Silica Nanostructures Research Articles

Super-Repellent Paper Coated with Electrospun Biopolymers and Electrosprayed Silica of Interest in Food Packaging Applications.

In the current work, a super-repellent biopaper suitable for food contact applications was developed. To do this, three different kinds of biopolymers, namely polylactide (PLA), poly(ε-caprolactone) (PCL), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), and hydrophobic silica microparticles (SiO2), were sequentially processed by electrohydrodynamic processing (EDHP). As a first step, the ultrathin biopolymer fibers were deposited onto a commercial food contact cellulose paper by electrospinning and, thereafter, the nanostructured silica was sequentially electrosprayed. The multilayer coated papers were annealed at different temperatures to promote adhesion between the layers and enhance the super-repellent properties. The developed coatings were characterized in terms of morphology, permeance to water vapor, adhesion, mechanical resistance, and contact and sliding angle. The resultant multilayer biopapers presented a hierarchical micro/nanostructured surface with an apparent water contact angle (WCA) higher than 155° and sliding angle (SA) lower than 10° for all the tested biopolymers used. Among the different multilayer approaches, it was observed that the paper/PHBV/SiO2 showed the best performance, in terms of water vapor permeance; resistance after the tape peeling-off test; and food super-repelling properties to water, yogurt, and custard. Overall, this study presents the successful generation of super-repellent biopapers coated with PLA, PCL, or PHBV along with hydrophobic silica microparticles and its effectiveness for easy emptying food packaging applications to reduce food waste.

Oral Tolerance Induction by Bothrops jararaca Venom in a Murine Model and Cross-Reactivity with Toxins of Other Snake Venoms.

Oral tolerance is defined as a specific suppression of cellular and humoral immune responses to a particular antigen through prior oral administration of an antigen. It has unique immunological importance since it is a natural and continuous event driven by external antigens. It is characterized by low levels of IgG in the serum of animals after immunization with the antigen. There is no report of induction of oral tolerance to Bothrops jararaca venom. Here, we induced oral tolerance to B. jararaca venom in BALB/c mice and evaluated the specific tolerance and cross-reactivity with the toxins of other Bothrops species after immunization with the snake venoms adsorbed to/encapsulated in nanostructured SBA-15 silica. Animals that received a high dose of B. jararaca venom (1.8 mg) orally responded by showing antibody titers similar to those of immunized animals. On the other hand, mice tolerized orally with three doses of 1 µg of B. jararaca venom showed low antibody titers. In animals that received a low dose of B. jararaca venom and were immunized with B. atrox or B. jararacussu venom, tolerance was null or only partial. Immunoblot analysis against the venom of different Bothrops species provided details about the main tolerogenic epitopes and clearly showed a difference compared to antiserum of immunized animals.

Synthesis and Luminescent Properties of Carbon Nanodots Dispersed in Nanostructured Silicas.

Luminescent carbon nanoparticles are a relatively new class of luminescent materials that have attracted the increasing interest of chemists, physicists, biologists and engineers. The present review has a particular focus on the synthesis and luminescent properties of carbon nanoparticles dispersed inside nanostructured silica of different natures: oxidized porous silicon, amorphous thin films, nanopowders, and nanoporous sol–gel-derived ceramics. The correlations of processing conditions with emission/excitation spectral properties, relaxation kinetics, and photoluminescence photodegradation behaviors are analyzed. Following the evolution of the photoluminescence (PL) through the “from-bottom-to-up” synthesis procedure, the transformation of molecular-like ultraviolet emission of organic precursor into visible emission of carbon nanoparticles is demonstrated. At the end of the review, a novel method for the synthesis of luminescent and transparent composites, in form of nanoporous silica filled with luminescent carbon nanodots, is presented. A prototype of white light emitting devices, constructed on the basis of such luminophores and violet light emitting diodes, is demonstrated.

