Core-shell-corona polymeric micelles as a versatile template for synthesis of inorganic hollow nanospheres.

Hollow, inorganic nanoscale capsules have many applications, from the delivery of encapsulated products for cosmetic and medicinal purposes to use as lightweight composite materials. Early methods for producing inorganic hollow nanospheres using hard templates suffered from low product yield and shell weakness upon template removal. In the past decade, researchers have turned to amphiphilic copolymers to synthesize hollow nanostructures and ordered mesoporous materials. Amphiphilic molecules self-assemble into well-defined nanostructures including spherical micelles. Micelles formed from simple, two-component AB diblock and ABA triblock copolymers, however, have been difficult to work with to construct inorganic hollow nanoparticles, because the corona of the micelle, which serves as the template for the shell, becomes unstable as it absorbs inorganic shell precursors, causing aggregates to form. Newly developed, three-component ABC triblock copolymers may solve this problem. They provide nanoassemblies with more diverse morphological and functional features than AB diblock and ABA triblock copolymers. Micelles formed from ABC triblock copolymers in selective solvents that dissolve only one or two of the blocks provide templates for these improved nanoassemblies. By manipulating individual polymer blocks, one can "encode" additional features at the molecular level. For instance, modifying the functional groups or substitution patterns of the blocks allows better morphological and size control. Insights into polymer self-assembly gained over years of work in our group have set the stage to systematically engineer inorganic spherical hollow nanoparticles using ABC triblock copolymers. In this Account, we report our recent progress in producing diverse, inorganic hollow spherical nanospheres from asymmetric triblock copolymeric micelles with core-shell-corona architecture as templates. We discuss three classes of polymeric micelles-with neutral, cationic, and anionic shell structures-that allow fabrication of a variety of hollow nanoparticles. Importantly, we synthesized all of these particles in water, avoiding use of hazardous organic solvents. We have designed the precursor of the inorganic material to be selectively sorbed into the shell domain, leaving the corona free from the inorganic precursors that would destabilize the micelle. The core, meanwhile, is the template for the formation of the hollow void. By rationally tailoring experimental parameters, we readily and selectively obtained a variety of hollow nanoparticles including silica, hybrid silicas, metal-oxides, metal-carbonates, metal-sulfates, metal-borates, and metal-phosphates. Finally, we highlight the state-of-the-art techniques we used to characterize these nanoparticles, and describe experiments that demonstrate the potential of these hollow particles in drug delivery, and as anode and cathode materials for lithium-ion batteries.

Fabrication of Al-beta/silicalite-1 hydrophilic-hydrophobic zeolite membranes.

Hydrophobic-hydrophilic composite membranes containing silicalite-1 and Al-beta zeolites are prepared on the outer surface of the porous alpha-alumina tube for the first time. The hydrophilic layer with aluminum serves as an active catalytic domain, whereas the hydrophobic layer containing silicalite-1 with medium pore-size is expected to assist in separating the reaction products based on their hydrophobicity as well as shape-selectivity. The continuous defect-free composite membranes are fabricated by two-step synthesis approach by initial deposition of Al-beta crystals on the outer surface of porous alumina tube followed by coating of silicalite-1 crystals over the Al-beta layer in the second step under hydrothermal conditions. The composite membranes exhibited a high thermal stability of up to 550 degrees C. The powder X-ray diffraction patterns of samples collected at the bottom of crystallization vessel as well as coated membranes indicated typical BEA and MFI structures consisting of ca. 0.5-0.7 nm size micropores, and free from impurity phase. The field emission scanning electron microscopic (FE SEM) analysis of the silicalite-1 sample exhibited uniform rectangular crystals of size about 20 microm; whereas Al-beta showed spherical morphology with crystal size of approximately 0.6-0.7 microm. The surface and cross-sectional analyses of composite membranes both before and after calcinations exhibited defect-free microstructures for the composite membranes. The calcined membranes exhibited single gas permeation and the observed values for composite membranes are an order of magnitude lower than that of the individual membranes.

