Titania‐Coated Metal Nanostructures

The synergistic effect between metal and TiO₂ nanoparticles brings about new, enhanced functionalities for a myriad of applications, ranging from labeling and sensing to catalysis and surface‐enhanced Raman scattering. Although extensive work has been done in the preparation of concentric TiO₂‐coated metal nanostructures, current methods for the synthesis of noncentrosymmetric morphologies are still very limited. This Focus review summarizes the various methods used to prepare TiO₂‐coated metal nanostructures, with a particular emphasis on noncentrosymmetric morphologies, their novel plasmonic properties, and their promising applications in the fields of catalysis and photocatalysis.     

Silica-metal core-shell nanostructures

Silica-metal nanostructures consisting of silica cores and metal nanoshells attract a lot of attention because of their unique properties and potential applications ranging from catalysis and biosensing to optical devices and medicine. The important feature of these nanostructures is the possibility of controlling their properties by the variation of their geometry, shell morphology and shell material. This review is devoted to silica-noble metal core-shell nanostructures; specifically, it outlines the main methods used for the preparation and surface modification of silica particles and presents the major strategies for the formation of metal nanoshells on the modified silica particles. A special emphasis is given to the St?ber method, which is relatively simple, effective and well verified for the synthesis of large and highly uniform silica particles (with diameters from 100 nm to a few microns). Next, the surface chemistry of these particles is discussed with a special focus on the attachment of specific organic groups such as aminopropyl or mercaptopropyl groups, which interact strongly with metal species. Finally, the synthesis, characterization and application of various silica-metal core-shell nanostructures are reviewed, especially in relation to the siliceous cores with gold or silver nanoshells. Nowadays, gold is most often used metal for the formation of nanoshells due to its beneficial properties for many applications. However, other metals such as silver, platinum, palladium, nickel and copper were also used for fabrication of core-shell nanostructures. Silica-metal nanostructures can be prepared using various methods, for instance, (i) growth of metal nanoshells on the siliceous cores with deposited metal nanoparticles, (ii) reduction of metal species accompanied by precipitation of metal nanoparticles on the modified silica cores, and (iii) formation of metal nanoshells under ultrasonic conditions. A special emphasis is given to the seed-mediated growth, where metal nanoshells are formed on the modified silica cores with deposited metal nanoparticles. This strategy assures a good control of the nanoshell thickness as well as its surface properties.     

Enzyme‐Responsive Multifunctional Magnetic Nanoparticles for Tumor Intracellular Drug Delivery and Imaging

Enzyme‐responsive, hybrid, magnetic silica nanoparticles have been employed for multifunctional applications in selective drug delivery and intracellular tumor imaging. In this study, doxorubicin (Dox)‐conjugated, enzyme‐cleavable peptide precursors were covalently tethered onto the surface of uniform silica‐coated magnetic nanoparticles through click chemistry. This enzyme‐responsive nanoparticle conjugate demonstrated highly efficient Dox release upon specific enzyme interactions in vitro. It also exhibits multiple functions in selective tumor intracellular drug delivery and imaging in the tumor cells with high cathepsin B expression, whereas it exhibited lower cytotoxicity towards other cells without enzyme expression.     

Modern Inorganic Aerogels

Essentially, the term aerogel describes a special geometric structure of matter. It is neither limited to any material nor to any synthesis procedure. Hence, the possible variety of materials and therefore the multitude of their applications are almost unbounded. In fact, the same applies for nanoparticles. These are also just defined by their geometrical properties. In the past few decades nano‐sized materials have been intensively studied and possible applications appeared in nearly all areas of natural sciences. To date a large variety of metal, semiconductor, oxide, and other nanoparticles are available from colloidal synthesis. However, for many applications of these materials an assembly into macroscopic structures is needed. Here we present a comprehensive picture of the developments that enabled the fusion of the colloidal nanoparticle and the aerogel world. This became possible by the controlled destabilization of pre‐formed nanoparticles, which leads to their assembly into three‐dimensional macroscopic networks. This revolutionary approach makes it possible to use precisely controlled nanoparticles as building blocks for macroscopic porous structures with programmable properties.     

