Silica Core-shell Particles Research Articles

Preparation of core–shell silica particles with tunable pore size by phenylethanol as swelling agent for chromatographic separation

The core–shell particles with tunable pore size were synthesized by a bi-phase reaction successfully. By adjusting the amount of phenylethanol, fibrous shells with tunable pore sizes ranging from 4 to 19 nm could be obtained in one pot. The obtained silica microspheres were used for chromatographic separation after modification with octyltrichlorosilane and end-capping with N-(trimethoxysilylpropyl)imidazole. Better resolutions of nitroimidazoles and anilines were obtained on the end-capped stationary phase. This particle could serve as an HPLC stationary phase with good reproducibility and particular selectivity.

In situ carbonization metamorphoses porous silica particles into biodegradable therapeutic carriers of lesser consequence on TGF-β1 mediated fibrosis.

Extensive modifications have been made to the synthesis protocol for porous silica particles to improve the shape, size and yield percentage, but problems associated with improvement in biodegradability and decrease in chances to induce side effects still remain a concern. To circumvent these limitations, a facile modification strategy has been employed through in situ carbonization of porous silica particles. Herein, carbon particles were integrated within porous silica core-shell particles (Si-P-CNPs) during the synthesis process and found to preserve the ordered structural morphology. Curcumin was used as a model drug for loading in prepared Si-P-CNPs whereas lung cancer cells were used as a model system to study the in vitro fate. These Si-P-CNPs showed improved drug loading, drug effectivity, biodegradability and avoidance of interaction with transforming growth factor β1 (TGF-β1) indicating the possibility of reducing the chances of lung fibrosis and thereby enhancing the safety profile over conventional porous silica particles.

Use graphene coated silica core shell particles to provide rapid, precise, and equivalent chemical composition distribution analysis for polyolefin materials by high temperature thermal gradient interaction chromatography

High temperature thermal gradient interaction chromatography (HT-TGIC) has been widely used to measure chemical composition distribution due to its applicability to separate crystalline and non-crystalline amorphous polyolefin materials. The compatibility of HT-TGIC with various detectors (infrared (IR), light scattering (LS), and viscometer) has also allowed a comprehensive analysis of molecular architecture of polyolefin and recycled plastics. The introduction of an easy-to-fabricate graphene coated onto non-porous silica particles as HT-TGIC column in 2020 showed a superior chromatographic performance over the traditional graphite column. A reduction in peak broadness (∼47 %) under identical experimental conditions was demonstrated in that research. This paper similarly uses a graphene column but with the focus on optimization of experimental parameters (concentration, and thermal cooling and heating rates etc.). Equivalent chemical composition distribution (CCD) data to that obtained by the incumbent graphite column over a wide range of polyolefins products was achieved, in addition to a shortened analysis time from 120 min down to 88 min per sample. The materials studied included semicrystalline linear low-density polyethylene (LLDPE), elastomers, terpolymers, model blends to mimic recycled plastics. The results also suggest that the elimination of substrate pores enable a better HT-TGIC separation. Coupling the ease and reproducibility of the graphene column fabrication process enables long term chromatographic robustness. This not only results in equivalent CCD data compared to the traditional graphite column but also a 27 % reduction in analysis time. These results demonstrate a substantial advancement of technology in the high throughput industrial laboratory setting where fast testing turnaround time is critical. In addition, simple fabrication with commercially available silica particles and graphene nanopowder provides a cost-effective approach to make HT-TGIC columns reproducibly.

Mesoporous silica particles by aerosol spray synthesis; solid core and porous shell structure study

Mesoporous silica core shell particles are materials of high interest especially due to pharmaceutical and catalytic applications. In the current work we presented the synthesis of uniformly porous and solid core porous particles by aerosol spray pyrolysis route according to the principles of EISA, by a one step process. The particles are evaluated morphologically by TEM and by nitrogen adsorption and desorption isotherms for pore size distribution and pore connectivity, validating the effect of synthesis parameters on the core size, surface area and porosity of the uniformly porous and core-shell structures. Three different surfactants Brij-58, CTAB, P123 at various concentrations and combinations as well as three different core type compositions of NaCl, CeO2 and, Ce0.8Zr0.2O2 have been evaluated for the controlled synthesis of silica core-shell particles by a scalable synthesis method.

