Hollow Silica Shells Research Articles

Polymer-Mediated Particle Coarsening within Hollow Silica Shell Nanoreactors

Polymer-Mediated Particle Coarsening within Hollow Silica Shell Nanoreactors

A high active sites exposed hollow Co@SiO2 nanoreactor for high performance fischer–tropsch synthesis

Optimizing catalyst geometry to break current limitations of Fischer-Tropsch synthesis (FTS) activity and the selectivity of long-chain hydrocarbons is a promising and challenging subject. Herein, a hollow Co@SiO2 catalyst with high dispersion of cobalt species anchored inside mesoporous hollow silica shell was successfully synthesized with the help of Co-metal organic framework materials, which displayed a surprisingly high C5+ hydrocarbons selectivity of 93.3% with a low methane selectivity of 3.4% at a remarkable high activity (CTY = 5.1 × 10-5 molCO gCo-1 s−1). The catalyst remained excellent stability for 200 h under industrially relevant conditions. The hollow core–shell structure provided an internal cavity environment that shortened the diffusion distance and contact area between Co metal and support, and improved exposed active cobalt sites and residence time of intermediates, inducing the growth of the catalytic activity and long-chain hydrocarbons selectivity. Protection of silica shell prevented the aggregation of active cobalt nanoparticles, further promoting the catalyst stability. This work provides a new insight into the design of high efficient and stable catalysts for FTS reaction.

One-pot synthesis of pompon-like magnetic hollow SiO2-supported Ag nanoparticles for catalytic application

In this paper, we develop a novel pompon-like magnetic hollow SiO2 -supported Ag (SiO2 @Ag) nanoparticles, in which small silver and magnetic nanoparticles were loaded on the hollow silica shell by one-pot solvothermal method. FT-IR, XRD, SEM, TEM and BET were applied to characterized the structure and morphology of the magnetic hollow SiO2 @Ag nanoparticles. The synthesized material has not only high stability and monodispersity, but also uniform surface element distribution along with good magnetic response. On this basis, we studied the catalytic performance of this pompon-like magnetic hollow SiO2 @Ag nanoparticles for the reduction of aromatic nitro compounds, and further carried out extended researches on substrates scope. Research results indicate that the pompon-like magnetic hollow SiO2 @Ag nanoparticles have broad-spectrum catalytic activity for the reduction of aromatic nitro compounds. After recycling for 8 times, it can still maintain 90% catalytic efficiency. This study provides a facile strategy for constructing hollow hierarchical structure, and expands the application of noble metal nanoparticles in organic transformation.

Preparation of hollow mesoporous prussian blue coated with mesoporous silica shell nanocubes for photothermal therapy and drug carrier

The nanocubes with hollow mesoporous Prussian blue core and mesoporous silica shell (HMPB@mSiO2) were prepared. According to the SEM and TEM, the material showed a regular hollow core-shell cubic structure. Up to 879 m2/g of the surface area and 4.2 nm of average pore size were measured by N2 adsorption-desorption. The nanocubes exhibited excellent photothermal conversion efficiency under 808 nm NIR. The UV–vis spectrophotometry showed that the drug loading content of the materials were 868.27 μg/mg (drug/carrier) and which can accelerate the release of DOX under acidic and NIR conditions.

Ru-Catalyzed Reverse Water Gas Shift Reaction with Near-Unity Selectivity and Superior Stability

Cascade catalysis of reverse water gas shift (RWGS) and well-established CO hydrogenation holds promise for the conversion of greenhouse gas CO2 and renewable H2 into liquid hydrocarbons and methanol under mild conditions. However, it remains a big challenge to develop low-temperature RWGS catalysts with high activity, selectivity, and stability. Here, we report the design of an efficient RWGS catalyst by encapsulating ruthenium clusters with the size of 1 nm inside hollow silica shells. The spatially confined structure prevents the sintering of Ru clusters while the permeable silica layer allows the diffusion of gaseous reactants and products. This catalyst with reduced particle sizes not only inherits the excellent activity of Ru in CO2 hydrogenation reactions but also exhibits nearly 100% CO selectivity and superior stability at 200–500 °C. The ability to selectively produce CO from CO2 at relatively low temperatures paves the way for the production of value-added fuels from CO2 and renewable H2.

