Porous Silica Spheres Research Articles

Fundamental evaluation and optimization of porous spherical silica for developing functional fine particles via fluidized bed coating.

Particle coating, a taste-masking technique for drugs, is limited by its long manufacturing time, which is caused by the decrease in the spray rate required to prevent particle agglomeration. Mesoporous silica particles, which have a high surface area and pore sizes in the range of 2-50 nm, possess high surface free energy; they have attracted significant interest for numerous applications in adsorption, separation, and catalysis and drug delivery. A form of mesoporous silica, microbead silicate, can prevent particle aggregation because of its good water absorbency and drying properties. Hence, it has been suggested to be applicable for particle coating. This study evaluated the physical properties and drug release capability of microbead silicate with different pore sizes. Although microbead silicate with small pores displayed a rapid drug release profile, drug release was incomplete. Contrastingly, microbead silicate with large pores achieved complete drug release even with high drug loading. Furthermore, in the case of 100% layering, the porosity of microbead silicate was maintained, thus sufficiently preventing aggregation due to the prevention of formation of liquid bridging of the coating solution. These results suggest that using microbead silicate with large pores for particle coating enables complete drug release while improving manufacturability.

Self-assembly of silica spheres on silk fibroin spheres for synthesis of porous hollow silica spheres and their in vitro biocompatibility and drug delivery property

Porous hollow silica spheres were synthesized using silk fibroin spheres as novel single sacrificial template via a sol-gel route and their in vitro biocompatibility and drug delivery property were evaluated. TEM observation showed that silica spheres had a hollow cavity and a porous shell, while BET measurement showed that they had the pore size of 22 nm and specific surface area of 45 m2/g. FT-IR spectrum showed that silica spheres contained SiOSi bonds. After exposure to Hela cells, MTT assay indicated that silica spheres were in vitro biocompatible. It was found that silica spheres not only supported adsorption of tetracycline hydrochloride (TH, one of the representative antibiotics) with adsorption efficiency of 17.4%, but also exhibited a sustained release behavior for TH. The TH-loaded silica spheres showed antibacterial property to inhibit the growth of two representative bacteria: Escherichia coli and Staphylococcus aureus, indicating that the released TH was biologically active.

Formation of porous silica nanoparticles at higher reaction kinetics

This work deals with the analysis of the formation of porous spherical silica particles without adding any surfactants. The use of a wide range of measurement techniques allows the particle formation process to be tracked with regard to the particle size, structure and density. The analysis of the pore inlet diameter distribution based on the Kelvin effect indicates a change in the particle structure at higher reaction temperatures. Measurements with UV–Vis spectroscopy and TEM showed a collapse toward smaller particle sizes within the first minutes of the reaction. The higher the synthesis temperature, the more pronounced the collapse is and the sooner it takes place. Time-resolved SAXS data correlate a drastic increase in scattering intensity with an increase in particle density due to a collapse in particle size.

Sn Nanoparticles Confined in Porous Silica Spheres for Enhanced Thermal Cyclic Stability

We report a facile method for preparing a silica (SiO2)-based material containing Sn nanoparticles (NPs) distributed inside for enhancing the thermal cyclic stability of the inserted Sn NPs. Absorption of a Sn precursor (i.e., an aqueous SnCl2 solution) into a mesoporous SiO2 matrix resulted in confinement of the Sn precursor in a mesoporous SiO2 matrix. Hydrogen thermal reduction of the above composite yielded Sn nanoparticles with a diameter of ca. 30 nm uniformly distributed inside porous SiO2 (p-SiO2) spheres: Sn NPs@p-SiO2. Our investigation of the transformation of the porous SiO2 structure to hold Sn NPs revealed that the process was closely related to the transformation of the amorphous hydrolyzed Sn precursor into Sn oxides followed by, probably, the rearrangement of the SiO2 matrix via its interaction with the melting Sn. This led to the formation of stable Sn NPs@p-SiO2. The SiO2 matrix effectively prevented the coalescence of the Sn NPs, and the obtained product exhibited negligible changes in...