Biochemical and pharmacological properties of reporter systems and nanoparticles: For better tumors imaging and treatment

Reporter systems can analyze the biochemical and molecular processes in viable cells and organs and help imaging of cancer. That includes gene transcription activity, protein–protein interactions, sub-cellular localization and proteases activities. This helps studying the aspects of neoplastic trans¬formation, drug development, monitoring specific cancer-related events and tracing complex patho¬logical events (angiogenesis, apoptosis, proto-oncogene activity, oncongenes, tumor suppressor genes and tumor promoting signals). Resolution and sensitivity govern the choice of reporters. Nanoparticles have diverse uses (magnetic, catalytic, optical, thermodynamic, and electrochemical). Nanoparti¬cles include aptamers, quantum dots, core-shell silica particles, gold nanoparticles, carbon nanotubes, liposomes, dendrimers, oligonucleotides and magnetic nanoparticles. Superparamagnetic iron oxide nanoparticles (SPIONs) have the advantages of easy visualization using Magnetic resonance imaging (MRI), easy cellular targeting, possibility of generating hyperthermia, and easy biodegradation into metabolizable iron particles. Magnetic nanoparticles can be used in chemotherapy, magnetic hyper¬thermia, photodynamic therapy and photothermal therapy. MRI is the most valuable noninvasive imaging techniques to overcome magnetic nanoparticles colloidal instability. In conclusion, SPIONs are among the best nanoparticles to date owing to their easy visualization using MRI, easy cellular targeting, possibility of generating hyperthermia, and easy biodegradation into metabolizable iron particles. Research regarding reporter systems and nanoparticles is quite interesting and challenging. More research efforts are needed to optimize in vivo cancer imaging and therapeutics monitoring.

The reinforcement and toughening of jute/PLA (lactic acid) composite material with modified-rubber/SiO2 core-shell particles

In this paper, the sol-gel method is used to prepare styrene butadiene rubber (SBR)/silica (SiO2) core-shell particles. A polylactic acid (PLA) composite film containing modified-SBR/SiO2 (MSBR/SiO2) core-shell particles was then prepared by solution casting, and then jute/PLA laminated composites were prepared by hot pressing technique. The mechanical properties of hybrid jute/PLA composite materials containing different types and mass fractions were studied. The results show that the bending fracture mode of the composite materials changed from brittle fracture to ductile fracture after adding MSBR/SiO2 core-shell particles. When 4% MSBR/SiO2 core-shell particles is combined into the PLA matrix, the bending fracture strain and maximum bending strength, respectively increase by 266.7% and 82.1%, while the elongation at break and the maximum tensile breaking strength, respectively increase by 77.8% and 333.3%. The toughening mechanism is attributable to the matrix plastic deformation caused by the addition of MSBR/SiO2 core-shell particles and the matrix cavitation caused by MSBR/SiO2 core-shell particles.

Improved tribological performance of epoxy composites containing core–shell PE wax@SiO2 nanoparticles

AbstractThe poor tribological performance of epoxy limits its application in the field of lubrication and wear protection, but there is still great potential for improvement. In this paper, polyethylene wax contained by silica core–shell particles was prepared and incorporated into the epoxy resin. The effects of particle content, normal load, and reciprocating linear velocity on the friction and wear properties of epoxy‐based composites were investigated. Due to the lubricating and anti‐wear effect of core–shell particles, the 10 wt.% amount can reduce at most the friction coefficient and wear rate of epoxy by 57% and 94%, respectively. The inflatable and burst core–shell particles, transfer film, and corrosion were observed on the worn surface. A mechanism referring to fracture, the release of lubricating core, and transfer film formed by a mixture of core and shell materials were deduced to explain the enhancement effect of core–shell particles in the epoxy matrix. That also suggests that the polyethylene wax@silica core–shell particles will be a potential lubricating and wear‐resistant additive of epoxy.

