Two-phase synthesis of monodisperse silica nanospheres with amines or ammonia catalyst and their controlled self-assembly

Magnetically recoverable Fe3O4@SiO2@SBA-3@2-ATP-Cu: an improved catalyst for the synthesis of 5-substituted 1H-tetrazoles

Functionalization of Fe3O4@SiO2@SBA-3 with double-charged 3-chloropropyltrimethoxysilane (CPTMS) and 2-aminophenol, followed by mechanical mixing of the solid product with copper(i) chloride produces a new, greener and efficient Fe3O4@SiO2@SBA-3@2-ATP-Cu catalyst for the synthesis of 5-substituted 1H-tetrazoles. XRD, SEM, atomic absorption, TGA, N2 adsorption-desorption, and VSM analyses were performed for the characterization of the Fe3O4@SiO2@SBA-3@2-ATP-Cu structure. Nitrogen adsorption-desorption analysis revealed that Fe3O4@SiO2@SBA-3@2-ATP-Cu has a surface area of 242 m2 g-1 and a total pore volume of 55.72 cm3 g-1. In synthesizing 5-substituted 1H-tetrazoles, Fe3O4@SiO2@SBA-3@2-ATP-Cu shows superior yields in short reaction times at 120 °C. This catalyst also showed high thermal stability and recyclability at least for 4 runs without apparent loss of efficiency.

Silica nanoparticles inhibit cadmium uptake by the protozoan Tetrahymena thermophila without the need for adsorption

The simultaneous presence of nanoparticles (NPs) and heavy metals in the environment may affect their mutual biological uptake. Although previous studies showed that NPs could alter the cellular uptake of heavy metals by their adsorption of heavy metals, whether they could affect metal uptake without the need for adsorption is unknown. This study examined the effects of silica (SiO2) NPs on the uptake of Cd ion by the protozoan Tetrahymena thermophila. We found that, even with negligible levels of adsorption, SiO2 NPs at concentrations of 3 to 100 mg/L inhibited Cd uptake. This inhibitory effect decreased as the ambient Cd concentration increased from 1 to 100 μg/L, suggesting the involvement of at least two transporters with different affinities for Cd. The transporters were subsequently identified by the specific protein inhibitors amiloride and tariquidar as NCX and ABCB1, which are responsible for the uptake of Cd at low and high Cd levels, respectively. RT-qPCR and molecular dynamics simulation further showed that the inhibitory effects of SiO2 NPs were attributable to the down-regulated expression of the genes Ncx and Abcb1, steric hindrance of Cd uptake by NCX and ABCB1, and the shrinkage of the central channel pore of the transporters in the presence of SiO2 NPs. SiO2 NPs more strongly inhibited Cd transport by NCX than by ABCB1, due to the higher binding affinity of SiO2 NPs with NCX. Overall, our study sheds new light on a previously overlooked influence of NPs on metal uptake and the responsible mechanism.

Modifying the Stöber Process: Is the Organic Solvent Indispensable?

The Stöber method is one of the most important and fundamental processes for the synthesis of inorganic (nano)materials but has the drawback of using a large amount of organic solvent. Herein, ethanol was used as an example to explore if the organic solvent in a typical Stöber method can be omitted. It was found that ethanol increases the particle size of the obtained silica spheres and aids the formation of uniform silica particles rather than forming a gel. Nevertheless, the results indicated that an organic solvent in the initial synthesis mixture is not indispensable. An initially immiscible synthesis method was discovered, which can replace the organic solvent-based Stöber method to successfully synthesize silica particles with the same size ranges as the original Stöber process without addition of organic solvents. Moreover, this process can be of further value for the extension to synthesis processes of other materials based on the Stöber process.