Preparation and evaluation of maltose modified polymer-silica composite based on cross-linked poly glycidyl methacrylate as high performance liquid chromatography stationary phase

A new maltose modified polymer-silica composite was fabricated and applied as high performance liquid chromatography (HPLC) stationary phase. The cross-linked poly glycidyl methacrylate (pGMA) layer was chemically bonded to the outer surface as well as pore inner surface of silica beads via in-situ polymerization, and then maltose was modified onto the polymer layer via a [3 + 2] “click” reaction. The porous spherical silica (4 μm diameter) with 300 Å pore size was selected as the matrix so that the 3.25 nm-thick polymer layer fabricated on the pore inner surface would not affect its permeability. The typical ‘U-shape’ retention curves indicated a mixed-mode retention mechanism of the as-synthesized stationary phase. Both polar and non-polar analytes could be well separated on the stationary phase with column efficiency reaching 123809 plates/m for guanosine in hydrophilic interaction liquid chromatography (HILIC) mode and 46808 plates/m for fluorene in reversed-phase liquid chromatography (RPLC) mode, respectively. Nucleotides and their bases were baseline separated with good peak shape without any buffer salt in mobile phase, suggesting the effective shielding of the silanol groups. The packing material also showed excellent chromatographic repeatability with intraday RSDs of the retention time of five nucleosides less than 0.048% (n = 3) and interday RSDs less than 0.33% (n = 7) and great pH stability (from 1.5 to 10.2). Finally, the stationary phase was applied to the separation of ginseng extract.

Silica microspheres from rice husk: A good opportunity for chromatography stationary phase

The aim of this research is to produce spherical and porous silica particles from rice husk for chromatographic applications in HPLC columns. After complete combustion of rice husk, white powder of silica was obtained which was dissolved in NaOH and subsequently heated to produce sodium silicate solution. Spherical porous silica gel was synthesized from the prepared sodium silicate in the presence of Pluronic P123 as the surfactant, under acidic solution. Different porosities were prepared by applying various factors including different vacuums, temperatures and reaction times in order to obtain the optimum conditions for particle aging. An analytical column was packed with the prepared silica microspheres and evaluated for the separation of 10-deacetylbaccatin III and rutin from taxol and hesperidin, respectively.

Correction to: Preparation of Controlled-Release Particles Based on Spherical Porous Silica Used as the Drug Carrier by the Dry Coating Method.

In the present notation, the formula names and the formulas (page 7, left column, lines 20-21) do not correspond to each other. It is a completely incorrect description, due to a typesetting mistake by the publisher. See below for details. The original article has been corrected.

Efficient and rapid adsorption of iodide ion from aqueous solution by porous silica spheres loaded with calcined Mg-Al layered double hydroxide

Abstract In this study, magnesium and aluminum ion was firstly inhaled into the silica sphere by low-vacuum impregnation technique, and subsequently hydrotalcite (Mg-Al-LDH) was synthesized inside the silica-based mesoporous material using in-hole precipitation method. Metal composite oxide (Mg-Al-LDO) was the calcined product by calcining Mg-Al-LDH at 450 °C and the composite material Mg-Al-LDO/SiO2 was the main absorbent for absorbing iodine ion (I−) in this study. The characteristics of SEM inner-morphology, FT-IR spectroscopy and X-ray diffraction strongly demonstrated hydrotalcite admirably grew in the channel of silica matrix. The influence of composite material dosage, pH values of aqueous solution, and initial concentration of I− on adsorption capacity was investigated in detail. The batch experiment results showed that Mg-Al-LDO/SiO2 had an excellent adsorption performance on I− and the removal efficiency reached 99.81% from a 30 mg/L I− solution in 5 min, with a dosage of 0.05 g/100 ml. The adsorption kinetics was fitted well by pseudo -second-order model. The column experiment data demonstrated that the application of Mg-Al-LDO/SiO2 in a column model for the continuous treatment of iodine ion effluents exhibited optimum breakthrough curves by adjusting the bed heights. The experimental breakthrough curves were correlated with Thomas, Adams–Bohart and Yoon–Nelson models.

Preparation of Controlled-Release Particles Based on Spherical Porous Silica Used as the Drug Carrier by the Dry Coating Method.