The first urea‐based ionic liquid‐stabilized magnetic nanoparticles: an efficient catalyst for the synthesis of bis(indolyl)methanes and pyrano[2,3‐d]pyrimidinone derivatives

Urea‐based ionic liquid stabilized on silica‐coated Fe₃O₄ magnetic nanoparticles, {Fe₃O₄@SiO₂@(CH₂)₃‐Urea‐SO₃H/HCl}, as an unexceptionable and smooth releasing urea fertilizer in alkali soils was synthesized and fully characterized using Fourier transform infrared, UV–visible and energy‐dispersive X‐ray spectroscopies, X‐ray diffraction, scanning and transmission electron microscopies, atomic force microscopy and thermogravimetric analysis. The nanostructure catalyst as a novel, green and efficient catalyst was applied for the synthesis of bis(indolyl)methane derivatives via the condensation reaction between 2‐methylindole and aldehydes at room temperature under solvent‐free conditions. Also, pyrano[2,3‐d]pyrimidinone derivatives were prepared in the presence of the nanomagnetic urea‐based catalyst by the one‐pot three‐component condensation reaction of 1,3‐dimethylbarbituric acid, aldehydes and malononitrile under solvent‐free conditions at 60 °C. To the best of our knowledge, this is the first report of the synthesis of urea‐based ionic liquid stabilized on silica‐coated Fe₃O₄ magnetic nanoparticles. So the present work can open up a new and promising insight in the course of rational design, synthesis and applications of task‐specific fertilizer‐based nanomagnetic ionic liquids with desirable properties as unexceptionable substances for sustainable processes. Copyright © 2016 John Wiley & Sons, Ltd.     

Facile Fabrication of Well‐Dispersed Pt Nanoparticles in Mesoporous Silica with Large Open Spaces and Their Catalytic Applications

In this paper, a facile strategy is reported for the preparation of well‐dispersed Pt nanoparticles in ordered mesoporous silica (Pt@OMS) by using a hybrid mesoporous phenolic resin‐silica nanocomposite as the parent material. The phenolic resin polymer is proposed herein to be the key in preventing the aggregation of Pt nanoparticles during their formation process and making contributions both to enhance the surface area and enlarge the pore size of the support. The Pt@OMS proves to be a highly active and stable catalyst for both gas‐phase oxidation of CO and liquid‐phase hydrogenation of 4‐nitrophenol. This work might open new avenues for the preparation of noble metal nanoparticles in mesoporous silica with unique structures for catalytic applications.     

Mesoscale Characterization of Nanoparticles Distribution Using X‐ray Scattering

The properties of many functional materials depend critically on the spatial distribution of an active phase within a support. In the case of solid catalysts, controlling the spatial distribution of metal (oxide) nanoparticles at the mesoscopic scale offers new strategies to tune their performance and enhance their lifetimes. However, such advanced control requires suitable characterization methods, which are currently scarce. Here, we show how the background in small‐angle X‐ray scattering patterns can be analyzed to quantitatively access the mesoscale distribution of nanoparticles within supports displaying hierarchical porosity. This is illustrated for copper catalysts supported on meso‐ and microporous silica displaying distinctly different metal distributions. Results derived from X‐ray scattering are in excellent agreement with electron tomography. Our strategy opens unprecedented prospects for understanding the properties and to guide the synthesis of a wide array of functional nanomaterials.     

Stable photochromism and controllable reduction properties of surfactant-encapsulated polyoxometalate/silica hybrid films

In this paper, we present a novel strategy for fabricating polyoxometalate (POM)-based photochromic silica hybrid films. To combine metal nanoparticles (NPs) into the POMs embedded silica matrix, furthermore, we realized the controllable in situ synthesis of metal NPs in the film by utilizing the reduction property of POMs existing in the reduced state. Through electrostatic encapsulation with hydroxyl-terminated surfactants, the POMs with good redox property can be covalently grafted onto a silica matrix by means of a sol-gel approach, and stable silica sol-gel thin films containing surfactant-encapsulated POMs can be obtained. The functional hybrid film exhibits both the transparent and easily processible properties of silica matrix and the stable and reversible photochromism of POMs. In addition, well-dispersed POMs in a hydrophobic microenvironment within the hybrid film can be used as reductants for the in situ synthesis of metal NPs. More significantly, the size and location of NPs can be tuned by controlling the adsorption time of metal ions and mask blocking the surface. The hybrid film containing both POMs and metal NPs with patterned morphology can be obtained, which has potential applications in optical display, memory, catalysis, microelectronic devices and antibacterial materials.     