3D hexagonal mesoporous silica and its organic functionalization for high CO2 uptake.

Highly ordered 3D-hexagonal mesoporous silica HMS-3 and its vinyl- and 3-chloropropyl-functionalized analogues HMS-4 and -5, respectively, are synthesized under strongly alkaline conditions at 277 K. Tetraethyl orthosilicate, vinyltrimethoxysilane, and 3-chloropropyltrimethoxysilane are used as silica sources, and cetyltrimethylammonium bromide as the structure-directing agent. The 3D-hexagonal pore structures of HMS-3, 4-, and -5 were confirmed by powder XRD and high-resolution TEM studies. Brunauer-Emmett-Teller surface areas of these materials are 1353, 1211, and 603 m(2) g(-1) for HMS-3, -4, and -5, respectively. Among these materials, vinyl-functionalized mesoporous material HMS-4 adsorbs the highest CO(2) (5.5 mmol g(-1) , 24.3 wt%) under 3 bar pressure at 273 K. The 3D-hexagonal pore openings, very high surface area, and cagelike mesopores as well as organic functionalization could be responsible for very high CO(2) uptakes of these materials compared to other related mesoporous silica-based materials.

Designing the synthesis of catalytically active Ti-ß by using various new templates in the presence of fluoride anion.

Crystallization of large-pore Ti-ß by using a variety of diquaternary ammonium derivatives of dibromoalkane and amines such as triethylamine, 1,4-diazabicyclo[2,2,2]octane (DABCO), and quinuclidine as structure-directing agents (SDA) is described. The size of hydrophobic bridging alkyl-chain length of the template [R(3)N(+)-(CH(2))(x)-N(+)R(3)](OH(-))(2) directs the final crystalline product: Ti-ß, Ti-ZSM-12, Ti-nonasil or Ti-ZSM-5, as x gradually changes from 6 to 1, in the fluoride medium under hydrothermal conditions. A dense phase such as Ti-nonasil (clathrasil type) is crystallized as the size of hydrophobic bridging alkyl-chain length decreases. The use of F(-) anions as a mineralizer and Ti(4+) as a heteroatom in the synthesis gel also influences the selectivity of final crystalline product. The phase purity and incorporation of Ti(4+) into the lattice of ß (BEA) and ZSM-12 frameworks are confirmed using XRD, UV-visible, FT-IR, (29)Si NMR spectroscopes, elemental analysis (ICP), surface area measurements and catalytic test reactions. The morphology of Ti-ß samples is dependent on the nature of the structure-directing agent as revealed by the scanning electron microscopic (SEM) observations. The catalytic activity in the epoxidation of 4-vinyl-1-cyclohexene is increased with the amount of tetrahedral Ti(4+) atoms in the framework. The new templates can be effectively used for preparation of catalytically active Ti-ß with the minimum number of framework defect sites.

Investigation of the Photoluminescence and Nonlinear Optical Properties of Ce2O3-TiO2 Nanocomposites.

This paper reports the photoluminescence and nonlinear optical (NLO) properties of Ce2O3-TiO2 nanocomposites synthesized via sol-gel process with different concentrations of cerium. The physical characterization studies by means of XRD indicated for the successful incorporation of Ce into the lattice of TiO2, while the UV-visible spectra for an absorption edge shift of TiO2 to the higher wavelength side following the Ce addition, and FESEM analysis for the morphology and particles sizes of the synthesized materials. On testing of the photoluminescence properties recorded through time-resolved fluorescence (TCSPC) technique, a decrease in the intensity of TiO2 with that of increased Ce concentration was observed and is due to an escalation in the number of oxygen vacancies. Further, the observation NLO properties for Ce2O3-TiO2 was done by a Z-scan technique of 5ns continuous wave (cw) laser at 532 nm, where the involvement of active mechanisms in the nonlinear refraction and nonlinear absorption are due to the saturable absorption (SA) and nonlinear thermal effects.

