Silica Structure Research Articles

Novel Aerosol‐Based Approach toward Mesoporous Silica Nanoparticles

This study introduces a novel gas‐phase method for the synthesis of mesoporous silica nanoparticles (MSNs). The method is a two‐step templating approach by first forming silicon‐coated carbon structures in a hybrid microwave‐plasma/hot‐wall reactor followed by an annealing step to produce mesoporous silica with distinct nanostructure and porosity. Two different (sacrificial) carbonaceous templates have been prepared (plasma reactor) and coated (hot‐wall reactor), 2D few‐layer graphene (FLG) flakes and soot‐like fractal aggregates. Results show that the wall thickness of the porous silica structures can be adjusted by changing the concentration of the silicon precursor (monosilane). High monosilane concentrations, however, result in solid silica particles after annealing. Using soot‐like particle templates permitted to control of the shell thickness of the hollow porous particles, while the FLG template results in ultrathin silica sheets after heat treatment. The pore volume and specific surface area increase up to 263 m2 g−1 and 0.6 cm3 g−1, respectively, by the formation of hollow porous particles. An adsorption study on carbamazepine reveals up to ≈86% removal. The gas‐phase aerosol‐based template method presented here offers scalability and versatility, and it is capable of producing MSNs with a controlled structure and porosity by modifying the carbonaceous templates.

Magnetic Mesoporous Silica Nanoparticles Functionalized with 5,5′-Dithiobis(2-Nitrobenzoic Acid) for Highly Efficient Removal of Organic Dyes from Contaminated Water

The removal of organic pollutants has become an increasingly important environmental concern. In recent years, there has been significant research into the use of nanomaterials for removing organic dyes in single-component systems. In this study, magnetic mesoporous silica nanoparticles (magnetic MSNs) were prepared with an average particle size of 170 nm. Iron oxide nanoparticles (20 nm) were embedded within the mesoporous silica structure. These nanoparticles were functionalized with amine, derivatized with thiol, and then reacted with 5,5′-dithiobis-(2-nitrobenzoic acid) (DTNB). The presence of DTNB molecules attached to the surface was confirmed by FTIR spectra, as evidenced by the appearance of peaks at ∼1528 cm−1 and ∼1365 cm−1. The nanoadsorbents demonstrated high removal efficiency for bromothymol blue (BT) and methyl orange (MO) at a pH below 5, with a maximum adsorption capacity of 139.27 mg/g and 101.62 mg/g for BT and MO, respectively. The linear regression coefficient value suggested that the adsorption of BT and MO onto magnetic MSNs-DTNB followed the Langmuir isotherm and second-order process. Overall, these findings suggest that magnetic MSNs-DTNB could be a promising nanoadsorbent for removing organic pollutants from contaminated water sources.

Anomalous Diffusion of Helium and Neon in Low-Density Silica Glass.

The diffusion properties of low-density non-porous silica glasses (expanded silica glasses) were researched with the aim of searching for the molecular structure of membrane materials intended for the effective separation of helium-neon gas mixtures. It has been shown on a large number (84) of computer models of such glasses that there are molecular structures of silica in which various helium and neon diffusion mechanisms are simultaneously implemented: superdiffusion for helium and subdiffusion for neon. This makes it possible to significantly (by 3-5 orders of magnitude) increase the helium permeability of such glasses at room temperature and maintain a high selectivity for the separation of helium and neon (at the level of 104-105) at the same time.