Diffusive Formation of Hollow Mesoporous Silica Shells from Core–Shell Composites: Insights from the Hydrogen Sulfide Capture Cycle of CuO@mSiO2 Nanoparticles

Mesoporous silica is often employed as a coating material in core-shell nanoparticles to decrease the possibility of sintering or aggregation of the core particles. In this work, we discovered a surprising morphological transformation during the sulfidation and regeneration (oxidation) of core-shell CuO@mSiO2 materials designed for H2S capture. Although CuS cores were still encapsulated within the silica shells after in situ sulfidation, hollow silica shells formed during the regeneration step as CuO leached out of the shell and aggregated into larger particles. The successful sulfidation of pristine CuO@mSiO2 was facilitated by the restraining effect of silica shells on lattice growth from CuO into CuS, and the mesopores allowed for volume expansion. The phase and morphology changes during the regeneration (oxidation) process leading to the hollow shells were investigated by X-ray diffraction and transmission electron microscopy. It was observed that the cores remained encaged during the disproportionation of CuS to Cu2S, which is the first step in the oxidation of CuS. However, voids were generated when Cu2S was oxidized and reacted with water generated from the condensation of silica. A possible mechanism for this transformation involves the outward diffusion of copper ions through the mesoporous silica, leading to the migration of core particles. This migration was further accelerated by the elevated temperature in the regeneration process and promoted by the formation of the copper sulfate hydroxide through the reaction with water. This work provides key insights into the chemical stability of such core-shell structures under the influence of diffusion-driven structural transformations.

Supramolecular Valves Functionalized Rattle-Structured UCNPs@hm-SiO2 Nanoparticles with Controlled Drug Release Triggered by Quintuple Stimuli and Dual-Modality Imaging Functions: A Potential Theranostic Nanomedicine.

Integrating multimodality bioimaging and multiple stimuli-responsive controlled drug release properties into one single nanosystem for therapeutic application is highly desirable but still remains a challenge. Herein, we coated a hollow mesoporous silica shell on to upconversion nanoparticles (UCNPs) and conjugated pillarene-based supramolecular valves on to surface of UCNPs@hm-SiO2 using amine-coumarin phototriggers to obtain the multifunctional nanoparticles, UCNPs@hm-SiO2-Cou-Cys-DOX/WP[5]. Benefiting from the core-shell structured UCNPs, the UCNPs@hm-SiO2-Cou-Cys-DOX/WP[5] can serve as efficient contrast agents for upconversion luminescence and T1-weighted magnetic resonance imaging in vitro/in vivo. More importantly, depending on exquisitely designed supramolecular valves, UCNPs@hm-SiO2-Cou-Cys-DOX/WP[5] can realize zero-premature release under normal physiological conditions (pH 7.4), which produces minimal damage to normal tissue, whereas this nanosystem can respond to several disease-related signals, including acid (most cancers), alkali (metabolic alkalosis), and Zn2+ (Alzheimer's disease), along with two external stimuli, including near-infrared (NIR) light and reductive electrical potential, via altering the spatial structure of pseudorotaxanes, disassembling the molecular stalks, or undergoing photochemical reactions, ultimately resulting in opening of the gatekeepers and release of encapsulated drugs. The multifunctional UCNP-based nanoparticles were endowed with such quintuple stimuli-responsive controlled release characteristics. Specifically, in anticancer application, the rational utilization of the two of them, acid and NIR light, could regulate the release amount and rate of DOX from UCNPs@hm-SiO2-Cou-Cys-DOX/WP[5], accelerate the accumulation of DOX in cell nuclei, and thereby promote the cancer cell apoptosis, indicating that the nanomaterials have promising application in cancer treatment. This study provides a novel design strategy for constructing multifunctional UCNP-based nanoparticles with multiple stimuli-responsive drug release features, which have great potential in diagnosis and therapy of relevant diseases as theranostic nanomedicines.

