Silica Capsule Research Articles

Chitosan/tannic acid phenamine networks-hollow mesoporous silica capsules with reversible pH response: Controlled-releasing amino acid derivatives as “green” corrosion inhibitor

A novel amino acid derivative (SM) was synthesized through Schiff base reaction between syringaldehyde (SA) and methionine (MTI), and loaded to obtain a reversible pH-responsive releasing corrosion inhibitor silica capsule (CS/TA@SM@HMSs) with chitosan/tannic acid phenamine networks on the surface. The corrosion inhibition effect of SM and CS/TA@SM@HMSs on Q235 was studied using electrochemical techniques and surface analysis. The results showed the maximum inhibition efficiency of SM reached to 93.2 % at 200ppm by immersing Q235 in 3.5 wt% NaCl solution. The theoretically calculated electron parameter (the energy gap ΔE = 4.492 eV) indicated that SM molecules were more susceptible to electron transfer with iron surfaces therefore allowing better adsorption on carbon steel surfaces to prevent corrosion. Meanwhile, UV–visible measurements showed that the chitosan/tannic acid phenamine network on the capsule surface responded to changes in pH. The reversible pH-responsive corrosion inhibitor capsule can be switched on and off several times to release SM, demonstrating reversible release and efficient corrosion protection. This study proposes a novel class of “green” amino acid derivative corrosion inhibitors, and establishes a controllable, efficient and reversible pH-responsive release system. A new approach is provided to stimulating the release of corrosion inhibitors in response to long-term corrosion protection of metals.

浸渍法制备尺寸均一可调的贵金属纳米团簇及其尺 寸依赖的催化性质

Noble metal nanoclusters, as a bridge between atoms and nanoparticles, show extraordinary catalytic activities because of their unique electronic structures. Such nanoclusters are usually synthesized by a wet chemical approach through unfavorable surface passivation by ligands and have not been obtained by an impregnation approach with satisfactory size uniformity. Herein, we report highly uniform ligand-free noble metal nanoclusters, such as Pd nanoclusters, synthesized each in a silica capsule by an impregnation strategy, with their size accurately engineerable in the range of 0.9–2.9 nm. The key is to ensure the impregnation synthesis with strict control over the nucleation and growth of noble metal nanoclusters by involving hollow silica nanoreactors and non-noble metal competitor ions, thereby showing unprecedented advantages of operational simplicity, scalability, and excellent size controllability. These Pd nanoclusters exhibit a strong size effect on catalysis exemplified by the alcohol oxidation-Knoevenagel condensation sequential reaction, with those of 1.3 nm exhibiting the highest catalytic activity. We believe this novel strategy opens new opportunities for rationally designing efficient noble metal nanocluster-type catalysts for a broad range of important reactions and bringing laboratory-quality nanoclusters into large-scale applications.

Photoactivatable Immunostimulatory Nanomedicine for Immunometabolic Cancer Therapy.

A rationally designed immunostimulant (CC@SiO2-PLG) with a photoactivatable immunotherapeutic function for synergetic tumor therapy is reported. This CC@SiO2-PLG nanoplatform comprises catalase and a photosensitizer (Ce6) co-encapsulated in a silica capsule, to which an immunostimulant is conjugated through a reactive oxygen species-cleavable linker. After accumulating in tumor tissue, CC@SiO2-PLG generates O2 to relieve tumor hypoxia and promotes the production of singlet oxygen (1O2) upon laser irradiation, resulting in not only tumor destruction but also the release of tumor-associated antigens (TAAs). Simultaneously, the linker breakage by the photoproduced 1O2 leads to the remote-controlled release of conjugated indoleamine 2,3-dioxygenase (IDO) inhibitor from CC@SiO2-PLG and consequent immunosuppressive tumor microenvironment reversion. The released TAAs in conjunction with the inhibition of the IDO-mediated tryptophan/kynurenine metabolic pathway induced a boosted antitumor immune response to the CC@SiO2-PLG-mediated phototherapy. Therefore, the growth of primary/distant tumors and lung metastases in a mouse xenograft model was greatly inhibited, which was not achievable by phototherapy alone.