Modified Mesoporous HMS Supported V/W for Oxidative Desulfurization of Dibenzothiophene

Two V/W-HMS (hexagonal mesoporous silica) nanostructures were synthesized with various vanadium and tungsten loadings. And their catalytic activities were investigated in oxidative desulphurization of dibenzothiophene (DBT) in model diesel fuel. The catalysts were characterized using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, and N_2 physical adsorption-desorption (BET/BJH) techniques. The best V/W-HMS catalyst exhibited high catalytic activity, capable of converting more than 95% of DBT in the model diesel fuel under the optimum reaction condition (0.05 gr 1:4 of catalyst, T=60°C, t=2h). After doping of vanadium with tungsten, it was found that bandgap of the catalyst was reduced and its catalytic performance was improved effectively. The catalytic activity remained unchanged even after 6 recycling processes. The reaction kinetics, mechanism, and bandgap energy of the catalysts were also investigated.

Oral vaccination of piglets against Mycoplasma hyopneumoniae using silica SBA-15 as an adjuvant effectively reduced consolidation lung lesions at slaughter

Mycoplasma (M.) hyopneumoniae is the main pathogen of porcine enzootic pneumonia (PEP). Its controlling is challenging, and requires alternative strategies. This study aimed to develop an oral vaccine against M. hyopneumoniae using a nanostructured mesoporous silica (SBA-15) as an adjuvant, and compare its effect with an intramuscular (IM) commercial vaccine (CV). Fifty 24 day-old M. hyopneumoniae-free piglets composed five equal groups for different immunization protocols, consisting of a CV and/or oral immunization (OI). Control piglets did not receive any form of immunization. All piglets were challenged with M. hyopneumoniae strain 232 on D49 by tracheal route. IgA antibody response in the respiratory tract, bacterial shedding and serum IgG were evaluated. The piglets were euthanized on 28 (D77) and 56 (D105) days post-infection. Lung lesions were macroscopically evaluated; lung fragments and bronchoalveolar fluid (BALF) were collected for estimation of bacterial loads by qPCR and/or histopathology examination. All immunization protocols induced reduction on Mycoplasma-like macroscopic lung lesions. IgA Ab responses anti-M. hyopneumoniae, the expression of IL-4 cytokine and a lower expression of IL-8 were induced by CV and OI vaccines, while IgG was induced only by CV. Oral immunization using silica as a carrier-adjuvant can be viable in controlling M. hyopneumoniae infection.

Self-Assembly of Au-Fe3O4 Hybrid Nanoparticles Using a Sol-Gel Pechini Method.

The Pechini method has been used as a synthetic route for obtaining self-assembling magnetic and plasmonic nanoparticles in hybrid silica nanostructures. This manuscript evaluates the influence of shaking conditions, reaction time, and pH on the size and morphology of the nanostructures produced. The characterization of the nanomaterials was carried out by transmission electron microscopy (TEM) to evaluate the coating and size of the nanomaterials, Fourier-transform infrared spectroscopy (FT-IR) transmission spectra to evaluate the presence of the different coatings, and thermogravimetric analysis (TGA) curves to determine the amount of coating. The results obtained show that the best conditions to obtain core–satellite nanostructures with homogeneous silica shells and controlled sizes (<200 nm) include the use of slightly alkaline media, the ultrasound activation of silica condensation, and reaction times of around 2 h. These findings represent an important framework to establish a new general approach for the click chemistry assembling of inorganic nanostructures.

Dendritic Fibrous Colloidal Silica Internally Cross-linked by Bivalent Organic Cations: An Efficient Support for Dye Removal and the Reduction of Nitrobenzene Derivatives.

We designed a new unique amphoteric monodisperse colloid with a large complex internal structure, in which silica surfaces are bridged with an organic cross-linker. The rationale was that such colloids would be excellent adsorbents for cationic and anionic dyes and, when doped with noble metal nanoparticles, would be an excellent catalyst for the reduction of a variety of organic compounds. In the first step, the organo-silica bridging agent (bivalent organic cross-linkers) DABCO-S (silanated DABCO) was prepared through a simple nucleophilic substitution reaction between (3-chloropropyl)triethoxysilane and bivalent 1,4-diazabicyclo[2.2.2]octane (DABCO) (a strong base). In the second step, a DABCO-S bridge was introduced into dendritic fibrous nanostructured colloidal silica (DFNS) under open-vessel reflux conditions. We refer to the product obtained by incorporating DABCO-S in DFNS as DDS. The unique characteristics of DFNS are completely preserved in this new type of periodic mesoporous organo-silica-DFNS. The produced nanocomposite has a high surface area of about 807 m2 g-1, a large pore volume of 1.9 cm3 g-1, and a bimodal pore size distribution, with small 2.5 nm pores and large 30 nm pores. As such, DDS is an efficient adsorbent for dye removal from wastewater. The results show that DDS can adsorb positive and negative dyes such as methylene blue, orange II sodium salt (OR), and procion red mx-58 (PR) with a capacity of 678, 3192, and 3190 mg dye/g adsorbent. Introducing silver nanoparticles in situ into DDS leads to a composite with excellent accessibility of reactants to the Ag surface, resulting in an efficient catalytic reduction of nitro aromatic compounds (NACs) in aqueous media.

