Microporous Silica Research Articles

One-step immobilization of tungsten oxide on microporous silica surface as a photocatalyst for water pollutant removal

Improving photocatalytic properties of semi-conductor materials and Band-gap engineering are a major challenge. Herein, we report, a successful immobilization of tungsten oxide and tungstite on the surface of microporous silica by simple one-step method. The surface area decreased from 607 to 588 m 2 /g after immobilization due to the loading of tungsten oxide species on silica pores. While, the band-gap energies were found to be 2.21, 2.41 eV for SiO 2 /WO 3 and SiO 2 /WO 3 –C, respectively. Thereafter, the photocatalytic activity of the composites was studied through the oxidative degradation of sulfamethazine under UV–visible light irradiation, SiO 2 /WO 3 exhibited relatively good stability and reusability after four cycles of photocatalytic experiment in respect to the calcinated sample. The high photocatalytic activity and recyclability of the non-calcinated sample are attributed to the presence of water molecules in tungstite structure, assuming that tungsten oxide species are bonded to microporous silica via hydrogen bond interaction. • One-step immobilization of Tungsten trioxide on the surface of mesoporous silica. • The effect of tungstite and tungsten trioxide structures on the photocatalytic activity. • The role of intercalated water on the stability and reusability of the photocatalyst.

High-pressure Helium as a Template for the Formation of a Microporous Silica Structure

The modeling of various modes of formation of microporous silica using high-pressure helium was carried out by the methods of molecular dynamics. It is shown that by controlling the helium pressure in the process of quenching the silica melt, the structure of the obtained glasses can be changed continuously and within wide limits. The density of the obtained glasses varies in the range from 2.2 to 1.5 g / cm3 and the Ostwald solubility coefficients for helium and neon are more than an order of magnitude

CO2 capture and CO2/CH4 separation by silicas with controlled porosity and functionality

Microporous, mesoporous and hydrophobic silica materials with high specific surface area are obtained by an easy and cheap sol–gel synthesis. The effect of pore size and of water content on gas adsorption and separation are investigated. We also identified the relative amounts of different types of water in the porous silica, around 25% and 75% for bound and free water. The kinetics of rehydration is extremely slow, 60% recovery after 4 days implying that the material can be used as is over several hours. Adsorption isotherms of pure gaseous CO2 and CH4, and of their mixtures at different pressures, show that among the materials synthesised, the microporous hydrophilic silica exhibits the best performance in terms of CO2 adsorption capacity (2.8 mmol.g−1) and a separation factor over 10 at low CO2 content and low pressure. Both properties are highly sensitive to the presence of residual water and to terminal chemical groups. This work highlights the possibility to develop competitive and cheap silica materials that could be scaled up to industrial uses.

Comparison of Hydrogen Permeation and Structural Properties of a Microporous Silica Membrane and a Dense Bace0.9y0.1o3-Δ (Bcy) Perovskite Membrane

Comparison of Hydrogen Permeation and Structural Properties of a Microporous Silica Membrane and a Dense Bace0.9y0.1o3-Δ (Bcy) Perovskite Membrane

Monodisperse fusiform microporous silica formed by evaporation-induced self assembly of polyamino acid copolymer template

Monodisperse fusiform microporous silica formed by evaporation-induced self assembly of polyamino acid copolymer template

Cyclized conjugated microporous polymer-coated silica nanospheres as fluorescent sensors for iron (III) and chromium (III)

Schiff-base condensation reaction was often used to prepare conjugated microporous polymers (CMPs). However, due to the relatively unstable imine bond in the product, the application of CMPs in some strong acid-base environments was limited. Therefore, it was necessary to further strengthen the stability of CMPs by “bottom-up” strategy. For this purpose, three kinds of cyclized CMPs (x-CMP x = m, p, bi) were successfully prepared by Schiff-base reaction followed by an acid-catalyzed in situ cyclization with 1,5,9-triamine-triphenylene (TATP) and m-phthalaldehyde (m-PA), p-phthalaldehyde (p-PA) or 4,4'-biphenyldicarboxaldehyde (bi-PA) as precursors. The in situ cyclization at the imine bond was demonstrated by X-ray photoelectron spectroscopy and Raman spectroscopy. Because cyclized CMPs were amorphous powder, their dispersity were not ideal, which affects them further applications. Therefore, through a “one-pot” method, these CMPs were also coated onto silica nanospheres, assigned as x-CMP@SiO2 (x = m, p, bi), exhibiting core–shell structure and excellent monodispersity. Due to the difference dispersity of three x-CMP@SiO2 (x = m, p, bi) in aqueous solution, the fluorescence quantum yields were different, which were 15.3%, 14.4% and 11.2%, respectively. As fluorescent sensors, three cyclized x-CMP@SiO2 (x = m, p, bi) could selectively generated fluorescence quenching response to Fe3+ and Cr3+ in aqueous solution. Compared with amorphous CMPs, the resulting CMP@SiO2 nanomaterials not only improved the dispersity and mechanical strength, but also offered the convenience for subsequent applications. It is expected this feasible method would facilitate CMPs to be widely explored in fluorescence detection and other research fields.

