Hollow Mesoporous Silica Microspheres Research Articles

The adsorption of cesium by sulfonic acid functionalized hollow mesoporous silica microspheres

With the development of nuclear industry, radioactive elements such as 137Cs put a threat on the water environment. It is a challenging task to remove the Cs+ in the nuclear wastewater. In the current study, we prepared a new Cs+-adsorbing material by introducing sulfhydryl group onto the surface of hollow mesoporous silica microspheres, then oxidizing the sulfhydryl group to sulfonic acid group. The obtained HMSS-SO3H material had an excellent adsorption capacity for Cs+ in the aqueous solution, with an adsorption capacity of 51.53 mg g−1 in 30 min. Characterization approaches, such as FT-IR and EDS, were used to confirm the result of modification. Adsorption experiments were carried out under. The influence of various parameters on the adsorption process was investigated under the conditions of changing pH, temperature, and time. The effect of competitive ions was also explored. The results indicated that the adsorption process followed the pseudo-second-order model and the main adsorption mechanisms are electrostatic interaction and coordination. The material had a best adsorption performance at a neutral pH. The adsorption process could well-fit the Langmuir's model, with a theoretical maximum adsorption capacity of 81.31 mg g−1. And the adsorption capacity was slightly affected by competing ions such as Mg2+ and Ca2+. The results indicate that the HMSS-SO3H prepared in this study is a promising adsorbent for Cs+, with the advantages of high adsorption capacity, fast adsorption rate and high selectivity.

Magnetic relaxation switching biosensor for one-step detection of Vibrio parahaemolyticus based on click chemistry-mediated sol-gel system

In this study, a magnetic relaxation switching (MRS) biosensor was developed for one-step detection of pathogenic bacteria Vibrio parahaemolyticus (VP). The biosensor is based on a click chemistry-mediated sol-gel system and utilizes low-field nuclear magnetic resonance (LF NMR) detection. VP aptamer (Apt)-coated hollow mesoporous silica microspheres (HMSMs) with saturated sodium ascorbate (SAA) solution sealed inside, HMSMs@SAA&Apt, are designed as the signal unit. When the target VP is present, the Apt binds to VP and releases SAA from the signal unit. The released SAA reduces Cu2+ in the test solution to Cu+, which catalyzes the click chemistry reaction between azide-modified polyethylene glycol (PEG-Azide) and acetylene-modified polyacrylic acid (PAA-Alkyne). The sol-gel transition is triggered, a large amount of "free" water is converted into "bound" water, resulting in the decrease of transverse relaxation time (T2). Under the optimal experimental conditions, the variation of T2 (ΔT2) was linearly related to the logarithm of VP concentration in the range of 10 ∼ 1.0 × 108 CFU/mL, with a limit of detection of 5 CFU/mL. The assay demonstrated good selectivity, stability, and reproducibility. It is completed in one step, holding promising applications in the rapid field detection of pathogenic bacteria.

Construction and properties of venlafaxine hydrochloride sustained release system based on hollow mesoporous silica microspheres

The aim of this work is to develop a venlafaxine hydrochloride sustained release system based on hollow mesoporous silica microspheres (HMSMs). HMSMs were innovatively prepared with tetraethyl silicate (TEOS) as the precursor and volatile n-heptane as a soft template. The obtained HMSMs show a well-defined hollow structure with an average size of 967 nm and pore volume of 0.85 cm3/g, implying it is a potential drug carrier. Subsequently, venlafaxine hydrochloride (VF) was absorbed in the HMSMs with a content of 37.67% or so. The sustained release effect is further measured by the dissolution instrument at 37 °C and 50 rpm in ultrapure water. The results showed that the HMSMs/VF system shows good sustained release properties compared with sustained release tablets with hydroxypropyl methylcellulose as the main component. This HMSMs sustained release system appears to be a promising candidate for a sustained drug release.

Brief History, Preparation Method, and Biological Application of Mesoporous Silica Molecular Sieves: A Narrative Review.

It has been more than 30 years since the first ordered mesoporous silica molecular sieve (MCM-41) was reported, but the enthusiasm for exploiting mesoporous silica is still growing due to its superior properties, such as its controllable morphology, excellent hosting capability, easy functionalization, and good biocompatibility. In this narrative review, the brief history of the discovery of mesoporous silica and several important mesoporous silica families are summarized. The development of mesoporous silica microspheres with nanoscale dimensions, hollow mesoporous silica microspheres, and dendritic mesoporous silica nanospheres is also described. Meanwhile, common synthesis methods for traditional mesoporous silica, mesoporous silica microspheres, and hollow mesoporous silica microspheres are discussed. Then, we introduce the biological applications of mesoporous silica in fields such as drug delivery, bioimaging, and biosensing. We hope this review will help people to understand the history of the development of mesoporous silica molecular sieves and become familiar with their synthesis methods and applications in biology.