Rapid Microwave-Assisted Synthesis of Organo-Modified Nanostructured Silica Coatings with Tunable Water-Repellence Properties

A simple method to fabricate organo-modified silane coatings for water-repellent surface modification was proposed, by using a microwave sol-gel synthesis of hybrid materials. Low-cost fluorine-free tetraethoxysilane (TEOS) and dodecyltriethoxysilane (DDTES) were used as silane derivatives. The organo-modified silica coatings were prepared by the drop-casting method and were characterized by UV-VIS, FTIR spectroscopy, and AFM and SEM microscopy. The morphology of the film show the existence of submicrometer scale roughness due to the aggregation of modified silica nanoparticles. Contact angles of water and diiodomethane on surfaces modified with as prepared nanostructured film were determined in order to assess the hydrophobic and oleophobic properties. The TEOS/DDTES ratio was proved to be a crucial factor in tuning the wettability properties. The results suggest that significant increase of hydrophobicity could be achieved by using non-fluorinated cost-effective silica nanomaterials produced with a rapid ecofriendly method.

Nonenzymatic Hydrogen Peroxide Detection Using Surface-Enhanced Raman Scattering of Gold-Silver Core-Shell-Assembled Silica Nanostructures.

Hydrogen peroxide (H2O2) plays important roles in cellular signaling and in industry. Thus, the accurate detection of H2O2 is critical for its application. Unfortunately, the direct detection of H2O2 by surface-enhanced Raman spectroscopy (SERS) is not possible because of its low Raman cross section. Therefore, the detection of H2O2 via the presence of an intermediary such as 3,3,5,5-tetramethylbenzidine (TMB) has recently been developed. In this study, the peroxidase-mimicking activity of gold–silver core–shell-assembled silica nanostructures (SiO2@Au@Ag alloy NPs) in the presence of TMB was investigated using SERS for detecting H2O2. In the presence of H2O2, the SiO2@Au@Ag alloy catalyzed the conversion of TMB to oxidized TMB, which was absorbed onto the surface of the SiO2@Au@Ag alloy. The SERS characteristics of the alloy in the TMB–H2O2 mixture were investigated. The evaluation of the SERS band to determine the H2O2 level utilized the SERS intensity of oxidized TMB bands. Moreover, the optimal conditions for H2O2 detection using SiO2@Au@Ag alloy included incubating 20 µg/mL SiO2@Au@Ag alloy NPs with 0.8 mM TMB for 15 min and measuring the Raman signal at 400 µg/mL SiO2@Au@Ag alloy NPs.

3D-printed silica with nanoscale resolution.

Fabricating inorganic materials with designed three-dimensional nanostructures is an exciting yet challenging area of research and industrial application. Here, we develop an approach to 3D print high-quality nanostructures of silica with sub-200 nm resolution and with the flexible capability of rare-earth element doping. The printed SiO2 can be either amorphous glass or polycrystalline cristobalite controlled by the sintering process. The 3D-printed nanostructures demonstrate attractive optical properties. For instance, the fabricated micro-toroid optical resonators can reach quality factors (Q) of over 104. Moreover, and importantly for optical applications, doping and codoping of rare-earth salts such as Er3+, Tm3+, Yb3+, Eu3+ and Nd3+ can be directly implemented in the printed SiO2 structures, showing strong photoluminescence at the desired wavelengths. This technique shows the potential for building integrated microphotonics with silica via 3D printing.

