Showing papers on "Silicon dioxide published in 2015"

An Interface Coassembly in Biliquid Phase: Toward Core–Shell Magnetic Mesoporous Silica Microspheres with Tunable Pore Size

Abstract: Core–shell magnetic mesoporous silica microspheres (Magn-MSMs) with tunable large mesopores in the shell are highly desired in biocatalysis, magnetic bioseparation, and enrichment. In this study, a shearing assisted interface coassembly in n-hexane/water biliquid systems is developed to synthesize uniform Magn-MSMs with magnetic core and mesoporous silica shell for an efficient size-selective biocatalysis. The synthesis features the rational control over the electrostatic interaction among cationic surfactant molecules, silicate oligomers, and Fe3O4@RF microspheres (RF: resorcinol formaldehyde) in the presence of shearing-regulated solubilization of n-hexane in surfactant micelles. Through this multicomponent interface coassembly, surfactant-silica mesostructured composite has been uniformly deposited on the Fe3O4@RF microspheres, and core–shell Magn-MSMs are obtained after removing the surfactant and n-hexane. The obtained Magn-MSMs possess excellent water dispersibility, uniform diameter (600 nm), large...

Loading of Silica Nanoparticles in Block Copolymer Vesicles during Polymerization-Induced Self-Assembly: Encapsulation Efficiency and Thermally Triggered Release.

Abstract: Poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) diblock copolymer vesicles can be prepared in the form of concentrated aqueous dispersions via polymerization-induced self-assembly (PISA). In the present study, these syntheses are conducted in the presence of varying amounts of silica nanoparticles of approximately 18 nm diameter. This approach leads to encapsulation of up to hundreds of silica nanoparticles per vesicle. Silica has high electron contrast compared to the copolymer which facilitates TEM analysis, and its thermal stability enables quantification of the loading efficiency via thermogravimetric analysis. Encapsulation efficiencies can be calculated using disk centrifuge photosedimentometry, since the vesicle density increases at higher silica loadings while the mean vesicle diameter remains essentially unchanged. Small angle X-ray scattering (SAXS) is used to confirm silica encapsulation, since a structure factor is observed at q ≈ 0.25 nm–1. A new two-population model provid...

Controllable Synthesis of Functional Hollow Carbon Nanostructures with Dopamine As Precursor for Supercapacitors.

Abstract: N-doped hollow carbon spheres (N-HCSs) are promising candidates as electrode material for supercapacitor application. In this work, we report a facile one-step synthesis of discrete and highly dispersible N-HCSs with dopamine (DA) as a carbon precursor and TEOS as a structure-assistant agent in a mixture containing water, ethanol, and ammonia. The architectures of resultant N-HCSs, including yolk–shell hollow carbon spheres (YS-HCSs), single-shell hollow carbon spheres (SS-HCSs), and double-shells hollow carbon spheres (DS-HCSs), can be efficiently controlled through the adjustment of the amount of ammonia. To explain the relation and formation mechanism of these hollow carbon structures, the samples during the different synthetic steps, including polymer/silica spheres, carbon/silica spheres and silica spheres by combustion in air, were characterized by TEM. Electrochemical measurements performed on YS-HCSs, SS-HCSs, and DS-HCSs showed high capacitance with 215, 280, and 381 F g–1, respectively. Moreover...

Silicon in Soils and Plants

Abstract: The crust of the earth is largely composed of silicon that is found primarily as silicate minerals, secondary alumino silicates and various forms of silicon dioxide. However, the abundance of silicon in soils is not an indication that sufficient supplies of soluble silicon are available for plant uptake. In this chapter, the outcomes of many years of research conducted on silicon are consolidated to understand the state of knowledge for silicon fertilization guidelines in crop production. Monosilicic acid (H4SiO4) is the form of silicon used by plants, which is found both in liquid and adsorbed phases of silicon in soils. The concentration of the H4SiO4 in the soil solution is influenced by the soil pH and the amounts of clay, minerals, organic matter and Fe/Al oxides/hydroxides, which are collectively related to the geologic age of the soil. Fertilization can rapidly increase the concentration of H4SiO4 in the soil solution; therefore, fertilization has become a common practice in areas with intensive cropping systems, particularly for those soils that are inherently low in soluble silicon. The establishment of procedures to estimate the plant-available silicon and the critical soil silicon levels and the method (5-day Na2CO3-NH4NO3 extraction) to analyze the soluble silicon fraction in solid fertilizers were among the advances in research on silicon in agriculture in recent years. These measurements were the key components required for the development and implementation of effective silicon fertilizer management in crop production. However, many aspects of the role of silicon in soil science remain understudied, and these aspects should be the focus of future research.