A Polished-D-Shape SPR-Based Photonic Crystal Fiber Sensor with High Sensitivity for Measuring Refractive Index

In the correspondence, a novel polished-D-shape photonic crystal fiber sensor structure on the basis of surface plasmon resonance is proposed for measuring analyte refractive index. With the help of the finite element method, sensing performances of the structure have been analyzed through numerical simulations along with a step-by-step optimization . In this design, different capillaries are gathered and processed to form a D-shape silica structure and nano-scale gold material is coated on the flattened surface. With utilization of a thin gold film and solid silica background, the resonance effect is excited and the loss curve has red shift along with an increase in refractive index, which is applied for sensing. From the simulation and calculation results, the final sensor structure achieves the optimal performance where values of maximum and average sensitivity reach 32,000 and 12,167 nm/RIU along with a sensing coverage of refractive index from 1.26 to 1.32. Also, the proposed design obtains a range of resonant wavelength from 1810 to 2540 nm. We believe the proposed sensor can be a potential candidate for organic and biological detection and related applications.

Подготовка тетраэтоксисилана для получения сферических частиц кремнезема. Часть 2. Примеси и их влияние на размеры формирующихся глобул

Monodisperse spherical silica particles, as a basis for creating supramolecular 3D matrices, are currently of increasing interest due to the prospects for their wide application in the synthesis of new nanocomposite materials. At the same time, one of main problems of their large-scale synthesis is associated with the unstable behavior of tetraethoxysilane (TEOS) during hydrolysis, which leads both to the deviation of the particles from a given size and their shape from a spherical one. In this paper, on the basis of the study of tetraethoxysilane from various manufacturers, we continued to work on determining factors that can influence the process of hydrolysis of tetraethoxysilane and, as a result, the monodispersity and size of the formed particles, and also other factors. To solve this task, all TEOS samples were studied by various physicochemical methods of analysis, including Fourier IR and Raman spectroscopy, gas chromatography-mass spectrometry. As a result of the studies, we showed that the presence of di- and trisiloxanes in the system did not significantly affect the size of the formed silica particles, while significantly accelerating the rate of formation of silica spheres. Moreover, the presence of methoxyl groups in the initial silane, and an insignificant content of ethanol in the system did not affect the size stability of the formed particles. At the same time, the replacement of part of the ethoxy groups in the initial TEOS by methyl or ethyl groups, as they are not capable of participating in the hydrolysis reaction, largely contribute to the deviation of sizes of the formed silica particles from each other. The results obtained on the effect of impurities on the size of the formed silica globules are important, among other things, for understanding the processes of formation of natural supramolecular structures of silica.

Neodymium upgrading of tin slag using acid leaching and multistage precipitation

Tin metal production in Indonesia increased in 2018 and 2019. As the production of tin metal increases, the production of slag from tin smelting also increases. Tin slag can be further utilized by extracting valuable metals from it, such as rare earth elements (REE). One of the rare earth elements observed in this study is neodymium (Nd). The use of Nd includes the manufacture of Nd-based permanent magnets. According to individual REE oxide demand and production data in the world, the supply of Nd2O3 in the world is experiencing a shortage of 2,025 tons per year. The purpose of this study is to determine the optimal concentration and ratio of solids to nitric acid in tin slag leaching after the alkaline fusion process and the pH of Nd precipitation. Alkaline fusion as a pre-treatment step to open the silica structure in the slag fusion was carried out for 2 h at 700 °Cwith a ratio of NaOH: slag (gram: gram) = 2:1 to produce frit, which will be leached using water. The residue from water leaching was followed by nitric acid leaching with a concentration variation of 1.75 M, 2.25 M, 2.75 M, 3.25 M, and 3.75 M, then continued with a solid percentage variation of 8%, 11%, 15%, 20%, and 26%. The nitric acid leaching filtrate was precipitated with ammonia at pH 6, 8, and 10. The results obtained were a percent of Nd extraction of 65.172% obtained at a concentration of 3.25 M, a solid percent ratio of 15% with a temperature of 60 °C, a grain size of −200 + 325 mesh, a stirring speed of 250 rpm, and a leaching time of 60 min. Nd deposition efficiency occurred at a pH 6 of 47.79%. Increased Nd content from 1.036% to 3.257%.

