Porous Silica Particles Research Articles

Flow regimes in slurry bubble column: Effect of column height and particle concentration

This is an experimental study focussed on the flow regimes and gas holdup behaviour in a lab-scale slurry bubble column (vertical plexiglass cylinder, 0.14 m dia, total height 2 m). The gas distributor was a fine perforated brass plate (0.5 mm dia orifices, free plate area 0.19%), producing both homogeneous (HoR) and heterogeneous (HeR) flow regimes, and the transition between them (TrR). The three-phase gas-liquid-solid mixture was composed of local air, tap water and fine porous silica particles (size 100 μm). The particles were characterized by several methods for their individual and collective properties (optical and electron microscopy, granulometry, porosimetry, effective density and viscosity, granular rheology and bulk properties, effects on liquid conductivity and surface tension). The gas holdup e was measured by bed expansion method, using free layer height evaluated visually or by digital image analysis. Three experimental parameters were tested: gas input q, initial slurry layer height H and concentration of solid particles c. It was found that increasing both H and c reduces gas holdup and destabilizes HoR and enhances its breakdown. At low solid load, the three flow regimes exist for all H tested. At higher solid load, only one regime is observed, the turbulent Pure HeR (PHeR). The experimental data were described with suitable models, based on simple physical concepts used for gas-liquid systems, which were successfully applied also to gas-liquid-solid systems. All four flow regimes observed (HoR, HeR, TrR, PHeR) were fitted with few easy formulas, at the price of few adjustable parameters with clear physical meaning.

Enhancing the lipase-mediated bioaccessibility of omega-3 fatty acids by microencapsulation of fish oil droplets within porous silica particles

Solid-state fish oil formulations composed of omega-3 (ω-3)-rich lipid droplets internalised within a nanostructured porous silica matrix have been engineered for the first time to optimise the bioaccessibility of ω-3 fatty acids. Silica-fish oil hybrid (SFOH) particles were fabricated by spray drying a submicron fish oil emulsion stabilised by hydrophilic porous silica particles. The integrity of the bioactive polyunsaturated acyl chain was preserved during synthesis and mid-term storage, highlighting the ability for silica to impart oxidative stability towards PUFA. 1H NMR analysis elucidated that the nanostructured silica network acted as a substrate-enzyme immobilisation template that facilitated enhanced fish oil hydrolysis kinetics through the interfacial activation of lipolytic enzymes, resulting in a 1.4-fold improvement in bioaccessibility compared to crude fish oil. Subsequently, this novel solid-state fish oil formulation has the potential to overcome stability drawbacks associated with PUFA and optimise the degree of ω-3 absorption into the systematic bloodstream.

Direct analysis of vitamin A, vitamin E, carotenoids, chlorophylls and free sterols in animal and vegetable fats in a single normal-phase liquid chromatographic run

The present method was optimized and validated to enable quantification of more than twenty compounds from four chemical classes of important lipid substances, including vitamin E and A derivatives, sterols and chlorophylls. After lipid dissolution in the mobile phase, chromatographic separation is accomplished with the newest generation of ultrapure unbounded fully porous silica particles and, finally, target analytes are quantified by diode-array tandem fluorescence detection. A broad working range was achieved for most compounds (r2 > 0.999), with selectivity/specificity confirmed for each analyte by high resolution factors. Limits of detection and quantification were generally as low as a few nanograms per milliliter. The method also showed adequate repeatability and intermediate precision (RSD < 5%) and proved to be very accurate (89–116 %) when applied to the analysis of several vegetable and animal fats.The proposed method is a faster, cost-effective and environmental-friendly alternative for routine analyses in the food quality control field, providing extensive information in one single injection, without sample pre-treatment. Moreover, it preserves the identity of the sample components, thus enabling fingerprints for authenticity purposes.

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.

Synthesis of Advanced Mesoporous Materials by Partial Pseudomorphic Transformation.

The structure of porous silica particles can be reorganized without alteration of the particle size and shape by the process of pseudomorphic transformation. Partial pseudomorphic transformation leads to ordered mesoporous silica with bimodal pore size distributions and bottleneck pores. Compared to the classical pathways of mesoporous silica synthesis, pseudomorphic transformation implies less compromise between pore structure and particle shape, while enabling the preparation of complex pore architectures.