Synthesis of highly monodisperse superparamagnetic iron oxide core@mesoporous silica shell particles with independently tunable size, and porosity

Superparamagnetic iron oxide nanoparticles, SPIONs, especially in the form of nanoscopic aggregates thereof, find broad applications as magnetic resonance imaging contrast agents, as biological tools for straightforward separation of biomolecules and cells, as magnetically tunable colorimetric sensors exhibiting structural colors, etc. Furthermore, if the SPIONs are covered with another oxide, typically silica, the size and refractive index of the particles can be modified. In addition, if the silica layer is mesoporous additional functionalities can be introduced. Such particles could serve as, for example, theranostic nanoparticles capable of serving both as drug carriers and contrast agents, as easily separable high-capacity adsorbers, and if the particles are monodisperse, colorimetric sensors. Many reports cover the synthesis of such SPION core-silica shell particles, but to date the structural tunability and reproducibility aspect has not received deserved attention. Here we report highly reproducible syntheses leading to SPION cores carrying silica shells with independently tunable shell thicknesses and porosities. The products are highly monodisperse in all cases, as evidenced by the fact that pellets of the particles show structural colors. The shell formation process is followed in detail, and is related to the applied synthesis parameters, which allows for rational further fine-tuning of the structural characteristics of the core-shell particles for a given application. • We report results related to the synthesis of highly monodisperse, superparamgnetic aggregates of iron oxide nanoparticles of various sizes with different silica shells of various thicknesses, and porosities. • The silica shell porosity can be adjusted independently of the total particle size and the silica shell thickness. • The possibility for independent tuning of total particle size, shell thickness, and shell porosity makes it possible to rationally optimize these core-shell particles for a given application.

Titania coated silica core-shell spheres with dual grain size as efficient photocatalysts

The TiO2 nanoclusters were modified into the pores of silica core-shell particles (SiO2@dSiO2) by the sol-gel method, and the loading amount reached 47%. Based on the Ostwald ripening theory, by simply extending the reaction time, a part of the TiO2 in the pores of the shell was dissolved and then re-deposited on the outer surface of the shell to form a TiO2 layer. Using this method, TiO2 crystalline grains of different sizes were obtained simultaneously inside and outside the shell of silica core-shell spheres. Small-sized crystalline grains were located in the pores of the shell, and they had a strong quantum size effect. The large crystalline grains were located in the TiO2 layer on the outer surface of the shell of SiO2@dSiO2. Due to the formation of larger-sized crystalline grains, the recombination probability of photogenerated electron-hole pairs was reduced. When used as photocatalysts for the degradation of Rhodamine B under UV irradiation, the catalytic activity of SiO2@dSiO2@TiO2 was 5.4 times higher than that of the commercial P25 TiO2 photocatalyst.

Synthesis of Porous Hollow Organosilica Particles with Tunable Shell Thickness.

Porous hollow silica particles possess promising applications in many fields, ranging from drug delivery to catalysis. From the synthesis perspective, the most challenging parameters are the monodispersity of the size distribution and the thickness and porosity of the shell of the particles. This paper demonstrates a facile two-pot approach to prepare monodisperse porous-hollow silica particles with uniform spherical shape and well-tuned shell thickness. In this method, a series of porous-hollow inorganic and organic-inorganic core-shell silica particles were synthesized via hydrolysis and condensation of 1,2-bis(triethoxysilyl) ethane (BTEE) and tetraethyl orthosilicate (TEOS) in the presence of hexadecyltrimethylammonium bromide (CTAB) as a structure-directing agent on solid silica spheres as core templates. Finally, the core templates were removed via hydrothermal treatment under alkaline conditions. Transmission electron microscopy (TEM) was used to characterize the particles′ morphology and size distribution, while the changes in the chemical composition during synthesis were followed by Fourier-transform infrared spectroscopy. Single-particle inductively coupled plasma mass spectrometry (spICP-MS) was applied to assess the monodispersity of the hollow particles prepared with different reaction parameters. We found that the presence of BTEE is key to obtaining a well-defined shell structure, and the increase in the concentration of the precursor and the surfactant increases the thickness of the shell. TEM and spICP-MS measurements revealed that fused particles are also formed under suboptimal reaction parameters, causing the broadening of the size distribution, which can be preceded by using appropriate concentrations of BTEE, CTAB, and ammonia.