Machining fused silica surface by continuous-wave CO2 laser beams and their nanostructure characterizations

Fused silica surface machined using continuous-wave CO2 laser beams with an energy density of 0.5 J/mm2 presented U-shaped grooves (approximately 47 μm-deep and 250 μm-wide) and asymmetrical craters (2–5 μm high). The fully reacted valley in the groove center exhibited porous microstructures and agglomerated silica nanoparticles in the size of 33–118 nm; whereas, the less reacted peak in the groove edge only presented uneven solidified films from silica ablations. Distinct morphologies in the valley and peak areas were supposed to result from the Gaussian energy distribution of laser beams. The selected area electron diffraction pattern suggested that the laser-reacted silica nanostructures were still amorphous with no obvious composition change. The x-ray photoelectron spectrometric results showed that both Si 2p and O 1s peaks shifted to higher energy sides, implying a more oxidized state of Si4+ and absorbed oxygen or hydroxides on nanostructured silica after CO2 laser machining.

SBA-Pr-Is-TAP Functionalized Nanostructured Silica as a Highly Selective Fluorescent Chemosensor for Fe3+ and Cr2O72- Ions in Aqueous Media.

SBA-Pr-Is-TAP was synthesized via functionalization of SBA-15. The synthesized hybrid nanomaterial was characterized by various techniques including FT-IR, TGA, XRD, SEM, and BET. SBA-Pr-Is-TAP could precisely bind Fe3+ and Cr2O72− ions among a range of different species in aqueous media, consequently acting as a nanoporous chemosensor of Fe3+ and Cr2O72− ions. An excellent linear relation was observed between the nanoporous chemosensor and ion concentrations, with acceptable detection limits of 2.43 × 10−6 M and 3.96 × 10−7 M for Fe3+ and Cr2O72− ions respectively.

Newly Designed Mesoporous Silica and Organosilica Nanostructures Based on Pentablock Copolymer Templates in Weakly Acidic Media.

We developed a new category of porous silica and organosilicas nanostructures in a facile method based on weakly acidic aqueous-ethanol media by utilizing two different pentablock copolymer templates of type PLGA-PEO-PPO-PEO-PLGA. Pluronic block templates were used mainly to prepare these pentablock copolymers with different molecular weights and volume ratios. Silica precursor tetraethyl orthosilicate and organosilicas precursor 1,4-bis(triethoxysilyl)benzene have been used as main source for synthesizing the silica and organosilicas samples. Weak Lewis acids iron(III) chloride hexahydrate, aluminum(III) chloride hexahydrate, and boric acid were utilized as catalyst instead of any strong inorganic acids and the molar ratio of catalyst/precursor has been optimized to 1–2 for preparation of ordered mesostructures. Reaction temperatures have been optimized to 25 °C for pure silica and both 25 °C as well as 40 °C for organosilicas to get the best result for mesostructures. A detailed analysis by using various analytical techniques like synchrotron small angle X-ray scattering, nitrogen sorption, transmission electron microscopy, scanning electron microscope, solid-state 29Si CP-MAS nuclear magnetic resonance (NMR), and so on has revealed well developed mesostructures with surface area of 388–836 m2/g for silica and 210–691 m2/g for organosilica samples, respectively. Furthermore, bimodal typepores have been observed from pore size distribution plot of the samples. Thermal stability of the materials was up to 400 °C as analyzed by thermogravimetric analysis.

Harnessing the potential of nanostructured formulations to mimic the food effect of lurasidone

Lurasidone is an important antipsychotic drug indicated for the treatment of schizophrenia and bipolar disorder, with an oral bioavailability of 9–19% owing to its poor aqueous solubility. Additionally, lurasidone exhibits a 2-fold positive food effect, such that patients must administer their medication with a meal, leading to significant non-compliance. The aim of this research was to evaluate the in vitro and in vivo performance of lurasidone when engineered as nanostructured systems. Specifically, a nanosuspension, nano-emulsion and silica-lipid hybrid (SLH) microparticles were formulated and the influence of composition and nanostructure on the mechanism of solubilisation was compared. Formulations were shown to enhance fasted state solubilisation levels in vitro by up to 5.9-fold, compared to pure drug. Fed- and fasted-state solubilisation profiles revealed that in contrast to the nanosuspension and nano-emulsion, lurasidone SLH mitigated the positive pharmaceutical effect of lurasidone. In vivo pharmacokinetic evaluations revealed that the nanosuspension, nano-emulsion and SLH enhanced the bioavailability of lurasidone by 3-fold, 2.4-fold and 8.8-fold, respectively, compared to pure drug after oral administration. For lurasidone, the combination of lipid-based nanostructure and porous silica nanostructure (SLH) led to optimal fasted state bioavailability which can ultimately result in enhanced treatment efficacy, easier dosing regimens and improved patient outcomes.