A controlled-release formulation is a dosage form that could improve a patient's quality of life by reducing the frequency of administration, while ensuring the continued effect of the medicine and reducing the side effects. To prepare these controlled-release particles, a wet coating method in which a drug is coated with a controlled-release material using water or an organic solvent is used, but with this method, the coating process is very time-consuming and requires large amounts of energy for the drying phase. In addition, contact with water or an organic solvent may cause problems such as alteration of the drug. Therefore, the use of a dry coating method has attracted attention as a means of overcoming these issues. However, since the drug is fixed to the surface of a core particle, it is necessary to further coat it with a water-soluble material. We used spherical porous silica (SPS) particles, considering that the drug fixation via a water-soluble material would not be necessary if the drug were to be placed in the pores of these particles. We used SPS filled with theophylline (TP), a model drug, as the core particles. To prepare controlled-release particles (CRP), a controlled-release layer consisting of hydrogenated castor oil (HCO) was applied to the core particle surface by a dry coating method. The paddle method using 1% w/v polysorbate 80 solution as the test medium was employed to estimate the TP dissolution rate of the resulting CRPs. The 50% dissolution time of TP extended from 14 to 405min with increasing the amount of the coated HCO. The Korsmeyer-Peppas model applied to the TP dissolution behavior yielded an n value of around 1. Moreover, the K value was comparable with the case in which a zero-order model was applied. It is thought that the dissolution of TP from CRPs will conform to the zero-order model.

Preparation of porous hollow silica spheres via a layer-by-layer process and the chromatographic performance

Hollow silica spheres possessing excellent mechanical properties were successfully prepared through a layer-by-layer process using uniform polystyrene (PS) latex fabricated by dispersion polymerization as template. The formation of hollow SiO2 micro-spheres, structures and properties were observed in detail by zeta potential, SEM, TEM, FTIR, TGA and nitrogen sorption porosimetry. The results indicated that the hollow spheres were uniform with particle diameter of 1.6 μm and shell thickness of 150 nm. The surface area was 511 m2/g and the pore diameter was 8.36 nm. A new stationary phase for HPLC was obtained by using C18-derivatized hollow SiO2 micro-spheres as packing materials and the chromatographic properties were evaluated for the separation of some regular small molecules. The packed column showed low column pressure, high values of efficiency (up to about 43 000 plates/m) and appropriate asymmetry factors.

Preparation and characterization of carbon dot-decorated silica stationary phase in deep eutectic solvents for hydrophilic interaction chromatography.

In this paper, N-doped carbon dots (NCDs) were successfully decorated on the spherical porous silica surface in deep eutectic solvents (DESs) as a novel class of green solvents. The appropriate density and hydrophility of DESs guaranteed the fine dispersibility of silica particles and NCDs, resulting in a homogeneous and thin layer of NCDs immobilization. As compared with traditional organic solvents (DMF and THF), higher surface coverage was obtained in the medium of DES, proving its feasibility as a new kind of alternative solvent for hydrophilic nanomaterial-based surface modification of silica spheres. The resulting NCDs-decorated silica particles (Sil-NCDs) were characterized in detail and packed into chromatographic columns to study their initial feasibility as adsorbent material for liquid chromatography. The resultant packing materials demonstrate a selective behavior for polar compounds in hydrophilic interaction liquid chromatography (HILIC) mode. This work gives a typical example of using carbon dots as stationary phase component, and such material is hopeful to be used in other research fields such as solid absorbents, recycling catalysts, and solid-state electrochemistry etc. Graphical Abstract N-doped carbon dots (NCDs) were successfully coupled on the surface of porous silica spheres in a green strategy using deep eutectic solvents (DES) as media for HILIC.

Deposition of a titania layer on spherical porous silica particles and their nanostructure-induced vapor sensing properties

A titania-stearic acid hybrid layer was deposited onto well-defined silica-hexadecyltrimethylammonium hybrid spherical particles with 854 nm size to obtain nanoporous particles with a useful hierarchical core-shell structure. The deposition of a 35 nm-thick titania layer was confirmed by transmission electron microscopy. The core-shell particles were washed with acidic ethanol (solvent extraction) and calcined at 550 °C for 5 h to remove the template, resulting in the formation of nanoporous titania coated nanoporous silica spherical particles, which have a bimodal pore size distribution attributed to the hierarchical porous core and porous shell structure. The nanoporous titania coated particles exhibited an unusual crystal phase transition; only anatase was present even after the calcination at 1000 °C for 1 h. This would be due to the interfacial bonding between the core silica and the shell titania, preventing the crystal phase transition from anatase to rutile. On the other hand, the direct calcination of the titania-stearic acid coated particles without solvent extraction led to a shell composed of both anatase and rutile. The transformation to rutile could be caused by the strong exothermic reaction during the oxidative decomposition of the occluded stearic acid. Furthermore, the intense exothermic reaction induced the formation of a yolk-shell structure, which played a role in the sensitive/selective sensing properties for acetic acid when the yolk-shell particles were coated onto a nanomechanical Membrane-type Surface stress Sensor (MSS).