CO2 adsorption capacities of amine-functionalized microporous silica nanoparticles

Efforts on CO2 capture have intensified as climate change compromises ecosystems and biodiversity. Therefore, it is crucial to develop different methods for CO2 sequestration to improve solid sorbent capabilities (NPs). To this end, the surface of 200-nm silica nanoparticles (SiO2NPs) was covalently anchored with aminated ligands, 3-aminopropyltriethoxysilane (APTES), poly(amidoamine) dendrimers (PAMAM) and a short peptide comprising two lysine units, aiming for CO2 adsorption over a wide range of pressures. Our goal was to explore the influence of functional chemical groups (attached to the SiO2NPs) on CO2 sequestration. The observed results showed that at low and high CO2 gas pressure conditions, typical APTES functionalized SiO2Np surpassed the CO2 adsorption capacities of dendritic and peptide-based nanoparticles bearing amine-polymer functionalities, a remarkable effect that was investigated in this work. In addition, a convenient and facile method to decorate and quantify SiO2 nanoparticles with PAMAM and a short peptide is reported.

Enhanced Refractive Index Sensitivity through Combining a Sol-Gel Adsorbate with a TiO2 Nanoimprinted Metasurface for Gas Sensing.

We combine a gas-adsorbent microporous hybrid silica layer and a dense TiO2 Mie resonator array (metasurface), both obtained by sol-gel deposition and nanoimprint lithography, to form nanocomposite systems with high sensitivity for refractive index (RI) variations induced by gas adsorption. Using optical transduction based on direct specular reflection, we show spectral shifts of 4470 nm/RIU corresponding to 0.2 nm/ppm gas (air concentration) and reflection intensity changes of R* = 17 (R/RIU) and 0.55 × 10-3 R/ppm (air concentration). The metasurface is composed of hexagonally arranged TiO2 nanopillar arrays, whereas the surrounding sensitive material is a class II microporous hybrid silica, containing methyl and phenyl covalently bonded organic functions. This hybrid layer shows efficient adsorption capability of volatile organic molecules such as isopropanol, which is used to induce slight variations of RI around the TiO2 antennas. Specular reflectance variations at 45° incidence and refractive index measurements are performed using a spectroscopic ellipsometer. The presence of the titania metasurface enhances the signal by almost an order of magnitude with respect to the 2D counterpart (simulated as an effective medium approximation) and is attributed to the antenna effect, enhancing the interaction of the confined electromagnetic wave with the sensitive microporous medium. This sol-gel nanocomposite system presents many advantages such as high throughput and low-cost elaboration of elements and a high chemical, mechanical, and thermal resistance, ensuring high stability as a potential gas-sensitive nanocomposite layer for long periods. This work is a case study of improving the sensitivity of sol-gel gas-sensitive materials in optical transduction, which will be exploited in further works to develop artificial noses.

Preparation of core‐shell microporous organic polymer‐coated silica microspheres for chromatographic separation and N‐glycopeptides enrichment

Through a "one-pot" strategy, a layer of microporous organic polymer was coated onto the surface of monodisperse amino-functionalized silica microsphere via amino-aldehyde condensation reaction with core-shell structure. The change in chemical structure of material before and after modification was determined by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. Due to existence of a large number of amino and aldehyde groups in microporous organic polymer shell, the water contact angle decreased from 56.8° (silica microspheres) to 34.7° (microporous organic polymer-coated silica microspheres). Based on these properties, microporous organic polymer-coated silica microspheres were employed as the stationary phase for capillary liquid chromatography and successfully offered baseline separation of polar small molecules. Additionally, the material could also be served as the sorbent of hydrophilic interaction chromatography to enrich glycopeptides from human serum digest. A total of 470 unique N-glycopeptides and 342 N-glycosylation sites mapped to 112 N-glycosylated proteins were unambiguously identified from 2μL of human serum, exhibiting a promising application prospect of microporous organic polymer-coated silica microspheres in the pretreatment of proteomics samples.