Self‐healing waterborne polyurethane coating by pH‐dependent triggered‐release mechanism

ABSTRACTIn this study, effect of high‐loaded silica capsules with corrosion inhibitor on thermal degradation and self‐healing properties of waterborne polyurethane (WPU) was investigated. Silica capsules were synthesized using an oil in water (O/W) microemulsion and WPU was prepared via the prepolymer method. Assembled capsules demonstrated pH dependent release of their core. Incorporating silica capsule as an inorganic component resulted to improve thermal and barrier properties of WPU coatings. WPU coating with 1% silica capsules demonstrated better barrier quality in corrosive media and adding more than that resulted a rapid deterioration in barrier properties. Furthermore, such coatings possess an excellent adhesive strength with steel substrate. Electrochemical impedance spectroscopy was used in corrosion monitoring and healing procedure. Moreover, capsule morphology and thermal degradation of the WPU coating has been investigated separately by scanning electron microscopy and thermal gravimetric analysis. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47082.

Comparative behavior between sunscreens based on free or encapsulated UV filters in term of skin penetration, retention and photo-stability

BackgroundThe growing incidence of photodamaging effects caused by UV radiation (e.g. sunburn, skin cancer) has increased the attention from health authorities which recommend the topical application of sunscreens to prevent these skin damages. The economic stakes for those companies involved in this international market are to develop new UV filters and innovative technologies to provide the most efficient, flexible and robust sunscreen products. Today the development of innovative and competitive sunscreen products is a complex formulation challenge. Indeed, the current sunscreens must protect against skin damages, while also being safe for the skin and being sensory and visually pleasant for the customers when applied on the skin. Organic UV filters, while proposing great advantages, also present the risk to penetrate the stratum corneum and diffuse into underlying structures with unknown consequences; moreover, their photo-stability are noted thorny outcomes in sunscreen development and subsequent performance. In recent years, the evaluation of the interaction between skin and sunscreen in terms of penetration after topical application has been considered from European authority but still its testing as their photo-stability assessment are not mandatory in most countries. ObjectiveThis study, based on in-vitro approaches, was performed to evaluate and compare the retention and the penetration of organic UV filters in free or encapsulated form inside the skin as well as their respective photo-stability. MethodsSunscreen formulation with a combination of Avobenzone and Octocrylene in “free form” and a formulation using the same UV filters but encapsulated in a sol-gel silica capsule, were analyzed and compared by FTIR Imaging Spectroscopy. Tape stripping method was used to investigate the penetration of these UV filters inside the stratum corneum. Their photo-stabilities were evaluated by spectroscopic measurements (FTIR, UV/Vis) and standard measurements were calculated: AUC (Area Under the Curve) and SPF (Sun Protection Factor). ResultWith traditional formulation, the organic UV filters penetrated significantly into the stratum corneum while the same UV filters combined with encapsulation technology remained on the skin surface. The encapsulation technology also improved significantly their stability. ConclusionEncapsulation technology is a promising strategy to improve the efficacy of sunscreen product using organic UV filters and to reduce safety problem. On the other hand, this study highlighted the pertinence of the FTIR Spectroscopy to test, compare and investigate sunscreen formulations.

Raman spectroscopic characterization of cracking and hydrolysis of n-pentane and n-octadecane at 300–375℃ with geological implications