Self-assembled cyclodextrin-modified gold nanoparticles on silica beads as stationary phase for chiral liquid chromatography and hydrophilic interaction chromatography

A facile strategy based on self-assembly of Au nanoparticles (AuNPs) (60±10nm in size) on the surfaces of amino-functionalized porous silica spheres under mild conditions was proposed. The resulting material possessed a core-shell structure in which AuNPs were the shell and silica spheres were the core. Then, thiolated-β-cyclodextrin (SH-β-CD) was covalently attached onto the AuNPs as chiral selector for the enantioseparation. The resultant packing material was evaluated by high-performance liquid chromatography (HPLC). The separations of nine pairs of enantiomers were achieved by using the new chiral stationary phase (CSP) in the reversed-phase liquid chromatography (RPLC) mode, respectively. The results showed the new CSP have more sufficient interaction with the analytes due to the existence of AuNPs on silica surfaces, resulting in faster mass transfer rate, compared with β-CD modified silica column. The result shed light on potential usage of chemical modified NPs as chiral selector for enantioseparation based on HPLC. In addition, the new phase was also used in hydrophilic interaction liquid chromatography (HILIC) to separate polar compounds and highly hydrophilic compounds.

CO2 sorption performance by aminosilane functionalized spheres prepared via co‐condensation and post‐synthesis methods

Amine functionalized silica microspheres were synthesised via a modified Stöber reaction for carbon dioxide (CO2) adsorption. A number of adsorbents were synthesized by co‐condensation and post synthesis immobilization of amines on porous silica spheres. CO2 adsorption studies were carried out on a fixed bed gas adsorption rig with online mass spectrometry. Amine co‐condensed silica spheres were found to adsorb up to 66 mg CO2 g−1 solid in a 0.15 atm CO2 stream at 35°C. Simple post‐synthesis addition of aminopropyltriethoxysilane to amine co‐condensed silica was found to significantly increase the uptake of CO2 to 211 mg CO2 g−1 under similar conditions, with CO2 desorption commencing at temperatures as low as 60°C. The optimum temperature for adsorption was found to be 35°C. This work presents a CO2 adsorbent prepared via a simple synthesis method, with a high CO2 adsorption capacity and favorable CO2 adsorption/desorption performance under simulated flue gas conditions. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2825–2832, 2016

Hydrodesulfurization Catalysts: Hierarchically Structured Porous Silica Spheres by Microemulsion/Vesicle Templating for Hydrodesulfurization of Fluid Catalytic Cracking Diesel (Part. Part. Syst. Charact. 4/2016)

Hydrodesulfurization Catalysts: Hierarchically Structured Porous Silica Spheres by Microemulsion/Vesicle Templating for Hydrodesulfurization of Fluid Catalytic Cracking Diesel (Part. Part. Syst. Charact. 4/2016)

Hierarchically Structured Porous Silica Spheres by Microemulsion/Vesicle Templating for Hydrodesulfurization of Fluid Catalytic Cracking Diesel

A series of hierarchically structured porous silica sphere (HSPSS) materials are successfully fabricated by a facile, one‐step microemulsion/vesicle bimodal method in a multicomponent microemulsion system of P123/n‐butanol/1,3,5‐trimethylbenzene/KCl/H2O (surfactant/cosurfactant/oil/salt/water). The pore structures of the obtained HSPSS products consist of mesocellular foam and mesostructured vesicles. In contrast to the traditional porous silica materials the new structures combine two separate, distinct mesophases with different‐sized mesovoids in a single porous sphere. Moreover, the proportion of every mesophase in obtained HSPSS can be easily adjusted by tuning the initially added amount of n‐butanol or KCl in this multicomponent microemulsion system. When the molar ratio of KCl/tetraethoxysilane is 2.15, the obtained HSPSS material is turned into uniform mesostructured vesicle silica spheres, which consist of many small diameter vesicle particles. The hydrodesulfurization (HDS) activity of fluid catalytic cracking diesel over the HSPSS was tested. HSPSS‐0.75‐1.43 catalyst support with multiple mesoporous structures shows the highest HDS efficiency (98.5%) among all the studied catalysts.