Hollow Silica Nano and Micro Spheres with Polystyrene Templating: A Mini-Review

Synthesis of monodisperse hollow silica nanospheres, especially using a hard template route, has been shown to be successful, but a high yield is needed for this strategy to be used on an industrial scale. On the other hand, there is a research gap in the synthesis of hollow silica microspheres due to the popularity and easiness of the synthesis of silica nanospheres despite the larger spheres being beneficial in some fields. In this review, current trends in producing hollow silica nanospheres using hard templates, especially polystyrene, are briefly presented. Soft templates have also been used to make highly polydisperse hollow silica spheres, and complex designs have improved polydispersity. The effect of the main parameters on the coating is presented here to provide a basic understanding of the interactions between the silica and template surface in the absence or presence of surfactants. Surface charge, surface modification, parameters in the sol-gel method and interaction between the silica and templates need to be further improved to have a uniform coating and better control over the size, dispersity, wall thickness and porosity. As larger organic templates will have lower surface energy, the efficiency of the micro sphere synthesis needs to be improved. Control over the physical structure of hollow silica spheres will open up many opportunities for them to be extensively used in fields ranging from waste removal to energy storage.

Degradation of Methylene Blue with a Cu(II)-Quinoline Complex Immobilized on a Silica Support as a Photo-Fenton-Like Catalyst

A Cu(II)-quinoline complex immobilized on a silica support was prepared to enhance the degradation of dyes. Mesoporous silica functionalized with this Cu(II) complex was turned into a photo-Fenton-like catalyst. Various techniques were used to characterize the resulting material, and the catalytic activity was determined by the degradation of methylene blue (MB) under UV light irradiation. The Cu(II) ion was successfully coordinated to the quinoline ligand on a silica support. The dye degradation investigation has shown that 95% of the dye was degraded in 2.5 h. The active radical species involved in the reaction were OH^• and O₂ ^•-, suggesting that a peroxo complex intermediate might be formed during degradation processes.

Nonlinear charge regulation for the deposition of silica nanoparticles on polystyrene spherical surfaces

HYPOTHESIS

We describe the deposition behavior of monodispersed silica nanoparticles on polystyrene spherical particles by using modified pairwise DLVO (Derjaguin-Landau-Verwey-Overbeek) interaction force profiles at pH values between two and twelve. Our modified model contains a new nonlinear charge regulation parameter that considers redistribution of ions, which allows us to realistically express the electrical double layer (EDL) interaction forces.

EXPERIMENTS

Silanol-terminated silica nanoparticles (7.6 ± 0.4 nm), l-lysine-covered silica nanoparticles (7.8 ± 0.4 nm), and polyallylamine hydrochloride-covered polystyrene (PAH/PS) particles (348 ± 1 nm) were synthesized. Then, each type of silica nanoparticle was deposited on the PAH/PS particles at a range of pH values.

FINDINGS

Our new regulation parameter describes the realistic redistribution of charges governed by pH, total salt concentration, ionic strength of solution, and separation distance of particles. We find that this regulation parameter can be roughly approximated from the absolute values of theoretically calculated surface charge density and potential distributions, as well as experimentally measured ζ-potentials. Morphological analysis using electron microscopy of the experimental systems shows that the modified pairwise DLVO interaction forces exceptionally describe the deposition behavior of the silica nanoparticles physically adsorbed on the PAH/PS particle substrates.

Emerging Applications of Silica Nanoparticles as Multifunctional Modifiers for High Performance Polyester Composites

Nano-modification of polyester has become a research hotspot due to the growing demand for high-performance polyester. As a functional carrier, silica nanoparticles show large potential in improving crystalline properties, enhancing strength of polyester, and fabricating fluorescent polyester. Herein, we briefly traced the latest literature on synthesis of silica modifiers and the resultant polyester nanocomposites and presented a review. Firstly, we investigated synthesis approaches of silica nanoparticles for modifying polyester including sol-gel and reverse microemulsion technology, and their surface modification methods such as grafting silane coupling agent or polymer. Then, we summarized processing technics of silica-polyester nanocomposites, like physical blending, sol-gel processes, and in situ polymerization. Finally, we explored the application of silica nanoparticles in improving crystalline, mechanical, and fluorescent properties of composite materials. We hope the work provides a guideline for the readers working in the fields of silica nanoparticles as well as modifying polyester.