Mullite photonic glasses with exceptional thermal stability for novel reflective thermal barrier coatings

Thermal barrier coatings are essential materials systems for insulating and protecting substrates exposed to high temperatures. In such systems, the heat transfer has three possible paths: conduction, convection and irradiation. The higher the operating temperature, the more important it is to control or protect against the radiative component, since the radiative heat flux becomes non-negligible. The radiation can be controlled by the use of ceramic-based photonic nanostructures, namely photonic crystals and photonic glasses, creating so-called reflective thermal barrier coatings. In this work, mullite inverse photonic glasses (PhG) have been produced by thermally induced reaction on sol–gel-based silica structures coated with nanometric films of Al2O3 by atomic layer deposition. The conversion to mullite was carried out following a two-stage heat-treatment. The pre-annealing associated with the further mullite formation results in an excellent structural stability of these PhGs up to 1500 °C, being able to retain their high reflectivity in the near infrared range. Therefore, this structure can be considered for next-generation reflective thermal barrier coatings.Graphical abstract

Removal of fipronil by advanced oxidative processes using sulfite activated by cobalt immobilized on silica

Sulfite auto-oxidation catalyzed by cobalt complexed with ammonia deposited on silica (CoNSi) was used to generate sulfate radicals. The material was characterized by ATR–FTIR, suggesting that the silica structure did not change, and SEM–EDS, indicating an uniform dispersion of cobalt across the material surface according with XRD results. BET analysis provided information on a mesoporous material (type IV isotherm) with regular morphology (H1 hysteresis). The DSC analysis showed that CoNSi is thermally stable under the studied conditions. Quantitative analysis of Fipronil (FIP) was performed by HPLC-DAD, where the applied method was selective and linear. The Box–Behnken experimental design (BBD) method was used to define the best condition for removing the analyte in water. It was found that in 60 min, 76% removal of 1.8 mg L−1 of FIP was reached by adding 0.30 g of the material and 0.30 g of the sulfite in a solution under stirring, aeration, pH 8.0, and room temperature and protected from radiation. However, analysis of cobalt leaching into the solution by FAAS showed a small amount of the metal (0.44 mg L−1) informing that the synthesis of the material must be improved.

Transparent and Robust Superhydrophobic Structure on Silica Glass Processed with Microstereolithography Printing.

Silica glass devices are widely used due to their exceptional physical and chemical properties. However, prolonged usage may result in abrasion and contamination of silica glass devices, adversely affecting the service life. One of the most effective solutions to this issue is surface modification, in which superhydrophobicity with high transmittance and mechanical robustness is highly desired. Inspired by the concept of protective armor, we proposed a novel approach for the direct integration of robust and transparent superhydrophobic structures on silica glass. In this method, microstereolithography synergistic heat treatment processes are used to create a micrometer-scale biomimetic frame on the surface of silica glass and then filled with in situ deposited nanoparticles. The superhydrophobicity of the surface can be obtained through the nanoparticles, and the biomimetic frame can protect the surface from direct contact with external objects to achieve durability. This process allows the preparation of superhydrophobic silica structures on the silica device surface at temperatures below its melting point, which prevents any damage to the devices during the heat treatment. Moreover, up to 90% transmittance does not affect the performance of silica devices. The composite structure maintains a contact angle of over 150° after multiple abrasion tests, verifying the mechanical robustness. This innovative process paves the way for forming a high mechanical robustness and excellent transmittance protective layer on silica glass devices, which expands the application field.