Design of P-Doped Mesoporous Carbon Nitrides as High-Performance Anode Materials for Li-Ion Battery.

Herein, we demonstrate a simple and unique strategy for the preparation of P-doped into the substructure of mesoporous carbon nitride materials (P-MCN-1) with ordered porous structures as a high-energy and high-power Li-ion battery (LIB) anode. The P-MCN-1 as an anode in LIB delivers a high reversible discharge capacity of 963 mAh g-1 even after 1000 cycles at a current density of 1 A g-1, which is much higher than that of other counterparts comprising s-triazine (C3H3N3, g-C3N4), pristine MCN-1, and B-containing MCN-1 (B-MCN-1) subunits or carbon allotropes like CNT and graphene (rGO) materials. The P-MCN-1 electrode also exhibits exceptional rate capability even at high current densities of 5, 10, and 20 A g-1 delivering 685, 539, and 274 mAh g-1, respectively, after 2500 cycles. The high electrical conductivity and Li-ion diffusivity (D), estimated from electrochemical impedance spectra (EIS), very well support the extraordinary electrochemical performance of the P-MCN-1. Higher formation energy, lower bandgap value, and high Li-ion adsorption ability predicted by first principle calculations of P-MCN-1 are in good agreement with experimentally observed high lithium storage, stable cycle life, high power capability, and minimal irreversible capacity (IRC) loss. To the best of our knowledge, it is an entirely new material with the combination of ordered mesostructures with P codoping in carbon nitride substructure which offers superior performance for LIB, and hence we believe that this work will create new momentum for the design and development of clean energy storage devices.

Electrochemical sensor and biosensor platforms based on advanced nanomaterials for biological and biomedical applications.

Introduction of novel functional nanomaterials and analytical technologies signify a foremost possibility for the advance of electrochemical sensor and biosensor platforms/devices for a broad series of applications including biological, biomedical, biotechnological, clinical and medical diagnostics, environmental and health monitoring, and food industries. The design of sensitive and selective electrochemical biological sensor platforms are accomplished conceivably by offering new surface modifications, microfabrication techniques, and diverse nanomaterials with unique properties for in vivo and in vitro medical analysis via relating a sensibly planned electrode/solution interface. The advantageous attributes such as low-cost, miniaturization, energy efficient, easy fabrication, online monitoring, and the simultaneous sensing capability are the driving force towards continued growth of electrochemical biosensing platforms, which have fascinated the interdisciplinary research arenas spanning chemistry, material science, biological science, and medical industries. The electrochemical biosensor platforms have potential applications in the early-stage detection and diagnosis of disease as stout and tunable diagnostic and therapeutic systems. The key aim of this review is to emphasize the newest development in the design of sensing and biosensing platforms based on functional nanomaterials for biological and biomedical applications. High sensitivity and selectivity, fast response, and excellent durability in biological media are all critical aspects which will also be wisely addressed. Potential applications of electrochemical sensor and biosensor platforms based on advanced functional nanomaterials for neuroscience diagnostics, clinical, point-of-care diagnostics and medical industries are also concisely presented.

Mesoporous BaTiO3@SBA-15 derived via solid state reaction and its excellent adsorption efficiency for the removal of hexavalent chromium from water.

We report the synthesis of a barium-titanate/mesoporous silica nanocomposite material BaTiO3@SBA-15 via aerosol assisted solid state reaction using SBA-15 as a hard template. Hexavalent chromium is one of the most harmful contaminants of industrial waste-water. We have used BaTiO3@SBA-15 nanocomposite as an adsorbent for the removal of chromium(vi)-contaminated water and it showed an adsorption capacity of 98.2 wt% within only 40 min contact time in a batch reactor. This mesoporous composite has retained this excellent adsorption efficiency of hexavalent chromium for several repetitive cycles, suggesting its future potential for the remediation of water contaminated with Cr(vi).

Self-degrading niosomes for encapsulation of hydrophilic and hydrophobic drugs: An efficient carrier for cancer multi-drug delivery.