Nanobiomechanical behavior of Fe3O4@SiO2and Fe3O4@SiO2-NH2nanoparticles over HeLa cells interfaces

In this work, we studied the impact of magnetic nanoparticles (MNPs) interactions with HeLa cells when they are exposed to high frequency alternating magnetic field (AMF). Specifically, we measured the nanobiomechanical properties of cell interfaces by using atomic force microscopy (AFM). Magnetite (Fe₃O₄) MNPs were synthesized by coprecipitation and encapsulated with silica (SiO₂): Fe₃O₄@SiO₂and functionalized with amino groups (-NH₂): Fe₃O₄@SiO₂-NH₂, by sonochemical processing. HeLa cells were incubated with or without MNPs, and then exposed to AMF at 37 °C. A biomechanical analysis was then performed through AFM, providing the Young's modulus and stiffness of the cells. The statistical analysis (p < 0.001) showed that AMF application or MNPs interaction modified the biomechanical behavior of the cell interfaces. Interestingly, the most significant difference was found for HeLa cells incubated with Fe₃O₄@SiO₂-NH₂and exposed to AMF, showing that the local heat of these MNPs modified their elasticity and stiffness.

Thermochromic VO2-SiO2composite coating from ammonium citrato-oxovanadate(IV)

Vanadium dioxide (VO₂) coating plays an important role in energy saving and environmental protection due to its unique reversible phase transition. To solve the daylighting issue of VO₂coating, a VO₂(M)-silicon dioxide (SiO₂) composite coating is fabricated from ammonium citrato-oxovanadate(IV) by a SiO₂-assisted coating method. The VO₂(M)-SiO₂composite coating possesses excellent thermochromic properties that have produced varying results, i.e. 49.2% of visible transmittance, 52.3% of transmittance reduction at 2000 nm wavelength, 12% of solar energy modulation (ΔT_sol) and a phase transition temperature of 56.0 °C. Our findings may pave the way to extending the large-scale application of smart windows based on thermochromic VO₂.

Monodispersed CsPb2Br5@SiO2 Core-Shell Nanoparticles as Luminescent Labels for Biosensing

Despite the rising advances in the field of metal halide perovskite nanocrystals (NCs), the exploitation of such nanoparticles as luminescent labels for ex vivo imaging and biosensing is still unclear and in the early stages of investigation. One of the major challenges toward the implementation of metal halide perovskite NCs in biosensing applications is to produce monodispersed nanoparticles with desired surface characteristics and compatible with aqueous environments. Here, we report the synthesis of monodispersed spherical CsPb₂Br₅@SiO₂ core-shell nanoparticles by post-synthetic chemical transformation of 3D CsPbBr₃ NCs in the presence of tetraethyl orthosilicate and a critical water/ammonia ratio. This method involves an ammonia-mediated and ammonia-induced "top-down" transformation of as-synthesized 3D CsPbBr₃ NCs to smaller CsPb2Br5 nanoclusters (ca. 2-3 nm), which trigger a seed-mediated silica growth, yielding monodispersed spherical blue luminescent (λ_emission = 432 nm) CsPb₂Br₅@SiO₂ perovskite nanoparticles. By adjusting the reaction conditions, core-shell nanoparticles of a 36.1 ± 4.5 nm diameter, which preserve their optical properties in water, were obtained. Besides that, the viability of the developed nanoparticles as a luminescent label for biosensing has been proven by specific biorecognition of the IgG protein in a direct immunoassay. Our work sheds light on the chemical processes and transformations involved in the silica nucleation mechanism in the presence of perovskite nanoparticles and opens the way for the future rational design of the next generation of semiconductor NC luminescent biological labels.

Exploring alkaline routes for production of TEOS-based consolidants for carbonate stones using amine catalysts

TEOS-based sols following basic catalysis routes were explored and showed high potential and important advantages for consolidation of soft limestone.

