Controllable Synthesis Of Complex Hollow Structures With Hierarchically Porous Features And Their Structure-function Relationships

In this article, we synthesized three kinds of complex hollow materials with hierarchically porous features, that is multi-shell or multi-core structure materials.Due to the structural specificity and the superior performance, micro/nano-scaled materials with varied inner core/shell structures have drawn more and more attention. These materials usually show the advantages of lower density, enhanced surface area, higher loading capacity and catalysis performance, and could effectively shorten the length of mass or charge transference. Thus they could be widely used as micro-scaled reactor, drug carrier and so on. However, it still remains a great challenge to controllably synthesize hollow spheres with complex inner core/shell structures for the moment.On the other hand, as a new kind of porous materials, the hierarchically porous structured materials have been gradually developed. Different from materials with only single pore diameter, these hierarchically porous products usually possess two or more than two different sized pore structures, and the pores distributed in an organized way through the structures. Such hierarchically porous structures would guarantee the products with not only enhanced surface areas and active adsorption sites, but also reduced resistance during the diffusion process. With these excellent performance all around, materials with such properties are gaining increasing popularity. However, materials with both different inner core/shell structures and hierarchically porous features have not been reported.Based on current research status and tendency, in this work, we focused our goal on the synthesis of materials combining the two features together, namely materials with different inner core/shell and hierarchically porous structures, and mainly adopted the template method. Products were characterized by X-ray diffraction(XRD), scanning electron microscope(SEM), transmission electron microscope(TEM) and scanning transmission electron microscope(STEM) et al, and their performance in related application fields were also studied. Detailed observation with the reaction process helps us to elucidate the formation mechanism of the products, which may provide a guidance for the synthesis of materials with analogous structures.Our work consists of the following components.(1) We controllably synthesized hierarchical ZnO porous hollow spheres with different inner structures, studied the formation mechanism and its photo-catalysis perfomance. We adopted a simplified template method to synthesize hierarchical ZnO porous hollow spheres with single-, double- and triple-shelled structures, respectively. Characterizations were conducted to confirm the size distribution, morphology and inner structures of the products. Through monitoring the calcination procedure, we put forward the temperature gradient crystallization mechanism. Further we studied the products’ performance in photo-catalysis application, and it turns out that with the increasing of shell number, their photo degradation effect toward RhB and cycle efficiency both improve, which demonstrates their promising potential in waste-water treatment. Especially study on the formation mechanism would gain assistance to better control the synthesis of porous materials with different inner structures, and further provide a guidance for fabrication of similar construction.(2) We controllably synthesized hierarchically porous CaCO3 hollow spheres with different shell numbers, and studied their formation mechanism. Through skillfully utilizing the decomposition of calcium acetate and regulating the reaction condition, we could realize the effective control over the morphology of products obtained. We achieved hierarchically porous CaCO3 hollow spheres with single-, double- and triple-shelled structures. Characterizations offer information about the structures and related characters of the products. Also we studied the formation mechanism of different-shelled hollow spheres, which we called a layer-by-layer templates heating mechanism. Besides multishelled metal oxide, we obtained multishelled CaCO3 hollow spheres. This would be an enrichment for multishelled hollow spheres, and the method could be extended to obtain other carbonate materials with similar structures.(3) We discussed the targeting anticancer delivery performance of the obtained CaCO3 hierarchically porous triple-shelled hollow microspheres(denoted as HPTHMs). We studied its drug loading and pH-stimulating release behavior adopting DOX-HCl as probe drug. It could be confirmed that the synthesized HPTHMs present high loading efficiency and loading capacity as drug carrier, and the drug release is pH related. Analysis with flow cytometry(FCM) and confocal laser scanning microscopy(CLSM) suggests that there is enhancement in the DOX uptake by cancer cells when loaded with the HPTHMs carrier, and resulting in enhanced anticancer efficacy. In vitro/ vivo experiments further verify that the HPTHMs-DOX exhibit selective damage to cancer cells and tumor tissues. It could be demonstrated that HPTHMs represent great potential in targeting anticancer drug delivery.(4) We synthesized the hierarchically porous multi-core La2O2CO3 micropheres, and studied the formation mechanism preliminarily. We adopted the template method, and utilized the thermal decomposition of lanthanum acetate to obtain hierarchically porous La2O2CO3 with different number of inner cores. A series of measurements were conducted to survey the morphologies and porous structures of the products. Observations with products obtained during the calcination procedure provided information about the speculative formation mechanism. With the hierarchically porous and multi-core structure, it will be beneficial for La2O2CO3 to contact with phosphate, enhance its precipitation efficiency, and offer the possibility to act as an efficient phosphate binding agent.