Indocyanine green modified silica shells for colon tumor marking

Marking colon tumors for surgery is normally done with the use of India ink. However, non-fluorescent dyes such as India ink cannot be imaged below the tissue surface and there is evidence for physiological complications such as abscess, intestinal perforation and inconsistency of dye injection. A novel infrared marker was developed using FDA approved indocyanine green (ICG) dye and ultrathin hollow silica nanoshells (ICG/HSS). Using a positively charged amine linker, ICG was non-covalently adsorbed onto the nanoparticle surface. For ultra-thin wall 100 nm diameter silica shells, a bimodal ICG layer of <3 nm is was formed. Conversely, for thicker walls on 2 μm diameter silica shells, the ICG layer was only bound to the outer surface and was 6 nm thick. In vitro testing of fluorescent emission showed the particles with the thinner coating were considerably more efficient, which is consistent with self-quenching reducing emission shown in the thicker ICG coatings. Ex-vivo testing showed that ICG bound to the 100 nm hollow silica shells was visible even under 1.5 cm of tissue. In vivo experiments showed that there was no diffusion of the ICG/nanoparticle marker in tissue and it remained imageable for as long as 12 days.

Thickness and Sphericity Control of Hollow Hard Silica Shells through Iron (III) Doping: Low Threshold Ultrasound Contrast Agents.

Silica particles are convenient ultrasound imaging contrast agents because of their long imaging time and ease of modification; however, they require a relatively high insonation power for imaging and have low biodegradability. In this study, 2 μm ultrathin asymmetric hollow silica particles doped with iron (III) (Fe(III)-SiO2) are synthesized to produce biodegradable hard shelled particles with a low acoustic power threshold comparable with commercial soft microbubble contrast agents (Definity) yet with much longer in vivo ultrasound imaging time. Furthermore, high intensity focused ultrasound ablation enhancement with these particles shows a 2.5-fold higher temperature elevation than with Definity at the same applied power. The low power visualization improves utilization of the silica shells as an adjuvant in localized immunotherapy. The data are consistent with asymmetric engineering of hard particle properties that improve functionality of hard versus soft particles.

Design and Preparation of Hallow Mesoporous Silica Spheres Include CuO and Its Catalytic Performance for Synthesis of 1,2,3-Triazole Compounds via the Click Reaction in Water

Here, a novel nanostructured catalyst based on CuO included hallow mesoporous silica spheres (CuO–HMSS) was prepared for synthesis of 1,2,3-triazole compounds. The hallow silica spheres were synthesized via the hydrothermal procedure. The characterization of prepared catalyst was also performed applying several analysis techniques such as TEM and SEM, EDX, XRD, and ICP. CuO active sites in a hollow mesoporous silica shell are stably and efficiently attainable for conversion of precursors to triazole compounds.

GD Doped Hollow Silica Shells for Tumor Ablation and MRI

Author(s): Badaracco, Adrian | Abstract: Recently, Hollow Silica Shells have been explored for various biomedical applications due to their biocompatibility. Hollow silica shells offer the exibility to adjust their physical and mechanical properties (diameter, shell thickness, shell strength, etc.) as well as their chemical properties via elemental doping or surface chemical modi cation. Hollow silica shells are formed by a unique polymerization reaction between silicic acid into SiO2, creating a layer covering a polystyrene beads as sacri cial templates. The template is then removed via solvent dissolution or heat, yielding a hollow SiO2 shell.

Synthesis and characterisation of robust emulsion-templated silica microcapsules

Robust silica microcapsules were synthesised using an emulsion template via a seeded growth strategy. Multiple additions of the silica precursor tetraethyl orthosilicate (TEOS) were observed to result in a number of physical and property changes of the capsule shells as compared to a single coating. Scanning electron microscopy indicated a morphological transition from a smooth to a roughened surface. Improved cargo retention and consolidation of the pore structure of the silica shells were observed using dye release experiments and nitrogen porosimetry respectively. In comparison to a typical hollow silica shell synthesis procedure, this one-pot loading and synthesis allows the simple production of robust capsules that are capable of sustained release, using mild conditions and reagents.