Bioinspired One-Step Synthesis of Pomegranate-like Silica@Gold Nanoparticles with Surface-Enhanced Raman Scattering Activity

Gold-silica (Au-SiO₂) nanohybrids are of great technological importance, and it is crucial to develop facile synthetic protocols to prepare Au-SiO₂ nanohybrids with novel structures. Here we report the bioinspired synthesis of pomegranate-like SiO₂@Au nanoparticles (P-SiO₂@Au NPs) via one-step aqueous synthesis from chloroauric acid and tetraethyl orthosilicate mediated by a basic amino acid, arginine. Effects of chloroauric acid, tetraethyl orthosilicate, and arginine on the morphology and optical property of the products are investigated in detail. The P-SiO₂@Au NPs achieve tunable plasmon resonance depending on the amount of chloroauric acid, which affects the size and shape of the P-SiO₂@Au NPs. Finite-difference time-domain simulations are performed, revealing that the plasmon peak red-shifts with increasing particle size. Arginine serves as the reducing and capping agents for Au as well as the catalyst for SiO₂ formation and also promotes the combination of Au and SiO₂. Formation process of the P-SiO₂@Au NPs is clarified through time-course analysis. The P-SiO₂@Au NPs show good sensitivity for both colloidal and paper-based surface-enhanced Raman scattering measurements. They achieve enhancement factors of 4.3 × 10⁷-8.5 × 10⁷ and a mass detection limit of ca. 1 ng using thiophenol as the model analyte.

Strong Lewis Acid-Base and Weak Hydrogen Bond Synergistically Enhancing Ionic Conductivity of Poly(ethylene oxide)@SiO2 Electrolytes for a High Rate Capability Li-Metal Battery

Solid-state composite polymer electrolytes (CPEs) usually suffer from intrinsic low ionic conductivity and a solid-solid interface, badly inhibiting their widespread commercial application in all-solid-state Li-metal battery (ASSLMB) energy storage. Herein, a synergetic strategy using strong Lewis acid-base and weak hydrogen bonds was employed for self-assembly in situ construction of three-dimensional (3D) network-structured poly(ethylene oxide) (PEO) and SiO₂ CPEs (PEO@SiO₂). Ascribed to this synergistically rigid-flexible coupling dynamic strategy, a harmonious incorporation of monodispersed SiO₂ nanoparticles into PEO could remarkably reduce crystallinity of PEO, significantly enhancing the ionic conductivity (∼1.1 × 10^-4 S cm^-1 at 30 °C) and dramatically facilitating solid electrolyte interface stabilization (electrochemical stability window > 4.8 V at 90 °C). Moreover, the PEO@SiO₂-based ASSLMBs possess excellent rate capability over a wide temperature range (∼105 mA h g^-1 under 2 C at 90 °C), high temperature cycling capacity (retaining 90 mA h g^-1 after 100 cycles at 90 °C), and high specific capacity (146 mA h g^-1 under 0.3 C at 90 °C). Unambiguously, these high ionic conductivity CPEs along with excellent flexibility and safety can be one of the most promising candidates for high-performance ASSLMBs, evidently revealing that this synergistically rigid-flexible coupling dynamic strategy will open up a way to exploit the novel high ionic conductivity solid-state electrolytes.

Dye-doped silica nanoparticles: synthesis, surface chemistry and bioapplications

Background

Fluorescent silica nanoparticles have been extensively utilised in a broad range of biological applications and are facilitated by their predictable, well-understood, flexible chemistry and apparent biocompatibility. The ability to couple various siloxane precursors with fluorescent dyes and to be subsequently incorporated into silica nanoparticles has made it possible to engineer these fluorophores-doped nanomaterials to specific optical requirements in biological experimentation. Consequently, this class of nanomaterial has been used in applications across immunodiagnostics, drug delivery and human-trial bioimaging in cancer research.

Main body

This review summarises the state-of-the-art of the use of dye-doped silica nanoparticles in bioapplications and firstly accounts for the common nanoparticle synthesis methods, surface modification approaches and different bioconjugation strategies employed to generate biomolecule-coated nanoparticles. The use of dye-doped silica nanoparticles in immunoassays/biosensing, bioimaging and drug delivery is then provided and possible future directions in the field are highlighted. Other non-cancer-related applications involving silica nanoparticles are also briefly discussed. Importantly, the impact of how the protein corona has changed our understanding of NP interactions with biological systems is described, as well as demonstrations of its capacity to be favourably manipulated.