Hydrous and anhydrous isothermal experiments on n-pentane and n-octadecane were conducted at 300–375℃ for durations up to 1094 h to evaluate the cracking and hydrolysis of hydrocarbons, using fused silica capillary capsules as micro-reactors. The chemical compositions of the gaseous products during cracking of n-octadecane at 350 and 375℃ were methane, ethane, propane, and n-butane. The aqueous product in the hydrolysis of n-pentane and n-octadecane at 300–375℃ was alcohol. Alkenes and hydrogen were not detected throughout all the isothermal experiments. Results showed that the gaseous yields were characterized by higher contents of wet gas than those in natural gas accumulations. Mechanisms regulating the enrichment of methane in reservoirs should be further studied. The hydrolysis and oxidation of hydrocarbon were relatively limited in the absence of iron-bearing mineral buffers, suggesting that hydrocarbons might be more stable in iron-poor reservoirs (e.g. carbonate and quartz arenite) than in iron-bearing-mineral-rich ones (e.g. mudstone and arkose) under deep burial conditions. The absence of hydrogen was ascribed to its high diffusion rate in fused silica than in gold tube; any hydrogen produced in the reaction tends to diffuse out of the fused silica capsule with no or limited hydrogen accumulation, similar to those in geological environment. The diffusion of hydrogen should be considered during calculating the volume and pressure changes in the thermal cracking of oil to gas in reservoirs, because the loss of hydrogen would result in a decrease in the conversion rate of oil to gas.

Silica nanoparticles catalyse the formation of silica nanocapsules in a surfactant-free emulsion system

Interplay between methylated silica nanoparticles and polyethoxysiloxane at oil/water interface leads to a variety of silica capsule structures.

Yeast-based self-organized hybrid bio-silica sol-gels for the design of biosensors.

The methylotrophic Pichia angusta VKM Y-2559 and the oleaginous Cryptococcus curvatus VKM Y-3288 yeast cells were immobilized in a bimodal silica-organic sol-gel matrix comprised of tetraethoxysilane (TEOS), the hydrophobic additive methyltriethoxysilane (MTES) and the porogen polyethylene glycol (PEG). Under carefully optimized experimental conditions, employing basic catalysts, yeast cells have become the nucleation centers for a silica-organic capsule assembled around the cells. The dynamic process involved in the formation of the sol-gel matrix has been investigated using optical and scanning electron microscopic techniques. The results demonstrated the influence of the MTES composition on the nature of the encapsulation of the yeast cells, together with the architecture of the three-dimensional (3D) sol-gel biomatrix that forms during the encapsulation process. A silica capsule was found to form around each yeast cell when using 85 vol% MTES. This capsule was found to protect the microorganisms from the harmful effects that result from exposure to heavy metal ions and UV radiation. The encapsulated P. angusta BKM Y-2559 cells were then employed as a biosensing element for the detection of methanol. The P. angusta-based biosensor is characterized by high reproducibility (Sr, 1%) and operational stability, where the biosensor remains viable for up to 28 days.

Distribution of mixed-valence ions in Mn1+xFe2-xO4ferrites

Mn ferrite has a spinel structure to show the ferrimagnetism, where the magnetic moments show a collinear ferrimagnetic ordering between tetrahedral A and octahedral B sites. Since Mn2+ and Fe3+ have the same electronic configuration, it is not easy to determine the cation distribution of Mn ferrite from usual magnetization measurements. Especially in Mn ferrite, both Mn2+ and Fe3+ have a large spin polarization to give strong magnetic moments through the super exchange interaction between the two sites. Replacing Fe3+ by Mn2+ and Mn4+, the ferrimagnetic property weakens through magnetic balance between the sites. Since Mn and Fe ions may have multiple valences in the oxide structure, the scheme of site preference, based on careful study of various valence states, has been investigated for Mn1+xFe2-xO4. Single crystals for Mn1+xFe2-xO4 (x = 0.05, 0.20, 1.36 and 1.50) were synthesized from stoichiometric proportions of Mn3O4 and Fe3O4 in an evacuated silica capsule at 1353 K for 96 h. Each of spherical or parallel-piped crystals, ranging 0.05 to 0.08 mm, was mounted on the glass fiber. Conventional intensity measurements were made using a Rigaku AFC-5S four-circle diffractometer with a graphite (002) monochromator for Mo Kα radiation. Least-squares refinements were made to obtain atomic parameters, converged with R factors ranging 0.023 to 0.029. The site occupancy of Mn and Fe atoms was then determined on the basis of the resonant scattering effect at the Fe K absorption edge (λ = 1.7535 Å), by using a vertical-type four-circle diffractometer at PF-BL-10A. The results show that 89, 82, 100 and 100 percent of Mn atoms occupy the A site for the four samples, respectively. In the third step of analyses, absorption experiments were performed at PF-BL-6C. XANES and XMCD spectra were used at Mn and Fe K edges for determining the valence states of Mn and Mn ions. Finally, the distribution of mixed-valence ions for Mn1.20Fe1.80O4 was determined by the valence-difference contrast method, where the intensity data were collected for a spherical single crystal of 0.08 mm in a diameter at both threshold and pre-edge regions of Mn K edge, by using an AFC-5u four-circle diffractometer installed in PF-BL-6C. The site occupancy with the valence state will be discussed in the presentation, compared with the other type of transition-metal ferrites.