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.

Development of a Novel Spontaneous Emulsification Method for Peptide Delivery Using Porous Silica Particles.

A new emulsification technique using porous silica particles was studied as a facile and instantaneous formation method for thermodynamically unstable emulsions. In this study, oil encapsulated in silica particles was released instantly upon the addition of a phosphate buffer, forming an oil-in-water (O/W) emulsion. Emulsion formation was inhibited or promoted using lipophilic or hydrophilic surfactant additives, respectively. We concluded that this phenomenon is affected by the wettability of the soybean oil on the silica surface, which is controlled by the surfactant. We prepared submicron size emulsions in a simple method involving the addition of the silica particles to an aqueous solution. This spontaneous emulsification technique could be applied to the formation of solid-in-oil-in-water (S/O/W) emulsions for oral delivery of hydrophilic peptide medicine.

Thermoresponsive Polymer Grafted Porous Silicas as Smart Nanocarriers

Porous silica particles grafted with various stimuli-responsive polymers are investigated with great interest for their use as smart pharmaceutical nanocarriers in advanced drug delivery systems (DDS). In particular, porous silica particles grafted with thermoresponsive polymers that exhibit thermally triggered on/off gating mechanisms have shown improved performance as hybrid DDS capable of controlling the release of different drugs in various mediums which resemble complex biological environments. In addition, the tuning of the drug release profiles as per requirements has proved possible with modifications to the porous core and the grafted thermoresponsive polymers. This highlight presents a brief discussion of basic preparation techniques and some recent significant developments in the field of thermoresponsive polymer grafted porous silica particles as smart pharmaceutical nanocarriers.

Preparation of high wear-resisting superamphiphobic robust film by self-assembled monolayer surface reaction

Abstract Artificial superamphiphobic surfaces have been arousing great attention in recent years for improved durability in practical applications. In this study, composite of dual-sized porous silica of micro-/nanoparticles and epoxy resin was coated on the glassy substrate as the micro-/nanostructure, then 60 nm porous silica particles modified by 3-aminopropyltriethoxysilane were covered on it. The monolayer of low-surface-energy fluoride-chains was grafted by click reaction of 2-(((3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10- heptadecafluorodecyl)-oxy)-methyl)oxirane with amino groups in the micro-/nanostructure surface. The low free-energy long perfluorinated chain and topological features established a super-repellent surface. The surface was of the superamphiphobic property with a wide range of liquids (surface tension ranging from 72.0 to 27.2 mN m −1 ). Because of EP’s wearability and the long perfluorinated chains’ automatically migrating from the inner surface of porous silica particles to the new surface, the super-repellent surface is of not only the self-cleaning feature like the lotus’ effect, but also the durability, the self-healing and high wear-resisting abilities, even after it was heavily scratched by the knife or abraded by sandpaper. After the superamphiphobic coating had been rubbed, under a weight of 100 g, 40 sandpaper abrasion cycles, the coating still keeps its contact angles (CAs) to water; diiodomethane and ethylene glycol over 155 ± 2°, and all its sliding angles (SAs) lower than 2.7 ± 1°, respectively. These abilities are anticipated to have important practical applications because of their satisfactory of the long-life use in outdoor and large-scale fabrications.

Extraction and recovery of soft metal ion by porous silica coated by hydrophilic polymer gel with hexavalent nitrogen-donor ligand

ABSTRACTA hydrophilic N-isopropylacrylamide (NIPA) gel copolymerized with a hexavalent nitrogen donor ligand, N,N,N’,N’-tetrakis(4-propenyloxy-2-pyridylmethyl)ethylenediamine (TPPEN), adsorbs soft metals selectively from the acidic aqueous phase. We are developing porous silica particles coating the TPPEN-NIPA gel with high TPPEN content thinly on the pore surface of porous silica by a new gel-coating method using surface tension. Half of the pore volume of the silica particles remained by the coating of the TPPEN-NIPA gel with the high TPPEN content of 30 mol%. A large separation factor (SF) of Cd(II)/Eu(III) of 60 was observed at pH 2. The proposed chromatographic agent with the high TPPEN content is applicable for practical use.