Porous silica composites as efficient adsorbents for dye removal from aqueous solution

This study aimed to analyze the feasibility of removing Alizarin red S (ARS) used as model pollutant from aqueous solutions using the preparative porous silica composites (PSCs) as adsorbents which were prepared via hydrothermal approach. The physicochemical properties of materials were characterized by means of Transmission electron microscope (TEM), Scanning electron microscope (SEM), Energy dispersive spectrometer (EDS), Brunauer-Emmett-Teller (BET) method, Barret-Joyner-Halenda (BJH) method, Fourier Transform Infrared Spectrometer (FTIR) and X-Ray Diffractometer (XRD). PSCs possessed the specific surface area were 731.6 m2/g, 420.9 m2/g, 294.6 m2/g, respectively. The presence of silica structures was confirmed by FTIR spectra. In order to confirm efficiency of composites as adsorbents and reveal adsorption mechanism, the impacts of pH, contact time, initial ARS concentration, temperature on adsorption were conducted. The adsorption experiment results showed that the adsorption efficiency of ARS onto PSC-3 was better than that of PSC-1 and PSC-2 at pH = 11. Furthermore, the adsorption kinetic models, isotherm models and thermodynamic model were analyzed for comprehensive adsorption process. The maximum adsorption capacity of PSC-3 for ARS was 43.1 mg/g. The pseudo-second-order kinetic model and Sips isotherm model were more suitable for experimental results. The adsorption process was endothermic according to the adsorption thermodynamic model. The free energy of adsorption required for ARS onto PSCs was less than 8 kJ/mol, indicating physical adsorption. What’s more, PSC-3 possessed advantages of higher adsorption capacity and shorter equilibration time. Overall, these results made it potentially applicable as an effective adsorbent for ARS dye from effluent.

Engineering more sustainable catalysts based in ecological and economic synthesis routes from renewable raw material: Novel mesoporous silicas for remediation technologies

Iron modified mesoporous silica structures were achieved from biomass-derived renewable molding agents (glyceryl monostearate and glycerol) and can become potential substitutes for conventional mesoporous catalysts synthesized from petrochemical-derived precursors. These materials were prepared by different methods (wet impregnation with iron contents of 2.5, 5, 10 and 20% w/w and direct incorporation using a molar ratio Si/Fe = 20) and characterized by XRD, N2 adsorption and desorption isotherms, UVvis-DR and ICP. By using these solid as heterogeneous catalysts in the wet oxidation reaction of the herbicide glyphosate with air under extremely mild reaction conditions (atmospheric pressure and room temperature), herbicide degradation/fragmentation levels of around 70% were achieved. The methodology employed for the synthesis played a key role in the development of the structure and dispersion of Fe species as well as in the stability of the catalytic system. In this way, an advanced technology with low environmental impact for the treatment of a pollutant of great concern at the global level was developed, which adds sustainability to the chemical industry from the use of residual glycerol and/or glyceryl monostearate in the catalyst synthesis.

Effectiveness of polyethylene glycol-coated silica on ions adsorption in industrial wastewater

The effect of coating silica with polyethylene glycol on the adsorption of iron and phosphate ions in industrial wastewater was investigated. Variable factors were temperature and time of coating, PEG concentration, and PEG to silica ratio. Infrared spectroscopy and scanning electron microscopy were used to evaluate the chemical structure and morphology of PEG-coated silica. Optimum iron and phosphate ions removal efficiency was obtained using a coating temperature of 50°C, a coating time of 15 min, a PEG concentration of 20%, and a PEG to silica ratio of 1:3.

A novel method to additively repair micro-damaged fused silica using localized CO2 laser

A novel method to additively repair localized laser-damaged sites in fused silica optics using CO2 laser was developed with coating nanomaterials. Optimal composition of coating solution for filling damaged sites was engineered. The composition of repaired sites was found typical fused silica structure, and there is no obvious difference than commercial fused silica KN7980 substrate. The developed technique has repaired damage points up to 35 % of their depth, while the localized treatment could generate smooth repaired surfaces. The repair depth of the damaged points was affected by the volume of fused silica nano-powder solution used and depth of the original damage sites.