Enzyme Shielding in a Large Mesoporous Hollow Silica Shell for Improved Recycling and Stability Based on CaCO3 Microtemplates and Biomimetic Silicification.

We report a novel "anchor-shield" approach for synthesizing a yolk-shell-structured biocatalytic system that consists of a phenylalanine ammonia lyase (PAL) protein particle core and a hollow silica shell with large mesopores by a combination of CaCO3 microtemplates and biomimetic silicification. The method is established upon filling porous CaCO3 cores with PAL via co-precipitation, controlled self-assembly and polycondensation of silanes, cross-link of the PAL molecules, and subsequent CaCO3 dissolution. During this process, the self-assembled layer of cetyltrimethylammonium bromide served as a structure-directing agent of the mesostructure and directed the overgrowth of the mesostructured silica on the external surface of PAL/CaCO3 hybrid microspheres; after CaCO3 dissolution, the cross-linked PAL particles were encapsulated in the hollow silica shell. The hollow silica shell around the enzyme particles provided a "shield" to protect from biological, thermal, and chemical degradation for the enzyme. As a result, the recycling of the PAL enzyme was improved remarkably in comparison to adsorbed PAL on CaCO3. PAL particles with a hollow silica shell still retained 60% of their original activity after 13 cycles, whereas adsorbed PAL on CaCO3 microparticles lost activity after 7 cycles. Moreover, immobilized PAL exhibited higher stability against a proteolytic agent, denaturants, heat, and extreme pH than adsorbed PAL on CaCO3 microparticles. These results demonstrated that the "anchor-shield" approach is an efficient method to obtain a stable and recycled biocatalyst with a yolk-shell structure.

A Generalized Method for the Synthesis of Ligand-Free M@SiO2 (M = Ag, Au, Pd, Pt) Yolk-Shell Nanoparticles.

A universal method is reported for the synthesis of ligand free noble metal M@SiO2 (M = Ag, Au, Pd, Pt) yolk-shell nanoparticles (YSNs). Mesoporous hollow silica shells (mHSS) are used as smart nanoreactors for the synthesis of noble metal yolk-shell nanoparticles. The nanocavity of a mHSS and anionic metal ions play a critical role in the formation of yolk-shell nanoparticles. The synthesis mechanism can be tuned by simply varying the pH of the noble metal precursor aqueous solution. A critical pH ≥ 4 is required for the formation of YSNs. The anionic metal ions can pass freely through the mesopores of mHSS and eventually lead to the formation of YSNs, whereas the cationic metal ions can show strong interaction with the surface of mHSS which hinders the formation of YSNs. The syntheses of YSNs are achieved without using any external capping ligands and reducing agents in the reaction.

Mesoporous hollow silica shells modified with functional diamine groups show high-performance absorption capacity and selective colorimetric response to copper ions in aqueous solutions

High-performance measurement and removal of copper ions is highly desirable in both clinical and environmental applications. Herein, an efficient, reliable and recyclable functional material was prepared to adsorb and determine Cu2+ using N-[3-(trimethoxysilyl) propyl] ethylenediamine modified mesoporous hollow shells (HMS-NHs). By stepwise coating with mesoporous silica at highly mono-dispersed PS spheres, removal of template materials, and modification with functional diamine groups, higher absorption capacity of about 138.58mg/g was obtained. After optimization of PS template size, thickness of SiO2 layers, pore size of the shell, and etc, as-prepared HMS-NHs gave clear colorimetric response after color development using cupron solution. Selectively measure Cu2+ in a wide concentration ranges from 0.025 to 49μΜ was observed with a detection limit around 0.025μΜ (3δ). More importantly, the functional absorbent can be regenerated by treatment with hydrochloric acid and maintains high efficiency upon repeated use for at least 10 times. Extensive investigation demonstrated that the HMS-NHs can serve as not only high-performance absorption materials but also sensitive sensor for Cu2+, thus offering a good alternative for potential removal and detection of copper ions in real applications.