Surface radical chain-transfer reaction in deep eutectic solvents for preparation of silica-grafted stationary phases in hydrophilic interaction chromatography

In this paper, deep eutectic solvents (DESs) were firstly used as new and green solvents for the preparation of polymer-grafted silica stationary phases. 1-Vinylimidazole and acrylic acid were homopolymerized and copolymerized on silica via surface radical chain-transfer reaction in the DESs. Three stationary phases including poly(1-vinylimidazole)-, poly(acrylic acid)-, poly(1-vinylimidazole-co-acrylic acid)-grafted silica were obtained and characterized by elemental analysis and Fourier transform infrared spectroscopy. Their hydrophilic interaction chromatographic properties were investigated for separation of nucleosides, nucleobases, saccharides and amino acids. The retention changes of nucleosides and nucleobases on these columns were investigated under different chromatographic conditions including acetonitrile content, salt concentration, pH of mobile phase and column temperature. The repeatability of these columns was also investigated. The results demonstrate that DESs can be used as new media for the synthesis of silica-based stationary phases by homopolymerization and copolymerization on the surface of porous silica particles.

Fast ultra-high-performance liquid chromatography with diode array and mass spectrometry method for determination of tadalafil drug substance and its impurities.

Tadalafil is used for the treatment of erectile dysfunction. Its related patents expired in 2016, and so related generic drug production is predicted to be increased. This work is focused on developing a fast ultra-high-performance liquid chromatography with diode array detection and/or mass spectrometry detection for the separation and determination of tadalafil and its impurities in pharmaceutical samples. A modern reversed-phase stationary phase with sub-2 μm particle size, Zorbax StableBond Rapid Resolution High Definition with octylsilane chemically bonded phase to totally porous silica particles, was used for the solving this problem. Column temperature was set at 40 ± 0.1°C. A mobile phase consisting of acetonitrile and aqueous solution of 0.1% (v/v) trifluoroacetic acid for diode array detection detection and 0.05% (v/v) formic acid, both running at a flow rate of 0.62 mL/min, were used to achieve the required separation of all components within a 5 min run. The limit of detection was 3.5 μg/L and the limit of quantification was 10.0 μg/L for the method for both UV and MS detectors. Accurate mass spectra of tadalafil's related impurities are shown for advanced confirmation. The method is directly transferable to routine analysis of tadalafil in pharmaceutical and control laboratories.

Ex vivo skin permeation and penetration of nonivamide from and in vivo skin tolerability of film-forming formulations containing porous silica

AimThe purpose of this study was to evaluate skin permeation and penetration of nonivamide which has been formulated in novel film-forming formulations (FFFs). These formulations aim to prolong the availability of capsaicinoids which are used in long-term treatment of chronic pruritus. MethodsAn oily solution of nonivamide was loaded into porous silica particles which then were suspended in an aqueous dispersion of a sustained release polymer. Permeation and penetration experiments were performed ex vivo with postauricular porcine skin using modified Franz diffusion cells. The penetrated drug amount was assessed ex vivo by skin surface biopsy followed by cryo-sectioning. Furthermore, in vivo skin irritation experiments were performed to compare the potential skin irritation caused by the FFFs to conventionally used semi-solid formulations. ResultsPermeation rates of nonivamide from FFF through the skin are comparable to that from clinically used immediate release formulations. This elucidates the therapeutic safety profile of the novel FFF. Penetration studies confirmed the prolonged drug availability at the site of action. FFFs were found not to irritate the skin of healthy volunteers. ConclusionFFFs with sustained nonivamide penetration represent safe and easy-to-use formulations. They therefore may improve the treatment of chronic pruritus with capsaicinoids by enhancing patient compliance through a sustained release regime.