Factors that affect Pickering emulsions stabilized by mesoporous hollow silica microspheres

HypothesisClassical (solid particles stabilized) Pickering emulsions have been widely studied due to the irreversible adsorption of solid particles at the oil-water interface. Mesoporous hollow silica microspheres (MHSMs) are promising stabilizers for Pickering emulsion owing to its larger specific surface area and lower apparent density. However, this type of Pickering emulsion has not attracted enough attention. The stabilization mechanism of Pickering emulsion by MHSMs has not been studied in detail yet. ExperimentsHerein, stable Pickering emulsions were prepared using only MHSMs as stabilizers. In order to investigate its stabilization mechanism, the effect factors of size, shell thickness, wettability and concentration of MHSMs, and oil/water ratio on the stability of Pickering emulsions were analyzed deeply. FindingsAs a result, the stability of Pickering emulsion can be improved by MHSMs with smaller particle size and shell thickness. Also, MHSMs with the intermediate hydrophobicity and suitable oil/water ratio actually do favour for the stability of Pickering emulsion. As expected, the stability of Pickering emulsion can be enhanced by increasing the concentration of MHSMs in a certain range. The Pickering emulsions tend to achieve excellent stable state when the concentration of MHSMs is 1.25 mg/mL. All those results suggested that the stability of Pickering emulsions correlates directly to particle size, shell thickness, wettability and concentration of MHSMs, and oil/water ratio. This research paves a way for the fabrication of functional materials via Pickering emulsions.

Corrosion protection performance of a coating with 2-aminino-5-mercato-1,3,4-thiadizole-loaded hollow mesoporous silica on copper

Hollow mesoporous silica microspheres (HMSN) were selected as carriers for storing 2-aminino-5-mercato-1,3,4-thiadizole (ATM) in this experiment. The synthesised microspheres were uniformly dispersed, with a diameter of approximately 500 nm, as identified by scanning electron microscopy. HMSN, as excellent nanocarriers, were used to encapsulate ATM with a 19 wt% loading rate. Then, 18 wt% HMSN loaded with ATM was added to the coating. Electrochemical impedance spectroscopy and scanning Kelvin probes were used to investigate the self-healing ability of the coating with ATM encapsulated in hollow mesoporous silica microspheres. The copper corrosion caused by microdefects in the coating was delayed by controlling the slow release of ATM from the microspheres. The active corrosion resistance of the coatings was strengthened. By optimising the coating, the service life of the coating can be extended to achieve the long-term corrosion protection of copper.

Amino-Modified Hollow Mesoporous Silica Microspheres Loaded with Cresol Red-Boric Acid for Potent Reversible Thermochromic Performance

In this study, two reversible thermochromic composites were obtained, hollow mesoporous silica (HMS) and amino group-modified hollow mesoporous silica (HMS-NH2) microspheres loaded with cresol red-boric acid (CR-BA), respectively. Owing to the rigid structure of hollow interior and mesoporous shell layers, CR-BA was easily encapsulated into a relatively high loading capacity micro-carrier. The composites analysed were characterized by Fourier transform infrared spectroscopy transmission electron microscopy, scanning and transmission electron microscopy and dynamic light scattering. By amino functionalization, a more obvious thermal colour-change was observed in HMS-NH2 loaded with CR-BA. In addition, both HMS and HMS-NH2 loaded with CR-BA illustrated a sever colour reversibility, which were 5min and 3min respectively.