Entrapment of chlorophyll from Chlorella vulgaris and Chlorella protothecoides into microporous silica synthesized by a sol-gel method

This study presents results of the preparation, absorption and emission characterizations of chlorophyll samples extracted from green microalgae, based on the importance of this pigment and its optical properties. In this work, we characterized extracts containing chlorophyll from green microalgae of the genus Chlorella (C. vulgaris and C. protothecoides) via absorption and emission spectroscopies. The present results were compared with those of chlorophyll extracted from grass, previously reported. Microalgal chlorophyll samples were covalently bonded to the pore surface of organo-modified silica xerogels for a major spectroscopic analysis. Our findings indicate that the composition of green microalgal extracts corresponds mainly to chlorophyll a with a minimal amount of β-carotene. UV-VIS, IR absorption and UV-VIS emission spectra of the samples displayed the typical bands of chlorophyll a, and some other bands ascribed to β-carotene. Both the obtained absorption and emission spectra identify the algae chlorophyll bands and are unique. An effect of a radiative energy transfer mechanism between the silica matrix and the microalgal chlorophyll was observed as reabsorption bands in the emission spectra, and this effect was more evident in the C. vulgaris sample with respect to C. protothecoides.

A hollow in hollow nanoreactor of H-PtCu@SiO2 for the selective transfer hydrogenation

Hollow metal nanoparticles have attracted great interest in heterogeneous catalysis research due to their unique structures as nanoreactors. Here, we report hollow PtCu nanoparticles encapsulated in microporous silica shells (H-PtCu@SiO2), which can serve as the nanoreactor with high catalytic activity and high stability. The H-PtCu@SiO2 nanoreactor shows the state-of-the-art catalytic performance for the transfer hydrogenation of benzonitrile to dibenzylamine, which achieves up to 100% conversion and 99% selectivity in only 0.5 h. The void-confinement effect of H-PtCu@SiO2 is crucial for the outstanding catalytic performance by encaging the reactants in the nanoreactor. The computation demonstrates the limiting diffusion effect of the silica shell toward the ammonia borane, thus reduces the concentration of reductant species and prolongs the lifetime of the intermediate imine to improve the selectivity of secondary amine. Moreover, the silica shells can effectively enhance the catalytic stability of the H-PtCu@SiO2 nanoreactor.

Engineering the Surface Pattern of Microparticles: From Raspberry-like to Golf Ball-like.

Control of the shape and uniformity of colloid particles is essential for realizing their functionality in various applications. Herein, we report a facile approach for the synthesis of narrowly dispersed anisotropic microparticles with well-defined raspberry-like and golf ball-like surface patterns. First, we demonstrate that hybrid raspberry-like particles can be achieved through a one-pot polymerization method using glycidyl polyhedral oligomeric silsesquioxane (GPOSS) and pentaerythritol tetra(3-mercaptopropionate) (PETMP) as monomers. Varying the polymerization parameters such as catalyst loading, monomer concentration, and the molar ratio of monomers, we are able to regulate the sizes and surface protrusion numbers of these raspberry-like microparticles. The formation mechanism is attributed to a competition balance between thiol-epoxy reaction and thiol-thiol coupling reaction. The former promotes rapid formation of large core particles between PETMP and GPOSS droplets (which can serve as core particles), while the latter allows for generation of surface protrusions by PETMP self-polymerization, leading to the formation of raspberry-like surface patterns. Based on the different POSS contents in the surface protrusions and cores of the raspberry-like microparticles, we demonstrate that they can be used as precursors to produce microporous silica (sub)microparticles with golf ball-like morphology via pyrolysis subsequently. Overall, this work provides a facile yet controllable approach to synthesize narrowly dispersed anisotropic microparticles with diverse surface patterns.