Porous Au–Ag Nanospheres with High-Density and Highly Accessible Hotspots for SERS Analysis

Colloidal plasmonic metal nanoparticles have enabled surface-enhanced Raman scattering (SERS) for a variety of analytical applications. While great efforts have been made to create hotspots for amplifying Raman signals, it remains a great challenge to ensure their high density and accessibility for improved sensitivity of the analysis. Here we report a dealloying process for the fabrication of porous Au-Ag alloy nanoparticles containing abundant inherent hotspots, which were encased in ultrathin hollow silica shells so that the need of conventional organic capping ligands for stabilization is eliminated, producing colloidal plasmonic nanoparticles with clean surface and thus high accessibility of the hotspots. As a result, these novel nanostructures show excellent SERS activity with an enhancement factor of ∼1.3 × 10(7) on a single particle basis (off-resonant condition), promising high applicability in many SERS-based analytical and biomedical applications.

Synthesis and Application of Ni-M@Silica Yolk-Shell Nanostructures as Versatile Catalytic Materials

Recent developments in nanochemistry offer precise morphology control of nanomaterials, which has significant impacts in the field of heterogeneous catalysis. Rational design of bifunctional catalysts can influence various aspects of catalytic properties. In the present work, a new type of Ni-M(Co, Zr, Ce)@SiO2 yolk-shell nanoreactor framework comprising Ni-M cores inside hollow silica shells has been prepared through direct silica coating. The Ni-M@SiO2 nanoreactor structure is employed as a model catalyst for the partial oxidation of methane reaction. The Ni/ZrO2@SiO2 catalyst proved to be more active and possessed less carbon deposition reduced effectively by movable lattice oxygen. This nanoreactor framework is remarkably stable at high temperatures up to 750 °C, because the silica hollow shells around the cores essentially block particle sintering. The catalyst exhibited a continuous conversion rate of methane and significantly enhanced stability at high temperatures.

Levelling the playing field: screening for synergistic effects in coalesced bimetallic nanoparticles.

Depending on the synthetic methods, bimetallic nanoparticles can have either core-shell, phase segregated, alloy, or partially coalesced structures, presenting different degrees of atomic mixing on their surface. Along with the variations of size and morphology, the structural differences make it difficult to compare the catalytic activity of bimetallic nanoparticles. In this article, we developed a facile screening method that can focus on the synergistic effects rather than structural differences. Prefabricated nanoparticles are mixed together to form linear aggregates and coalesced to form bimetallic junctions. Their hollow silica shells allow materials transport but prevent further aggregation. With a level playing field, this screening platform can identify the best bimetallic combination for a catalytic reaction, before optimizing the synthesis. This approach is more advantageous than the conventional approaches where structural difference may have dominant effects on the catalytic performance.

Encapsulation of folic acid in different silica porous supports: A comparative study

Although folic acid is essential to numerous bodily functions, recent research indicates that a massive exposition to the vitamin could be a double-edged sword. In this study, the capacity of different caped mesoporous silica particles (i.e. Hollow Silica Shells, MCM-41, SBA-15 and UVM-7) to dose FA during its passage through the gastrointestinal tract has been evaluated. Results confirmed that the four capped materials were capable to hinder the delivery of FA at low pH (i.e. stomach) as well as able to deliver great amounts of the vitamin at neutral pH (i.e. intestine). Nevertheless, the encapsulation efficiency and the deliver kinetics differed among supports. While supports with large pore entrance exhibited an initial fast release, MCM-41, showed a sustained release along the time. This correlation between textural properties and release kinetics for each of the supports reveals the importance of a proper support selection as a strategy to control the delivery of active molecules.

Morphology-controlled functional colloids by heterocoagulation of zein and nanoparticles

A general and reproducible heterocoagulation method is presented to prepare sub-micron sized zein protein particles, loaded with negatively charged nanoparticles. These composite carrier particles can be obtained in three different morphologies, and each morphology can be prepared using nanoparticles of various size, shape and composition. An important feature of the zein composites is their long-term stability in water even in conditions where free nanoparticles often aggregate within days. Additionally, we modify the composite particles by coating them with a thin layer of silica via condensation of sodium silicate, opening possibilities for highly specific, functionalized carrier particles. Finally, the formation of hollow silica shells containing negatively charged nanoparticles is demonstrated, using the zein composites as a template.