Nonionic surfactant-templated mesoporous silica as supports for nickel active catalysts in liquid phase organic compounds oxidation

Three surfactants were selected from a series of EOx/POy/EOx triblock copolymers and ethoxylated octylphenol as nonionic templating agents for the synthesis of silica mesoporous materials at room temperature and by hydrothermal treatment. The surfactants were ethylene oxide-propylene oxide-ethylene oxide tri-block copolymers (Pluronic F68) and a polydisperse ethoxylated octylphenol (Triton X-100). The obtained materials were compared with SBA-15 mesoporous silica synthesized with Pluronic P123 surfactant and were used as support to obtain Ni and NiTi-silica catalysts (2.5% NiO, 5% TiO2). The synthesized materials were characterized by X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption-desorption, IR and UV-Vis spectroscopy. Catalytic and photocatalytic activity of Ni and NiTi-silica samples were tested, with and without H2O2, for phenol and Brilliant Blue FCF dye oxidative degradation in the liquid phase. The obtained results showed a significant effect of surfactant on silica structure, morphology and texture, and catalytic and photocatalytic properties.

Investigating densification processes of amorphous silica phases through activation energy distribution

We investigated thermal stability of silica glass that underwent high-temperature (HT), high-pressure (HP) densification followed with electron irradiations. We performed isothermal annealing and in situ Raman spectroscopy to observe changes in the silica structure. By determining the activation energy distributions at the root of the densification process, we aimed to gain insights into the relaxation pathway of densified silica and its relationship with the structural properties. Of particular interest we observed a non monotonous behavior of D2 band in Raman spectra in HP-HT samples exposed at low dose ≤107 Gy, which we attribute to presence of a specific phase of silica glass known as the high-density amorphous phase. Our study highlights the impact of irradiation on the ratio between high-density amorphous and low-density amorphous phases, and on relative activation energy distributions. These findings have important implications for development of high-performance optical devices based on silica densification for a wide range of applications.

Bubble-free diatoms polymerase chain reaction

Polymerase chain reaction (PCR) in small fluidic systems not only improves speed and sensitivity of deoxyribonucleic acid (DNA) amplification but also achieves high-throughput quantitative analyses. However, air bubble trapping and growth during PCR has been considered as a critical problem since it causes the failure of DNA amplification. Here we report bubble-free diatom PCR by exploiting a hierarchically porous silica structure of single-celled algae. We show that femtoliters of PCR solution can be spontaneously loaded into the diatom interior without air bubble trapping due to the surface hydrophilicity and pore structure of the diatom. We discover that a large pressure gradient between air bubbles and nanopores rapidly removes residual air bubbles through the periodically arrayed nanopores during thermal cycling. We demonstrate the DNA amplification by diatom PCR without air bubble trapping and growth. Finally, we successfully detect DNA fragments of SARS-CoV-2 with as low as 10 copies/μl by devising a microfluidic device integrated with diatoms assembly. We believe that our work can be applied to many PCR applications for innovative molecular diagnostics and provides new opportunities for naturally abundant diatoms to create innovative biomaterials in real-world applications.

Highly luminescent graphene core N-doped carbon nanodots prepared under spatial nanoconfinement

Nitrogen-dopped carbon nanodots (CNDs) with an extremely high quantum yield of photoluminescence (up to 95%) have been obtained by thermal treatment of citric acid embedded in the porous structure of silica with immobilized N-[3-(Trimethoxysilyl)propyl]ethylenediamine. Spatial isolation of molecular precursors in nanoreactors permits the preparation of high-quality nanoparticles with spheroidal geometry and size 2–5 nm. The particles obtained at 110–180 °C for 60–600 min demonstrate excitation-independent photoluminescence at 453 nm. HRTEM reveals that the CNDs demonstrate ordered crystalline structures of graphic materials, indicating the catalytic effect of the nanoreactor. The high-resolution XPS experiment proves the N-doping of CNDs with 4.0 at.% of nitrogen atoms incorporated into the graphene core as pyrrolic and ternary fragments.