Nanoreactors: An Efficient Tool To Control the Chain-Length Distribution in Fischer–Tropsch Synthesis

One of the main problems of the Fischer–Tropsch synthesis is the overly broad distribution of the produced hydrocarbons due to the Anderson–Schulz–Flory law. This work is directed toward the solution of this problem by the application of nanoreactors with incorporated metal nanoparticles. Our results show that encapsulation of Co nanoparticles in nanosized porous silica spheres results in higher activity per catalyst weight and stability with a shift of the chain length distribution of hydrocarbons to lower values in comparison with Fischer–Tropsch synthesis over impregnated catalysts. These effects are due to the presence of well-dispersed isolated and stable Co nanoparticles inside of nanoreactors and shape selectivity effects which restrict the chain growth by the walls of nanoreactors. The proposed new strategy can be further extended to synthesis of olefins and alcohols with desired chain-length distribution from syngas by encapsulation of other metals (Fe, Cu, Rh, etc.).

Preparation of alumina nanoshell coated porous silica spheres for inorganic anions separation

It had been reported that alumina nanoshell coating could be obtained on the external surface of various substrates in one-nanometer precision in aqueous solution. In this work, alumina nanoshell coated mesoporous silica microbeads (nanoAl2O3/mesoSiO2) were prepared with the similar method, and were successfully applied to inorganic anions separation. As the mass transfer speed is largely constrained in the mesopore compared with that on the open surface, it was found that a complete alumina nanoshell coating could be obtained within the mesopore until the five-time coating was carried out. After characterization by BET, SEM and FTIR, it was found that the obtained nanoAl2O3/mesoSiO2 particles are smooth and well dispersed, and the mesopores are well reserved. In addition, the full coverage of nanoAl2O3 shell in mesopores was also confirmed by the binding capacity experiments with berberine. Finally, the nanoAl2O3/mesoSiO2 particles were packed in silica capillary for the separation of inorganic anions I−, SCN−, Br−, NO2− and NO3− with ion chromatography (IC), and a column efficiency of 3.8×104 plates per meter was obtained for I−.

Transcription of G-quartet supramolecular aggregates into hierarchical mesoporous silica nanotubes.

The use of 5-guanosine monophosphate (GMP) with Sr(2+) ions to form G-quadruplex bundles as supramolecular templates for the preparation of hierarchical mesoporous silica nanotube materials is reported here, and some mesopores with a diameter of 4-22 nm were obtained. Furthermore, some mesopore channels which run perpendicularly to the center axis of the tube and penetrate right through the outer wall of the nanotubes were achieved by removing the templates. Besides, porous hollow silica spheres were obtained by changing some of the reaction conditions during the process of preparation. Their structures are stable even after high temperature calcination. A formation mechanism was proposed and discussed, and their structures were characterized using a number of means including X-ray diffraction, IR spectra, N2 adsorption-desorption isotherms, scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

Fabrication of Hollow Porous Silica Using a Combined Emulsion Sol-Gel Process and Amphiphilic Triblock Copolymer for Loading of Quercetin.

Flavonoids have recently attracted significant interest as potential reducing agents, hydrogen-donating antioxidants, and singlet oxygen-quenchers. Quercetin, in particular, induces the expression of a gene, known to be associated with cell protection, in dose- and time-dependent manners. Therefore, quercetin may be used as an effective cosmeceutical material useful in the protection of dermal skin. In this study, hollow porous silica spheres used to load quercetin were prepared by using a combined emulsion sol-gel process and triblock copolymer as a template. Fabrication of hollow porous silica spheres was performed under various conditions such as the molar ratios of H2O/TEOS (Rw) and weight ratios of poloxamer 184/poloxamer 407. Loading of quercetin in hollow porous silica spheres was devised to improve the stability of quercetin and to consider the possibility as a raw cosmetic material. The surface of inclusion complexes of quercetin in hollow porous silicas was modified to enhance the stability of quercetin. The physicochemical properties of the samples were investigated using scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA)-differential thermal analysis (DTA) and Brunauer-Emmett-Teller (BET) surface area and porosity analysis. Determination of quercetin concentration was carried out by high-performance liquid chromatography (HPLC) analysis.