Rapid and sensitive simultaneous separation and electrochemical detection of tetracaine hydrochloride and oxymetazoline hydrochloride in pharmaceutical formulations via core-shell reversed-phase liquid chromatography

Tetracaine hydrochloride (TCH) is a nasal anesthetic and oxymetazoline hydrochloride (OZH) is a nasal decongestant. A moderate to acute overdosage of OZH and TCH can lead to mydriasis, nausea, cyanosis, tachycardia, dyspnoea, cardiovascular failure, disorientation, seizures, and even death. Liquid chromatography (LC) has been mainly utilized for the individual determination of either TCH or OZH; however, there is a need for rapid and efficient methods for simultaneous analysis in pharmaceutical formulations and aqueous samples. This study highlights the use of the fast and efficient separation capabilities of core-shell silica particles in liquid chromatography (LC) for the simultaneous determination of TCH and OZH using UV detection and the enhanced selectivity afforded by electrochemical detection at a boron-doped diamond (BDD) electrode. Rapid reversed-phase (RP) separation and detection of OZH and TCH in nasal spray and eye drops was achieved within 45 s using a poroshell 120 EC-C18 column, by adjusting the ratio of organic solvent, mobile phase pH, detection potential and mobile phase flow rate. Sensitivity was compared using ultraviolet (UV) detection at 280 nm, and ECD at + 1.3 V with detection limits of 40 and 70 nM for TCH and OZH, respectively. The developed rapid method was utilized successfully in the analysis of pharmaceutical formulations, where the estimated levels of TCH and OZH in these formulations are in agreement with the specified values outlined by the manufacturers.

Pore size control of monodisperse mesoporous silica particles with alkyl imidazole ionic liquid templates for high performance liquid chromatography applications

The control of pore size in mesoporous silica particles is still a topic of considerable research attention for the preparation of chromatographic packing materials. In this study, three alkyl imidazole ionic liquid surfactants ([BRIJOn-MIM]Ts (n = 2, 10, 20)) were synthesized from polyoxyethylene oleyl ether (BRIJ™On, n = 2, 10, 20), 1-methylimidazole, and p-toluenesulfonyl chloride. [BRIJOn-MIM]Ts (n = 2, 10, 20) exhibited different template behaviors in the preparation of mesoporous silica, and hollow silica with worm-like vesicle structures, spherical silica, and gel were obtained, respectively. Monodisperse sub-3 µm core-shell silica particles (CSSPs) with narrow pore size distribution were successfully prepared by the ultrasound-assisted sol-gel method using [BRIJO10-MIM]Ts as the template. A shell thickness of up to 300 nm was obtained, and the pore size was expanded from 4.7 to 7.3 nm by adjusting the reaction parameters, overcoming the limitation of pore size to less than 4 nm when using organic alkyl quaternary ammonium or alkyl imidazolium surfactants as the templates. The synthesized 2.7 µm CSSPs were functionalized with tert-butylcarbamoylated quinine and used as an anion exchange chiral stationary phase, exhibiting excellent separation performance for N-substituted amino acid enantiomers.