Conclusions

Dye-doped silica nanoparticles have found success in the immunodiagnostics domain and have also shown promise as bioimaging agents in human clinical trials. Their use in cancer delivery has been restricted to murine models, as has been the case for the vast majority of nanomaterials intended for cancer therapy. This is hampered by the need for more human-like disease models and the lack of standardisation towards assessing nanoparticle toxicity. However, developments in the manipulation of the protein corona have improved the understanding of fundamental bio–nano interactions, and will undoubtedly assist in the translation of silica nanoparticles for disease treatment to the clinic.

l-Arginine-Catalyzed Synthesis of Nanometric Organosilica Particles through a Waterborne Sol-Gel Process and Their Porous Structure Analysis

We report an efficient and easy-to-implement waterborne sol-gel process for the synthesis of nanometric organosilica particles. In this process, tetraethyl orthosilicate (TEOS) and 3-(methacryloxy)propyl trimethoxy silane (γ-MPS), employed as silica sources, were heterogeneously delivered in an aqueous solution of l-arginine, a basic amino acid used as a catalyst, from a top organic layer. Co-condensation of TEOS with γ-MPS led to the formation of organosilica particles with diameters between 30 and 230 nm when increasing the γ-MPS content from 0 to 10.1 mol % in the silica source. Nitrogen sorption analyses confirmed the microporous nature of the obtained particles after calcination. The Brunauer-Emmett-Teller (BET) surface areas increased from 27 (before calcination) to 684 m² g^-1 (after calcination) for the organosilica particles containing 10.1 mol % of γ-MPS. Fourier transform infrared spectroscopy and ²⁹Si NMR were employed to analyze the chemical structure of the organosilica spheres and provide insight into the mechanism of particle formation. In the second part, hybrid organosilica particles with a core-shell morphology were synthesized through the combination of Pickering emulsion and the sol-gel process. γ-MPS emulsion droplets stabilized by tiny silica particles (formed in a separate step) were first generated and used as seeds to grow a silica shell on their surface through TEOS addition from the top organic layer. Transmission electron microscopy and pore size analyses of the resulting particles after calcination revealed a unique dual-porosity structure with a mesoporous inner core and a micro/mesoporous silica shell with ink-bottle-type pores.

Synthesis of highly stable cyanine-dye-doped silica nanoparticle for biological applications

Cyanine dyes are widely used in biological labeling and imaging because of their narrow near infrared emission, good brightness and high flexibility in functionalization, which not only enables multiplex analysis and multi-color imaging, but also greatly reduces autofluorescence from biological matter and increases signal-to-noise ratio. Unfortunately, their poor chemical- and photo-stability strongly limits their applications. The incorporation of cyanine dyes in silica nanoparticles provides a solution to the problem. On one hand, the incorporation of cyanine dyes in silica matrix can enhance their chemical- and photo-stability and increase brightness of the nanomaterials. On the other hand, silica matrix provides an optimized condition to host the dye, which helps to maintain their fluorescent properties during application. In addition, the well-established silane technique provides numerous functionalities for diverse applications. However, commercially available cyanine dyes are not very stable at high alkaline conditions, which will gradually lose their fluorescence over time. Our results showed that cyanine dyes are very vulnerable in the reverse micelle system, in which they will lose their fluorescence in less than half an hour. The existence of surfactant could greatly promote degradation of cyanine dyes. Fluorescent silica nanoparticles cannot be obtained at the high alkaline condition with the existence of surfactant. In contrast, the cyanine dyes are relatively stable in Stöber media. Owing to the fast formation of silica particles in Stöber media, the exposure time of cyanine dye in alkaline solution was greatly reduced, and highly fluorescent particles with good morphology and size distribution could be obtained via Stöber approach. However, the increasing water content in the Stöber could reduce the stability of cyanine dyes, which should be avoided. This research here provides a clear guidance on how to successfully synthesize cyanine dye-doped silica nanoparticles with good morphology, size distribution, stability and brightness.