Preparation of Mannitol@Silica core–shell capsules via an interfacial polymerization process from water-in-oil emulsion

Mannitol@Silica core–shell capsules were prepared from W/O emulsion by adding silicon precursor into the oil-continuous phase to form silica shell through interfacial polymerization reaction. The bicomponent mixture of tetraethoxysilane (TEOS) and 3-aminopropyl triethoxysilane (APTS) was used as silicon precursor to form relatively thick silica shell. The reaction was triggered by the penetration of APTS from oil-continuous phase into the aqueous phase and the silica shell formed as both TEOS and APTS hydrolyzed and polymerized after diffusing through the W/O interface. The growth of the shell layer was believed to be an outside-in mode. The mannitol crystal was well sealed inside the silica capsule under an optimized condition and the leakage was successfully avoided. The Mannitol@Silica core–shell capsules own irreversible phase change character in the range of 142.1–166.2°C with latent heat of 147.4J/g.

Fabrication of biconcave discoidal silica capsules and their uptake behavior by smooth muscle cells

Biconcave discoidal silica microcapsules were fabricated by reaction of tetraethoxysilane (TEOS) on biconcave discoidal Ca(OH)2 templates, followed by core removal. The biconcave discoidal morphology of microcapsules was characterized by confocal laser scanning microscopy (CLSM) and transmission electron microscopy (TEM). The thickness of silica capsule shell can be tuned by two methods, “Gradient concentration” method and “Multi-step growth” method. Through the latter one, the shell thickness can be controlled more effectively. Compared with spherical microcapsules, the biconcave discoidal ones were internalized into smooth muscle cells (SMCs) with a slower rate.

Preparation of Micro-/Macroporous Carbons and Their Gas Sorption Properties

Micro-/macroporous carbons (MMCs) were prepared using a hollow mesoporous silica capsule (HMSC) as a sacrificial hard template. The carbonization process after the infiltration of furfuryl alcohol into the template-free HMSC material afforded MMC materials in high yield. The hard template HMSC could be removed by HF etching without deteriorating the structure of MMC. The MMC materials were fully characterized by SEM, TEM, PXRD, XPS, and Raman spectroscopy. The replication processes were so successful that MMCs exhibited a hollow capsular structure with multimodal microporosity. Detailed textural properties of MMC materials were investigated by volumetric <TEX>$N_2$</TEX> adsorption-desorption analysis at 77 K. To explore the gas sorption abilities of MMCs for other gases, <TEX>$H_2$</TEX> and <TEX>$CO_2$</TEX> sorption analyses were also performed at various temperatures. The multimodal MMC materials were found to be good sorbents for both <TEX>$H_2$</TEX> and <TEX>$CO_2$</TEX> at low pressure.