Computational fluid dynamics study of potential solutions to alleviate viscous heating band broadening in 2.1 millimeter liquid chromatography columns

We report on a numerical simulation study of a number of potential column technology solutions to minimize the plate height contribution (Hvh) originating from the use of ultra-high pressures and their concomitant viscous heating effect. Looking as far as possible into the future of UHPLC, all main results are obtained for the case of a 2500 bar pressure gradient. However, to generalize the result, a correlation is given that can be used to interpolate the results to lower pressures with some 10% accuracy. For the considered case of a 2.1mm column, a liquid flow rate of 0.45 ml/min, an analyte with retention factor k(25°C)=3 and a retention enthalpy chosen such that ΔHR/R= -1000 K, it is found that, in order to keep the global plate height as measured at the column outlet (Hvh,glob,out) below 1 μm, the bed conductivity would need to be raised to λbed=2.4 W/m•K, i.e., 4 times higher than a typical packed bed of fully-porous or core-shell silica particles. An equivalent effect on the band broadening could be obtained if it would be possible to replace the steel column wall with a low conductivity material. In this case, a wall conductivity of 0.25 W/m•K, i.e., 64 times smaller than the conductivity of steel, would be needed to keep Hvh,glob,out below 1 μm. Results are also interpreted based on contour plots of the axial and radial velocity variation of a retained analyte.

Evaluating the interplay among stationary phases/ion-pairing reagents/sequences for liquid chromatography mass spectrometry analysis of oligonucleotides

The correlation among stationary phases, ion-pairing reagents (IPR) and sequences for ion-pair reversed-phase liquid chromatography mass spectrometry (IP-RP LC-MS) analysis of oligonucleotide (ODN) remains unclear. The present study aimed to evaluate such correlation using particle-packed C18 columns in order to search for the optimal combination among them. Five C18 columns packed with core-shell silica, polymer, porous silica and hybrid particles, respectively, were evaluated for the analysis of synthetic and chemically modified ODNs with six different IPRs. Our results showed that silica-based porous particles, compared to other particles, retained ODN the strongest no matter which IPR was used. Meanwhile, among the six IPRs hexylamine (HA) produced the longest retention for all ODNs, regardless of the types of C18 particles. For the separation of ODNs, C18 columns performed similarly under identical LC conditions. However, the separation ability of C18 columns is highly dependent on the type of IPR and ODN sequences. Moreover, the type of particles has little impact on the signals of ODNs for the majority of synthetic sequences, but such impact could be dramatic for chemically modified sequences. On the other hand, both the type of IPR and ODN sequence have a significant effect on MS signals for synthetic and chemically modified ODNs.

Nanoscale zero-valent iron/cobalt@mesoporous hydrated silica core–shell particles as a highly active heterogeneous Fenton catalyst for the degradation of tetrabromobisphenol A

Degradation of TBBPA by NZVI/NZVC@mHS CSP/H 2 O 2 heterogeneous Fenton system. • Synthesis of NZVI/NZVC@mHS CSP materials by one-pot method. • The core–shell structure of the material reduced aggregation and increased the specific surface area. • The mesoporous network structure effectively prevented the leaching of Co (II). • NZVI/NZVC@mHS CSP efficiently degraded TBBPA as Fenton-like catalyst. While the bimetal heterogeneous Fenton system degraded organic pollutants, the leaching of heavy metals caused secondary pollution. To resolve this problem, nanoscale zero-valent iron/cobalt@mesoporous hydrated silica core–shell particles (NZVI/NZVC@mHS CSP) were synthesized as a novel Fenton-like catalyst for the rapid degradation of Tetrabromobisphenol A (TBBPA). The performance of NZVI/NZVC@mHS CSP in the degradation of TBBPA and the mechanism of their action were investigated through scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. NZVI/NZVC@mHS CSP exhibited a regular spherical shape with a surface area (115.44 m 2 ·g −1 ) that was 5 times more than that of the ordinary NZVI/NZVC (23.59 m 2 ·g −1 ). The core of NZVI/NZVC was covered with a hydrated silica shell that formed a mesoporous network that effectively prevented the leaching of cobalt ions from the core. The best catalytic performance of NZVI/NZVC@mHS CSP was obtained by optimizing the iron-to-cobalt ratio, H 2 O 2 concentration, and the dosage of the catalyst. The optimized NZVI/NZVC@mHS CSP exhibited the greatest mineralization activity (97.13%) for TBBPA removal than those in NZVI/NZVC bimetal (84.49%) and pure NZVI/NZVC@mHS CSP (59.37%). Thus, our results demonstrated that NZVI/NZVC@mHS CSP exhibited excellent reactivity in potential application as a highly active heterogeneous Fenton catalyst for degradation of TBBPA in soil and groundwater.