A Core‐Shell Cascade of Chloroperoxidase and Gold Nanoclusters for Asymmetric Hydroxylation of Ethylbenzene

AbstractDirect functionalization of C−H bonds catalyzed by chloroperoxidase (CPO) is featured by using H2O2 as both oxygen and electron donor. The catalytic process circumvents expensive electron transporters such as NAD(P)H, making it advantageous for green production of fine chemicals with complex structures. In situ generation and collaborative supplement of H2O2 is strongly desired for an improved productivity and enzyme stability. The present study describes a novel CPO cascade for asymmetric hydroxylation of ethylbenzene yielding (R)‐1‐phenylethanol, in which H2O2 is generated by oxidation of monosaccharides catalyzed by gold nanoclusters (AuNCs). A core‐shell structure of CPO−AuNCs cascade was prepared by using hollow mesoporous silica microspheres (HMSMs) as the support. AuNCs were immobilized on the external surface of HMSMs while CPOs were encapsulated inside the microspheres. Different monosaccharides were examined for H2O2 production as a function of the particle size. It was found that galactose exhibits the highest productivity. The high compatibility of CPO and AuNCs against temperature and pH is advantageous in catalyzing a wide spectrum of reactions for C−H functionalization.

Hollow Mesoporous Silica by Ion Exchange-Induced Etching Strategy for High Temperature Proton Exchange Membrane

Hollow mesoporous silica (HMS) has attracted significant attention for fuel cell applications. The mesopores in the shell can accelerate proton transport and the void in the center of the particle is advantageous for proton storage. However, the conventional methods for HMS fabrication are complicated, which is not conducive to scaling up the fabrication of HMS. In this work, a new, simple strategy to synthesize HMS has been developed via OH− ion exchange-induced etching of mesoporous silica (mSiO2). The mSiO2 immersed in an alkaline Na2CO3 solution led to an exchange of the Br− ions in the surfactant with the OH− ions in the solution, resulting in a high concentration of OH− ions in the mesoporous channels of mSiO2 close to the core, and a low concentration of OH− ions close to the surface. This demonstrated that the etching of the core of mSiO2 was induced, which extended from the core to the surface of the nanoparticles. Furthermore, the success of the ion exchange-induced etching process was demonstrated by the gradient distribution of the Na+ ion in mesoporous silica microspheres through microscopy. In addition, the proton conductivity of the phosphoric acid-impregnated HMS membrane at 180°C under anhydrous conditions was found to be 0.025 S.cm−1. These results demonstrate the simplicity of the ion exchange-induced etching strategy for the fabrication of HMS microspheres and its promising application in high temperature proton exchange membrane fuel cells.

Aerosol-Assisted Synthesis of Tailor-Made Hollow Mesoporous Silica Microspheres for Controlled Release of Antibacterial and Anticancer Agents.

Hollow mesoporous silica microsphere (HMSM) particles are one of the most promising vehicles for efficient drug delivery owing to their large hollow interior cavity for drug loading and the permeable mesoporous shell for controlled drug release. Here, we report an easily controllable aerosol-based approach to produce HMSM particles by continuous spray-drying of colloidal silica nanoparticles and Eudragit/Triton X100 composite (EUT) nanospheres as templates, followed by template removal. Importantly, the internal structure of the hollow cavity and the external morphology and the porosity of the mesoporous shell can be tuned to a certain extent by adjusting the experimental conditions (i.e., silica to EUT mass ratio and particle size of silica nanoparticles) to optimize the drug loading capacity and the controlled-release properties. Then, the application of aerosol-synthesized HMSM particles in controlled drug delivery was investigated by loading amoxicillin as an antibiotic compound with high entrapment efficiency (up to 46%). Furthermore, to improve the biocompatibility of the amoxicillin-loaded HMSM particles, their surfaces were functionalized with poly(allylamine hydrochloride) and alginate as biocompatible polymers via the layer-by-layer assembly. The resulting particles were evaluated toward Escherichia coli (Gram-negative) bacteria and indicated the bacterial inhibition up to 90% in less than 2 h. Finally, we explored the versatility of HMSMs as drug carriers for pancreatic cancer treatment. Because the pH value of the extracellular medium in pancreatic tumors is lower than that of the healthy tissue, chitosan as a pH-sensitive gatekeeper was grafted to the HMSM surface and then loaded with a pro-apoptotic NCL antagonist agent (N6L) as an anticancer drug. The obtained particles exhibited pH-responsive drug releases and excellent anticancer activities with inhibition of cancer cell growth up to 60%.

One-Step Production of Amine-Functionalized Hollow Mesoporous Silica Microspheres via Phase Separation-Induced Cavity in Miniemulsion System for Opaque and Matting Coating

Compared to other well-developed synthetic methods, we developed a novel “phase separation inside monomer droplets” strategy in miniemulsion polymerization to fabricate hollow mesoporous silica mic...