One-Step Synthesis of Amine-Functionalized Hollow Mesoporous Silica Nanoparticles as Efficient Antibacterial and Anticancer Materials

Abstract: In this study, amine-functionalized hollow mesoporous silica nanoparticles with an average diameter of ∼100 nm and shell thickness of ∼20 nm were prepared by an one-step process. This new nanoparticulate system exhibited excellent killing efficiency against mycobacterial (M. smegmatis strain mc2 651) and cancer cells (A549).

Core‐Cone Structured Monodispersed Mesoporous Silica Nanoparticles with Ultra‐large Cavity for Protein Delivery

Abstract: A new type of monodispersed mesoporous silica nanoparticles with a core-cone structure (MSN-CC) has been synthesized. The large cone-shaped pores are formed by silica lamellae closely packed encircling a spherical core, showing a structure similar to the flower dahlia. MSN-CC has a large pore size of 45 nm and a high pore volume of 2.59 cm(3) g(-1). MSN-CC demonstrates a high loading capacity of large proteins and successfully delivers active β-galactosidase into cells, showing their potential as efficient nanocarriers for the cellular delivery of proteins with large molecular weights.

Reduction of Acute Inflammatory Effects of Fumed Silica Nanoparticles in the Lung by Adjusting Silanol Display through Calcination and Metal Doping.

Abstract: The production of pyrogenic (fumed) silica is increasing worldwide at a 7% annual growth rate, including expanded use in food, pharmaceuticals, and other industrial products. Synthetic amorphous silica, including fumed silica, has been generally recognized as safe for use in food products by the Food and Drug Administration. However, emerging evidence from experimental studies now suggests that fumed silica could be hazardous due to its siloxane ring structure, high silanol density, and "string-of-pearl-like" aggregate structure, which could combine to cause membrane disruption, generation of reactive oxygen species, pro-inflammatory effects, and liver fibrosis. Based on this structure-activity analysis (SAA), we investigated whether calcination and rehydration of fumed silica changes its hazard potential in the lung due to an effect on silanol density display. This analysis demonstrated that the accompanying change in surface reactivity could indeed impact cytokine production in macrophages and acute inflammation in the lung, in a manner that is dependent on siloxane ring reconstruction. Confirmation of this SAA in vivo, prompted us to consider safer design of fumed silica properties by titanium and aluminum doping (0-7%), using flame spray pyrolysis. Detailed characterization revealed that increased Ti and Al doping could reduce surface silanol density and expression of three-membered siloxane rings, leading to dose-dependent reduction in hydroxyl radical generation, membrane perturbation, potassium efflux, NLRP3 inflammasome activation, and cytotoxicity in THP-1 cells. The reduction of NLRP3 inflammasome activation was also confirmed in bone-marrow-derived macrophages. Ti doping, and to a lesser extent Al doping, also ameliorated acute pulmonary inflammation, demonstrating the possibility of a safer design approach for fumed silica, should that be required for specific use circumstances.

Water Contact Angle Dependence with Hydroxyl Functional Groups on Silica Surfaces under CO2 Sequestration Conditions.