Fluorescent Silica Nanoparticles with Well-Separated Intensity Distributions from Batch Reactions

Silica chemistry provides pathways to uniquely tunable nanoparticle platforms for biological imaging. It has been a long-standing problem to synthesize fluorescent silica nanoparticles (SNPs) in batch reactions with high and low fluorescence intensity levels for reliable use as an intensity barcode, which would greatly increase the number of molecular species that could be tagged intracellularly and simultaneously observed in conventional fluorescence microscopy. Here, employing an amino-acid catalyzed growth, highly fluorescent SNP probes were synthesized with sizes <40 nm and well-separated intensity distributions, as mapped by single-particle imaging techniques. A seeded growth approach was used to minimize the rate of secondary particle formation. Organic fluorescent dye affinity for the SNP during shell growth was tuned using specifics of the organosilane linker chemistry. This work highlights design considerations in the development of fluorescent probes with well-separated intensity distributions synthesized in batch reactions for single-particle imaging and sensing applications, where heterogeneities across the nanoparticle ensemble are critical factors in probe performance.

Unraveling the Growth Mechanism of Silica Particles in the Stöber Method: In Situ Seeded Growth Model

In this work, we investigated the kinetic balance between ammonia-catalyzed hydrolysis of tetraethyl orthosilicate (TEOS) and subsequent condensation over the growth of silica particles in the Stöber method. Our results reveal that, at the initial stage, the reaction is dictated by TEOS hydrolysis to form silanol monomers, which is denoted as pathway I and is responsible for nucleation and growth of small silica particles via condensation of neighboring silanol monomers and siloxane network clusters derived thereafter. Afterward, the reaction is dictated by condensation of newly formed silanol monomers onto the earlier formed silica particles, which is denoted as pathway II and is responsible for the enlargement in size of silica particles. When TEOS hydrolysis is significantly promoted, either at high ammonia concentration (≥0.95 M) or at low ammonia concentration in the presence of LiOH as secondary catalyst, temporal separation of pathways I and II makes the Stöber method reminiscent of in situ seeded growth. This knowledge advance enables us not only to reconcile the most prevailing aggregation-only and monomer-addition models in literature into one consistent framework to interpret the Stöber process but also to grow monodisperse silica particles with sizes in the range 15-230 nm simply but precisely regulated by the ammonia concentration with the aid of LiOH.

Poly(methyl methacrylate) Surface Modification for Surfactant-Free Real-Time Toxicity Assay on Droplet Microfluidic Platform

Microfluidic droplet reactors have many potential uses, from analytical to synthesis. Stable operation requires preferential wetting of the channel surface by the continuous phase which is often not fulfilled by materials commonly used for lab-on-chip devices. Here we show that a silica nanoparticle (SiNP) layer coated onto a Poly(methyl methacrylate) (PMMA) and other thermoplastics surface enhances its wetting properties by creating nanoroughness, and allows simple grafting of hydrocarbon chains through silane chemistry. Using the unusual stability of silica sols at their isoelectric point, a dense SiNP layer is adsorbed onto PMMA and renders the surface superhydrophilic. Subsequently, a self-assembled dodecyltrichlorosilane (DTS) monolayer yields a superhydrophobic surface that allows the repeatable generation of aqueous droplets in a hexadecane continuous phase without surfactant addition. A SiNP-DTS modified chip has been used to monitor bacterial viability with a resazurin assay. The whole process involving sequential reagents injection, and multiplexed droplet fluorescence intensity monitoring is carried out on chip. Metabolic inhibition of the anaerobe Enterococcus faecalis by 30 mg L^-1 of NiCl₂ was detected in 5 min.

Bright fluorescent silica-nanoparticle probes for high-resolution STED and confocal microscopy

In recent years, fluorescent nanomaterials have gained high relevance in biological applications as probes for various fluorescence-based spectroscopy and imaging techniques. Among these materials, dye-doped silica nanoparticles have demonstrated a high potential to overcome the limitations presented by conventional organic dyes such as high photobleaching, low stability and limited fluorescence intensity. In the present work we describe an effective approach for the preparation of fluorescent silica nanoparticles in the size range between 15 and 80 nm based on L-arginine-controlled hydrolysis of tetraethoxysilane in a biphasic cyclohexane-water system. Commercially available far-red fluorescent dyes (Atto647N, Abberior STAR 635, Dy-647, Dy-648 and Dy-649) were embedded covalently into the particle matrix, which was achieved by aminosilane coupling. The physical particle attributes (particle size, dispersion, degree of agglomeration and stability) and the fluorescence properties of the obtained particles were compared to particles from commonly known synthesis methods. As a result, the spectroscopic characteristics of the presented monodisperse dye-doped silica nanoparticles were similar to those of the free uncoupled dyes, but indicate a much higher photostability and brightness. As revealed by dynamic light scattering and ζ-potential measurements, all particle suspensions were stable in water and cell culture medium. In addition, uptake studies on A549 cells were performed, using confocal and stimulated emission depletion (STED) microscopy. Our approach allows for a step-by-step formation of dye-doped silica nanoparticles in the form of dye-incorporated spheres, which can be used as versatile fluorescent probes in confocal and STED imaging.