In this study, we have examined the encapsulation and release of hydrophilic and hydrophobic drugs in self-degrading niosomes as a unique method for anticancer therapy. Niosomes were prepared by amphiphilic self-assembly of Tween 80 and cholesterol through film hydration method. Encapsulation studies with two active molecules curcumin and doxorubicin hydrochloride (Dox) showed that curcumin is supposed to accumulate in the shell whereas Dox accumulates in the inner aqueous core of the niosome. Confocal studies indicated that nile red adsorbs preferentially to the head group of the Tween 80 and forms two separate layers in the shell. It was also seen that the niosomes undergo self-degradation in PBS through a sequential process, forming interconnected pores followed by complete collapse after 1week. The release profile shows two phases: i) initial Dox release in the first two days, followed by ii) curcumin release over 7days. Enhanced (synergistic) cytotoxicity was observed for dual-drug loaded niosomes against HeLa cell lines. Thus these niosomes are shown to offer a promising delivery system for hydrophobic and hydrophilic drugs collectively.

The dual role of micelles as templates and reducing agents for the fabrication of catalytically active hollow silver nanospheres.

We report a simple and efficient protocol for fabrication of colloidal hollow silver nanospheres of size less than 30 nm using an ABC triblock copolymer poly(styrene-b-vinyl-2-pyridine-b-ethylene oxide) in the absence of any reducing agents. The colloidal silver hollow nanoparticles serve as an efficient heterogeneous catalyst for Baeyer-Villiger oxidation of ketones to the corresponding lactones in the presence of anhydrous tert-butylhydroperoxide under liquid-phase conditions.

Novel and mild synthetic strategy for the sulfonic Acid functionalization in periodic mesoporous ethenylene-silica.

A new postsynthetic method has been developed for sulfonic acid functionalization of hybrid periodic mesoporous organosilica (PMO) materials containing carbon-carbon double bonds (-C═C-) located in mesoporous wall structures. Hexagonal mesoporous ethenylene-silicas (HME) with different pore sizes were synthesized by using P123, Brij76, and Brij56 surfactants and investigated for postsynthetic functionalization. The present functionalization strategy involves epoxidation of double bonds at -5 °C followed by conversion of the resulting epoxide with bisulfite ions at 65 °C and involves neither the use of well-known mercaptol/H2O2 nor harsh concentrated H2SO4 reagents during the course of -C═C- functionalization. The epoxidation step plays a crucial role in determining the amount of -SO3H groups functionalized onto the silica support which is optimized with respect to different synthesis parameters. The ethenylene-silicas both before and after chemical modification were thoroughly characterized by powder XRD, TEM, N2 adsorption, Raman spectroscopy, 13C and 29Si MAS NMR, and catalytic test reactions. X-ray powder diffraction measurements and sorption data indicated that the mesostructure was intact during the postsynthetic chemical modification. Raman spectra exhibited two strong bands at 1567 and 1290 cm(-1) for ethenylene-silica attributed to -C═C and -C-H stretching vibrations, respectively; whereas after epoxidation and sulfonation, new bands were observed at 1215 and 1035 cm(-1) corresponding to the epoxide and -SO3 stretching vibrations, respectively. 13C CP MAS NMR of surfactant extracted ethenylene-silica exhibits a signal at 146 ppm along with signals at 16.4 and 17.4 ppm. The appearance of new signals at 47.7 and 46.5 ppm is attributed to carbon atom with ≡C-OH and ≡C-SO3H groups, respectively. 29Si MAS NMR spectra exclusively showed T2 and T3 species at -73 and -82 ppm, respectively both before and after chemical modification and negligible amount of Q3 or Q4 species confirms the stability of Si-C bonds during the functionalization. The sulfonic acid-functionalized mesoporous ethenylene-silicas show high catalytic activity in esterification of acetic acid with ethanol under liquid-phase reaction conditions.

Synthesis of mesoporous hollow silica nanospheres using polymeric micelles as template and their application as a drug-delivery carrier.