Abstract: Functional groups on silica surfaces under CO2 sequestration conditions are complex due to reactions among supercritical CO2, brine and silica. Molecular dynamics simulations have been performed to investigate the effects of hydroxyl functional groups on wettability. It has been found that wettability shows a strong dependence on functional groups on silica surfaces: silanol number density, space distribution, and deprotonation/protonation degree. For neutral silica surfaces with crystalline structure (Q(3), Q(3)/Q(4), Q(4)), as silanol number density decreases, contact angle increases from 33.5° to 146.7° at 10.5 MPa and 318 K. When Q(3) surface changes to an amorphous structure, water contact angle increases 20°. Water contact angle decreases about 12° when 9% of silanol groups on Q(3) surface are deprotonated. When the deprotonation degree increases to 50%, water contact angle decreases to 0. The dependence of wettability on silica surface functional groups was used to analyze contact angle measurement ambiguity in literature. The composition of silica surfaces is complicated under CO2 sequestration conditions, the results found in this study may help to better understand wettability of CO2/brine/silica system.

Synthesis and Characterization of SiO2 Nanoparticles by Sol-Gel Process and Its Degradation of Methylene Blue

Abstract: Nanomaterials are used for the miniaturization of particular electronic device. But new era of technology demands a cheaper and more commercial method to produce excellent material especially silicon dioxide. The present work deals with the sol-gel synthesis of SiO2 material and also provides a basic understanding of the effect of calcination temperature on the growth of SiO2 by hydrolysis of TEOS with ethanol, deionized water and catalyst mixture. The properties of resulting materials were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), AFM and optical properties through UV-visible spectroscopy and Photo Luminescence (PL). The XRD study of pure SiO2 with calcination temperature at 300°C shows well crystalline characteristics and having hexagonal crystal structure. SEM results show obtained silica particles were having spherical morphology. The proper temperature the PL intensity was reduced and the shape of the emission spectrum slightly split into sharp peaks. UV-visible absorbance spectra of the silica samples having wide band gap showing absorbance in the ultra violet region. The

Interaction Between Graphene Oxide Nanoparticles and Quartz Sand

Abstract: In this study, the influence of pH, ionic strength (IS), and temperature on graphene oxide (GO) nanoparticles attachment onto quartz sand were investigated. Batch experiments were conducted at three controlled temperatures (4, 12, and 25 °C) in solutions with different pH values (pH 4, 7, and 10), and ionic strengths (IS = 1.4, 6.4, and 21.4 mM), under static and dynamic conditions. The surface properties of GO nanoparticles and quartz sand were evaluated by electrophoretic mobility measurements. Derjaguin–Landau–Verwey–Overbeek (DLVO) potential energy profiles were constructed for the experimental conditions, using measured zeta potentials. The experimental results showed that GO nanoparticles were very stable under the experimental conditions. Both temperature and pH did not play a significant role in the attachment of GO nanoparticles onto quartz sand. In contrast, IS was shown to influence attachment. The attachment of GO particles onto quartz sand increased significantly with increasing IS. The exper...

Protein Adsorption From Biofluids on Silica Nanoparticles: Corona Analysis as a Function of Particle Diameter and Porosity.

Abstract: A study on the adsorption of proteins from fetal bovine serum (FBS) on spherical dense and mesoporous silica nanoparticles with a wide range of diameters, from 70 to 900 nm, is presented Monodisperse populations of particles with a range of diameters were obtained through modifications of the Stober method Extensive characterization of the particles was then performed using N2 physisorption, TEM, DLS, and ζ-potential Following serum exposure, proteomic evaluation in concert with thermogravimetric analysis revealed the associated concentrations of each protein identified in the hard corona Small particles adsorbed the largest amount of protein, due to their larger external surface area Proteins with low molecular weights (<50 kDa) constituted the majority of the protein corona, totaling between 60 and 80% of the total mass of adsorbed protein Here, the higher surface curvature of small particles favors the enrichment of smaller proteins Porosity does not promote protein adsorption but improves deposition of the low molecular weight protein fraction due to the size-exclusion effect related to pore diameter These results have important implications for the use of dense and porous silica nanoparticles in biomedical applications

Revisiting the paradigm of silica pathogenicity with synthetic quartz crystals: the role of crystallinity and surface disorder