Highly selective magnetic affinity purification of histidine-tagged proteins by Ni2+ carrying monodisperse composite microspheres

A magnetic sorbent based on monodisperse-porous silica microspheres was developed for His-tagged protein purification by immobilized metal affinity chromatography.

Regenerated CO anti-poisoning ability by anchoring highly oxidized platinum on oxygen-functionalized carbon spheres in one-step & two-phase synthesis for methanol electro-oxidation

A Pt@C–O catalyst with oxidized species of carbon and platinum obtained in two-phase synthesis exhibits regenerated CO anti-poisoning ability for MOR.

Kinetically-controlled synthesis of ultra-small silica nanoparticles and ultra-thin coatings

The understanding of silica as a polymer-like globule allows us to synthesize ultra-small silica nanoparticles (NPs) via a kinetic controlled process. The synthetic system is quite simple with Tetraethyl orthosilicate (TESO) as the precursor and H2O as the solvent and reactant. The reaction conditions are gentle with a temperature of around 35 to 60 °C with an incubation time of 7-12 hours. The final product of the silica NPs is very uniform and could be as small as 10 nm. The silica NPs can further grow up to 18 nm under the controlled addition of the precursors. Also, these silica NPs can be used as seeds to generate larger silica NPs with sizes ranging from 20 to 100 nm, which can be a useful supplement to the size range made by the traditional Stöber method. Moreover, these ultra-small Au NPs can be used as a depletion reagent or as building blocks for an ultrathin silica coating, which has significant applications in fine-tuning the plasmons of AuNPs and thin spacers for surface enhanced spectroscopies.

High Ionic Conductivity of Composite Solid Polymer Electrolyte via In Situ Synthesis of Monodispersed SiO2 Nanospheres in Poly(ethylene oxide)

High ionic conductivity solid polymer electrolyte (SPE) has long been desired for the next generation high energy and safe rechargeable lithium batteries. Among all of the SPEs, composite polymer electrolyte (CPE) with ceramic fillers has garnered great interest due to the enhancement of ionic conductivity. However, the high degree of polymer crystallinity, agglomeration of ceramic fillers, and weak polymer-ceramic interaction limit the further improvement of ionic conductivity. Different from the existing methods of blending preformed ceramic particles with polymers, here we introduce an in situ synthesis of ceramic filler particles in polymer electrolyte. Much stronger chemical/mechanical interactions between monodispersed 12 nm diameter SiO2 nanospheres and poly(ethylene oxide) (PEO) chains were produced by in situ hydrolysis, which significantly suppresses the crystallization of PEO and thus facilitates polymer segmental motion for ionic conduction. In addition, an improved degree of LiClO4 dissociation can also be achieved. All of these lead to good ionic conductivity (1.2 × 10(-3) S cm(-1) at 60 °C, 4.4 × 10(-5) S cm(-1) at 30 °C). At the same time, largely extended electrochemical stability window up to 5.5 V can be observed. We further demonstrated all-solid-state lithium batteries showing excellent rate capability as well as good cycling performance.

Plant opal-mimetic bunching silica nanoparticles mediated by long-chain polyethyleneimine

Plant opal-mimetic structures of bunching silica nanoparticles were produced through polymer-mediated polycondensation of hydrolyzed silicate species in a matrix of long-chain branched polyethyleneimine.

Controlling aqueous silica nanoparticle synthesis in the 10-100 nm range

We describe the control of size and homogeneity in silica nanoparticle dispersions, prepared by a two-phase arginine catalysed aqueous method, through varying the upper organic solvent phase. The final particle dispersion characteristics can be controlled by varying features including solvent type and interfacial area, related to the rate of monomer transfer at the TEOS/water interface.

