Hollow Micro/Nanostructured Ceria-Based Materials: Synthetic Strategies and Versatile Applications

Hollow micro/nanostructured CeO₂ -based materials (HMNCMs) have triggered intensive attention as a result of their unique structural traits, which arise from their hollowness and the fascinating physicochemical properties of CeO₂ . This attention has led to widespread applications with improved performance. Herein, a comprehensive overview of methodologies applied for the synthesis of various hollow structures, such as hollow spheres, nanotubes, nanoboxes, and multishelled hollow spheres, is provided. The synthetic strategies toward CeO₂ hollow structures are classified into three major categories: 1) well-established template-assisted (hard-, soft-, and in situ template) methods; 2) newly emerging self-template approaches, including selective etching, Ostwald ripening, the Kirkendall effect, galvanic replacement, etc.; 3) bottom-up self-organized formation synthesis (namely, oriented attachment and self-deformation). Their underlying mechanisms are concisely described and discussed in detail, the differences and similarities of which are compared transversely and longitudinally. Niche applications of HMNCMs in a wide range of fields including catalysis, energy conversion and storage, sensors, absorbents, photoluminescence, and biomedicines are reviewed. Finally, an outlook of future opportunities and challenges in the synthesis and application of CeO₂ -based hollow structures is also presented.

Post-synthesis isomorphous substitution of layered Co-Mn hydroxide nanocones with graphene oxide as high-performance supercapacitor electrodes

Layered metal hydroxides are promising materials for electrochemical energy conversion and storage. Generally, compared with layered monometallic hydroxides, layered bimetallic hydroxides have more excellent electrochemical performance due to abundant redox reactions. Unfortunately, layered bimetallic hydroxides cannot be usually achieved through coprecipitation and/or homogeneous precipitation. Herein, we demonstrate that layered Co-Mn hydroxide nanocones (NCs) can be successfully fabricated via post-synthesis isomorphous substitution under mild conditions. In particular, the specific capacity and cycling stability of layered Co-Mn hydroxide NCs are remarkably enhanced in comparison with those of layered Co hydroxide NCs. Furthermore, the resulting layered Co-Mn hydroxide NCs and graphene oxide (GO) composite (GO/Co-Mn NCs) exhibits a high specific capacity of 677 C g-1 at 3 A g-1 and an excellent capacity retention of 95% after 2000 cycles. Asymmetric supercapacitor cells employing GO/Co-Mn NCs as the positive electrode and activated carbon (AC) as the negative electrode can achieve a high specific capacity of 189 C g-1 at 3 A g-1. This method provides a viable protocol for constructing efficient electrodes of layered bimetallic hydroxides for sustainable electrochemical energy storage.

Controllable Fabrication and Optical Properties of Uniform Gadolinium Oxysulfate Hollow Spheres

Uniform gadolinium oxysulfate (Gd2O2SO4) hollow spheres were successfully fabricated by calcination of corresponding Gd-organic precursor obtained via a facile hydrothermal process. The Gd2O2SO4 hollow spheres have a mean diameter of approximately 550 nm and shell thickness in the range of 30-70 nm. The sizes and morphologies of as-prepared Gd2O2SO4 hollow spheres could be deliberately controlled by adjusting the experimental parameters. Eu-doped Gd2O2SO4 hollow spheres have also been prepared for the property modification and practical applications. The structure, morphology, and properties of as-prepared products were characterized by XRD, TEM, HRTEM, SEM and fluorescence spectrophotometer. Excited with ultraviolet (UV) pump laser, successful downconversion (DC) could be achieved for Eu-doped Gd2O2SO4 hollow spheres.

Shape-controlled synthesis and lithium storage properties of SnO2 nonspherical hollow structures

SnO₂ hollow structures, such as peanuts, capsules and pseudocubes, have been controlled-synthesized by using SiO₂ colloids with different shapes as templates, and show enhanced lithium storage performances.

Lanthanide-doped hollow nanomaterials as theranostic agents

The field of theranostics has sprung up to achieve personalized medicine. The theranostics fuses diagnostic and therapeutic functions, empowering early diagnosis, targeted drug delivery, and real-time monitoring of treatment effect into one step. One particularly attractive class of nanomaterials for theranostic application is lanthanide-doped hollow nanomaterials (LDHNs). Because of the existence of lanthanide ions, LDHNs show outstanding fluorescent and paramagnetic properties, enabling them to be used as multimodal bioimaging agents. Synchronously, the huge interior cavities of LDHNs are able to be applied as efficacious tools for storage and delivery of therapeutic agents. The LDHNs can be divided into two types based on difference of component: single-phase lanthanide-doped hollow nanomaterials and lanthanide-doped hollow nanocomposites. We describe the synthesis of first kind of nanomaterials by use of hard template, soft template, template-free, and self-sacrificing template method. For lanthanide-doped hollow nanocomposites, we divide the preparation strategies into three kinds (one-step, two-step, and multistep method) according to the synthetic procedures. Furthermore, we also illustrate the potential bioapplications of these LDHNs, including biodetection, imaging (fluorescent imaging and magnetic resonance imaging), drug/gene delivery, and other therapeutic applications.