Mesoporous hollow silica nanospheres with uniform particle sizes of 31-33 nm have been successfully synthesized by cocondensation of tetramethoxysilane (TMOS) and alkyltrimethoxysilanes [RSi(OR)3], where the latter also acts as a porogen. ABC triblock copolymer micelles of poly(styrene-b-2-vinyl pyridine-b-ethylene oxide) (PS-PVP-PEO) with a core-shell-corona architecture have been employed as a soft template at pH 4. The cationic shell block with 2-vinyl pyridine groups facilitates the condensation of silica precursors under the sol-gel reaction conditions. Phenyltrimethoxysilane, octyltriethoxysilane, and octadecyltriethoxysilanes were used as porogens for generating mesopores in the shell matrix of hollow silica and the octadecyl precursor produced the largest mesopore among the different porogens, of dimension ca. 4.1 nm. The mesoporous hollow particles were thoroughly characterized by small-angle X-ray diffraction (SXRD), thermal (TG/DTA) and nitrogen sorption analyses, infra-red (FTIR) and nuclear magnetic resonance ((13)C-CP MAS NMR and (29)Si MAS NMR) spectroscopies, and transmission electron microscopy (TEM). The mesoporous hollow silica nanospheres have been investigated for drug-delivery application by an in vitro method using ibuprofen as a model drug. The hollow silica nanospheres exhibited higher storage capacity than the well-known mesoporous silica MCM-41. Propylamine functionalized hollow particles show a more sustained release pattern than their unfunctionalized counterparts, suggesting a huge potential of hollow silica nanospheres in the controlled delivery of small drug molecules.

La2O3 hollow nanospheres for high performance lithium-ion rechargeable batteries.

An efficient and simple protocol for synthesis of novel La(2)O(3) hollow nanospheres of size about 30 ± 2 nm using polymeric micelles is reported. The La(2)O(3) hollow nanospheres exhibit high charge capacity and cycling performance in lithium-ion rechargeable batteries (LIBs), which was scrutinized for the first time among the rare-earth oxides.

Novel LaBO3 hollow nanospheres of size 34±2 nm templated by polymeric micelles.

Novel lanthanum borate (LaBO(3)) hollow nanospheres of size 34±2 nm have been reported for the first time by soft-template self-assembly process. Poly(styrene-b-acrylic acid-b-ethylene oxide) (PS-PAA-PEO) micelle with core-shell-corona architecture serves as an efficient soft template for fabrication of LaBO(3) hollow particles using sodium borohydride (NaBH(4)) and LaCl(3)⋅7H(2)O as the precursors. In this template, the PS block (core) acts as a template of the void space of hollow particle, the anionic PAA block (shell) serves as reaction field for metal ion interactions, and the PEO block (corona) stabilizes the polymer/lanthana composite particles. The PS-PAA-PEO micelles and the resulting LaBO(3) hollow nanospheres were thoroughly characterized by dynamic light scattering (DLS), transmission electron microscope (TEM), X-ray diffraction, magic angle spinning-nuclear magnetic resonance ((11)B MAS NMR), energy dispersive X-ray analysis, thermal analyses, Fourier transform infra red spectroscopy, and nitrogen adsorption/desorption analyses. The nitrogen adsorption/desorption analyses and TEM observation of the hollow particles confirmed the presence of disordered mesopores in the LaBO(3) shell domain. The solid state (11)B MAS NMR spectra of LaBO(3) hollow nanospheres revealed that the shell part contains both trigonal and tetrahedral boron species. The LaBO(3) hollow particles were applied to anode materials in lithium-ion rechargeable batteries (LIBs). The hollow particles exhibited high coulombic efficiency and charge-discharge cycling capacities of up to 100 cycles in the LIBs.

Micelles of poly(styrene-b-2-vinylpyridine-b-ethylene oxide) with blended polystyrene core and their application to the synthesis of hollow silica nanospheres.