Development and evaluation of hollow mesoporous silica microspheres bearing on enhanced oral delivery of curcumin

The aim of this work is to develop curcumin-loaded hollow mesoporous silica microspheres (HMSMs@curcumin) to improve the poor oral bioavailability of curcumin. Hollow mesoporous silica microspheres (HMSMs) were synthesized in facile route using a hard template. HMSMs and HMSMs@curcumin were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption/desorption measurements, differential scanning calorimetry (DSC), Fourier transform infrared (FTIR), and X-ray diffraction (XRD). In addition, to demonstrate the potential application of the HMSMs@curcumin, cytotoxicity, in vitro release behavior and in vivo pharmacokinetics of curcumin loaded in these HMSMs were investigated by using of Caco-2 cells and Sprague-Dawley (SD) rats, respectively. These mono-dispersed HMSMs exhibited high drug loading ratio and encapsulation efficiency due to the mesoporous shell and hollow core. The excellent characteristics of HMSMs such as mono-dispersed morphology, smooth surface, uniform, ordered and size-narrowing mesopores resulted in a good in vitro release profile of curcumin from HMSMs@curcumin. Moreover, an impressive improvement in the oral absorption of curcumin and prolonged systemic circulation time were achieved in the in vivo animal studies. In addition, the good biocompatibility of developed HMSMs with Caco-2 cells was confirmed based on the in vitro cytotoxicity assay. In conclusion, this system demonstrated a great potential for efficient delivery of curcumin in vitro and in vivo, suggesting a good prospect for its application in clinic for therapeutic drug delivery in future.

Fabrication of multi-compartmentalized mesoporous silica microspheres through a Pickering droplet strategy for enhanced CO2 capture and catalysis

It is a long-standing dream to fabricate micron-sized inorganic spheres that have nanocompartments enclosed by a permeable shell and thus resemble the shape of natural cells. Here, we demonstrate a novel synthesis protocol to attain this goal for the first time. This protocol unprecedentedly harnesses interfacial sol–gel growth around Pickering droplets coupled with a surfactant assembly-directed sol–gel process within droplet-confined spaces. This protocol enables us to fabricate novel mesoporous silica microspheres (MSMs) with tunable interior architectures, such as hollow MSMs, hollow nanosphere-containing MSMs (hn@MSMs), nanosphere-containing MSMs (n@MSMs), yolk-shell-structured MSMs (y@MSMs) and “solid” MSMs. The obtained multi-compartmentalized MSMs exhibit good permeability to external molecules and good mechanical strength against stress. Moreover, their structural features benefit practical applications of CO2 capture and enzymatic reactions. Due to the high dispersion of tetraethylenepentamine and enzyme in the spatially separated nanocompartments, the developed CO2 sorbents and catalysts exhibit significantly enhanced CO2 capture efficiency and catalysis efficiency. Meanwhile, owing to the encapsulation of these nanocompartments inside the hollow micron-sized spheres, these CO2 sorbents and catalysts can be packed directly in fixed-bed reactors, which is unattainable for nanoparticle materials.

Evaluation of scale-up strategies for the batch synthesis of dense and hollow mesoporous silica microspheres

Despite the wide application interest in mesoporous silica micro- and nano-particles and a number of synthesis routes reported in the literature, the question of chemical engineering scale-up of the synthetic routes has rarely been addressed. The present work reports the results of an experimental and computational study of batch scale-up by a factor of 40× in the specific case of two types of dense and hollow mesoporous silica microparticles produced by the hydrolysis of tetraethoxysilane (TEOS) using a CTAB surfactant template. Volume and concentration based scale-up approaches have been investigated and systematically compared using a similarity index that included parameters related to the particle size distribution (d10, d50, d90) and pore structure (mean pore diameter, specific surface area, total pore volume, sorption hysteresis loop). The particle size distribution was found to be dependent mainly on the hydrodynamic conditions, expressed by the homogenization time, while the pore structure and the overall yield of the process were found to depend mainly on the CTAB/TEOS ratio. Overall, successful scale-up criteria in both volume and concentration based approaches have been identified.