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.

Surface-initiated controlled radical polymerizations from silica nanoparticles, gold nanocrystals, and bionanoparticles

This review summarizes recent progress in surface-initiated controlled radical polymerizations from silica nanoparticles, gold nanocrystals, and bionanoparticles.

Sol-Gel processing of silica nanoparticles and their applications

Recently, silica nanoparticles (SNPs) have drawn widespread attention due to their applications in many emerging areas because of their tailorable morphology. During the last decade, remarkable efforts have been made on the investigations for novel processing methodologies to prepare SNPs, resulting in better control of the size, shape, porosity and significant improvements in the physio-chemical properties. A number of techniques available for preparing SNPs namely, flame spray pyrolysis, chemical vapour deposition, micro-emulsion, ball milling, sol-gel etc. have resulted, a number of publications. Among these, preparation by sol-gel has been the focus of research as the synthesis is straightforward, scalable and controllable. Therefore, this review focuses on the recent progress in the field of synthesis of SNPs exhibiting ordered mesoporous structure, their distribution pattern, morphological attributes and applications. The mesoporous silica nanoparticles (MSNPs) with good dispersion, varying morphology, narrow size distribution and homogeneous porous structure have been successfully prepared using organic and inorganic templates. The soft template assisted synthesis using surfactants for obtaining desirable shapes, pores, morphology and mechanisms proposed has been reviewed. Apart from single template, double and mixed surfactants, electrolytes, polymers etc. as templates have also been intensively discussed. The influence of reaction conditions such as temperature, pH, concentration of reagents, drying techniques, solvents, precursor, aging time etc. have also been deliberated. These MSNPs are suitable for a variety of applications viz., in the drug delivery systems, high performance liquid chromatography (HPLC), biosensors, cosmetics as well as construction materials. The applications of these SNPs have also been briefly summarized.

Large-scale high-quality 2D silica crystals: dip-drawing formation and decoration with gold nanorods and nanospheres for SERS analysis

High-quality colloidal crystals (CCs) are important for use in photonic research and as templates for large-scale plasmonic SERS substrates. We investigated how variations in temperature, colloid concentration, and dip-drawing parameters (rate, incubation time, etc) affect the structure of 2D CCs formed by highly monodisperse silica nanoparticles (SiNPs) synthesized in an l-arginine solution and regrown by a modified Stöber method. The best quality 2D CCs were obtained with aqueous 12 wt% colloids at a temperature of 25 °C, an incubation time of 1 min, and a drawing rate of 50 mm min(-1). Assembling of gold nanorods (GNRs) on 2D CCs resulted in the formation of ring-like chains with a preferential tail-to-tail orientation along the hexagonal boundaries. To the best of our knowledge, this is the first time that such nanostructures have been prepared. Owing to the preferential tail-to-tail packing of GNRs, 2D SiNP CC + GNR substrates demonstrated an analytical SERS enhancement of about 8000, which was 10 to 15 times higher than that for self-assembled GNRs on a silicon wafer. In addition, the analytical SERS enhancement was almost 60 times lower after replacing the nanorods in 2D SiNP CC + GNR substrates with 25 nm gold nanospheres.

Accurate amorphous silica surface models from first-principles thermodynamics of surface dehydroxylation

Accurate atomically detailed models of amorphous materials have been elusive to-date due to limitations in both experimental data and computational methods. We present an approach for constructing atomistic models of amorphous silica surfaces encountered in many industrial applications (such as catalytic support materials). We have used a combination of classical molecular modeling and density functional theory calculations to develop models having predictive capabilities. Our approach provides accurate surface models for a range of temperatures as measured by the thermodynamics of surface dehydroxylation. We find that a surprisingly small model of an amorphous silica surface can accurately represent the physics and chemistry of real surfaces as demonstrated by direct experimental validation using macroscopic measurements of the silanol number and type as a function of temperature. Beyond accurately predicting the experimentally observed trends in silanol numbers and types, the model also allows new insights into the dehydroxylation of amorphous silica surfaces. Our formalism is transferrable and provides an approach to generating accurate models of other amorphous materials.