Molecularly imprinted polymeric shell coated monodisperse‐porous silica microspheres as a stationary phase for microfluidic boronate affinity chromatography

Molecular imprinting of cis‐diol functionalized agents via boronate affinity interaction has been usually performed using nanoparticles as a support which cannot be utilized as a stationary phase in continuous microcolumn applications. In this study, monodisperse‐porous, spherical silica particles in the micron‐size range, with bimodal pore diameter distribution were selected as a new support for the synthesis of a molecularly imprinted boronate affinity sorbent, using a cis‐diol functionalized agent as the template. A specific surface area of 158 m²/g was achieved with the imprinted sorbent by using monodisperse‐porous silica microspheres containing both mesoporous and macroporous compartments as the support. High porosity originating from the macroporous compartment and sufficiently high particle size provided good column permeability to the imprinted sorbent in microcolumn applications. The mesoporous compartment provided a large surface area for the parking of imprinted molecules while the macroporous compartment facilitated the intraparticular diffusion of imprinted target within the microsphere interior. A microfluidic boronate affinity system was first constructed by using molecularly imprinted polymeric shell coated monodisperse‐porous silica microspheres as a stationary phase. The synthetic route for the imprinting process, the reversible adsorption/ desorption behavior of selected target and the selectivity of imprinted sorbent in both batch and microfluidic boronate affinity chromatography systems are reported.     

Synthesis of novel magnetic nanoparticles with urea or urethane moieties: Applications as catalysts in the Strecker synthesis of α‐aminonitriles

Four novel magnetic nanoparticle catalysts with urea or urethane moieties are reported. The silica‐coated magnetic nanoparticles were simply functionalized via addition of 3‐(triethoxysilyl)propylisocyanate (TESPIC), amine or amino alcohol. TESPIC with dual labile functional groups was used as a suitable precursor for the synthesis of urethane‐based catalysts. The newly synthesized catalysts were fully characterized using a variety of techniques. These functionalized magnetic nanoparticles were used as reusable catalysts in the Strecker synthesis of α‐aminonitrile derivatives under solvent‐free conditions at 50 °C.     

Active Salt/Silica‐Templated 2D Mesoporous FeCo‐Nx‐Carbon as Bifunctional Oxygen Electrodes for Zinc–Air Batteries

Two types of templates, an active metal salt and silica nanoparticles, are used concurrently to achieve the facile synthesis of hierarchical meso/microporous FeCo‐N_x‐carbon nanosheets (meso/micro‐FeCo‐N_x‐CN) with highly dispersed metal sites. The resulting meso/micro‐FeCo‐N_x‐CN shows high and reversible oxygen electrocatalytic performances for both ORR and OER, thus having potential for applications in rechargeable Zn–air battery. Our approach creates a new pathway to fabricate 2D meso/microporous structured carbon architectures for bifunctional oxygen electrodes in rechargeable Zn–air battery as well as opens avenues to the scale‐up production of rationally designed heteroatom‐doped catalytic materials for a broad range of applications.     

Fabrication of Mesoporous‐Silica‐Coated Upconverting Nanoparticles with Ultrafast Photosensitizer Loading and 808 nm NIR‐Light‐Triggering Capability for Photodynamic Therapy