Ag-deposited hollow mesoporous silica microspheres for rapid decolorizing of dye pollutants

In this paper, we demonstrate a facile electroless plating method for fabricating silver nanoparticles deposited onto hollow mesoporous silica microspheres (Ag-HMSM), which were developed as an novel catalyst for catalytic reduction of rhodamine B (Rh-B). The products were characterized by transmission electron microscopy, scanning electron microscopy image, and energy dispersive spectrometer spectrum. The results reveal the Ag-HMSM possess uniform spherical shape and diameter (about 410 nm) with well-dispersed Ag nanoparticles of about 5 nm. The catalytic activity of Ag-HMSM for the reduction of Rh-B in presence of NaBH4 was investigated by UV–Vis spectrophotometry. The study shows that Rh-B (2.0 × 10−4 M) could be reduced by Ag-HMSM within 12 min at a concentration of 25 ppm or within 2 min at 125 ppm. Ag nanoparticle-deposited HMSM provide new insight on the preparation of a catalyst for rapidly decolorizing dye pollutants.

Preparation, characterization and oxygen sensing properties of luminescent carbon dots assembled mesoporous silica microspheres

In this paper, our effort was focused on preparation and oxygen sensing of luminescence carbon dots (CDs) assembled hollow mesoporous silica microspheres (HMSMs) and mesoporous silica microspheres (MSMs). MSMs doped with CDs showed shorter response time and recovery time comparing with HMSMs doped with CDs. This feature can be attributed to ordered channel structure of mesoporous carrier which can promote the gas diffusion effectively. While HMSMs doped with CDs shows a higher oxygen quenching response and the degree of quenching reach 80.35%. The response time was determined to be about 7s and the emission intensities of the samples were effectively reduced as the concentration of oxygen increased. These results indicate that the system we have developed can be used for oxygen detection in wide concentration range and is especially accurate for very low oxygen concentrations. The obtained CDs grafted hollow mesoporous silica microspheres (HMSMs) and mesoporous silica microspheres (MSMs) samples appears to be a promising sensing material for environmental detection application and would also find applications in catalyst, electrode, or related fields.

Encapsulating quantum dots with amino functionalized mesoporous hollow silica microspheres for the sensitive analysis of formaldehyde in seafood

We developed a hybrid fluorescent material using amino functional mesoporous hollow silica microspheres (MHSM) encapsulated with CdTe quantum dots (QDs).

Facile fabrication of hollow mesoporous silica microspheres with hierarchical shell structure via a sol–gel process

A facile method for the preparation of polystyrene/silica (PS/SiO2) composite microspheres via sol–gel process of tetraethylorthosilicate (TEOS) employing polyvinylpyrrolidone-functionalized monodispersed PS microspheres as template is proposed. Hollow mesoporous silica microspheres containing surface silica nanoparticles are successfully fabricated after the calcination of the composite microspheres. The shell thickness, the size of surface silica nanoparticles and the surface morphology of hollow mesoporous silica microspheres can be readily tailored by adjusting the concentrations of TEOS and ammonia (NH4OH). The formation mechanism of the products is detailed through the investigation of the products at different reaction conditions. At the low NH4OH/TEOS volume ratio (<1), intact hollow mesoporous silica microspheres with hierarchical raspberry-like structure can be obtained. This synthesis method is simple, straightforward and suitable for the preparation of the other biomineral nanostructures that are unique carriers in drug delivery, biological and catalytic applications.

A facile and universal method to prepare hydrophilic molecularly imprinted microspheres by encapsulating a polymer in hollow mesoporous silica microspheres.

Hydrophilic molecularly imprinted microspheres (MIP@SiO2) for the adsorption of water-soluble molecules in real aqueous samples were successfully synthesized. In this strategy, a molecular imprinted polymer (MIP) was encapsulated in the hollow core of hollow mesoporous silica (HMS) particles via a 'ship-in-a-bottle' process. As the HMS shell contains plenty of Si-OH groups, the as-prepared microspheres proved to be hydrophilic and could be well dispersed in water. On the other hand, the MIP encapsulated in the HMS could specifically recognize small molecules with good binding efficiency through the mesoporous silica shell. Binding experiments in real aqueous solutions showed that the MIP@SiO2 composites have excellent recognition ability for specific molecules. Thus, MIP@SiO2 are highly promising alternatives to biological receptors with great potential for many analytical applications, such as environmental, food, and clinical analyses and other areas.

Fabrication of hybrid membranes by incorporating acid–base pair functionalized hollow mesoporous silica for enhanced proton conductivity

Hollow mesoporous silica microspheres are synthesized, functionalized by three different acid–base pairs, and then incorporated into a Nafion matrix to prepare novel hybrid membranes. Hydrophilic ionic channels are adjusted by inorganic fillers, as a result, the membranes display greatly improved proton conductivity, especially under low humidity.