Polarization control investigation based on an integrated graphene-assisted microring cavity

In this paper, we propose and analyze an integrated polarization-selective structure of a graphene-assisted silica microring cavity to realize polarization control due to different optical distributions of whispering-gallery modes in the microring and polarization-dependent absorptions of graphene. A graphene stripe is partially side coupled with a silica microring to distinctly influence the propagations of a TE mode and TM mode in the microring. Especially, the appearance of the plasmonic mode in the groove between the graphene and the microring enhances light–matter interaction between the graphene and the TM-polarized mode, while without that for the case of TE mode propagation. By applying voltage on the graphene stripe along with its electro-optic modulation effect, the difference in the polarization extinction ratio of 20.6 dB is obtained between the cases of the polarized TM mode and TE mode in the microring. Furthermore, a second silica microring is added in this hybrid structure to couple the original microring along with a graphene stripe embedded in between finally realizing an electromagnetically induced transparency line shape because of the plasmonic coupling in both cavities with the condition of TM mode propagation, while without any line-shape change for the case of TE mode propagation. This compact hybrid structure offers a good integrated photonic platform to realize an excellent polarization-selective device.

Silicon in Plants: Alleviation of Metal(loid) Toxicity and Consequential Perspectives for Phytoremediation.

For the majority of higher plants, silicon (Si) is considered a beneficial element because of the various favorable effects of Si accumulation in plants that have been revealed, including the alleviation of metal(loid) toxicity. The accumulation of non-degradable metal(loid)s in the environment strongly increased in the last decades by intensified industrial and agricultural production with negative consequences for the environment and human health. Phytoremediation, i.e., the use of plants to extract and remove elemental pollutants from contaminated soils, has been commonly used for the restoration of metal(loid)-contaminated sites. In our viewpoint article, we briefly summarize the current knowledge of Si-mediated alleviation of metal(loid) toxicity in plants and the potential role of Si in the phytoremediation of soils contaminated with metal(loid)s. In this context, a special focus is on metal(loid) accumulation in (soil) phytoliths, i.e., relatively stable silica structures formed in plants. The accumulation of metal(loid)s in phytoliths might offer a promising pathway for the long-term sequestration of metal(loid)s in soils. As specific phytoliths might also represent an important carbon sink in soils, phytoliths might be a silver bullet in the mitigation of global change. Thus, the time is now to combine Si/phytolith and phytoremediation research. This will help us to merge the positive effects of Si accumulation in plants with the advantages of phytoremediation, which represents an economically feasible and environmentally friendly way to restore metal(loid)-contaminated sites.

Defect generation mechanisms in silica under intense electronic excitation by ion beams below 100 K: Interplay between radiative emissions

Ion-beam effects on bulk silica at low temperature have been studied with the aim of understanding the routes and mechanisms leading from the initial generation of free carriers and self-trapped excitons (STEs) to the production of two stable defect structures in irradiated silica, non-bridging oxygen hole centers (NBOHCs) and oxygen deficient centers (ODCs). Ion beam induced luminescence (ionoluminescence, IL) spectra were obtained using 3 MeV H, 3.5 MeV He, 19 MeV Si, and 19 MeV Cl ions and a range of cryogenic irradiation temperatures from 30 to 100 K. The kinetic behavior of three emission bands centered at 1.9 eV (assigned to NBOHCs), 2.1 eV (assigned to the intrinsic decay of STEs), and 2.7 eV (assigned to ODCs) reveal the physical origin of these emissions under intense electronic excitation. The creation of NBOHCs is governed by a purely electronic mechanism. The kinetics curve of the NBOHC band shows two main contributions: an instantaneous (beam-on) contribution, followed by a slower fluence- and temperature-dependent process correlated with the concentration of STEs. The beam-on contribution is proportional to deposited ionization energy. The growth of the ODC band is linear in fluence up to around 2 × 1012 cm−2. The growth rate is independent of temperature but proportional to the number of radiation-induced oxygen vacancies per ion, showing, unambiguously, that the 2.7 eV emission can be associated with ODCs created in an excited state.