A novel photodynamic therapy nanoplatform based on mesoporous‐silica‐coated upconverting nanoparticles (UCNP) with electrostatic‐driven ultrafast photosensitizer (PS) loading and 808 nm near infrared (NIR)‐light‐triggering capabilities has been fabricated. By positively charging inner channels of the mesoporous silica shell with amino groups, a quantitative dosage of negatively charged PS, exemplified with Rose Bengal (RB) molecules, can be loaded in 2 min. In addition, the electrostatic‐driven technique simultaneously provides the platform with both excellent PS dispersity and leak‐proof properties due to the repulsion between the same‐charged molecules and the electrostatic attraction between different‐charged PS and silica channel walls, respectively. The as‐coated silica shell with an ultrathin thickness of 12±2 nm is delicately fabricated to facilitate ultrafast PS loading and efficient energy transfer from UCNP to PS. The outside surface of the silica shell is capped with hydrophilic β‐cyclodextrin, which not only enhances the dispersion of resulting nanoparticles in water but also plays a role of “gatekeeper”, blocking the pore opening and preventing PS leaking. The in vitro cellular lethality experiment demonstrates that RB molecules can be activated to effectively generate singlet oxygen and kill cancer cells upon 808 nm NIR light irradiation.     

Functionalized silica nanoparticles for trapping Pb2+ ions via diazo‐azomethine scaffolds

Diazo‐azomethine coated silica sorbent for the adsorption of Pb²⁺ ions has been fabricated. The sorbent was obtained by one‐pot synthesis of silica nanoparticles in the presence of diazo‐azomethine molecules possessing silatranyl side chains for grafting via covalent bond formation. The functionalized silica nanoparticles exhibited characteristic physicochemical properties of diazo‐azomethine scaffolds as determined using Fourier transform infrared spectroscopy, scanning and transmission electron microscopies and thermogravimetric analysis. Various adsorption parameters such as pH, weight of adsorbent, time taken for equilibration and recovery of lead ions were optimized using a batch method. The sorbent showed high adsorption capacity for lead ions of 460.4 mg g^?1 at pH = 4. The effect of various competing ions on the adsorption of lead ions was studied and interference was removed by using a masking agent. The sorbent can be regenerated and reused, and is compatible for the adsorption of Pb²⁺ ions from green leafy vegetables. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis and Characterization of Fluorescent Silica Nanoparticles Functionalized with Collagens of Variable Lengths

Collagen, the most abundant protein in human body, has been widely used as an excellent natural material for diverse biomedical applications due to its superior properties such as ample biological interaction sites, minimal immunogenicity and high biocompatibility. Collagens of different lengths are produced by recombinant technology and utilized to functionalize fluorescent silica nanoparticles (FNPs). The collagen‐functionalized FNPs display mono‐disperse distribution, but their sizes are dependent on the length of collagen. These modified FNPs all show nice fluorescence profile as well as low cytotoxicity, suggesting promising applications in bioimaging. We have demonstrated that various types of collagen, conveniently produced by recombinant technology, can be used to modify silica nanoparticles with nice characteristics such as mono‐dispersion, non‐interference in fluorescence and low toxicity. It may endow fluorescent silica nanoparticles with broad biological applications.     

Synthesis of Small‐Sized,Porous, and Low‐Toxic Magnetite Nanoparticles by Thin POSS Silica Coating

In this communication, we report the synthesis of small‐sized (<10 nm), water‐soluble, magnetic nanoparticles (MNPs) coated with polyhedral oligomeric silsesquioxanes (POSS), which contain either polyethylene glycol (PEG) or octa(tetramethylammonium) (OctaTMA) as functional groups. The POSS‐coated MNPs exhibit superparamagnetic behavior with saturation magnetic moments (51–53 emu g^?1) comparable to silica‐coated MNPs. They also provide good colloidal stability at different pH and salt concentrations, and low cytotoxicity to MCF‐7 human breast epithelial cells. The relaxivity data and magnetic resonance (MR) phantom images demonstrate the potential application of these MNPs in bioimaging.     

KIT‐6 Mesoporous Silica‐coated Magnetite Nanoparticles: A Highly Efficient and Easily Reusable Catalyst for the Synthesis of Benzo[d]imidazole Derivatives

KIT‐6 mesoporous silica‐coated magnetite nanoparticles as highly ordered large‐pore nanoparticles supply an environmentally friendly procedure for the synthesis of benzo[d]imidazoles through condensation of 1,2‐diaminobenzene with aryl aldehydes. These compounds were obtained in high yields and short reaction times. The catalyst could be easily recovered using an external magnet and reused for six cycles with almost consistent activity. All of the synthesized compounds were characterized by their physical constant, comparison with authentic samples, ir, 1H nmr, 13C nmr spectroscopy, and elemental analysis.     