Abstract: Exposure to some - but not all - quartz particles is associated to silicosis, lung cancer and autoimmune diseases. What imparts pathogenicity to any single quartz source is however still unclear. Crystallinity and various surface features are implied in toxicity. Quartz dusts used so far in particle toxicology have been obtained by grinding rocks containing natural quartz, a process which affects crystallinity and yields dusts with variable surface states. To clarify the role of crystallinity in quartz pathogenicity we have grown intact quartz crystals in respirable size. Quartz crystals were grown and compared with a fractured specimen obtained by grinding the largest synthetic crystals and a mineral quartz (positive control). The key physico-chemical features relevant to particle toxicity - particle size distribution, micromorphology, crystallinity, surface charge, cell-free oxidative potential - were evaluated. Membranolysis was assessed on biological and artificial membranes. Endpoints of cellular stress were evaluated on RAW 264.7 murine macrophages by High Content Analysis after ascertaining cellular uptake by bio-TEM imaging of quartz-exposed cells. Quartz crystals were grown in the submicron (n-Qz-syn) or micron (μ-Qz-syn) range by modulating the synthetic procedure. Independently from size as-grown quartz crystals with regular intact faces did not elicit cellular toxicity and lysosomal stress on RAW 264.7 macrophages, and were non-membranolytic on liposome and red blood cells. When fractured, synthetic quartz (μ-Qz-syn-f) attained particle morphology and size close to the mineral quartz dust (Qz-f, positive control) and similarly induced cellular toxicity and membranolysis. Fracturing imparted a higher heterogeneity of silanol acidic sites and radical species at the quartz surface. Our data support the hypothesis that the biological activity of quartz dust is not due to crystallinity but to crystal fragmentation, when conchoidal fractures are formed. Besides radical generation, fracturing upsets the expected long-range order of non-radical surface moieties - silanols, silanolates, siloxanes - which disrupt membranes and induce cellular toxicity, both outcomes associated to the inflammatory response to quartz.

Fumed silica-based organogels and ‘aqueous-organic’ bigels

Abstract: We report the use of fumed silica (hydrophilic colloidal silica particles) to generate triglyceride solvent-based soft matter systems (organogels and bigels). Interestingly, the bigels showed a better gel strength compared to organogels while showing a comparatively weaker thixotropic recovery. Electron microscopy and energy dispersive X-ray spectroscopy were used to understand the microstructure of these new thixotropic molecular gel systems with respect to the fractal-like aggregation of silica particles as well as the percolating network of organic-aqueous phases.

Unique Biological Degradation Behavior of Stöber Mesoporous Silica Nanoparticles from Their Interiors to Their Exteriors.

Abstract: The degradation behavior of mesoporous silica nanoparticles (MSNs) influences their biological applications. The present study was a systematic investigation of the biological degradation behavior of mesoporous silica synthesized by the Stober method. Different sized Stober mesoporous silica nanoparticles were prepared and immersed in simulated body fluid, and degradation curves were obtained by measuring the dissolved silicon content of the fluid. Structural changes during degradation were observed by transmission electron microscope (TEM). The Stober mesoporous silica nanoparticles tended to become hollow during the degradation process, and each particle was almost completely degradable from its interior to its exterior. Because of this unique degradation behavior, the morphology of the Stober mesoporous silica nanoparticles can be retained even after over 85% of the silica degraded. Thus, during degradation, the dispersibility of the silica particles was superior to that of MSNs prepared in aqueous phases. Furthermore, the degradation behavior, intracellular distribution, and structural transformation of Stober mesoporous silica nanoparticles in human embryo kidney 293T cells were investigated by measuring the silicon content in culture medium and analyzing TEM images. When these silica nanoparticles degraded in cells, their size and dispersibility remained unchanged, which would reduce the biological toxicity associated with the accumulation of silica aggregates in tissues. Overall, these results demonstrate that Stober mesoporous silica nanoparticles can degrade in biological medium from inside to outside and maintain their good dispersibility, which suggests that these nanoparticles have great potential for applications as degradable biomedical materials such as drug carriers.

Modulation of Silica Nanoparticle Uptake into Human Osteoblast Cells by Variation of the Ratio of Amino and Sulfonate Surface Groups: Effects of Serum.

