Periodic Mesoporous Organosilica Hollow Spheres with Tunable Wall Thickness

Syntheses and applications of periodic mesoporous organosilica nanoparticles

Periodic Mesoporous Organosilica (PMO) nanomaterials are envisioned to be one of the most prolific subjects of research in the next decade. Similar to mesoporous silica nanoparticles (MSN), PMO nanoparticles (NPs) prepared from organo-bridged alkoxysilanes have tunable mesopores that could be utilized for many applications such as gas and molecule adsorption, catalysis, drug and gene delivery, electronics, and sensing; but unlike MSN, the diversity in chemical nature of the pore walls of such nanomaterials is theoretically unlimited. Thus, we expect that PMO NPs will attract considerable interest over the next decade. In this review, we will present a comprehensive overview of the synthetic strategies for the preparation of nanoscaled PMO materials, and then describe their applications in catalysis and nanomedicine. The remarkable assets of the PMO structure are also detailed, and insights are provided for the preparation of more complex PMO nanoplatforms.

Mesoporous TiO2 Mesocrystals: Remarkable Defects-Induced Crystallite-Interface Reactivity and Their in Situ Conversion to Single Crystals

Oriented self-assembly between inorganic nanocrystals and surfactants is emerging as a route for obtaining new mesocrystalline semiconductors. However, the actual synthesis of mesoporous semiconductor mesocrystals with abundant surface sites is extremely difficult, and the corresponding new physical and chemical properties arising from such an intrinsic porous mesocrystalline nature, which is of fundamental importance for designing high-efficiency nanostructured devices, have been rarely explored and poorly understood. Herein, we report a simple evaporation-driven oriented assembly method to grow unprecedented olive-shaped mesoporous TiO2 mesocrystals (FDU-19) self-organized by ultrathin flake-like anatase nanocrystals (∼8 nm in thickness). The mesoporous mesocrystals FDU-19 exhibit an ultrahigh surface area (∼189 m(2)/g), large internal pore volume (0.56 cm(3)/g), and abundant defects (oxygen vacancies or unsaturated Ti(3+) sites), inducing remarkable crystallite-interface reactivity. It is found that the mesocrystals FDU-19 can be easily fused in situ into mesoporous anatase single crystals (SC-FDU-19) by annealing in air. More significantly, by annealing in a vacuum (∼4.0 × 10(-5) Pa), the mesocrystals experience an abrupt three-dimensional to two-dimensional structural transformation to form ultrathin anatase single-crystal nanosheets (NS-FDU-19, ∼8 nm in thickness) dominated by nearly 90% exposed reactive (001) facets. The balance between attraction and electrostatic repulsion is proposed to determine the resulting geometry and dimensionality. Dye-sensitized solar cells based on FDU-19 and SC-FDU-19 samples show ultrahigh photoconversion efficiencies of up to 11.6% and 11.3%, respectively, which are largely attributed to their intrinsic single-crystal nature as well as high porosity. This work gives new understanding of physical and chemical properties of mesoporous semiconductor mesocrystals and opens up a new pathway for designing various single-crystal semiconductors with desired mesostructures for applications in catalysis, sensors, drug delivery, optical devices, etc.

Hierarchical mesoporous In2O3 with enhanced CO sensing and photocatalytic performance: distinct morphologies of In(OH)3 via self assembly coupled in situ solid-solid transformation

The present investigation details our interesting findings and insights into the evolution of exotic hierarchical superstructures of In(OH)3 under solvothermal conditions. Controlled variation of reaction parameters such as, reactant concentration, solvent system, crystal structure modifiers, water content along with temperature and time, yielded remarkable architectures. Diverse morphologies achieved for the first time includes (i) raspberry-like hollow spheres, (ii) nanosheet-assembled spheres, (iii) nanoparticle-assembled spheres, (iv) nanocube-assembled hollow spheres, (v) yolk-like spheres, (vi) solid spheres, (vii) nanosheets/flakes, and (viii) ultrafine nanosheets. A plausible mechanism is proposed based on the evidence gathered from a comprehensive analysis aided by electron microscopy and X-ray diffraction studies. Key stages of morphological evolution could be discerned and rationally correlated with nucleation, growth, oriented attachment, and Ostwald ripening mediated by dissolution-redeposition mechanism coupled with solid evacuation. Remarkably phase-pure bcc-In2O3 with retention of precursor morphology could be realized postcalcination at 400 °C, which underlines the advantage of this strategy. Two typical hierarchical structures (raspberry-like hollow spheres and nanoparticles assembled spheres) were investigated for their gas sensing and photocatalytic performances to highlight the advantages offered by nanostructuring. An impressive sensor response, Smax ≈ 7340 and 4055, respectively for the two structures along with appreciably fast response/recovery times over a wide concentration range and as low as 1 ppm exhibits the superior sensitivity toward carbon monoxide (CO). When compared to commercial In2O3, estimated rate constant indicates ∼3-4 times enhancement in photocatalytic activity of the substrates toward Rhodamine-B.