Mesoporous Silica Nanoparticles of Hydroxyurea: Potentially Active Therapeutic Agents

Background: Present malignant cancer medicines have the advantage of magnetic nanoparticles as delivery carriers to magnetically accumulate anticancer medication in malignant growth tissue. Aim: In the present investigation, a silica nanoparticles (MSNs) stacked with hydroxyurea were combined and was optimized for dependent and independent variables. Methods: In this study, microporous silica nanoparticles stacked with neoplastic medication were prepared through emulsification followed by the solvent evaporation method. Prepared MSNs were optimized for dependent and independent variables. Different formulations were prepared with varying ratios of polymer, lipid and surfactant which affect drug release and kinetics of drug release pattern. The obtained MSNs were identified by FTIR, SEM, drug entrapment, in-vitro drug release, drug release kinetics study, and stability testing in order to investigate the nanoparticle characteristics. Results: The percentage drug entrapment of the drug for the formulations F1, F2, F3 was found to be 27.78%, 65.52% and 48.26%. The average particle size for F2 formulation was found to be 520 nm through SEM. The cumulative drug release for the formulations F1, F2, F3 was found to be 64.17%, 71.82% and 32.68%. The formulations were found to be stable which gives controlled drug delivery for 6 hours. Conclusion: From the stability studies data it can be culminated that formulations are most stable when stored at lower temperature or in refrigerator i.e. 5˚C ± 3˚C. It can be concluded that MSN’s loaded with hydroxyurea is a promising approach towards the management of cancer due to its sustained release and less side effects.

Hydrothermal stability of fluorine‐induced microporous silica membranes: Effect of steam treatment conditions

AbstractA fluorine‐SiO2 membrane was prepared using triethoxyfluorosilane (TEFS) as a Si precursor, and its hydrothermal stability was evaluated. The TEFS membrane calcined at 750°C had fewer Si‐OH and Si‐F groups in its network structure and showed H2 permeance that was greater than 10−6 mol m−2 s−1 Pa−1 with H2/N2 and N2/SF6 permeance ratios of 10 and 210, respectively. This membrane performance was relatively stable under the temperature (< 500°C) used for steam treatment, regardless of the steam partial pressure (30, 90 kPa). On the other hand, when the steam treatment temperature was increased beyond 500°C, gas permeance decreased significantly and the membrane became highly selective for He and H2 over smaller molecules (He/N2: > 600, H2/N2: > 100). The relationship between the activation energy of H2 and the permeance ratios (He/H2, He/H2O, H2/H2O) of a TEFS‐derived membrane under steam treatment higher than 600°C resulted in a network pore size that approximated in conventional microporous SiO2 membranes.

Effect of Water Saturation on the Electrical Conductivity of Microporous Silica Glass

The electrical conductivity of porous dielectric materials saturated with water is usually determined by the bulk water conduction. However, the unsaturated state can be affected by a water film covering the unsaturated grain surface. Thus far, a few studies have been conducted on the study of the electrical conductivity with respect to water film covering the grain surface. In this study, the electrical conductivities of the Shirasu porous glass with three different uniform pore sizes (1.0, 0.5, and 0.2 $$\upmu \mathrm{m}$$ ) soaked in various NaCl solutions (0.001, 0.01, and 0.1 $$\mathrm{mol} {\mathrm{L}}^{-1}$$ ) were measured using an impedance meter while being dried at different water saturations. The resulting complex conductivities were fitted by a three-component Cole–Cole model to obtain Cole–Cole parameters. The conductivity values in these parameters were compared with the calculated conductivity values using tortuosities of surface and bulk conduction obtained from two different circuit models. The parallel model of bulk and surface water conduction could not reproduce accurate experimental results; however, the parallel plus series model, including the series connection of water film and bulk water around the meniscus, produced better results. This new model is expected to provide an improved quantitative evaluation of the electrical conductivity of unsaturated porous materials.

Effect of different silica coatings on the toxicity of upconversion nanoparticles on RAW 264.7 macrophage cells.

Upconversion nanoparticles (UCNPs), consisting of NaYF4 doped with 18% Yb and 2% Er, were coated with microporous silica shells with thickness values of 7 ± 2 and 21 ± 3 nm. Subsequently, the negatively charged particles were functionalized with N-(6-aminohexyl)-3-aminopropyltrimethoxysilane (AHAPS), which provide a positive charge to the nanoparticle surface. Inductively coupled plasma optical emission spectrometry (ICP-OES) measurements revealed that, over the course of 24h, particles with thicker shells release fewer lanthanide ions than particles with thinner shells. However, even a 21 ± 3 nm thick silica layer does not entirely block the disintegration process of the UCNPs. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays and cell cytometry measurements performed on macrophages (RAW 264.7 cells) indicate that cells treated with amino-functionalized particles with a thicker silica shell have a higher viability than those incubated with UCNPs with a thinner silica shell, even if more particles with a thicker shell are taken up. This effect is less significant for negatively charged particles. Cell cycle analyses with amino-functionalized particles also confirm that thicker silica shells reduce cytotoxicity. Thus, growing silica shells to a sufficient thickness is a simple approach to minimize the cytotoxicity of UCNPs.

