Cooperative Assembly Method To Construct Multifunctional Mesostructured Nanocomposites

Significant research efforts in recent years have been devoted to the developmentof mesostructured nanocomposites for applications in diverse fields. Their nanoscaledsize, high surface area and large porosity make ordered mesoporous nanoparticlesuseful in adsorption, catalysis, energy storage, controlled drug release, and cellulardelivery. The structure and composition of the nanocomposites are key to theachievable properties. Among mesostructured nanocomposites, mesoporous silicananoparticles have been extensively synthesized by a well-controllable sol–gelprocess due to facile surface modification potential, biocompatibility and low toxicity.Periodic mesoporous organosilica materials have some advantages over periodicmesoporous silica materials, such as excellent hydrothermal and mechanical stability,hydrophobic property within the pore wall, and high concentration of organicfunctional group in the framework; carbon nanomaterials are very attractive due totheir fascinating features such as large surface area, electrical conductivity,hydrophobic property, chemical and thermal stabilities, and biocompatibility;phenol–formaldehyde resin, one of the most popular carbon precursors, is also a goodsolid support due to its excellent physicochemical properties, such as good carbonyield, easy functionalization, hydrophobicity, and thermal stability; zirconia, titaniaand their binary oxides have been widely employed in many fields including catalysis,photocatalysis, dye-sensitized solar cells, photoluminescence, capillaryelectrophoresis, chromatography, inorganic pigments, dielectric ceramics, and heavymetal ion and radioactive waste sequestration. Therefore, it is highly desirable todevelop a simple and reproducible route to prepare other mesostructurednanocomposites.A general synthetic procedure for highly ordered and well-dispersed periodic mesoporous organosilica (PMO) nanoparticles is designed and achieved based on asingle cationic surfactant cetyltrimethylammonium bromide (CTAB) and simple silicasources with organic bridging groups via an ammonia-catalyzed sol–gel reaction. Bychanging the bridging group in the silica sources, the pore structures of the as-madeparticles with three-dimensional hexagonal (P63/mmc), cubic (Pm3n),two-dimensional hexagonal (p6mm), and wormlike structure were evidenced bypowder X-ray diffraction analysis (XRD) and transmission electron microscopy(TEM). The size range of the nanoparticles can be adjusted from30nm to500nm byvariation of the ammonia concentration or the co-solvent content of the reactionmedium. The PMO nanoparticles with high concentration of organic groups in theframework offered good thermal stability, good dispersion in low polarity solvent andhigh adsorption of small hydrophobic molecules. Finally, the dye functionalized PMOnanoparticles show low cytotoxicity and excellent cell permeability, which offersgreat potential for biomedical applications.A very simple cooperative template-directed coating method is developed for thepreparation of core-shell, hollow, and yolk-shell microporous carbon nanocomposites.Particularly, the cationic surfactant CTAB used in the coating procedure improves thecore dispersion in the reaction media and serves as the soft template formesostructured resorcinol–formaldehyde resin formation, which results in the uniformpolymer and microporous carbon shell coating on most functional cores with differentsurface properties. The core diameter and the shell thickness of the nanocompositescan be precisely tailored. This approach is highly reproducible and scalable. Severalgrams of polymer and carbon nanocomposites can be easily prepared by a facileone-pot reaction. The Au@hydrophobic microporous carbon yolk–shell catalystfavors the reduction of more hydrophobic nitrobenzene than hydrophilic4-nitrophenol by sodium borohydride, which makes this type of catalyst@carbonyolk–shell composites promising nanomaterials as selective catalysts for hydrophobicreactants.The design of hollow mesoporous nanostructures for cascade catalytic reactionscan inject new vitality into the development of nanostructures. In this study, we design and achieve a versatile cooperative template-directed coating method for thesynthesis of hollow and yolk–shell mesoporous zirconium titanium oxide nanosphereswith varying compositions (ZrO2content from0to100%), high surface areas (465m2·g–1) and uniform mesopores. In particular, the hexadecylamine (HDA) used in thecoating procedure serves as a soft template for silica@mesostructured metal oxidecore–shell nanosphere formation. By a facile solvothermal treatment route with anammonia solution and calcination in air, the silica@mesostructured zirconiumtitanium oxide spheres can be converted into highly uniform hollow zirconiumtitanium oxide spheres. By simply replacing hard template silica nanospheres withcore–shell silica nanocomposites, the synthesis approach can be further used toprepare yolk–shell mesoporous structures through the coating and etching process.The approach is similar to the preparation of mesoporous silica nanocomposites fromthe self-assembly of the core, the soft template cetyltrimethylammonium bromide(CTAB) and a silica precursor and can be extended as a general method to coatmesoporous zirconium titanium oxide on other commonly used hard templates (e.g.,mesoporous silica spheres, mesoporous organosilica ellipsoids, polymer spheres, andcarbon nanospheres). The presence of highly permeable mesoporous channels in thezirconium titanium oxide shells has been demonstrated by the reduction of4-nitrophenol with yolk–shell Au@mesoporous zirconium titanium oxide as thecatalyst. Moreover, a cascade catalytic reaction including an acid catalyzed step and acatalytic hydrogenation to afford benzimidazole derivatives can be carried out veryeffectively by using the accessible acidity of the yolk–shell structured mesoporouszirconium titanium oxide spheres containing a Pd core as a bifunctional catalyst,which makes the hollow zirconium titanium oxide spheres a practicable candidate foradvanced catalytic systems.Biodegradable yolk-shell mesoporous zirconia nanoparticles with potentialmedical applications have been designed and prepared by doping Ti into the shells ofnanoparticles. Vitamin C can remove the Ti from the zirconia particle shells andaccelerate their degradation in a simulated human body environment. Moreimportantly, it showed a very distinctive “one by one” degradation process. In summary, we develop three general methods for the preparation of highlyorder mesoporous organosilica nanoparticles,, mesostructured phenol-formaldehyderesin and microporous carbon core-shell nanocomposites, and mesoporous zirconiumtitanium oxide core-shell nanocomposites, which offers great potential forapplications in various fields.