Tunable stellate mesoporous silica nanoparticles for intracellular drug delivery

Stellate mesoporous silica nanoparticles with special radial pore morphology were easily synthesized using triethanolamine as the base catalyst in a wide range of synthesis conditions. By adjusting the surfactant composition, reaction temperature and time, and reagent ratio, the particle size of the material could be tailored continuously ranging from 50 to 140 nm and the pore size from 2 to 20 nm. By analyzing the effects of different synthesis parameters, it is concluded that the particles are formed following a nucleation-growth mechanism and the reaction kinetics play an important role in determining the particle size and pore structure. These stellate MSNs can be conveniently functionalized with a nontoxic low molecular weight poly(ethylene imine) (PEI, 800 Da) by a delayed condensation method. The resulting nanocomposites not only possess auto-fluorescence for suitable particle tracking but also demonstrate good potential for intracellular delivery of the anticancer doxorubicin drug.

One-pot construction of multipodal hybrid periodic mesoporous organosilica nanoparticles with crystal-like architectures

The design of hybrid multipodal PMO (mp-PMO) nanoparticles with crystal-like architectures elaborated in a one-pot, two-step process, involving the preparation of a benzene-based spherical PMO core followed by the formation of ethylene-based rod-shaped PMO pods on these cores is described.

Controllable synthesis of hollow mesoporous silica particles by a facile one-pot sol–gel method

A simple and facile one-pot sol–gel method is proposed for the fabrication of hollow mesoporous silica particles. Both the particle size and the shell thickness can be well controlled.

A soft–hard template approach towards hollow mesoporous silica nanoparticles with rough surfaces for controlled drug delivery and protein adsorption

Novel hollow mesoporous silica nanoparticles (HMSNs) with rough surfaces have been successfully prepared using a facile soft–hard template route.

Silica-based nanocapsules: synthesis, structure control and biomedical applications

Synthesis and structure engineering of silica-based nanocapsules for biomedical applications.

Design and synthesis of periodic mesoporous organosilica materials with a multi-compartment structure

Multi-compartment periodic mesoporous organosilica materials show desirable properties as anticancer drug carrier with high loading capacity and slow release rate.

Multi-shelled hollow micro-/nanostructures

Recent advances in multi-shelled hollow micro-/nanostructures were reviewed, and the correlation between their geometric properties and specific performance was highlighted.

One-step synthesis of structure controlled vinyl functionalized hollow mesoporous silica nanospheres

A simple synthetic strategy of vinyl functionalized hollow mesoporous silica nanospheres using CTAB as a template and ammonia as a catalyst.

Biodegradable ethylene-bis(propyl)disulfide-based periodic mesoporous organosilica nanorods and nanospheres for efficient in-vitro drug delivery

Periodic mesoporous organosilica nanorods and nanospheres are synthesized from 1,4-bis(triethoxysilyl)ethylene and bis(3-ethoxysilylpropyl)disulfide. The nanosystems present the long-range order of the hexagonal nanostructure. They are degraded in simulated physiological conditions. The loading and release of doxorubicin with these nanosystems are both pH dependent. These nanoparticles are endocytosed by breast cancer cells and are very efficient for doxorubicin delivery in these cells.

Hollow-structured mesoporous materials: chemical synthesis, functionalization and applications

Hollow-structured mesoporous materials (HMMs), as a kind of mesoporous material with unique morphology, have been of great interest in the past decade because of the subtle combination of the hollow architecture with the mesoporous nanostructure. Benefitting from the merits of low density, large void space, large specific surface area, and, especially, the good biocompatibility, HMMs present promising application prospects in various fields, such as adsorption and storage, confined catalysis when catalytically active species are incorporated in the core and/or shell, controlled drug release, targeted drug delivery, and simultaneous diagnosis and therapy of cancers when the surface and/or core of the HMMs are functionalized with functional ligands and/or nanoparticles, and so on. In this review, recent progress in the design, synthesis, functionalization, and applications of hollow mesoporous materials are discussed. Two main synthetic strategies, soft-templating and hard-templating routes, are broadly sorted and described in detail. Progress in the main application aspects of HMMs, such as adsorption and storage, catalysis, and biomedicine, are also discussed in detail in this article, in terms of the unique features of the combined large void space in the core and the mesoporous network in the shell. Functionalization of the core and pore/outer surfaces with functional organic groups and/or nanoparticles, and their performance, are summarized in this article. Finally, an outlook of their prospects and challenges in terms of their controlled synthesis and scaled application is presented.