Abstract: To study the importance of the surface charge for cellular uptake of silica nanoparticles (NPs), we synthesized five different single- or multifunctionalized fluorescent silica NPs (FFSNPs) by introducing various ratios of amino and sulfonate groups into their surface. The zeta potential values of these FFSNPs were customized from highly positive to highly negative, while other physicochemical properties remained almost constant. Irrespective of the original surface charge, serum proteins adsorbed onto the surface, neutralized the zeta potential values, and prevented the aggregation of the tailor-made FFSNPs. Depending on the surface charge and on the absence or presence of serum, two opposite trends were found concerning the cellular uptake of FFSNPs. In the absence of serum, positively charged NPs were more strongly accumulated by human osteoblast (HOB) cells than negatively charged NPs. In contrast, in serum-containing medium, anionic FFSNPs were internalized by HOB cells more strongly, despite the sim...

Reed Leaves as a Sustainable Silica Source for 3D Mesoporous Nickel (Cobalt) Silicate Architectures Assembled into Ultrathin Nanoflakes for High‐Performance Supercapacitors

Abstract: Mesoporous 3D architectures of silicon dioxide, nickel silicate, and cobalt silicate are for the first time prepared by using reed leafs as a sustainable silica source. Due to the 3D mesoporous architecture, nickel and cobalt silicate allow efficient charge transfer and mass transport, while at the same time buffering the volume changes during ion lithiation/delithiation processes. Especially, the nickel silicate electrode with the mesoporous 3D architecture shows a high specific capacitance, a good rate capability, and cycling stability for electrochemical capacitors.

Multifunctional Silica Nanoparticles for Covalent Immobilization of Highly Sensitive Proteins

Abstract: A convenient reverse micellar one-pot reaction yields multifunctional silica nanoparticles, which can be tailored to effectively suppress non-specific adsorption and, at the same time, enable efficient specific covalent immobilization of proteins. Using two highly sensitive proteins, it is demonstrated that the new particles provide a suitable microenvironment to maintain the protein's activity.

Silica nanoparticles increase human adipose tissue-derived stem cell proliferation through ERK1/2 activation.

Abstract: Background Silicon dioxide composites have been found to enhance the mechanical properties of scaffolds and to support growth of human adipose tissue-derived stem cells (hADSCs) both in vitro and in vivo. Silica (silicon dioxide alone) exists as differently sized particles when suspended in culture medium, but it is not clear whether particle size influences the beneficial effect of silicon dioxide on hADSCs. In this study, we examined the effect of different sized particles on growth and mitogen-activated protein kinase signaling in hADSCs. Methods Silica gel was prepared by a chemical reaction using hydrochloric acid and sodium silicate, washed, sterilized, and suspended in serum-free culture medium for 48 hours, and then sequentially filtered through a 0.22 μm filter (filtrate containing nanoparticles smaller than 220 nm; silica NPs). hADSCs were incubated with silica NPs or 3 μm silica microparticles (MPs), examined by transmission electron microscopy, and assayed for cell proliferation, apoptosis, and mitogen-activated protein kinase signaling. Results Eighty-nine percent of the silica NPs were around 50-120 nm in size. When hADSCs were treated with the study particles, silica NPs were observed in endocytosed vacuoles in the cytosol of hADSCs, but silica MPs showed no cell entry. Silica NPs increased the proliferation of hADSCs, but silica MPs had no significant effect in this regard. Instead, silica MPs induced slight apoptosis. Silica NPs increased phosphorylation of extracellular signal-related kinase (ERK)1/2, while silica MPs increased phosphorylation of p38. Silica NPs had no effect on phosphorylation of Janus kinase or p38. Pretreatment with PD98059, a MEK inhibitor, prevented the ERK1/2 phosphorylation and proliferation induced by silica NPs. Conclusion Scaffolds containing silicon dioxide for tissue engineering may enhance cell growth through ERK1/2 activation only when NPs around 50-120 nm in size are included, and single component silica-derived NPs could be useful for bioscaffolds in stem cell therapy.

SYNTHESIS AND APPLICATIONS OF Fe3O4/SiO2 CORE-SHELL MATERIALS.