One‐Pot Synthesis of Colloidal Nanobowls and Hybrid Multipod‐like Nanoparticles by Radiation Miniemulsion Polymerization

A facile approach is proposed to one‐pot synthesis of two kinds of nanoparticles: a new type of PS nanobowls (a hole appearing at the bottom of nanobowl) and PS/silica hybrid multipod‐like nanoparticles. The two type of nanoparticles generated together during polymerization could be separated easily by centrifugation. Furthermore, the structure of nanobowls could be easily controlled by the weight ratio of monomer/silica. In addition, we find that the multipod‐like nanoparticles play important roles in hydrophobic properties. The water contact angle increased from 24.0° to 143.3° after coated with the multipod‐like nanoparticles.

     

Bacterial synthesized metal and metal salt nanoparticles in biomedical applications: An up and coming approach

In the present scenario, metal nanoparticles have elicited a great deal of interest in biomedical applications because of their unique properties and antimicrobial potentials. Over the past few years, the green nanotechnology has materialized as a momentous approach for the synthesis and fabrication of noble metal salt and metal nanoparticles. The green route synthesis exploits diverse reducing and stabilizing agents from bacterial resources for the successful synthesis of metal nanoparticles. This review mainly focuses on the biosynthesis of the most commonly studied metal and metal salt nanoparticles such as gold, silver, platinum, palladium, copper, cadmium, titanium oxide, zinc oxide, zinc sulphate, cadmium sulphide and many more. These noble nanoparticles can be exploited in pharmaceutical industry as antimicrobial and anti-biofilm agents, targeted delivery of anticancer drugs, biosensors, etc.     

Bright luminescent, colloidal stable silica coated CdSe/ZnS nanocomposite by an in situ, one-pot surface functionalization

In this article, a systematic study of the design and development of surface-modification schemes for silica coated nanocomposite via an in situ, one-pot way is presented. Silica coated CdSe/ZnS nanoparticles were prepared in a water-in-oil microemulsion and subsequently surface modified via addition of various organosilane reagents to the microemulsion system. The resulting functionalized composite nanoparticles were characterized by different techniques like Transmission Electron Microscopy (TEM), photoluminescence spectroscopy and zeta-potential measurements. The results demonstrate that depending on the sequence of addition of silica precursors and organosilanes the product can show bright luminescence or considerable colloidal stability. The organosilanes molecules which are used here, act both as a stabilizer of the microemulsion system (regarding the charge compensation) and as a functional group the final product on top of silica shell. Using these surface-modification process, silica coated nanoparticles can be more readily conjugated with biomolecules and used as highly luminescent, sensitive, and reproducible labels in bioanalytical applications. Most importantly such surface functionalization could pave the way for controlled multi-mixed nanoparticles encapsulation (for example magnetic and QD nanoparticles).     

Synthesis of Multifunctional Metal‐ and Metal Oxide Core@Mesoporous Silica Shell Structures by Using a Wet Chemical Approach

We demonstrate a facile wet chemical approach for fabricating spherical metal/metal‐oxide core@mesoporous silica shell hybrid nanoparticles with different core and shell thicknesses. Vertically aligned mesoporous silica (mSiO₂) shells were fabricated over the pre‐synthesized spherical SiO₂ nanoparticles through a three‐step strategy: 1) synthesis of core materials, 2) covering the core with an organic–inorganic composite layer, and 3) removing the organic template through calcinations in air. The mechanisms of hybrid structure formation are proposed. The multifunctional nature of the hybrid structures could be induced by incorporating guest ions/molecules, such as Ag, Mn, and TiO₂, into the pores of an mSiO₂ shell. Mn and TiO₂ cluster‐ incorporated composite structures have been tested to be antioxidizing agents and effective photocatalysts through electron spin resonance, radical scavenging tests, and the photocatalytic degradation of rhodamine B. The possibility of incorporating several hetero‐element guest clusters in these mesoporous composite particles makes them highly attractive for multifunctional applications.