Construction of homogenous/heterogeneous hollow mesoporous silica nanostructures by silica-etching chemistry: principles, synthesis, and applications

Colloidal hollow mesoporous silica nanoparticles (HMSNs) are aspecial type of silica-based nanomaterials with penetrating mesopore channels on their shells. HMSNs exhibit unique structural characteristics useful for diverse applications: Firstly, the hollow interiors can function as reservoirs for enhanced loading of guest molecules, or as nanoreactors for the growth of nanocrystals or for catalysis in confined spaces. Secondly, the mesoporous silica shell enables the free diffusion of guest molecules through the intact shell. Thirdly, the outer silica surface is ready for chemical modifications, typically via its abundant Si-OH bonds. As early as 2003, researchers developed a soft-templating methodto prepare hollow aluminosilicate spheres with penetrating mesopores in a cubic symmetry pattern on the shells. However, adapting this method for applications on the nanoscale, especially for biomedicine, has proved difficult because the soft templating micelles are very sensitive to liquid environments, making it difficult to tune key parameters such as dispersity, morphology and structure. In this Account, we present the most recent developments in the tailored construction of highly dispersive and monosized HMSNs using simple silica-etching chemistry, and we discuss these particles' excellent performance in diverse applications. We first introduce general principles of silica-etching chemistry for controlling the chemical composition and the structural parameters (particle size, pore size, etching modalities, yolk-shell nanostructures, etc.) of HMSNs. Secondly, we include recent progress in constructing heterogeneous, multifunctional, hollow mesoporous silica nanorattles via several methods for diverse applications. These elaborately designed HMSNs could be topologically transformed to prepare hollow mesoporous carbon nanoparticles or functionalized to produce HMSN-based composite nanomaterials. Especially in biomedicine, HMSNs are excellent as carriers to deliver either hydrophilic or hydrophobic anti-cancer drugs, to tumor cells, offering enhanced chemotherapeutic efficacy and diminished toxic side effects. Most recently, research has shown that loading one or more anticancer drugs into HMSNs can inhibit metastasis or reverse multidrug resistance of cancer cells. HMSNs could also deliver hydrophobic perfluorohexane (PFH) molecules to improve high intensity focused ultrasound (HIFU) cancer surgery by changing the tissue acoustic environment; and HMSNs could act as nanoreactors for enhanced catalytic activity and/or durability. The versatility of silica-etching chemistry, a simple but scalable synthetic methodology, offers great potential for the creation of new types of HMSN-based nanostructures in a range of applications.

Periodic Mesoporous Organosilicas: from simple to complex bridges; a comprehensive overview of functions, morphologies and applications

Periodic Mesoporous Organosilicas (PMOs) were developed in 1999 and are basically ordered templated mesoporous organosilicas, prepared by the combination of a surfactant as template and a silsesquioxane as the organosilica precursor. They were one of the first examples of the so-called "hybrid" organic/inorganic materials. In the years that followed, an amazing variety of functional groups, morphologies and applications has been developed. Some of these high-end applications, like low-k buffer layers in microelectronics, chiral catalysts, chromatographic supports, selective adsorbents and light-harvesting devices, have clearly shown their potential. In this review, we will give a comprehensive overview of all these different functionalities and applications that have been created for Periodic Mesoporous Organosilicas.

Hydrothermal fabrication of hierarchically macroporous Zn2SnO4 for highly efficient dye-sensitized solar cells

