CeO₂@SiO₂/CeO₂spheres were prepared by using larger scale carbon spheres as templates. The resultsillustrated that the introducing of carbon spheres with large scale is the key to prepare hollowcore-shell spheres. With the increasing of diameter of templates, the adsorption layer is largeenough so that the templates are not that easy to be removed in a short period. As aconsequence, the separation of hollow shells and inner movable cores was resulted in to givethe final hollow core-shell structure. Moreover, it is found that the products experienced a great structural evolution from hollow core-shell to hollow with the increasing of startingannealing temperature. It is realized that increasing of starting annealing temperature leads tothe enhancing of driving force, which speeds up the trasition of sol nucleates from inner toouter surface of templates, and hollow particles with a single shell were resulted in.（3） Additionally, multiple shell hollow CoFe₂O₄, TiO₂, and CeO₂@SiO₂spheres havealso been prepared by using large scale carbon spheres as templates. The results furtherconfirm that extending the size of templates leads to the extending of adsorption layerthickness, which makes the repeated separations of hollow shells and inner cores easy tooccur, and multiple shell structure is created. The products were applicated as drug deliveriesand catalysts, and the results illustrate that these materials with unique multiple shell hollowstructure exhibit much better drug releasing properties and catalytic activities compared to thegeneral bulk materials and solid nanoparticles. Moreover, it is assumed that the presentapproach can be employed to fabricate a series of metal oxide multiple shell hollow spheres,and they may exhibit great application potentials in drug delivery systems, catalysts,lithium-ion batteries and gas-sensors.