Abstract: Multifunctional nanoparticles based on magnetite/silica core-shell, consisting of iron oxides coated with silica matrix doped with fluorescent components such as organic dyes (fluorescein isothiocyanate - FITC, Rhodamine 6G) or quantum dots, have drawn remarkable attention in the last years. Due to the bi-functionality of these types of nanoparticles (simultaneously having magnetic and fluorescent properties), they are successfully used in highly efficient human stem cell labeling, magnetic carrier for photodynamic therapy, drug delivery, hyperthermia and other biomedical applications. Another application of core-shell-based nanoparticles, in which the silica is functionalized with aminosilanes, is for immobilization and separation of various biological entities such as proteins, antibodies, enzymes etc. as well as in environmental applications, as adsorbents for heavy metal ions. In vitro tests on human cancerous cells, such as A549 (human lung carcinoma), breast, human cervical cancer, THP-1 (human acute monocytic leukaemia) etc. , were conducted to assess the potential cytotoxic effects that may occur upon contact of nanoparticles with cancerous tissue. Results show that core-shell nanoparticles doped with cytostatics (cisplatin, doxorubicin, etc.), are easily adsorbed by affected tissue and in some cases lead to an inhibition of cell proliferation and induce cell death by apoptosis. The goal of this review is to summarize the advances in the field of core-shell materials, particularly those based on magnetite/silica with applicability in medicine and environmental protection. This paper briefly describes synthesis methods of silica-coated magnetite nanoparticles (Stober method and microemulsion), the method of encapsulating functional groups based on aminosilanes in silica shell, as well as applications in medicine of these types of simple or modified nanoparticles for cancer therapy, MRI, biomarker immobilization, drug delivery, biocatalysis etc., and in environmental applications (removal of heavy metal ions and catalysis).

Optical and Electrochemical Applications of Silicon–Carbon Dots/Silicon Dioxide Nanocomposites

Abstract: Various colors of photoluminescent SiC-dots/SiO2 prepared through a simple heating process have been employed for optical and electrochemical applications. Blue (B)-, green (G)-, and tan (T)-SiC-dots/SiO2 powders have been prepared from SiC-dots that had been prepared from 3-aminopropyl trimethoxysilane through a hydrothermal route by simply controlling heating at 60 °C for 60 min and 300 °C for 10 and 20 min, respectively. The B-, G-, and T-SiC-dots/SiO2 nanocomposites emit at 455, 534, and 574 nm, respectively, under excitation at 360 nm. B-, G-, and T-SiC-dots/SiO2 glass films show at least seven colors when excited at 360, 460, and 520 nm. Through a heat-induced photoluminescence (PL) change, a representative lithographic pattern of B-SiC-dots/SiO2 films has been fabricated using a near-infrared laser. The B-, G-, and T-SiC-dots/SiO2 also possess high electrocatalytic activity for the oxygen reduction reaction. Having such interesting PL and electrical properties, the stable, low-toxic, and cost-effec...

Adsorption and thermal properties of the bovine serum albumin–silicon dioxide system

Abstract: The adsorption, electrokinetic, thermal and stability properties of the silicon dioxide (silica, SiO2)/bovine serum albumin (BSA) system were determined. All measurements were carried out as a function of solution pH value. The highest amount of BSA absorbed on the silica surface was observed at pH 4.6 [the value close to the BSA isoelectric point (pI)], which is primarily related to the packed albumin conformation and the lack of adsorbent–adsorbate electrostatic repulsion. At pH 4.6, largest mass decrease was also noticed (thermogravimetric measurements). At pH 3, 7.6 and 9, the adsorption levels were much lower. This phenomenon is associated with the electrostatic repulsion between the BSA macromolecules and the silica particles as well as the expanded BSA structure. During biopolymer adsorption, the whole solid surface is coated with the albumin macromolecules. Then, the properties of the silica particles become similar to those of the BSA macromolecules. In the presence of albumin, the silica pHiep point is identical to the BSA pI value. It should also be noted that the albumin adsorption affects the SiO2 suspension stability. The greatest change was observed at pH 3. Under these conditions, the BSA addition causes electrosteric system stabilization.