A highly sensitive strain sensor based on a silica@polyaniline core-shell particle reinforced hydrogel with excellent flexibility, stretchability, toughness and conductivity.

Hydrogel-based flexible strain sensors for personal health monitoring and human-machine interaction have attracted wide interest among researchers. In this paper, hydrophobic association and nanocomposite conductive hydrogels were successfully prepared by introducing polyaniline coated silica (SiO2@PANI) core-shell particles into an acrylamide-lauryl methacrylate (P(AM/LMA)) copolymer matrix. The hydrophobic interaction between the SiO2@PANI core-shell particles and the hydrophobic LMA in the P(AM/LMA) chains induced the hydrogels with outstanding mechanical properties. Furthermore, the polyaniline on the SiO2 surface and the inorganic salt formed a conductive network, which synergistically enhanced the conductivity of the hydrogels. The obtained hydrogels integrate high tensile strength (1398 kPa), ultra-stretchability (>1000%), wonderful strain sensitivity (gauge factor = 10.407 at 100-1100% strain), quick response (300 ms), and excellent durability (>300 cycles) due to the hydrophobic association and nanocomposite effect. The prepared SiO2@PANI-P(AM/LMA) hydrogel shows high stress sensitivity to detect human movements and displays a broad application prospect in flexible strain-sensor field.

Monodisperse core–shell silica particles as a high-performance liquid chromatography packing material: Facile in situ silica sol-gel synthesis

In recent years, core–shell silica particles (CSSPs) have been increasingly used for highly efficient separation at fast flow rates and relatively low back pressures in high-performance liquid chromatography (HPLC). However, material synthesis techniques for producing CSSPs economically in batch processes remain elusive. In this report, a practical and straightforward method for the preparation of CSSPs is presented. By refluxing freshly prepared nonporous silica particles in ammonia–water solution in the presence of poly(diallyldimethylammonium chloride) at 70–100 °C, CSSPs with shell thicknesses of up to 300 nm and pore sizes from 8 to 25 nm were easily prepared. The effects of the synthetic conditions on the shell thickness, surface area, and pore size were investigated in detail, and the method reproducibility was evaluated in scale-up experiments. A mechanism of CSSP formation is also proposed. The CSSPs were characterized via scanning electron microscopy, transmission electron microscopy, laser particle size (dynamic light scattering) analysis, and nitrogen adsorption and desorption experiments. The synthesized 3.4-μm CSSPs were functionalized with dimethyloctadecylchlorosilane and used as an HPLC packing material, exhibiting excellent separation performance for both small molecules and large biomolecules. In summary, we report the simplest method developed thus far for the preparation of monodisperse core–shell silica particles suitable for HPLC column packing.

Controlled manipulation of TiO2 nanoclusters inside mesochannels of core-shell silica particles as stationary phase for HPLC separation.

Basedon a detailed study of the hydrolysis process of tetrabutyl orthotitanate (TBOT), TiO2 nanoclusters were modified inside the pores of SiO2 core-shell particles instead of the outside. The pore size distribution of SiO2 core-shell spheres modified with TiO2 (SiO2@dSiO2@TiO2) was analyzed by Barrett-Joyner-Halenda (BJH) method and density functional theory (DFT) method, respectively. The results of the DFT calculations demonstrate that the TiO2 nanoclusters are always first formed in bulk solution and then enter the pores. By regulating the rate of hydrolysis of TBOT, almost all of the TiO2 nanoclusters are modified into the pores and the structure of the original SiO2 core-shell sphere is hardly affected. The morphology of the particles was characterized by scanning electron microscopy and transmission electron microscopy. The crystal phase of TiO2 was measured by XRD. SiO2@dSiO2@TiO2 spheres functionalized with C18 were packed into astainless steel column. The chemical stability of SiO2@dSiO2@TiO2 spheres under alkaline was tested by flushing of a mobile phase at pH13 for 7days. The efficiency of the column after the alkali solution treatment still reaches 98,430 plates m-1, which is only about 1.6% lower than that before the alkali solution treatment. A series of basic and acidic analytes were also separated on the column. Graphical abstract TiO2 nanocrystals were coated into the pore of core-shell silica spheres. The prepared particles were packed into the column and separation performance up to 98,430 plates per meter was achieved.