Hierarchical macroporous Zn(2)SnO(4) consisting of nanoparticles has been synthesized for the first time through an in situ hydrothermal and a following annealing process in the presence of a polystyrene (PS) template. Zn(2)SnO(4) macropore sizes are tuned in the range of 180-650 nm by selecting the appropriate size of PS spheres, and the building unit size of the Zn(2)SnO(4)macropore is 4.2 nm regardless of the PS sizes. The photovoltaic performances of the dye-sensitized solar cell based on hierarchical macroporous Zn(2)SnO(4) with 200, 400, 600 and 750 nm PS spheres are 5.01, 4.76, 4.39 and 3.92%, respectively. The smaller pore size of Zn(2)SnO(4) exhibits higher photovoltaic performance, which is ascribed to the higher dye loading, faster electron transport rate and slower electron recombination rate. These are confirmed by UV-vis absorption spectroscopy, intensity-modulated photocurrent spectroscopy, intensity-modulated photovoltage spectroscopy and electrochemical impedance spectroscopy. The double layered photoelectrode based on a Zn(2)SnO(4) nanoparticles dye adsorption layer (4.2 nm in particle size, 15 μm in film thickness) and a macroporous light scattering layer (180 nm in macropore size, 4.0 μm in thickness) shows a remarkable enhancement in power conversion efficiency (6.10%) compared to that of Zn(2)SnO(4) nanoparticles photoelectrode (5.36%) because of its superior light scattering ability.

Colloidal HPMO nanoparticles: silica-etching chemistry tailoring, topological transformation, and nano-biomedical applications

Hybridization produces the better: Colloidal hollow periodic mesoporous organosilica nanoparticles (HPMO NPs) with tunable compositions and highly hybridized nanostructures are successfully synthesized by a simple, easily scale-up but versatile silica-etching chemistry (alkaline or HF etching) for their applications in nano-fabrication and nano-medicine.

Gold nanorod-covered kanamycin-loaded hollow SiO2 (HSKAu(rod)) nanocapsules for drug delivery and photothermal therapy on bacteria

A hybrid bactericidal material, gold nanorod-covered kanamycin-loaded hollow SiO(2) (HSKAu(rod)) nanocapsules, is constructed. The hybrid material combines the features of a chemical drug with photothermal physical sterilization which decreases the dosage of broad-spectrum antibiotic and the physical damage of biological systems. Hollow SiO(2) nanocapsules are used as carriers for drug delivery. The nanocapsules load a model drug, kanamycin, and are covered with gold nanorods to avoid drug leakage and realize photothermal treatment. The sterilizing effect on the bacterial strain is investigated by incubating E. coli BL21 with the hybrid nanocapsules and irradiating under near-infrared light (NIR) for 20 min. A bactericidal effect, i.e., a sterilizing rate of 53.47%, is achieved for the HSKAu(rod) nanocapsules under NIR irradiation, with respect to a net sum sterilizing rate of 34.49% for the individual components of the HSKAu(rod) nanocapsules, e.g., carrier nanocapsules, chemical sterilization of kanamycin and physical sterilization due to the gold nanorods under NIR irradiation. It is demonstrated that the combination of chemical drug and physical sterilization results in an obvious synergistic effect and makes the sterilization more effective. This novel hybrid has great potential as an adjuvant therapeutic alternative material for sterilization or even for the control of disease.

Functionalization of SnO₂ photoanode through Mg-doping and TiO₂-coating to synergically boost dye-sensitized solar cell performance

Mg-doped SnO₂ with an ultrathin TiO₂ coating layer was successfully synthesized through a facile nanoengineering art. Mg-doping and TiO₂-coating constructed functionally multi-interfaced SnO₂ photoanode for blocking charge recombination and enhancing charge transfer in dye-sensitized solar cells (DSC). The designed nanostructure might play a synergistic effect on the reducing recombination and prolonging the lifetime in DSC device. Consequently, a maximum power conversion efficiency of 4.15% was obtained for solar cells fabricated with the SnO₂-based photoelectrode, exhibiting beyond 5-fold improvement in comparison with pure SnO₂ nanomterials photoelectrode DSC (0.85%).

Highly ordered periodic mesoporous organosilica nanoparticles with controllable pore structures

A general synthetic procedure for highly ordered and well-dispersed periodic mesoporous organosilica (PMO) nanoparticles is reported based on a single cationic surfactant cetyltrimethylammonium bromide (CTAB) and simple silica sources with organic bridging groups via an ammonia-catalyzed sol-gel reaction. By changing the bridging group in the silica sources, the pore structures of the as-made particles with three-dimensional hexagonal (P6(3)/mmc), cubic (Pm3n), two-dimensional hexagonal (P6mm), and wormlike structure were evidenced by powder X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM). The size range of the nanoparticles can be adjusted from 30 nm to 500 nm by variation of the ammonia concentration or the co-solvent content of the reaction medium. The PMO nanoparticles with high concentration of organic groups in the framework offered good thermal stability, good dispersion in low polarity solvent and high adsorption of small hydrophobic molecules. Finally, the dye functionalized PMO nanoparticles show low cytotoxicity and excellent cell permeability, which offers great potential for biomedical applications.