AC Susceptibility Studies of Magnetic Relaxation in Mn12-Stearate SMMs on the Spherical Silica Surface

The study of magnetic relaxations in Mn12-stearate single-molecule magnets deposited on the surface of spherical silica nanoparticles was performed. For such a purpose, the investigation of AC magnetic susceptibility dependence on the frequency and temperature was performed. Based on the Argand plots obtained for different temperatures and temperature dependencies of susceptibility, obtained for different frequencies of AC field, the corresponding relaxation times were derived. Fitting to the Arrhenius law revealed the values of an effective energy barrier and a mean relaxation time, which were consistent for both measuring techniques (Ueff/kB∼ 50 K and τ0∼ 10−7 s) and similar to the corresponding values for the analogous bulk compounds. Additionally, the obtained relaxation parameters for the Mn12-stearate molecules on the spherical silica surface were compared with corresponding values for the Mn12-based single-molecule magnets deposited upon other types of nanostructured silica surface.

Plant-based nanostructured silicon carbide modified with bisphosphonates for metal adsorption

Nanostructured silicon carbide possesses superior properties such as excellent hardness, high chemical stability, large surface area and good sintering ability at relatively low temperatures compared to bulk silicon carbide. However, its synthesis with conventional methods is still challenging. In the present study, we produced nanostructured silicon carbide from barley husks with a simple self-propagating high-temperature synthesis. Barley husks were chosen as the raw material because they are agricultural residues widely available and contain large amount of nanostructured silica suitable as a precursor in the synthesis. We studied the effect of two processes to valorize the barley husks on the extracted silica particles: burning in an industrial scale furnace to produce heat energy and pyrolysis to extract organic compounds as well as controlled calcination as a reference. The processing prior to the extraction affected morphology and composition of the nanostructured silica. The highest purity and surface area of 187 m2/g was obtained for the silica extracted from pristine barley husks through calcination. On the other hand, pyrolysis allows additional valorisation of the biomass by producing bio-based organic chemicals and still the silica particles with relatively high surface area, 105 m2/g, can be extracted. Nanostructured silicon carbide was produced from the extracted nanostructured silica with magnesiothermic reduction via self-propagating high-temperature synthesis. Nanostructured silicon carbide produced from silica particles undergone calcination had the highest surface area of 196 m2/g. Furthermore, it was functionalized with bisphosphonates to be used as a metal adsorbent and examined in adsorption of manganese from landfill water with pH 8. The functionalization of the silicon carbide with bisphosphonates increased the adsorption capacity by 32 % and the material was able to withstand at least 5 adsorption/desorption cycles.

High Surface Area Mesoporous Silica Nanoparticles with Tunable Size in the Sub-Micrometer Regime: Insights on the Size and Porosity Control Mechanisms.

Mesoporous silica nanostructures (MSNs) attract high interest due to their unique and tunable physical chemical features, including high specific surface area and large pore volume, that hold a great potential in a variety of fields, i.e., adsorption, catalysis, and biomedicine. An essential feature for biomedical application of MSNs is limiting MSN size in the sub-micrometer regime to control uptake and cell viability. However, careful size tuning in such a regime remains still challenging. We aim to tackling this issue by developing two synthetic procedures for MSN size modulation, performed in homogenous aqueous/ethanol solution or two-phase aqueous/ethyl acetate system. Both approaches make use of tetraethyl orthosilicate as precursor, in the presence of cetyltrimethylammonium bromide, as structure-directing agent, and NaOH, as base-catalyst. NaOH catalyzed syntheses usually require high temperature (>80 °C) and large reaction medium volume to trigger MSN formation and limit aggregation. Here, a successful modulation of MSNs size from 40 up to 150 nm is demonstrated to be achieved by purposely balancing synthesis conditions, being able, in addition, to keep reaction temperature not higher than 50 °C (30 °C and 50 °C, respectively) and reaction mixture volume low. Through a comprehensive and in-depth systematic morphological and structural investigation, the mechanism and kinetics that sustain the control of MSNs size in such low dimensional regime are defined, highlighting that modulation of size and pores of the structures are mainly mediated by base concentration, reaction time and temperature and ageing, for the homogenous phase approach, and by temperature for the two-phase synthesis. Finally, an in vitro study is performed on bEnd.3 cells to investigate on the cytotoxicity of the MNSs.