Carbohydrate-Conjugated Hollow Oblate Mesoporous Silica Nanoparticles as Nanoantibiotics to Target Mycobacteria

Abstract: Engineering nanomaterials with enhanced antibacterial activities remains a critical and practical challenge. Hollow oblate mesoporous silica nanoparticles (HOMSNs) are synthesized by a simple protocol of ammonia hydrothermal treatment of oblate mesoporous silica nanoparticles prepared using dibenzyl ether as a cosolvent. When conjugated with trehalose as the targeting ligand, the antibiotic-encapsulated HOMSNs exhibit high binding affinity and antibacterial efficacy toward mycobacteria.

A Monolithic Micro-Tensile Tester for Investigating Silicon Dioxide Polymorph Micromechanics, Fabricated and Operated Using a Femtosecond Laser

Abstract: Mechanical testing of materials at the microscales is challenging. It requires delicate procedures not only for producing and handling the specimen to be tested, but also for applying an accurate and controlled force. This endeavor is even more challenging when it comes to investigating the behavior of brittle materials such as glass. Here, we present a microtensile tester for investigating silica glass polymorphs. The instrument is entirely made of silica and for which the same femtosecond laser is not only used for fabricating the device, but also for operating it (loading the specimen) as well as for performing in situ measurements. As a proof-of-concept, we present a stress-strain curve of fused silica for unprecedented high tensile stress of 2.4 GPa, as well as preliminary results of the elastic modulus of femtosecond laser-affected zones of fused silica, providing new insights on their microstructures and mechanical behavior.

Enhanced adsorption of trivalent arsenic from water by functionalized diatom silica shells.

Abstract: The potential of porous diatom silica shells as a naturally abundant low-cost sorbent for the removal of arsenic in aqueous solutions was investigated in a batch study. The objective of this work was to chemically modify the silica shells of a diatom Melosira sp. with bifunctional (thiol and amino) groups to effectively remove arsenic in its toxic As(III) form (arsenite) predominant in the aquatic environment. Sorption experiments with this novel sorbent were conducted under varying conditions of pH, time, dosage, and As(III) concentration. A maximum adsorption capacity of 10.99 mg g-1 was achieved within 26 h for a solution containing 12 mg L-1 As(III) at pH 4 and sorbent dosage of 2 g L-1. The functionalized diatom silica shells had a surface morphological change which was accompanied by increased pore size at the expense of reduced specific surface area and total pore volume. As(III) adsorption was best fitted with the Langmuir-Freundlich model, and the adsorption kinetic data using pore surface diffusion model showed that both the external (film) and internal (intraparticle) diffusion can be rate-determining for As(III) adsorption. Fourier transform infrared spectroscopy (FTIR) indicated that the thiol and amino groups potentially responsible for As(III) adsorption were grafted on the surface of diatom silica shells. X-ray photoelectron spectroscopy (XPS) further verified that this unique sorbent proceeded via a chemisorption mechanism through the exchange between oxygen-containing groups of neutral As(III) and thiol groups, and through the surface complexation between As(III) and protonated nitrogen and hydroxyl groups. Results indicate that this functionalized bioadsorbent with a high As(III) adsorption capacity holds promise for the treatment of As(III) containing wastewater.

First-Principles Calculations of Lithiation of a Hydroxylated Surface of Amorphous Silicon Dioxide

Abstract: Amorphous silicon dioxide films arise naturally by exposure of silicon surfaces to atmospheric environments. When used as electrodes in Li-ion batteries, the characterization of surface lithiation is relevant to the understanding of the performance of Si anodes. In this work, density functional theory analyses of the lithiation of an amorphous silicon dioxide film reveal the lithiation mechanisms and the role of the surface functional groups on the lithiation reactions and on the structure of the lithiated film. The surface concentration of silanol groups and structure of the optimized model of amorphous hydroxylated silicon dioxide film agree with those observed experimentally. It is found that Li is incorporated via breaking of Si–O bonds and partial reduction of the Si atoms. Evaluation of the formation energy for lithiation of the film indicates that the film would saturate at a Li/Si ratio of 3.48. Analyses of radial distribution functions and coordination numbers show the evolution of the structure ...