Enzyme immobilization using two processing methods onto silica core-shell particles

Two methods of enzyme immobilization onto silica core-shell particles were developed. The first method involved the immobilization of Candida rugosa lipase inside a previously synthesized mesoporous silica layer (deposited at 80°C) surrounding a dense silica core. To prevent lipase leakage from the support, an outer mesoporous silica layer was deposited at 40°C around the first silica layer containing the immobilized lipase. The deposition of the second layer was performed at a relatively lower temperature, to prevent thermal inactivation of the immobilized enzyme. The internal silica layer was obtained by assembling primary silica nanoparticles generated from highly basic sodium silicate solution at 80°C on the surface of poly (diallyldimethylammonium chloride) (PDDA) functionalized silica core particles. The average shell thickness and pore size of the internal silica layer was ∼60nm and 24nm, respectively. The effect of process parameters on generation and aggregation of silica nanoparticles prepared from highly basic sodium silicate solution was also investigated. The aggregation of silica particles generated at 40°C and 80°C took place after 840s and 570 of reactions, respectively. The immobilization efficiency of lipase on the mesoporous silica monolayer was 80%. A decline of immobilized lipase activity was approximately 6 times after 10 reaction cycles due to lipase leakage from the monolayered shell. An outer mesoporous silica layer was deposited at 40°C onto the surface of previously PDDA-functionalized monolayered silica core-shell particles containing the immobilized lipase. The average thickness and pore size of outer mesoporous silica layer was ∼60nm and 17nm, respectively. The activity of lipase immobilized inside the bilayered shell was further reduced due to diffusion resistance within the outer silica layer and PDDA layer however, it was retained for the next reaction cycles.The pore size of mesoporous silica layer obtained at 80°C was insufficient to allow invertase immobilization. Thus, the second method for the immobilization of invertase was developed. It involved the preparation of the mesoporous silica layer simultaneously with invertase immobilization at 40°C. The immobilized invertase showed decreased activity, but it was not hampered by substrate inhibition, as in the case of the free enzyme, due to the location of the enzyme inside the mesoporous silica layer, where the mass transfer resistance for the substrate to the enzyme active site was present.

Effect of tortuosity on diffusion of polystyrenes through chromatographic columns filled with fully porous and porous –shell particles and monoliths

Abstract The tortuosity parameter, essential in the prediction of molecular transport properties, is determined for several materials with multiscale porosities: interparticular/interskeleton macropores and intraparticular/intraskeleton mesopores for beds of spherical porous particles and monoliths. Electrical measurements (impedance spectroscopy) and peak parking experiments are used. The former measures the electrical resistance between two electrodes surrounding the porous material impregnated with a concentrated electrolyte, while the latter uses a set of polystyrene molecules in non-adsorbing conditions within a chromatographic setup. Tortuosity measurements as well as characterization via mercury porosimetry, nitrogen adsorption and inverse size exclusion chromatography (ISEC) are performed on four materials: fully porous silica and alumina particles, core-shell silica particles and silica monoliths. The tortuosity determined by electrical measurements is in agreement with the value determined by peak parking with the smallest probe (toluene). For molecules which size is not negligible as compared to pore size, the apparent particle tortuosity is determined from the intraparticle diffusion coefficient obtained by the Maxwell model estimating the hindrance factor via the Renkin correlation. The apparent particle tortuosity is estimated from the Weissberg equation τp[rm] = l-pln(ep[rm]), where ep[rm] is the particle porosity accessible to a molecule of size rm and p a parameter depending on the material topology. A model with just one adjustable parameter p can thus estimate the intraparticle diffusion coefficient in non-adsorbing conditions.