Creating innovative composite materials to enhance the kinetics of CO2 capture by hydroquinone clathrates

This study addresses both the preparation of a reactive medium composed of porous particles impregnated with hydroquinone (HQ), an organic compound capable of forming gas clathrates, and an evaluation of the kinetic performance of these composite materials for CO2 capture. Two types of porous silica particles of different sizes and pore diameters were tested. The porous particles were impregnated with HQ by a dry impregnation (DI) method in a fluidized bed, and by a wet impregnation (WI) method. The impregnation effectiveness of the two methods is discussed, and the reactivity of the composite materials formed in terms of CO2 capture and storage capacity is studied experimentally. The experimental results showed that the HQ adheres well on the silica without any chemical modification of the deposit’s structure. We demonstrated that the impregnation technique plays a very important role in the kinetics of CO2 capture. A series of experiments performed using a magnetic suspension balance at 3.0MPa and 323K showed that the silica-based impregnated particles reversibly capture and store CO2, and that the CO2 capture kinetics are significantly enhanced compared to the results obtained with pure powdered HQ. Finally, we demonstrated that CO2 capture is faster with dry-impregnated particles.

Supercritical carbon dioxide versus toluene as reaction media in silica functionalisation: Synthesis and characterisation of bonded aminopropyl silica intermediate

This research reports supercritical carbon dioxide versus toluene as reaction media in silica functionalisation for use in liquid chromatography. Bonded aminopropyl silica (APS) intermediates were prepared when porous silica particles (Exsil-pure, 3μm) were reacted with 3-aminopropyltriethoxysilane (3-APTES) or N,N-dimethylaminopropyltrimethoxysilane (DMAPTMS) using supercritical carbon dioxide (sc-CO2) and toluene as reaction media. Covalent bonding to silica was confirmed using elemental microanalysis (CHN), thermogravimetric analysis (TGA), zeta potential (ξ), diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, scanning electron microscopy (SEM) and solid-state nuclear magnetic resonance (CP/MAS NMR) spectroscopy. The results demonstrate that under sc-CO2 conditions of 100°C/414bar in a substantial reduced time of 3h, the surface coverage of APS (evaluated from%C obtained from elemental analysis) prepared with APTES (%C: 8.03, 5.26μmol/m−2) or DMAPTES (%C: 5.12, 4.58μmol/m2) is somewhat higher when compared to organic based reactions under reflux in toluene at a temperature of 110°C in 24h with APTES (%C: 7.33, 4.71μmol/m2) and DMAPTMS (%C: 4.93, 4.38μmol/m2). Zeta potential measurements revealed a change in electrostatic surface charge from negative values for bare Exsil-pure silica to positive for functionalised APS materials indicating successful immobilization of the aminosilane onto the surface of silica.

Immobilization of Enzymes in Mesoporous Silica Particles: Protein Concentration and Rotational Mobility in the Pores

Enzyme immobilization in porous silica particles is used to improve enzyme function in biocatalytic applications. Here, we study the effective protein concentration and rotational mobility of lipase and bovine serum albumin in the pores, when confined in five types of mesoporous silica particles with different pore and particle sizes, exploiting the intrinsic UV-vis absorption and fluorescence anisotropy of the tryptophan residues. For all investigated combinations of proteins and particles, the steady-state anisotropy is higher than for the same protein in free solution, indicating a slower protein rotation inside the pores. The retardation is stronger in more narrow pores, but the proteins can still move, and there is no dependence on the particle size. The average number of proteins per particle, Nprot, varies with the particle diameter, D, as Nprot ∼ D2.95±0.02 for both proteins, which is close to the scaling D3.0±0.1 for the available pore volume. This observation indicates that both proteins are distributed evenly throughout the particles and rules out that the proteins are only externally bound to the particle surface. Secondly, the concentration of the protein in the pores depends on the pore and protein size but not on the particle size and corresponds to volume fractions in the range of 20-60%.

Design, synthesis and application of a new class of stimuli-responsive separation materials