Templated Synthesis and Chemical Behavior of Nickel Nanoparticles within High Aspect Ratio Silica Capsules

One-dimensional transition metal nanostructures are of interest in many magnetic and catalytic applications. Using a combination of wet chemical synthesis, optical (infrared), and structural characterization methods (powder X-ray diffraction, scanning and transmission electron microscopy), we have investigated four paths to access 1D nickel nanostructures: (1) direct chemical reduction of a self-assembled nickel–hydrazine coordination complex, (2) thermal decomposition of the silica encapsulated nickel–hydrazine complex, (3) treatment of the silica encapsulated nickel–hydrazine complex with sodium borohydride followed by thermal annealing, and (4) electroless nickel plating using silica encapsulated nickel seed particles. We find that only route 1, which does not require a silica template, results in the formation of nickel nanorods, albeit some particle aggregation is observed. Routes 2 and 3 result in the formation of isotropic nickel structures under a reducing atmosphere. Route 4 results in heterogeneous nucleation and growth of existing particles only when partial etching of the silica capsule occurs. Detailed examination of the encapsulated nickel particles allows studying the effect of silica surface silanols on the oxidation of encapsulated nickel particles, the presence of nanoparticle–silica support interactions, the sintering mechanism of nickel and nickel oxide particles, and the fate of boride impurities. Nickel/silica nanostructures are strongly magnetic at room temperature.

Nanoreactors for Simultaneous Remote Thermal Activation and Optical Monitoring of Chemical Reactions

We report herein the design of plasmonic hollow nanoreactors capable of concentrating light at the nanometer scale for the simultaneous performance and optical monitoring of thermally activated reactions. These reactors feature the encapsulation of plasmonic nanoparticles on the inner walls of a mesoporous silica capsule. A Diels-Alder cycloaddition reaction was carried out in the inner cavities of these nanoreactors to evidence their efficacy. Thus, it is demonstrated that reactions can be accomplished in a confined volume without alteration of the temperature of the bulk solvent while allowing real-time monitoring of the reaction progress.

Formation mechanism of highly luminescent silica capsules incorporating multiple hydrophobic quantum dots with various emission wavelengths

A synthesis process was reconsidered for encapsulating hydrophobic quantum dots (QDs) into silica capsules with high photoluminescent (PL) efficiency. The process comprises three steps: silanization of QD surfaces, seed formation by assembly of the QDs, and coating of the QD seeds with a silica shell. Analysis of the encapsulation mechanism enabled this process to be adapted for application to CdSe-based core–shell QDs with various organic ligands such as oleic acid and with various emission wavelengths. Formation of the seeds is the key step in synthesizing the silica capsules, so that they have high PL efficiency. Due to the differences in QD size and in the affinity of the ligands on their surfaces, the concentration of QDs used in the synthesis must be optimized to maximize emission efficiency. Contrary to an initial assumption, several ligands remained on the QD surfaces even after the QDs were transferred from organic solution to water. This greatly affected the size and PL efficiency of the seeds. Judicious selection of the conditions for seed and silica capsule synthesis resulted in seeds with PL efficiency greater than 70% and in silica capsules encapsulating multiple CdSe/CdZnS QDs with PL efficiency as high as 41%. Silica capsules incorporating QDs with various emission peak wavelengths from green to red were also prepared. The process presented serves as a guideline for encapsulating various types of hydrophobic QDs into silica capsules for biological tagging applications.

Topological Transformation of Thioether-Bridged Organosilicas into Nanostructured Functional Materials

The strong interest in nanostructured functional materials has motivated the scalable production of high quality mesoporous silicas and carbonaceous materials. Although many approaches have been explored for this goal, it is highly desired and still remains a challenge to develop a straightforward strategy for simple and cost-effective fabrication of nanostructured functional materials. Here we demonstrate a simple sol–gel preparation of bis[3-(triethoxysilyl)propyl]tetrasulfide-based organosilica nanostructured materials and their topological transformations, through which porous spherical silica or carbon and hollow silica or carbon capsule are synthesized. As a representative application, the hollow carbon capsule is employed as a catalyst support for dispersion of high loading of Pt, which exhibits much higher catalytic activity toward oxygen reduction reaction than other porous carbon materials prepared in this work due to its larger surface area and mesoporous volume, particularly the unique archite...