Core-shell-corona (CSC) micelles of asymmetric triblock copolymer, poly(styrene-b-2-vinylpyridine-b-ethylene oxide) (PS-PVP-PEO), containing polystyrene homopolymer (homo-PS) in the core were successfully prepared in aqueous media. The influence of homo-PS contents over the formation of the micelles was investigated thoroughly by various techniques such as dynamic light scattering (DLS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and fluorescence spectroscopy. It was found that the size of the PS core of the micelle was increased by the addition of homo-PS as observed by DLS and TEM techniques. The SEM and TEM measurements confirm the spherical morphology of the micelles and enlargement of PS core over the addition of homo-PS. The increase in the PS core volume of the PS-PVP-PEO micelles is attributed to the insertion of homo-PS in the PS core. The micelles have also been demonstrated as facile soft templates for synthesis of hollow silica nanospheres. The average diameter of the spherical hollow particles could be tuned between 30.6 and 38.8 nm with cavity sizes ranging from 20.7 to 28.5 nm using tetramethoxysilane as silica precursors under mild acidic conditions. The facile synthesis of hollow silica using the CSC micelles with different homo-PS contents indicates that the hollow void size can be controlled within a range of several nanometers.

Novel synthesis of bifunctional catalysts with different microenvironments.

Acid-base bifunctional activity governed by -NH(2) group's microenvironment is evident from two different catalysts scrutinized by interchanging the location of -SO(3)H/NH(2) groups on periodic mesoporous ethylenesilica. The hydrophobic local environment plays a significant role in one-pot deacetalization/nitroaldol condensation.

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.

Novel titania hollow nanospheres of size 28 ± 1 nm using soft-templates and their application for lithium-ion rechargeable batteries.

We report a novel protocol to prepare titania hollow nanospheres of size about 28 ± 1 nm with micelles of asymmetric triblock copolymers. The hollow particles exhibit unique electrochemical properties in lithium ion rechargeable batteries such as high capacity, very low irreversible capacity loss, and high cycling performance.

Naked eye detection of cadmium using inorganic-organic hybrid mesoporous material.

A novel and low-cost optical sensor for the naked eye detection of Cd2+ in aqueous media based on mesoporous silica containing 4-(2-pyridylazo)resorcinol (PAR) as a probe molecule anchored by N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride (TMAC) was prepared. The effects of various factors such as pH, solvent volume, temperature, reaction time, amount of the material, and the presence of various ions were studied in order to optimize operating conditions. The detection was based on the color change of PAR from orange-yellow to purple as a result of complexation with Cd2+. The intensity of the Cd-PAR complex varies linearly with the Cd2+ concentration, from zero to 1.78x10(-7) mol dm(-3). The detection and quantification limits for the method when determining Cd2+ were 1.75x10(-8) and 5.77x10(-8) mol dm(-3), respectively, with a correlation coefficient of 0.99. Good chemical stability of the material was observed for a period of five months. The developed sensor was applied to the analysis of various industrial effluents and tap water samples.

Optical sensor for the visual detection of mercury using mesoporous silica anchoring porphyrin moiety.

A low cost, solid optical sensor for the rapid detection of low concentrations of Hg2+ in aqueous media was prepared by the monolayer functionalization of mesoporous silica with 5,10,15,20-tetraphenylporphinetetrasulfonic acid (TPPS), anchored by N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride (TMAC). The detection is based on the color change of TPPS from orange to green as a result of the formation of a charge-transfer complex with Hg2+. The intensity of the charge-transfer band varies linearly with Hg2+ in the concentration range from zero to 2.5 x 10(-7) mol dm(-3). The lower detection limit observed for Hg2+ concentration is 1.75 x 10(-8) mol dm(-3). The material exhibits good chemical and mechanical stability, and did not show any degradation of TPPS for a period of eight months. The sensor was applied for the analysis of various environmental samples. The effects of pH, sample volume, reaction time, amount of material, and the presence of foreign ions on the detection method are discussed.