Mesoporous silica nanoparticles: synthesis, biocompatibility and drug delivery

In the past decade, mesoporous silica nanoparticles (MSNs) have attracted more and more attention for their potential biomedical applications. With their tailored mesoporous structure and high surface area, MSNs as drug delivery systems (DDSs) show significant advantages over traditional drug nanocarriers. In this review, we overview the recent progress in the synthesis of MSNs for drug delivery applications. First, we provide an overview of synthesis strategies for fabricating ordered MSNs and hollow/rattle-type MSNs. Then, the in vitro and in vivo biocompatibility and biotranslocation of MSNs are discussed in relation to their chemophysical properties including particle size, surface properties, shape, and structure. The review also highlights the significant achievements in drug delivery using mesoporous silica nanoparticles and their multifunctional counterparts as drug carriers. In particular, the biological barriers for nano-based targeted cancer therapy and MSN-based targeting strategies are discussed. We conclude with our personal perspectives on the directions in which future work in this field might be focused.

Periodic organosilica hollow nanospheres as anode materials for lithium ion rechargeable batteries

Polymeric micelles with core-shell-corona architecture have been found to be the efficient colloidal templates for synthesis of periodic organosilica hollow nanospheres over a broad pH range from acidic to alkaline media. In alkaline medium, poly (styrene-b-[3-(methacryloylamino)propyl] trimethylammonium chloride-b-ethylene oxide) (PS-PMAPTAC-PEO) micelles yield benzene-silica hollow nanospheres with molecular scale periodicity of benzene groups in the shell domain of hollow particles. Whereas, an acidic medium (pH 4) produces diverse hollow particles with benzene, ethylene, and a mixture of ethylene and dipropyldisulfide bridging functionalities using poly(styrene-b-2-vinyl pyridine-b-ethylene oxide) (PS-PVP-PEO) micelles. These hollow particles were thoroughly characterized by powder X-ray diffraction (XRD), dynamic light scattering (DLS), thermogravimetric analysis (TG/DTA), Fourier transformation infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), magic angle spinning-nuclear magnetic resonance ((29)Si MAS NMR and (13)CP-MAS NMR), Raman spectroscopy, and nitrogen adsorption/desorption analyses. The benzene-silica hollow nanospheres with molecular scale periodicity in the shell domain exhibit higher cycling performance of up to 300 cycles in lithium ion rechargeable batteries compared with micron-sized dense benzene-silica particles.

Spherical silica micro/nanomaterials with hierarchical structures: synthesis and applications

This paper reviews the progress made recently in synthesis and applications of spherical silica micro/nanomaterials with multilevel (hierarchical) structures. The spherical silica micro/nanomaterials with hierarchical structures are classified into four main structural categories that include (1) hollow mesoporous spheres, (2) core-in-(hollow porous shell) spheres, (3) hollow spheres with multiple porous shells and (4) hierarchically porous spheres. Due to the complex structures and being focused on spherical silica micro/nanomaterials, some novel methods based on the combination of two routine methods or two surfactants, and some special synthetic strategies are proposed to produce the spherical silica micro/nanomaterials with hierarchical structures. Compared with the same-sized solid, porous or hollow silica spheres, these fantastic spherical silica micro/nanomaterials with hierarchical structures exhibit enhanced properties which may enable them to be used in broad and promising applications as ideal scaffolds (carriers) for biological, medical, and catalytic applications.

Mesoporous silica nanoparticles for bioadsorption, enzyme immobilisation, and delivery carriers

Mesoporous silica nanoparticles (MSNs) provide a non-invasive and biocompatible delivery platform for a broad range of applications in therapeutics, pharmaceuticals and diagnosis. The creation of smart, stimuli-responsive systems that respond to subtle changes in the local cellular environment are likely to yield long term solutions to many of the current drug/gene/DNA/RNA delivery problems. In addition, MSNs have proven to be promising supports for enzyme immobilisation, enabling the enzymes to retain their activity, affording them greater potential for wide applications in biocatalysis and energy. This review provides a comprehensive summary of the advances made in the last decade and a future outlook on possible applications of MSNs as nanocontainers for storage and delivery of biomolecules. We discuss some of the important factors affecting the adsorption and release of biomolecules in MSNs and review of the cytotoxicity aspects of such nanomaterials. The review also highlights some promising work on enzyme immobilisation using mesoporous silica nanoparticles.