Role of microporous Janus silica nanosheets in the assembly of ultra-small Ag nanoparticles with high catalytic activity.

As an emerging nano-silica material, two-dimensional (2D) silica nanosheets (SiNSs) have been derived from natural layered kaolinite and applied as a substrate for the highly efficient and dispersed assembly of functional materials, such as noble metal nanoparticles (NPs). In this work, the nature of SiNSs and its particular role in the assembly of ultra-small AgNPs via the reduction-growth method using a Sn(ii) reductant were further researched. By adjusting the Sn(ii) content x (1.2-6.0 wt%), it was found that the surface areas of the Sn(ii)-activated SiNSs (xSn-SiNSs) had almost no change, and their reducibility did not fully increase with the increased x values, due to the saturated adsorption of the Sn(ii) reductant by the surface hydroxyls of the SiNSs, which subsequently caused the decrease of the adsorbed Ag(i) precursor by the hydroxyls on the xSn-SiNSs (x≥ 4.8 wt%). Accordingly, the sizes and loading amounts of the resultant AgNPs mainly showed a similar trend of increase before decrease. Furthermore, the regulated AgNPs with diverse mean sizes ranging from 1.71 to 2.16 nm were all ultra-small (more than half were nanoclusters < 2 nm) and highly dispersed, owing to the high electrostatic attraction of the negatively charged hydroxyls and the anchoring effect of the micropores on the hydroxylated surface of the Janus SiNSs. Therefore, the Ag/xSn-SiNSs nanocomposites displayed better catalytic properties for 4-nitrophenol reduction than most Ag-based supported catalysts, and the optimal Ag/2.4Sn-SiNSs catalyst exhibited quick reaction within 80 s and turnover frequency (TOF) of 3.34 min-1. It reveals the key role of negatively charged surface hydroxyls and micropores of Janus SiNSs in the highly efficient and dispersed assembly of functional materials.

Fluorescent Nanocomposites: Hollow Silica Microspheres with Embedded Carbon Dots.

Intrinsically fluorescent carbon dots may form the basis for a safer and more accurate sensor technology for digital counting in bioanalytical assays. This work presents a simple and inexpensive synthesis method for producing fluorescent carbon dots embedded in hollow silica particles. Hydrothermal treatment at low temperature (160 °C) of microporous silica particles in presence of urea and citric acid results in fluorescent, microporous and hollow nanocomposites with a surface area of 12 m2 /g. High absolute zeta potential (-44 mV) at neutral pH demonstrates the high electrosteric stability of the nanocomposites in aqueous solution. Their fluorescence emission at 445 nm is remarkably stable in aqueous dispersion under a wide pH range (3-12) and in the dried state. The biocompatibility of the composite particles is excellent, as the particles were found to show low genotoxicity at exposures up to 10 μg/cm2 .

Correction: Correction: Multi-scale microporous silica microcapsules from gas-in water-in oil emulsions.

Correction for 'Correction: Multi-scale microporous silica microcapsules from gas-in water-in oil emulsions' by Zenon Toprakcioglu et al., Soft Matter, 2020, 16, 3586-3586, DOI: .

Ultrafast Synthesis of Silica-Based Molecular Sieve Membranes in Dielectric Barrier Discharge at Low Temperature and Atmospheric Pressure.

Microporous silica membranes have shown promise as potential candidates for energy-efficient chemical separation. Herein, we report the ultrafast synthesis of silica membranes, on the order of minutes, in atmospheric-pressure, low-temperature plasma. Direct deposition in the discharge region of atmospheric-pressure plasma enables the immediate formation of a thin silica layer on a porous substrate. The plasma-deposited layer had a thickness of ∼13 nm and was confined to the immediate surface of the substrate. With an increase in deposition temperature, we observed an increase in the inorganic nature of the plasma-deposited layer and simultaneous improvement in the membrane performance. Consequently, the resulting membranes exhibited outstanding permeance for small-sized gas molecules, such as H2 (>10-6 mol m-2 s-1 Pa-1), with a high H2/SF6 permeance ratio of ∼6300, providing a nonthermal alternative for the fabrication of silica-based membranes.