New mesoporous silica/carbon composites by in situ transformation of silica template in carbon/silica nanocomposite

Hard template-based fabrication of mesoporous carbon unavoidably goes through the removal process of the template to generate template-free carbon replica, including troublesome disposal of template waste often accompanied by toxic etchant, which not only increases the fabrication cost of materials but also raises serious environmental concerns. As a novel strategy to overcome such problem, a direct in situ synthesis approach using silica waste in carbon/silica nanocomposite as a silica source and cetyltrimethylammonium bromide as a porogen under basic condition is reported in this study for the generation of a new composite composed of mesoporous MCM-41 silica and hollow carbon capsule. The resultant MCM-41/carbon capsule composite offers a 3-D interconnected multimodal pore system, which discloses a wide pore range of ordered uniform mesopores (ca 2.3 nm) resulting from MCM-41 silica and disordered uniform mesopores (ca 3.8 nm) and macropores (ca 300 nm) from hollow mesoporous carbon, respectively. The composite has a high specific surface area (ca 909 m2/g) and large pore volume (ca 0.73 cm3/g). The in situ transformation approach of silica waste into valuable mesoporous silica is considered as a promising scalable route for efficient new multi-functional composites useful for a wide range of applications such as adsorption of volatile organic compounds and radioactive wastes produced in a nuclear facility.

Stimuli-Free Auto-Modulated Material Release from Mesoporous Nanocompartment Films

Mesoporous nanocompartment films composed of silica particles and hollow silica capsules were prepared by the layer-by-layer (LbL) technique. The resulting mesoporous nanocompartment films possess special molecular encapsulation and release capabilities so that stimuli-free auto-modulated stepwise release of water or drug molecules was achieved through the mesopore channels of robust silica capsule containers embedded in the film. Stepwise release of water was reproducibly observed that originates in the non-equilibrated rates between evaporation of water from the mesopore channels to the exterior and the capillary penetration of water from container interior to the mesopore channels. It was generalized to evaporation of other substances, fragrances, limonene. Application was also tested in the controlled release of the sunscreen UV-absorber (UV-S1) for circumvention of its rapid dissolution in water and prolongation of its prophylactic effect toward harmful ultraviolet radiation. UV-S1 was successfully entrapped within the mesoporous nanocompartment films and was released in a prolonged stepwise mode. The nanocompartment films developed in this research are promising materials for drug delivery since they allow gradual release of therapeutic agents with likely related improvements in their efficacy.

A method of heat-treatment of near γ-TiAl to enhance oxidation resistance by the formation of a Ti5Si3 layer

It is shown that the heat-treatment of near γ-TiAl in a silica capsule under low oxygen partial pressure at 1283 K for 50 h produces a thin (1–2 μm) Ti5Si3 external film on the near γ-TiAl specimen. This layer confers significant improvements in oxidation resistance for at least 500 h in air at 1173 K. The silicide layer is thought to be produced as the result of gaseous transport of SiO from the walls of the silica vessel to the specimen surface and its reaction there. However, the production of SiO requires that particularly low values of oxygen partial pressure develop within the silica capsule. Mechanisms whereby this can be achieved are discussed but the likely process involves the solution of oxygen within the specimen. The outcome is that the heat-treatment procedure represents a cost-effective CVD-type process for enhancing the oxidation resistance of near γ-TiAl intermetallics.

A method of heat-treatment of near γ-TiAl to enhance oxidation resistance by the formation of a Ti5Si3 layer

Abstract It is shown that the heat-treatment of near γ-TiAl in a silica capsule under low oxygen partial pressure at 1283 K for 50 h produces a thin (1–2 μm) Ti 5 Si 3 external film on the near γ-TiAl specimen. This layer confers significant improvements in oxidation resistance for at least 500 h in air at 1173 K. The silicide layer is thought to be produced as the result of gaseous transport of SiO from the walls of the silica vessel to the specimen surface and its reaction there. However, the production of SiO requires that particularly low values of oxygen partial pressure develop within the silica capsule. Mechanisms whereby this can be achieved are discussed but the likely process involves the solution of oxygen within the specimen. The outcome is that the heat-treatment procedure represents a cost-effective CVD-type process for enhancing the oxidation resistance of near γ-TiAl intermetallics.