Weichen Sheng

Templated-assisted one-dimensional silica nanotubes: synthesis and applications

Silica (SiO2) is one of the most frequently used inorganic materials. This review covers the research progress in the synthesis of one-dimensional silica nanotubes as well as the newest aspects of silica nanotubes in applications where their structural attributes are exploited. The synthetic methods for well-defined silica nanotubes and a variety of specific silica nanotubes including hollow silica nanotubes, mesoporous silica nanotubes, chiral or helical silica nanotubes are summarized. One-dimensional tubular silica nanomaterials display structures that differ from those of other kinds of nanostructured silica materials and provide unique features such as very uniform diameter, open at both ends. In addition, sol–gel process and silane chemistry offer the reliable and robust surface modification or functionalization of silica nanotubes. Attractively, end functionalization of silica nanotubes may be able to control drug release, resulting in their wide applications in controlled drug and gene delivery; also their distinctive inner and outer surfaces can be differentially functionalized making silica nanotubes ideal multifunctional nanostructure candidates for biomedical applications in various areas such as biosensing, bioseparation and biocatalysis.

Unique double-shelled hollow silica microspheres: template-guided self-assembly, tunable pore size, high thermal stability, and their application in removal of neutral red

A novel type of monodisperse and double-shelled hollow silica microspheres was reported. This unique double-shelled structure was fabricated using a consecutive template-guided self-assembly. Cationic poly(styrene) (CPS) particles prepared by emulsifier-free polymerization were first used as the template to coat with tetraethylorthosilicate (TEOS) in the presence of coupling agent methacryloxypropyltrimethoxysilane (MPS), forming the core/shell type of CPS/SiO2 particles. The resulting CPS/SiO2 particles were further used as the template and in situ polymerized with styrene, a cationic co-monomer 2-(methacryloyl)ethyltrimethyl ammonium chloride (DMC), followed by electro-statically guided self-assembly and polymerization of TEOS on the surface, generating the sandwich-like CPS/SiO2/CPS/SiO2 particles. Finally, the unique double-shelled hollow silica spheres were produced by one-step removal of the CPS core and CPS layer from the sandwich-like particles. The structure of the monodisperse and intact double-shelled hollow silica microspheres was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET), Elemental Analysis (EA), and 29Si Nuclear Magnetic Resonance (29Si-NMR). Unlike previously reported hollow silica microspheres which have one single shell, the novel silica microspheres have two shells, enabling improved thermal stability and larger BET surface area. Notably, the interior cavity and shell-to-shell distance can be effectively tuned simply by controlling the interior CPS core diameter and the outer CPS template layer. The absorption and separation of the neutral red (NR) in synthesized hollow silica spheres showed favorable adsorption behavior, such as higher absorbent amount of dye and lower rate of dye desorbed for NR in comparison to single-shelled hollow silica, which thereby makes it potentially more applicable in environmental separation and adsorption.

High photocatalytic activity of hierarchical SiO2@C-doped TiO2 hollow spheres in UV and visible light towards degradation of rhodamine B

Ongoing research activities are targeted to explore high photocatalytic activity of TiO2-based photocatalysts for the degradation of environmental contaminants under UV and visible light irradiation. In this work, we devise a facile, cost-effective technique to in situ synthesize hierarchical SiO2@C-doped TiO2 (SCT) hollow spheres for the first time. This strategy mainly contains the preparation of monodisperse cationic polystyrene spheres (CPS), sequential deposition of inner SiO2, the preparation of the sandwich-like CPS@SiO2@CPS particles, and formation of outer TiO2. After the one-step removal of CPS templates by calcination at 450°C, hierarchical SiO2@C-doped TiO2 hollow spheres are in situ prepared. The morphology, hierarchical structure, and properties of SCT photocatalyst were characterized by TEM. SEM, STEM Mapping, BET, XRD, UV-vis spectroscopy, and XPS. Results strongly confirm the carbon doping in the outer TiO2 lattice of SCT hollow spheres. When the as-synthesized SCT hollow spheres were employed as a photocatalyst for the degradation of Rhodamine B under visible-light and ultraviolet irradiation, the SCT photocatalyst exhibits a higher photocatalytic activity than commercial P25, effectively overcoming the limitations of poorer UV activity for many previous reported TiO2-based photocatalysts due to doping.

The Preparation of Monodisperse Cationic Polystyrene and its Application to the Synthesis of Hollow Silica Spheres

The fabrication of hollow spheres with well defined size and morphology has been attracting much attention due to their unique structures and related physicochemical properties. Among the synthetic methods, the template-directed method is particularly interesting and extensively employed to fabricate hollow spheres due to templates available of essentially any size, shape, and chemistry. As a result, a new monodispersed cationic polystyrene (PS) template in this paper was fabricated by using 2-(methacryloyloxy) ethyltrimethylammonium chloride as co-monomer via emulsifier-free polymerization. The template not only can easily be tuned to the size, but can combine the advantages of hard-templating and soft-templating methods. Subsequently, we used cationic PS particles as templates to prepare hollow silica spheres – the results indicated that cationic templates can attract the assembly of tetraethylorthosilicate hydrolyzate on their surface and that the dissolution of templates can be done in the system of silica encapsulation by modification of the reaction conditions.