A new class of efficient stationary phase has been investigated for use in the liquid chromatographic separation of low molecular weight analytes and high molecular weight biomolecules, based on the application of immobilised stimuli-responsive polymers (SRPs). To this end, two polymeric units, namely poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) and poly(acrylic acid) (PAA) were tethered to a triazine core. The derived poly(2-dimethyl-aminoethyl methacrylate)-block-poly(acrylic acid) (PDMAEMA-b-PAA), as a diblock co-polymer, was then immobilised onto the surface of porous silica particles. The performance of this microparticulate adsorbent was evaluated under various temperature, ionic strength and/or pH conditions in packed columns in a high-performance liquid chromatography (HPLC) format. Baseline separations of a variety of low molecular weight analytes were achieved at different temperatures with this SRP-based adsorbent using 10 mM sodium phosphate buffer, pH 6.0, as the mobile phase. Moreover, when the ionic strength of the mobile phase was increased to 40 mM sodium phosphate buffer, pH 6.0, similar temperature changes resulted in further increases in resolution for the hydrophobic analytes. In addition, changes in the pH of the mobile phase from pH 6.0 to pH 8.0 led to significant changes in selectivity of the analytes, including reversal in their elution orders. Upon increasing the temperature, the retention times of all analytes decreased but without loss of resolution. These findings can be attributed to the consequence of the immobilised copolymer undergoing a phase transition at its lower critical solution temperature (LCST), which leads to changes in its solvated structure, including how the electrostatic, hydrophilic and hydrophobic regions/domains of the copolymer are exposed to the bulk mobile phase. Thermodynamic data were indicative of a temperature-related re-organisation of the structure of the immobilised PDMAEMA-b-PAA stationary phase with exothermic binding of the analytes occurring at temperatures below the lower critical solution temperature (LCST). In this manner; changes in the system temperature could directly be used to manipulate the adsorption and desorption behaviour of these analytes with this stimuli-responsive, polymer-modified porous silica stationary phase. Additional studies with several proteins further documented the versatility of these stimuli-responsive separation materials. The results indicated that these separations could be tuned by variation of the temperature with fully aqueous mobile phases at specific ionic strength and pH values, without the need to use an organic solvent as a component in the mobile phase.

Sol-gel hot injection synthesis of ZnO nanoparticles into a porous silica matrix and reaction mechanism

Despite the enormous interest in the properties and applications of porous silica matrix, only a few attempts have been reported to deposit metal and metal oxide nanoparticles (NPs) inside the porous silica matrix. We report a simple approach (i.e. sol-gel hot injection) for insitu synthesis of ZnO NPs inside a porous silica matrix. Control of the Zn:Si molar ratio, reaction temperature, pH value, and annealing temperature permits formation of ZnO NPs (≤10nm) inside a porous silica particles, without additives or organic solvents. Results revealed that a solid state reaction inside the ZnO/SiO2 nanocomposites occurs with increasing the annealing temperature. The reaction of ZnO NPs with SiO2 matrix was insignificant up to approximately 500°C. However, ZnO NPs react strongly with the silica matrix when the nanocomposites are annealed at temperatures above 700°C. Extensive annealing of the ZnO/SiO2 nanocomposite at 900°C yields 3D structures made of 500nm rod-like, 5–7μm tube-like and 3–5μm needle-like Zn2SiO4 crystals. A possible mechanism for forming ZnO NPs inside porous silica matrix and phase transformation of the ZnO/SiO2 nanocomposites into 3D architectures of Zn2SiO4 are carefully discussed.

Preparation of superficially porous core-shell silica particle with controllable mesopore by a dual-templating approach for fast HPLC of small molecules

A novel strategy to synthesize the monodisperse superficially porous core-shell silica microspheres (CSSMs) with enlarged mesopore channels perpendicular to the particles surface using a dual-templating approach was presented for the first time. With hexadecyl trimethyl ammonium bromide (CTAB) as the template and trioctylmethylammonium bromide (TOMAB) as an auxiliary chemical to enlarge the size of CTAB micelles, the pore size can be enlarged from 2.6nm to 10.6nm, the mesopore channels perpendicular to the surface of CSSMs can be obtained. The particles synthesized in this work have a uniform mesoporous shell of about 198.3nm in thickness over the silica core and possess a surface area of ca. 85.1m2/g, and narrow pore size distribution. This preparation method is highly versatile, controllable and easy to operate. The CSSMs obtained were modified with octadecyltrichlorosilane (ODS) to separate the alkyl benzene homologues. The higher efficient separation with fast flow rate and relatively low back pressure of the synthesized column demonstrate that the CSSMs have a great potential application for fast separation and analysis of small solutes with high performance liquid chromatography (HPLC).

Thermoresponsive copolymer-grafted SBA-15 porous silica particles for temperature-triggered topical delivery systems

Thermoresponsive copolymer-grafted SBA-15 porous silica particles for temperature-triggered topical delivery systems