Nanostructured KIT-6 materials functionalized with sulfonic groups for catalytic purposes

In the present study, a series of ordered nanostructured KIT-6 silica, functionalized with different numbers of sulfonic groups (–SO3H) introduced by grafting or co-condensation, were synthesized. The obtained samples were subjected to thorough physicochemical characterization using X-ray diffraction, transmission electron microscopy, low temperature nitrogen sorption, infrared spectroscopy and elemental analysis. It has been observed that the amount of the used functional group precursor clearly affects the structural and textural parameters of the studied materials synthesized by co-condensation. On the other hand, the samples modified by grafting, irrespective of the number of the introduced –SO3H groups, exhibit a stable mesoporous structure with Ia3d symmetry, characteristic of KIT-6 materials. The developed synthesis procedures yielded potential solid acid catalysts, which were used in the test catalytic reactions: Friedel-Crafts alkylation, fatty acid esterification and Pechmann condensation. Both the developed synthesis algorithm and the catalytic reaction procedures comprised elements of "green chemistry", as the transformation of the functional groups precursor (–SH to –SO3H) took place in the presence of H2O2, an oxidant considered to be environmentally friendly, while the catalytic reactions were carried out without solvents and under microwave-assisted conditions, which allowed a significant shortening of the reaction time.

Silica Jar‐with‐Lid as Chemo‐Enzymatic Nano‐Compartment for Enantioselective Synthesis inside Living Cells

AbstractNanodevices, harvesting the power of synthetic catalysts and enzymes to perform enantioselective synthesis inside cell, have never been reported. Here, we synthesized round bottom jar‐like silica nanostructures (SiJARs) with a chemo‐responsive metal‐silicate lid. This was isolated as an intermediate structure during highly controlled solid‐state nanocrystal‐conversion at the arc‐section of silica shell. Different catalytic noble metals (Pt, Pd, Ru) were selectively modified on the lid‐section through galvanic reactions. And, lid aperture‐opening was regulated by mild acidic conditions or intracellular environment which accommodated the metal nanocrystals and enzymes, and in turn created an open‐mouth nanoreactor. Distinct from the free enzymes, SiJARs performed asymmetric aldol reactions with high activity and enantioselectivity (yield &gt;99 %, ee=95 %) and also functioned as the artificial catalytic organelles inside living cells. This work bridges the enormous potential of sophisticated nanocrystal‐conversion chemistry and advanced platforms for new‐to‐nature catalysis.

Silica Jar-with-Lid as Chemo-Enzymatic Nano-Compartment for Enantioselective Synthesis inside Living Cells.

Nanodevices, harvesting the power of synthetic catalysts and enzymes to perform enantioselective synthesis inside cell, have never been reported. Here, we synthesized round bottom jar-like silica nanostructures (SiJARs) with a chemo-responsive metal-silicate lid. This was isolated as an intermediate structure during highly controlled solid-state nanocrystal-conversion at the arc-section of silica shell. Different catalytic noble metals (Pt, Pd, Ru) were selectively modified on the lid-section through galvanic reactions. And, lid aperture-opening was regulated by mild acidic conditions or intracellular environment which accommodated the metal nanocrystals and enzymes, and in turn created an open-mouth nanoreactor. Distinct from the free enzymes, SiJARs performed asymmetric aldol reactions with high activity and enantioselectivity (yield >99 %, ee=95 %) and also functioned as the artificial catalytic organelles inside living cells. This work bridges the enormous potential of sophisticated nanocrystal-conversion chemistry and advanced platforms for new-to-nature catalysis.